8

CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

This chapter deals with an extensive literature survey on the present

research work. This literature search provides a background and guide for the

entire study. This chapter includes the review on historical appraisal of

activated carbon, activated carbon preparation methods, application of

activated carbon, wastewater treatment methods, classification of textile dyes

and effect of process parameters on activated carbon preparation and

adsorption studies.

2.2 HISTORY OF ACTIVATED CARBON

Activated carbon is broadly defined to include a wide range of

amorphous carbon based materials prepared in such a way that exhibit a high

degree of porosity and an extended surface area. For many centuries the

activated carbon was used in the form of carbonized wood. The earliest

known use of carbon in the form of wood chars by the Egyptians and

Sumerians was in 3750 BC for the reduction of ores in the manufacturing of

bronze, domestic smokeless fuel and medicinal application. In 1500 BC,

Egyptian papyri was used as adsorbent for odorous vapours from putrefying

wounds and from within the abdominal tract. The wrecks of Phoenician

trading ships suggest that drinking water was stored in charred wooden

barrels. This practise was certainly still in use in the 18th century for extending

9

the use of potable water on long sea voyages. The ancient Hindus in India of

the same period (450 B.C) used sand and charcoal filters for purifying

drinking water. In 157 AD Claudius Galvanometer referred the use of carbons

of both vegetable and animal origin for the treatment of a wide range of

diseases. The specific adsorptive capacity of charcoal was recognized by

Scheele at 1773 AD, who measured the volumes of gases that could be

adsorbed by carbons derived from different sources. In 1785, Lowitz

reviewed the abilities of charcoals to adsorb odors and vapours from a range

of organic chemicals. He also studied the effectiveness of charcoal in

decolourizing tartaric acid. In 1794 wood charcoal was used to decolourize

the sugar cane syrups. In 1811, Figuier evaluated the decolourizing capacity

of bone char and wood char and during 1815, most of the sugar refining

industry had switched to the use of granulated bone char as a decolorant.

Joseph de Cavaillon patented a method for regenerating used bone chars in

1817. Bussy (1822) demonstrated that the decolorizing properties of carbons

were inherent to the source material and also depended on the thermal

processing and the particle size of the finished product. Kayser (1881) first

used the term adsorption to describe the uptake of gases by carbons. The basis

for the industrial production of activated carbon from coal was established in

1900 in order to replace the bone char in the sugar refining process.

The first powdered commercial activated carbon, eponite was

produced in Europe in 1909. During the First World War (1914), steam

activation of coconut shell and almond shell char was developed in the United

States for use in gas masks. It has been used subsequently for water treatment,

solvent recovery and air purification. This type of activated carbon mainly

contains fine pore structures suited for gas phase adsorption applications. In

Czechoslovakia two varieties of pelletized carbons were produced (1935–

1940) from sawdust by zinc chloride activation, for the recovery of volatile

solvents and for the removal of benzene from town gas. Nowadays the zinc

10

chloride process of chemical activation has been largely superseded by the

use of phosphoric acid. Barrer & Breck (1956) invented the method of zeolite

synthesis. In that year the North-American Linde Company started production

of synthetic zeolites on a commercial scale (Dabrowski 2001, Ferhan &

Ozgur 2011, John 1974). The use of carbon molecular sieves in gas

separation, in particular oxygen and nitrogen, has grown steadily in the past

years (Sircar et al 1996).

Activated carbons are useful adsorbents due to their porous

structures, the presence of various oxygenated functional surface groups

depending on the precursor’s nature and the procedures used in their

preparation, and thus activated carbons show differences in their adsorptive

behavior. To produce these carbons, chemical, physical and mixture of both

as activating agents are used and a number of activation procedures have been

reported in the literature (Bansal et al 1988) using the above said activating

agents. In general it can be classified either as single stage or two-stage

process.

2.3 ACTIVATED CARBON

Activated carbon also called activated charcoal, is a form of carbon

that has been processed with oxygen to create millions of tiny pores between

the carbon atoms. Commercial activated carbons have internal surface area

ranging from 500 to 1500 m2/g. Activated carbon can be prepared from feed

stock with high carbon and low inorganic content. The most common feed

stocks used for the production of activated carbon are wood, coconut shell,

bituminous coal, peat etc. The chars obtained from them could be activated

easily to produce reasonably high quality activated carbons. During the

activation process, the unique internal pore structure is created, which

provides the activated carbon its outstanding adsorptive properties.

11

Activated carbons have a number of unique characteristics such as

large internal surface area, chemical properties and good accessibility of

internal pores. According to IUPAC definitions three groups of pores can be

identified.

Macropores (above 50nm diameter)

Mesopores (2-50 nm diameter)

Micropores (Under 2 nm diameter)

Micropores generally contribute to a major part of the internal

surface area. Macro and micropores can generally be regarded as the

highways into the carbon particle, and are crucial for kinetics. The desirous

pore structure of an activated carbon product is attained by combining the

right raw material and suitable activation procedure.

2.4 PREPARATION OF ACTIVATED CARBON

Most carbonaceous substances can be converted into activated

carbon, the final properties of the carbon will depend significantly on the

nature of the starting material. A large number of processes for making

activated carbons have been developed over the past century. However, most

processes consist of the pyrolysis of the starting material, followed by a stage

of controlled oxidation or vice versa. The purpose of the oxidation stage is to

activate the carbon.

2.4.1 Pyrolysis

Pyrolysis step (or also called as Carbonization) involves heating the

source materials to temperatures ranging between 600 to 900ºC in the absence

of air (Cooney 1999). This process is to eliminate most of the non-carbon

elements such as hydrogen, nitrogen, oxygen and sulphur as volatile gaseous

12

products. Low molecular weight volatiles are first released, followed by light

aromatics and finally the hydrogen gas, the resultant product being a fixed

carbonaceous char. The residual carbon atoms are grouped into condensed

sheets of aromatic ring with a cross-linked structure in a random manner. The

mutual arrangement of these aromatic sheets is irregular and leaves free

interstices between the sheets, which may be filled with the tarry materials.

To remove these tarry materials, activation process is carried out. It also

enlarges the diameters of the pores, which were created during the

carbonization process and creating new porosity (Smisek & Cerny 1970).

2.4.2 Activation

The basic characteristics of a carbon are established during the

pyrolysis, and the ensuing oxidation step must be designed to complement the

pyrolysis step. During this step, the oxidising agent increasingly erodes the

internal surfaces of the carbon, develops an extensive and fine network of

pores in the carbon, and changes the atoms lying on the surface to specific

chemical forms which may have selective adsorption capabilities. This

activation step is done by two methods physical activation or chemical

activation.

2.4.2.1 Physical activation

Physical activation or partial gasification is generally carried out at

elevated temperatures between 750 and 1100 C using oxidants such as steam,

carbon dioxide, air or mixture of these gases. Chlorine, sulphur vapours,

sulphur dioxide, ammonia and a number of other substances having activation

effects are rarely used. Gasification of the carbonized material with steam and

carbon dioxide occurs by the following endothermic reactions:

C + H2O H2 + CO (2.1)

13

C + CO2 2CO (2.2)

The reaction of steam with carbon is accompanied by the water gas

formation reaction, which is catalyzed by the carbon surface as,

CO + H2O CO2 + H2 (2.3)

Since the reaction of carbon with steam and with carbon dioxide is

both endothermic, external heating is required to drive the reactions and to

maintain the reaction temperature. The activation process can be manipulated

to produce products of desired characteristics. Activation temperature, steam

and CO2 flow rates control the pore development, which in turn affect pore

size distributions and the level of activity of the activated carbon.

2.4.2.2 Chemical activation

Chemical activation is usually carried out by impregnating the raw

or pre-carbonized material with an activating agent and pyrolyzed between

400 and 800 C in the absence of oxygen. The most commonly used activating

agents are phosphoric acid, hydrochloric acid, sulphuric acid, alkalis namely

KOH and NaOH, zinc chloride and alkaline metal compounds. Phosphoric

acid and zinc chloride are used for the activation of lignocellulosic materials.

Phosphoric acid is the most preferred activating agent because of its low

environmental impact when compared to zinc chloride. The resultant

activated carbon is washed, dried till constant weight is obtained and ground

to required size. Activated carbons produced by chemical activation generally

exhibit a very open structure and bottle shaped, ideal for the adsorption of

large molecules.

14

2.4.2.3 Combination of physical and chemical activation

A combination of physical and chemical activation can be used to

prepare granular activated carbons with a very high surface area and porosity

adequate for certain specific applications such as gasoline vapour control, gas

storage, etc. Activated carbons of this types have been reported using

lignocellulosic precursors chemically activated with phosphoric acid and zinc

chloride and later activated under a flow of carbon dioxide. Uniform,

medium-size microporosity and surface areas above 3600 m2/g are obtained

with this mixed procedure (Bansal 1988).

2.4.2.4 Advantages of chemical activation over physical activation

An important advantage of chemical activation is that the process normally takes place at a lower temperature and for a shorter time than those

used in physical activation. In addition, very high surface area activated

carbons can be obtained with the yields of carbon in chemical activation being

usually higher than those in physical activation because the chemical agents used are substances with dehydrogenation properties that inhibit the formation

of tar and reduce the production of other volatile products. The activation of

wood using H3PO4 could be carried out at temperature less than 500oC(Bansal et al 1988), while ZnCl2 activation was carried at between 600oC to

709oC. The carbonization step generate the porosity, which becomes

accessible when the chemical is removed by washing (Caturla et al 1991,

Molina et al 1995). Consequently, the modification of chemical/precursor

ratio permits the adjustment of the porosity in the final activated carbon.

However, the most important disadvantage of chemical activation is the

incorporation of impurities, coming from the activating agent, which may affect the chemical properties of the activated carbon. Another disadvantage is

the investment needed for the unit for recovering chemical used for impregnation (Lozano et al 2001; Balci 1992).

15

2.4.2.5 Advantages of phosphoric acid over zinc chloride

The classical chemical used on a large scale for chemical activation was zinc chloride due to its efficiency and simplicity of the process. However,

its use is on the decline, because of the problems of corrosion, ineffective

chemical recovery and environmental disadvantages associated with zinc

chloride. This process produces activated carbons with large porosity, although the pore size distribution is determined for a given precursor mainly

by the degree of impregnation, that is, the larger the degree of impregnation,

the larger the average pore size of the final carbon. The activated carbon obtained using zinc chloride however, cannot be used in pharmaceutical and

food industries as it may contaminate the products. Hence, there have been

many studies reporting the activation of carbon using phosphoric acid,

because of the disadvantages associated with zinc chloride, phosphoric acid is used largely in industry to impregnate lignocellulosic materials, mainly wood.

Also, phosphoric acid includes important changes in the pyrolytic

decomposition of the lignocellulosic materials since it promotes

depolymerisation, dehydration and redistribution of constituent biopolymers (Jagtoyen and Derbyshire 1993), favouring the conversion of aliphatic to

aromatic compounds at temperatures lower than when heating in the absence

of an additive, thus increasing the yield. One of the reasons why activation with phosphoric acid has become popular is because of the improvements introduced in the process of acid recovery.

2.5 A REVIEW ON ACTIVATED CARBON PREPARATION

USING CHEMICAL ACTIVATION

The term chemical activation refers to the treatment of the

precursor with an activating agent used for restricting tar formation during the

thermal step. During thermal treatment, chemical activating agents such as

phosphoric acid and zinc chloride among others, provoke carbonization of the

precursor by dehydration, depolymerisation and redistribution of biopolymers

16

and cross linking of lignocellulosic materials (Jagtoyen and Derbyshire 1998).

Several coals (Ehrburger et al 1986, Ahmadpour & Do 1996, Teng et al 1998,

Lozano et al 2001), polymers (Park & Jung 2002, Puziy et al 2002), and some

agricultural by-products and forest wastes (Savova et al 2001, Garcia

et al 2003, Villegas et al 1993) have been used as raw materials to prepare

activated carbon.

Phosphoric acid activation has been used for a wide variety of

cellulosic precursors such as coconut shells (Laine et al 1989), white oak

(Jagtoyen & Derbyshire 1993), peach stones (Monlina et al 1996), nut shells

(Toles et al 1998), cotton stalks (Girgis & Ishak 1999), almond shells (Bevia

et al 1984, Toles et al 2000), pecan shells (Dastgheib & Rockstraw 2001),

Arundo donax cane (Vernerson et al 2002) and apple pulp (Garcia et al 2002),

peanut hull (Girgis et al 2002) and sugarcane bagasse (Girgis et al 1994,

Ahmedna et al 2000).

Ruiz et al (1984) prepared activated carbon from almond shell

using various activating agents like H3PO4, ZnCl2, K2CO3 and Na2CO3 at

700 C under N2 flow. Of the different activating reagents studied, zinc

chloride gave the highest surface area of 2111 m2 g-1. The surface area was

drastically reduced to 700 m2 g-1 for carbonization of ammonium chloride

impregnated almond and hazelnut shell in the flow of N2 at 700 C (Balci et al

1994). A good BET surface area activated carbon was reported (1071 m2 g-1)

at lower activation temperature (500 C) using pecan shell in the presence of

air and phosphoric acid (Dastgheib & Rockshaw 2001). Series of activated

carbons from almond, olive and peach stones chars by direct chemical

activation with zinc chloride at 800 C yielded a wide range of pore size

distribution (Rodriguez & Molina 1992).

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Hu & Vansant (1995) reported a similar wide range of pore size

distribution of activated carbon from walnut shell char using potassium

hydroxide in the absence of air at 500-900 C. They found that higher

temperatures, longer activation times and larger amounts of potassium

hydroxide favoured high adsorption capacity and wide pore size distribution.

Philip & Girgis (1996) produced activated carbon from apricot stones using

phosphoric acid which yielded high surface area and microporous structure.

Activated carbon produced from palm oil shell, coconut shell, almond,

hazelnut, walnut shell, pistachio nut and apricot stones using K2CO3 (Hayashi

et al 2002) at 900oC and ZnCl2 (Aygun et al 2003) under N2 flow at 750oC,

yielded high surface area and well-developed micropore structure

respectively. A similar well-developed microporous structure with very small

proportion of mesoporous network was obtained by the activation of peach

stones using phosphoric acid. These have been further activated in a CO2 gas

flow at 825oC for various range of burn-off (Molina et al 1995, 1996).

Phosphoric acid, potassium hydroxide and zinc chloride were used as

activating agents for various nutshell species. Girgis et al (2002) and Guo &

Lua (2000) produced activated carbon from peanut hull and oil palm stones

using all three agents and activated at 500 and 650 C respectively. They

reported that zinc chloride and phosphoric acid activation yielded essentially

microporous network whereas the use of potassium hydroxide gave well-

developed mesoporous activated carbon.

Production of activated carbon from biological sludge (Martin et al

2002) and sewage sludge (Rozada et al 2003) by chemical activation using

phosphoric acid at 700 C for 30 min yielded mesoporous network with

certain percentage of macropores. Preparation of activated carbon from cork

waste using potassium hydroxide at 800 C for 2h yielded surface area of

1415 m2 g-1 (Carvalho et al 2003)

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Srinivasakannan et al (2004) carried out a two-stage process for the

preparation of activated carbon from rubber wood saw dust. The two-stage

process with semi-carbonization up to 200 C for 15 min followed by

activation at 400 and 500 C for 30, 45, 60 and 90 min. Phosphoric acid was

used as an activating agent with various impregnation ratio (dry wt. of H3PO4/

dry wt. of rubber wood saw dust) of 1, 1.5, and 2. At the optimal conditions of

activation, activated carbon with iodine number and surface area of

1096 mg g-1 and 1496 m2 g-1 respectively were obtained.

Corcho et al (2006) prepared activated carbon from vineyard shoot

using phosphoric acid as the activating agent. They found the activated

carbons porosity was better when the raw material was impregnated and

heated at intermediate temperatures. Haimour & Emeish (2006) reported

phosphoric acid activated date pit carbon, the iodine number increased with

increasing activation temperature. Impregnation increases caused an

oscillation in the iodine number.

Senthilkumaar et al (2006a) prepared activated carbon from male

flowers of coconut tree and jute fibre using 15% phosphoric acid in the ratio

1:3. They found a porosity of 72.36% and 76.14%, surface area of 328 and

680 m2/g and pHzpc of 6.23 and 4.56 for coconut flower carbon and jute fibre

carbon respectively indicating that the fibrous materials gave a higher surface

area than the other cellulosic materials. The porosity of the carbon varied

based on the activating agent, activated carbon prepared from coconut male

flower using phosphoric acid and sulphuric acid (Senthilkumaar et al 2006b)

yielded carbons with 72.36% and 65% porosity respectively.

Baccar et al (2009) prepared activated carbon from olive-waste

cake using phosphoric acid as a activating agent, carbon preparation

parameters such as concentration of the activating agent, impregnation ratio

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and activation time were optimized. They found the surface area of the

sorbent increased rapidly from 716 to 1020 m2/g with an increase of acid

concentration from 35 to 65% phosphoric acid, and further increase in the

acid concentration (85%) did not show an appreciable increase in the surface

area. Chan et al (2009) prepared activated carbon from bamboo waste

scaffolding using phosphoric acid. They found the surface area up to

2500 m2/g of the activated carbon increased with impregnation ratio (2.4) and

activation temperature (400 or 600ºC).

Lim et al (2010) prepared activated carbon from palm shells by

phosphoric acid impregnation. They prepared carbon at low activation

temperature (425ºC) and activation time (30 min), while varying the

impregnation ratio of phosphoric acid from 0.5 to 3. The yield of activated

carbon was not vary with the impregnation ratio and was found to be about

50%. The textural characteristics were found to improve with increase in the

impregnation ratio, up to 2 and further increase in IR the textural character

decreased. The BET surface area of activated carbon corresponding to an

impregnation ratio of 3, with an iodine number of 1035 mg/g was found to be

1109m2/g with a pore volume of 0.903cm3/g and an average pore diameter of

3.2 nm. The textural characteristics of activated carbon reveal that the pore

size is widely distributed with the contribution of micropores around 50%.

Fabiana et al (2010) prepared activated carbon from piassava fibres

using chemical activation with zinc chloride and phosphoric acid and physical

activation with carbon dioxide or water vapour. Zinc chloride gave the highest

surface area of 1190 m2/g and phosphoric acid activated carbon gave largest

pore volume of 0.543 cm3/g. Li et al (2010) reported that activated carbon

prepared from polygonum orientale Linn by phosphoric acid activation gave a

surface area of 1398 m2/g.

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Bhari et al (2012) prepared activated carbon from grape seeds using

chemical activation with phosphoric acid. Grape seeds were pre-treated with

sulfuric acid to improve its wettability. Microporous activated carbons with

some contribution of mesoporosity were obtained. The best results in terms of

surface area (1139 m2/g) and mesopore volume (0.24cm3/g) development

were observed for a grape seeds to phosphoric acid ratio of 1:3 and a

carbonization temperature of 500°C. They found the activated carbon

morphology had an egg shell structure that favored applications in liquid

phase.

Mohamad & Paul (2012) studied the pore characteristics of

activated carbons obtained from the phosphoric acid activation of cotton

stalks. They concluded that the textural characteristics of the derived activated

carbons were found to be strongly dependent on the impregnation ratio and

activation temperature. The mesopore volume attained a maximum value

(0.61cm3/g) in the case of activated carbons produced at the highest

impregnation ratio and activation temperature.

Aghdas et al (2014) revealed the impregnation ratio of the

activating agent highly influenced the surface area and the porosity

development during activated carbon preparation. They prepared highly

microporous activated carbon from Eucalyptus camaldulensis wood by

chemical activation with H3PO4, ZnCl2 at different impregnation ratios as well

as by pyrolysis, followed by activation with KOH. Varying the

H3PO4/biomass ratio from 1.5 to 2.5, the prepared activated carbon displayed

BET surface areas in the range of 1875–2117 m2/g with micropores content of

69–97%. For the ZnCl2 activated carbon, BET surface areas varyied from

1274.8 to 2107.9 m2/g with micropores content of 93–100% for impregnation

ratios of 0.75–2.0. The activated carbon obtained by KOH activation had the

largest BET surface area of 2594 m2/g and a high micropore of 98%. From

21

the above they found that the activating agent and its concentration strongly

influenced the textural characteristics of the eucalyptus wood based activated

carbon.

Alicia et al (2014) studied the influence of activation atmosphere

used in the chemical activation of almond shell on the carbon characteristics.

They found activated carbons prepared at low and intermediate impregnation

ratios showed higher yields. This could be attributed to the decomposition of

the polymeric structures of the activated carbons during the activation stage

that release most elements different from carbon (N, H and O). Activating

agent employed permits the dehydration, depolymerization and redistribution

of the constituent polymers, and the conversion of aliphatic groups to

aromatics, increasing the yield of the activated carbons. Higher impregnation

ratios produce a higher elimination of tars of the pores decreasing the yield.

However, there are only a few publications reporting the

preparation of activated carbon from Agave sisalana fibre (Sisal fiber) and

Puninga granatum Peel (Pomegranate Peel) using phosphoric acid as

activating agent. One can design activated carbon for adsorption of specific

adsorbate, using approximate precursor and by optimizing the activation

process conditions. Cost effectiveness, cheap availability, higher adsorbate

loading capacity, relatively high surface area and high binding affinity were

the main criteria for choosing activated carbons to remove dyes from aqueous

solution. Taking this criteria into consideration, the present study was carried

out to determine the feasibility of using the relatively common, cheap and

thrown away waste Agave sisalana fibre (Sisal fiber) and Puninga granatum

Peel to prepare highly effective carbon with a large surface area. These

carbons were prepared using phosphoric acid as the impregnating agent by

chemical activation method followed by their characterization, for the

adsorption of reactive dye, acid dye and basic dye from aqueous solutions and

effluent, the studies being carried out in both batch and column mode.

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Table 2.1 Summary of H3PO4 activation on physiochemical properties of activated carbon

Precursor Activating

Agent/ Parameters

Physicochemical Properties of Activated Carbon

Author

Almond shell

H3PO4, ZnCl2,K2CO3 &Na2CO3. Temp400-700°C

Of the different activating reagents studied, zinc chloride gave the highest surface area of 2111 m2 g-1

Ruiz et al (1984)

Apricot Stone

H3PO4 Yielded high surface area and microporous structure

Philip & Girgis (1996)

Peach stones H3PO4

followed by activated in a CO2 gas flow at 825oC

Well-developed microporous structure with very small proportion of mesoporous network was obtained

Molinaet al 1995, 1996

Peanut hull and Oil palm stones

H3PO4, KOH and ZnCl2

with 500 and 650 C

They reported that zinc chloride and phosphoric acid activation yielded essentially microporous network whereas the use of potassium hydroxide gave well-developed mesoporous activated carbon.

Girgis et al (2002)and Guo & Lua (2000)

Sewage sludge

H3PO4

700 C for

30 min

Yielded mesoporous network with certain percentage of macropores

Rozadaet al 2003

Rubberwood saw dust

H3PO4 400 & 500 C for 30, 45,60 & 90min

Maximum iodine number and surface area of 1096 mg g-1

and 1496 m2 g-1 respectively

Srinivasakannan et al (2004)

23

Table 2.1 (Continued)

Vineyardshoot

H3PO4

Activation They found the activated carbons porosity was better when the raw material was impregnated and heated at intermediate temperatures.

Corchoet al (2006)

Date pit H3PO4

Activation the iodine number increased with increasing activation temperature. Impregnation increases caused an oscillation in the iodine number.

Haimour & Emeish (2006)

Maleflowers of coconut tree and Jute fibre

15% H3PO4 in 1:3 ratio

They found a porosity of 72.36% and 76.14%, surface area of 328 and 680 m2/g and pHzpc of 6.23 and 4.56 for coconut flower carbon and jute fibre carbon respectively indicating that the fibrous materials gave a higher surface area than the other cellulosic materials.

Senthilkumaar et al (2006a)

Maleflowers of coconut tree

H3PO4 and H2SO4

Activation

H3PO4 and H2SO4 activated carbons with 72.36% and 65% porosity respectively

Senthilkumaar et al (2006b)

Olive-waste cake

35 to 65% of H3PO4

Activation

They found the surface area of the sorbent increased rapidly from 716 to 1020 m2/g with an increase of acid concentration from 35 to 65% phosphoric acid, and further increase in the acid concentration (85%) did not show an appreciable increase in the surface area.

Baccaret al (2009)

24

Table 2.1 (Continued)

Bamboo waste

H3PO4 in 2.4 ration, temp 400 or 600ºC

They found the surface area up to 2500 m2/g

Chan et al (2009)

Palm shells H3PO4

impregnation ratio of H3PO4

from 0.5 to 3 with 425ºC, 30 min

The textural characteristics were found to improve with increase in the impregnation ratio, up to 2 and further increase in IR the textural character decreased. The BET surface area of activated carbon corresponding to an impregnation ratio of 3, with an iodine number of 1035 mg/g was found to be 1109m2/g with a pore volume of 0.903cm3/g and an average pore diameter of 3.2 nm. The textural characteristics of activated carbon reveal that the pore size is widely distributed with the contribution of micropores around 50%

Lim et al (2010)

Piassavafibres

H3PO4 and ZnCl2

Zinc chloride gave the highest surface area of 1190 m2/g and phosphoric acid activated carbon gave largest pore volume of 0.543 cm3/g

Fabianaet al (2010)

Polygonum orientaleLinn

H3PO4

Activation Yielded surface area of 1398 m2/g

Li et al (2010)

25

Table 2.1 (Continued)

Grape seeds H3PO4

Impregnation ratio of 1:3 and temp 500°C

The best results in terms of surface area (1139 m2/g) and mesopore volume (0.24cm3/g) development were observed

Bhari et al (2012)

Cottonstalks

H3PO4

Activation They concluded that the textural characteristics of the derived activated carbons were found to be strongly dependent on the impregnation ratio and activation temperature. The mesopore volume attained a maximum value (0.61cm3/g) in the case of activated carbons produced at the highest impregnation ratio and activation temperature.

Mohamad& Paul (2012)

Eucalyptuswood

H3PO4,ZnCl2

followed by KOH

H3PO4 activated carbon BET surface areas in the range of 1875–2117 m2/g with micropores content of 69–97%. For the ZnCl2 activated carbon, BET surface areas varyied from 1274.8 to 2107.9 m2/g with micropores content of 93–100% for impregnation ratios of 0.75–2.0. The activated carbon obtained by KOH activation had the largest BET surface area of 2594 m2/g and a high micropore of 98%.

Aghdas et al (2014)

26

2.6 APPLICATION OF ACTIVATED CARBON

Activated carbon is a unique and effective agent for purification

and isolation and recovery of trace material. During the last three decades,

treatment with active carbon has become an important unit process for

separation and purification in wide range of industries. The various

applications can be broadly divided into two categories, (i) liquid-phase

applications (ii) gas-phase applications.

2.6.1 Gas-Phase Applications

This includes separation, gas storage and catalysis. These products

are generally more expensive than liquid phase carbons (Allen et al 1998).

Some of the gas-phase applications are listed below.

Recovery of solvents, e.g in rotogravure printing operations,

from coatings and in the packaging, food and chemicals

industries.

Natural gas purification; removal of H2S and BTX

Flue gas cleaning at waste incineration plants for the

removal of dioxins and heavy metals

Exhaust air treatment following production processes for the

removal of organic impurities

Purification of process gases, e.g. CO2; scrubbing and

separation of oil from compressed air

Removal of pollutants in airconditioning, ventilation and

exhaust systems

Removal of odourous substances in kitchen exhaust hoods

and refrigerator filters

27

Emission control, e.g. at filling stations and during tank

ventilation for motor vehicle and industrial applications

Pollutant removal in car interior ventilation systems in gas

masks

In cigarette and cigar filters

As a carrier medium for special impregnating agents or

catalysts

2.6.2 Liquid-Phase Applications

In the water treatment sector, activated carbon is used either in

powdered (suspension process) or granular (fixed bed process) form,

depending upon the specific application and process. The objectives pursued

with the use of activated carbon in water treatment have changed significantly

in recent decades. Years ago, activated carbon was employed primarily for the

removal of excess chlorine and the elimination of substances affecting odour

and taste from relatively good-quality raw water. Increasingly exacting

quality requirements for drinking water, coupled with increasing pollution

levels in untreated water (groundwater and surface water), have led to the

optimization of activated carbon as a means of guaranteeing acceptable

drinking water quality. In parallel, changes in treatment processes, such as the

reduction of high-strength chorine treatment, have resulted in the elimination

of traditional applications.

In recent years, the use of activated carbon processes has become

widely established in drinking water treatment, groundwater rehabilitation

and the treatment of service water. Likewise, activated carbon is being used to

an increasing extent in waste water treatment, whether it be in the systematic

treatment of individual effluent streams (e.g. in the chemicals industry), in the

removal of substances toxic to bacteria in biological waste water treatment or

28

in tertiary waste water treatment, where effluent restrictions are particularly

severe.

Among the wide range of physical, chemical and biological

processes used in waste water treatment, activated carbon adsorption is

gaining steadily in importance. The use of activated carbon is especially

advisable in cases requiring the removal of toxic substances or pollutants that

are not easily biodegradable. Activated carbon is almost always employed in

the treatment of waste water in the paper, textile and petrochemical industries.

The textile finishing industry generates a large amount of wastewater.

Wastewaters from dyeing and subsequent rinsing steps form one of the largest

contributions to wastewater generation in the textile industry. Because dyes

are almost invariably toxic, their removal from effluent stream is ecologically

necessary (Santhy & Selvapathy 2006).

2.7 TREATMENT OF TEXTILE EFFLUENTS

Environment is the broad concept encompassing the whole range of

diverse surroundings, which we perceive, experience and react to events and

changes that are taking place on it. It includes land, water and air. One of the

main problems prevailing in this environment is pollution. It is the unhealthy

and undesirable change in the environment that is caused directly or indirectly

by the human beings, either in the process by living or through any industrial

processes. Considering the volume discharge and effluent composition, the

wastewater generated by the textile industry is rated as one of the most

polluting among the industrial sectors. The dye is the major polluting agent of

water among the various processes. The principal route by which the dye

enters the environment is through wastewater from the manufacturing activity

in both the dye manufacturing and the dye consuming industries. It produces

large volume of effluents that are toxic, resistant to physiochemical treatments

and not easily biodegradable. The dyeing, bleaching and printing departments

29

contribute to the maximum dyeing effluents. Conventionally the wastewater

from the textile industry is treated using the following methods,

Primary treatment

Secondary or Biological treatment

Tertiary treatment

2.7.1 Primary Treatment

Primary treatment is done to remove the suspended solids and to

some extent to remove the colour and odour. This process includes screening,

neutralization, coagulation, sedimentation etc., screening process is mainly

done to remove the floating materials such as yarn, rags etc., equalization is

the process done mainly to maintain the pH and uniform flow throughout the

process. Coagulation is done to remove the suspended particles by using

alum, ferric chloride, ferrous sulphate and calcium chloride.

2.7.2 Secondary Treatment

Secondary treatment is done to break the complex organic

molecules to simpler substances. The biological treatment is also known as

the secondary treatment. This process involves aerobic and anaerobic

treatment. In aerobic treatment, the destruction takes place mainly in the

presence of oxygen and in the anaerobic treatment, destruction takes place in

the absence of oxygen. The secondary treatment involves activated sludge

process, trickling filtration, aerated lagoons and oxidation ponds. In the

trickling filtration process, the wastewater is brought in contact with that of

the microbial population in the form of a film of slime attached to the solid

surface as the supporting medium. The slimes formed on the stones oxidize

the waste during its passage. Aerated lagoons are activated sludge units

operated with the sludge return. In this aerated lagoon treatment, the effluent

30

from the primary treatment process is passed on to a tank and it is

mechanically aerated. An oxidation pond is a shallow pond in which the

waste is added at one end and the effluent is removed at the other end. Among

all the above processes the activated sludge process is employed widely.

2.7.3 Tertiary Treatment

Tertiary treatment is also termed as the advanced wastewater

treatment. The main purpose of this treatment is the reclamation of the water

for reuse resulting from the primary and biological treatments. This process

includes chemical coagulation/flocculation, membrane process,

electrochemical method, photolysis, ozonation and adsorption.

2.7.3.1 Coagulation/flocculation

The chemical coagulation/flocculation process is used to remove

colour, to reduce COD and suspended solids with the help of the chemicals

such as Fe3+/Cr3+, alum with lime etc., 50% reduction of COD and 57%

reduction of suspended solids were achieved in wool dyeing effluents using

100 mg/L of flucculant Zetas 92 (Norman & Seddon 1991). Lime and alum

mixture in dosage between 200 and 300 mg/L was the best coagulant mixture

to remove 80% of colour and 65% of BOD (Tapas et al 1998). The main

disadvantages of this method is the additional chemical load on the effluent

(normally increases salt concentration) which increases the sludge production

and leads to the incomplete dye removal.

2.7.3.2 Membrane process

Membrane processes involving the diffusion of a fluid through a

semi permeable membrane separating two solutions of different

concentrations and tending to equalize the concentration on the both sides of

31

the membrane. Semi permeable membrane has the ability to prevent the

passage of dissolved molecules while allowing passage solvent through the

membrane under pressure gradient (Marcucci et al 2001). This membrane

processes include reverse osmosis, ultrafiltration and nano filtration.

Reverse Osmosis membranes are susceptible to fouling due to

organics, colloids and microorganism. Scale causing constituents like

hardness and carbonate. Silica, heavy metals, oil etc has to be removed from

the feed. As the membranes are sensitive to oxidizing agents like chlorine or

ozone, they should also be absent. Ultra-filtration process is similar to reverse

osmosis. The difference between reverse osmosis and ultrafiltration is

primarily the retention properties of the membranes. Reverse osmosis

membranes retain all solutes including salts, while ultrafiltration membranes

retain only macro molecules and suspended solids. Thus salts, solvents and

low molecular weight organic solutes pass through ultrafiltration membrane

with the permeate water.

Nanofiltartion can be positioned between reverse osmosis and

ultrafiltration. Nanofiltration is essentially a lower pressure version

membrane where the purity of permeate water less important. This process is

used where the high salt rejection of reverse osmosis is not necessary. The

nanofiltration is capable of removing hardness elements such as calcium or

magnesium together with bacteria, viruses, and colour. Nanofiltration is

operated at lower pressure than reverse osmosis and as such the treatment cost

is lower than reverse osmosis treatment (CPCB 2007). Membrane separation

process is a new separation technology, with high separation efficiency, low

energy consumption, easy operation, no pollution and so on. However, this

technology is still not promoted on a large scale because it has the limitation

of requiring special equipment, high investment, membrane fouling and so on

(Ranganathan et al 2007).

32

2.7.3.3 Electrochemical methods

This process has an advantage of operating at low temperatures and

does not need the addition of reagents. Electrochemical technique is based on

effluent electrolysis in which the molecules are partially destroyed to avoid

excessive power consumption. This destruction of organic compounds can

occur directly at the anode and/or indirectly by species generated by the

anode. In the direct electrolysis method, an electron transfer reaction to or

from the undesired pollutant occurs at the surface of an electrode and in the

indirect electrolysis the dissolved redox reagent either exists in or is generated

from the electrolyte or from the electrode phase in order to participate in a

targeted reaction.

2.7.3.4 Photolysis

Photocatalysis is defined as the acceleration of a photoreaction in

the presence of a catalyst, while photolysis is defined as a chemical reaction

in which a chemical compound is broken down by photons. Photochemical

oxidation has many advantages of the mild reaction conditions (ambient

temperature and pressure), powerful oxidation ability and fast speed, etc. It

can be divided into 4 kinds, which are light decomposition, photoactivate

oxidation, optical excitation oxidation and photocatalysis oxidation. Among

them, the photocatalysis oxidation has been more researched and applied

currently. This technology can effectively destroy a lot of organic pollutants

whose structure is stable and difficult to biologically degrade. Compared with

the physical treatment in traditional wastewater treatment process, the most

obvious advantages of this technology are significant energy efficiency,

complete degradation of pollutants and so on. Almost all of the organic matter

can be completely oxidized to CO2, H2O and other simple inorganic

substances under the light catalyst. However, towards high concentration

wastewater, the effect of the photocatalysis oxidation process is not ideal. The

33

research about photocatalytic degradation of dye is mainly focused on the

study of photocatalyst (Peter 2011).

2.7.3.5 Ozonation

Ozone is one of the strongest oxidizers commercially available and

popular for disinfection of potable water. Besides this it has multiple

applications. Large, complex organic molecules, detergents, phenols etc. can

be broken into simpler compounds by ozonation. Among the industrial

applications, oxidation of organics and inorganics, deodorisation, and

decolourisation are the main usages. Ozone is an unstable gas at temperature

and pressure encountered in water and waste water treatment plants. For most

industrial applications ozone has to be produced at insitu. Although, there are

several methods by which ozone can generated, the corona discharge method

is a widely used procedure. An ozone generation unit incorporates a series of

electrodes fitted with cooling arrangements mounted in a gas tight container.

When the source gas (air or oxygen) is passed through narrow gap separating

electrodes, the oxygen gets converted into ozone. Ozone is applied to waste

water by means of diffuser tubes or turbine mixers. Ozone doses in level of 2

mg/L have been reported to result in virtually complete removal of colour and

hard pollutants such as detergents. The treated water after sand filtration

becomes clean and sparkling (CPCB 2007). In textile effluent it initiates and

accelerates azo bond cleavage. The negative effect is the release of

carcinogenic aromatic amines and otherwise toxic molecules and, therefore, it

should not be used (Sheng et al 1997).

2.7.3.6 Adsorption

Adsorption is the most used method in physicochemical wastewater

treatment, which can mix the wastewater and the porous material powder or

granules, such as activated carbon and clay, or let the wastewater through its

34

filter bed composed of granular materials. Through this method, pollutants in

the wastewater are adsorbed and removed on the surface of the porous

material or filter. Commonly used adsorbents are activated carbon, silicon

polymers and kaolin. Different adsorbents have selective adsorption of dyes.

But, so far, activated carbon is still the best adsorbent for dye wastewater. The

chroma can be removed to 92.17% and COD can be reduced to 91.15% in

series adsorption reactors, which meet the wastewater standard in the textile

industry and can be reused as the washing water. Because activated carbon

has selection to adsorb dyes, it can effectively remove the water-soluble dyes

in wastewater, such as reactive dyes, basic dyes and azo dyes, but it cannot

adsorb the suspended solids and insoluble dyes. Moreover, the activated

carbon cannot be directly used in the original textile dyeing wastewater

treatment, while generally used in lower concentration of dye wastewater

treatment or advanced treatment because of the high cost of regeneration

(Peter 2011).

2.8 ADVANTAGES OF ADSORPTION OVER OTHER

METHODS

Colour in dye house effluents has always been a difficult problem

to solve and the utilization of dyes has made it even more serious. Cooper

(1993) summarized the technologies used until then in order to remove or

atleast reduce colour, mentioning that some them have certain efficiency:

Coagulation and/or flocculation, membrane technologies, chemical oxidation

technologies, biochemical oxidation and adsorbent utilization. Among various

treatment technologies, adsorption onto activated carbon has proven to be one

of the most effective and reliable physicochemical treatment methodology

(McKay 1996, Sankar et al 1993). Ramesh et al (2007) reviewed the

advantages and disadvantages of various treatment techniques and are

presented in Table 2.1. The adsorption process has an edge over the other

35

treatment methods due to its sludge free operation, and complete removal of

dyes even from dilute solutions. The wide usefulness of activated carbon is a

result of its chemical and mechanical stability, high adsorption capacity and

high degree of surface reactivity (Malik 2003).

Table 2.2 Possible treatments for cotton textile wastes and their associated advantages and disadvantages (Ramesh et al, 2007)

Process Advantages Disadvantages References

Biodegradation Rates of elimination by oxidizable substances about 90%

Low biodegradability dyes

Pala & Tokat 2002; Ledakowicz et al 2001

Coagulation/ flocculation Elimination of insoluble dyes Production of sludge

blocking filter Gaehr et al 1994

Adsorption on activated carbon

Suspended solids and organic substances well reduced

Cost of activated carbon

Arslan et al 2000

Ozone treatment Good decolourization No reduction of the COD

Adams et al 1995; Lin & Chen 1997

Electrochemical Process

Capacity of adaptation of different volumes and pollution loads

Iron hydroxide sludge

Lin & Peng 1994; Lin & Chen 1997

Reverse osmosis Removal of all minerals salts, hydrolyzes reactive dyes and chemical auxiliaries

High Pressure Ghayeni et al 1998

Nanofiltration

Separation of organiccompounds of low molecular weight and divalent ions from monovalent salts. Treatment of high concentrations

-

Erswell et al 1998; Xu et al 1999; Akbari et al 2002; Tang & Chen 2002

Ultrafiltration-microfiltration Low pressure

Insufficient quality of the treated wastewater

Watters et al 1991; Rott & Minke 1999; Ciardelli & Ranieri 2001; Ghayeni et al 1998

Cost effectiveness and adsorption properties are the main criteria

for choosing an adsorption process to remove dyes from aqueous solution.

Adsorption process has higher selectivity. Adsorption based process offer a

36

more reliable and highly efficient in the removal of complex structure dyes

than many other conventional treatment methods.

The adsorption process achieves higher removal levels in a wide

range of solution conditions and generally reduces the quantity of sludge or

solid residuals that need to be disposed (Smith 1996). The adsorption

phenomenon has still been found to be economically appealing for the

removal of toxic dyes from textile effluents by choosing adsorbents under

optimum operating conditions. Therefore, the adsorption process is reported

to be the best method for removal of textile dyes.

2.9 ADSORPTION PROCESS

Adsorption (Slejko 1985, Suzuki 1990, Noll et al 1992) involves

the preferential partitioning of substances from the gaseous or the liquid phase

accompanied by its accumulation or concentration onto the surface of a solid

substrate. The adsorbing phase is the adsorbent, and the material concentrated

or adsorbed at the surface of that phase is the adsorbate.

2.9.1 Gas Phase Adsorption

This is a condensation process where the adsorption forces

condense the molecule from the bulk phase within the pores of the adsorbent.

The driving force for adsorption is the ratio of the partial pressure and the

vapour pressure of the compound.

2.9.2 Liquid Phase Adsorption

The molecules go from the bulk phase to being adsorbed in the

pores in a semi-liquid state. The driving force for adsorption is the ratio of the

concentration to the solubility of the compound.

37

2.9.3 Adsorption Mechanism

The adsorption process results from interaction between carbon

surface and the adsorbate. Those interactions can be electrostatic or non-

electrostatic. When the adsorbate is an electrolyte that dissociates in aqueous

solution, electrostatic interactions occur; the nature of interactions, that can be

attractive or repulsive, depends on the: (i) change in density of the carbon

surface: (ii) chemical characteristics of adsorbate: and (iii) ionic strength of

solution. Non electrostatic interactions are always attractive and include:

(i) Vander waals forces: (ii) hydrophobic interactions; and (iii) hydrogen

bonding (Joana et al 2007).

According to Moreno (2004), the properties of the adsorbate that

mainly influence the adsorption process in activated carbons are:

(1) Molecular size; (2) Solubility; (3) Dissociation constant of solution (pKa)

and (4) Nature of the substituents (in the case of aromatic adsorbate). The

molecular size determines the accessibility of the adsorbate to the pores of the

carbon, solubility determines the degree of hydrophobic interactions between

the adsorbate and the carbon surface and pKa controls the dissociation of

adsorbate (if it is an electrolyte). When the adsorbate is aromatic, the

substituents of the aromatic rings have the ability to withdraw or release

electrons, which therefore affects the non-electrostatic interactions between

the adsorbate and activated carbon surface.

Adsorption process is classified as either physical or chemical. Physical adsorption occurs when the Vanderwaals forces bind the adsorbing molecule onto the solid substrate; these intermolecular forces are the same as the bond molecules to the surfaces of a liquid. It follows that heats of adsorption are comparable in magnitude to latent heats (10 to 70 KJ/mol). Specifics that are physically adsorbed to a solid can be released by applying heat; the process is reversible. An increase in temperature causes a decrease in adsorption efficiency and capacity.

38

Chemical adsorption occurs when covalent or ionic bonds are

formed between the adsorbing molecules and the solid substrate. This

bonding leads to a change in the chemical form of the adsorbed compounds,

and is therefore not reversible. The bonding forces for chemical adsorption

are much greater than for physical adsorption. Thus, more heat is liberated.

With chemical adsorption, higher temperatures can improve performance.

Young et al (2002) reported the novel synthesis and characterization of

activated carbon fiber and dye adsorption modelling. They explained Bottle-

neck diffusion modeling for the equilibrium isotherm. Figure 2.1 illustrates

the approximate dye adsorption on activated carbon. Firstly, dye particles

diffuse into the pore of activated carbon, and are then adsorbed in the order of

surface, pore entrance and pore interior. The pore diameter shrinks and the

pore length becomes short because of the dye adsorption. The narrow pore

hinders the dye diffusion into the pore interior. So, this phenomenon is called

bottle-neck diffusion in this study.

Figure 2.1 Conceptual diagram of dye adsorption on activated carbon fiber as proposed by the bottle-neck model

39

2.10 ADSORBENTS

Adsorbents (Noll et all 1992, Oscik et al 1982) are porous materials

that contain many miniscule internal pores. The most common industrial

adsorbents are activated carbon, silica gel and activated alumina, because they

present enormous surface areas per unit weight. Activated carbon is produced

by thermal degradation of organic material to decompose it to granules of

carbon. Agro waste and animal waste are the common source. Typical surface

areas are 300 to 1500 m2/g. Silica gel is a matrix of hydrated silicon dioxide.

Silica is used to separate hydrocarbons. Typical surface areas are 300 to

900 m2/g. Activated alumina are commonly used to remove oxygenenates and

mercaptans from hydrocarbons and fluorides from water. Typical surface

areas are 200 to 400 m2/g. The adsorbent such as zeolite, carbon molecular

sieve, bone char, iron and manganese coated sand, kaolinite clay, hydrated

ferric oxide, activated bauxite, titanium oxide, silicium oxide and other

synthetic media are also widely used.

Activated carbons are known as very effective adsorbents due to

their highly developed porosity, large surface area, variable characteristics of

surface chemistry, and high degree of surface reactivity (Bansal et al 1988).

However, due to high production cost, these materials tend to be more

expensive than other adsorbents. Currently there are many studies on the

development of low-cost adsorbents, namely by using waste materials for that

purpose.

Activated carbon production costs can be reduced by either

choosing a cheap raw material or by applying a proper production method

(Lafi 2001); nevertheless, it is still a challenge to prepare activated carbon

with very specific characteristics, such as a given pore size distribution, and

using low-cost raw materials processed at low temperature (less energy cost)

(Sudaryanto et al 2006). Therefore, it is of extreme relevance to find suitable

40

low-cost raw materials that are economically attractive from the point of view

of their contribution to decrease the costs of waste disposal, therefore helping

environmental protection (Joana et al 2007).

2.11 ADSORBATE

The industrial wastewater usually contains a variety of organic

compounds and toxic substances which are harmful to fish and other aquatic

life. Dyeing wastewater discharged to natural receiving waters may make

them unacceptable for public consumption. Thus, it is desirable to eliminate

dyes from textile wastewater. Dyes are one of the hazardous groups that are

emitted into wastewaters from various industrial branches, mainly from the

dye manufacturing and textile finishing. Reactive dyes, Acid dyes and Basic

dyes are commonly used dyes for dyeing of Cotton, Silk, Wool and Acrylic

materials. The detailed classification of dyes is presented in section 2.12.

2.12 TEXTILE DYES

The dyeing industry uses various types of dyes. The dye contains

two components in it namely the chromophore and the auxochrome. The

chromophore as its name indicates is the colour containing compound and the

auxochrome is the backbone which holds the chromophore. The chromophore

configurations are represented by the azo group (-N=N-), ethylene group

(=C=C=), methine group (-CH=), carbonyl group (=C=O), carbon-nitrogen

(=C=NH; -CH=N-), carbon-sulphur (=C=S; CS-S-C ), nitro (-NO2; -NO-

OH), nitrozo (-N=O; =N-OH) or chinoid groups. The auxochrome groups are

ionizable groups, that confer to the dyes the binding capacity onto the textile

material. The usual auxochrome groups are: amino (-NH2), carboxyl

(-COOH), sulphonate (-SO3H) and hydroxyl (-OH) (Suteu et al 2011;

Welham 2000). These dyes have a conjugated system, that is a structure with

alternating single and double bond. The chromophore should be a part of this

41

conjugated system. These conjugations are present in benzene and azo

compounds. (IARC-WHO).

2.12.1 Classification of Textile Colorants

Textile colourants are classified into two classes one is water

soluble called are dyes and the other water insoluble called pigments (Allen

1971). The dyes are mainly classified as two categories based on its chemical

nature and its application. The Colour Index recognizes 26 types of dyes by

chemical classification. They are as follows: (1) Nitrazo, (2) Mono, dis-,

tri- and poly azo, (4) Azoic, (5) Stilbene, (6) Carotenoid, (7) Diphenyl

methane, (8) Triphenylmethane, (9) Xanthene, (10) Accridine, (11) Quinoline

(12) Methine and polymethine, (13) Thiazole, (14) Indamine and indolphenol,

(15) Azine, (16) Oxize, (17) Triazine, (18) Sulfur (19) Amino-Ketone

(20) Hydroxyl Ketone, (21) Anthraquinone, (22) Indigoid,

(23) Phthalocyanine, (24) Natural organic colouring matter, (25) Oxidation

bases and (26) Inorganic colouring matter.

It is convenient to use the classification based on its application, the

US International Trade Commission classified dyes based on the application

as follows: (1) Acid dyes, (2) Azoic dyes, (3) Basic dyes, (4) Direct dyes, (5)

Reactive dyes, (6) Mordant dyes, (7) Solvent dyes, (8) Sulfur dyes and (9) Vat

dyes. The use-wise classification of dyestuffs is more important from a

practical point of view as for the manufacturers market name and number.

2.12.1.1 Direct dyes

Direct cotton dyes have inherent substantivity for cotton and for

other cellulosic fibres. Chemically, direct dyes are sodium salt of aromatic

sulphonic acids and most of them contain an ‘azo’ group as the main

chromophore. These classes of dyestuffs are applied directly to the substrate

42

in a neutral or alkaline bath. The bath is then gradually heated, usually to the

boil, and additions of salt promote dyeing. Direct dyes give bright shades but

exhibit poor wash fastness (Koushik & Antao 2003).

2.12.1.2 Reactive dyes

Reactive dye is a type of water soluble anionic dye having good

affinity for cellulose fibres. In the presence of alkali, they react with hydroxyl

groups present in the cellulose and thus are linked with the fibre by means of

covalent bond. Fibre reactive dyes are relatively new dyes and are used

extensively on cellulosics when bright shades are desired. Reactive dyes,

particularly those used for dyeing of cotton, have become one of the major

classes of dye because of their good washing fastness, ability to produce

bright shades and versatility in application either by batch or continuous

dyeing methods.

2.12.1.3 Acid dyes

Acid dyes are organic sulphonic acids, the commercially available

forms are usually sodium salts, which exhibit good water solubility. In

sequence of their importance, acid dyes are mostly used with certain fiber

types such as polyamide, wool, silk, modified acrylic, and polypropylene

fibers, as well as blends of the aforementioned fibers with other fibers such as

cotton, rayon, polyester, regular acrylic, etc. According to their structure, acid

dyes belong to the following chemical groups: azo, anthraquinone,

triphenylmethane, pyrazolone, nitro and quinoline. Azo dyes represent the

largest and most important group followed by anthraquinone and

triarylmethane dyes.

43

2.12.1.4 Basic dyes

Basic dyes are called so since they are salts of organic bases, it is

also called as cationic dyes as in aqueous solution their molecules ionize into

coloured cations and colourless anions. Basic dyes are used for dyeing wool,

silk, acrylic and modacrylic fibres. The outstanding characteristics of the

basic dyes are the brilliance and intensity of their colours. They have poor

fastness to light and poor to moderate washing fastness. Basic dyes belong to

different chemical classes such as azo, diphenylmethane, triphenylmethane,

methane, acridine, xanthane, azine, induline, oxazine, thiazine, thiazole, etc.

2.12.1.5 Azoic dyes

Azoic dyes are a type of azo compound which is formed on the

fibre by first treating the fibre with a phenolic compound. The fibre is then

immersed in a solution containing a diazonium salt that reacts with the

phenolic compound to produce a coloured azo compound. Since the phenolic

compound is dissolved in caustic solution, these dyes are mainly used for

cellulose fibre, although other fibres can be dyed by modifying the process.

2.12.1.6 Vat dyes

Vat dyes are one of the oldest types of dye. It gives the best overall

fastness properties with cellulosic fibres. Its application involves reduction to

the water soluble leuco compound, dyeing the cotton and re-oxidation of the

leuco dye in the fibres to the insoluble pigment. Vat dyes are among the most

resistant dyes to both washing and sunlight. They are widely used on cotton,

linen rayon, and other cellulosic fibres.

44

2.12.1.7 Sulphur dyes

Sulphur dyes are a class of water insoluble dye that are applied in a

soluble, reduced form from a sodium sulfide solution and are then reoxidized

to the insoluble form on the fibre. Sulfur dyes are mainly used on cotton for

economical dark shades of moderate to good fastness to washing and light.

They generally give very poor fastness to chlorine.

2.12.1.8 Disperse dyes

Disperse dyes are with extremely low water solubility in water

which is in finely dispersed state. The size of a disperse dye particles is in the

region of approximately 0.5 – 1 m. Disperse dyes are applied in the form of

fine aqueous dispersion. The fibres readily coloured by disperse dyes are

cellulose acetate, polyester, acrylic, and nylon. Chemically,the disperse dye

belong to various classes such as azo, anthroquinone, methane and

diphenylamine.

2.12.1.9 Metal complex dyes

Metal complex dyes are also called pre-metallised acid dyes. This is

because a metal, usually chromium, is incorporated in the dye molecule

during its manufacture. The incorporation of metal in the dye molecule

enables the dye to be more readily applied to the fibre and therefore

facilitates a dyeing process that is relatively short.

2.13 REVIEW OF ADSORPTION OF REACTIVE DYES

Low & Lee (1997) studied the sorption of hydrolysed Reactive

Blue 2 on quaternized rice husk they showed that the binding capacity of the

sorbent was not suppressed by dye bath conditions of high concentration

electrolytes. Its sorption capacity decreased with increasing concentration of

45

NaOH. Complete regeneration of dye-coated quaternized rice husk was not

possible under base treatment, suggesting chemisorption of dye molecules on

the sorbent material. The physical stability of the quaternized rice husk was

examined by treating it with various concentrations of NaOH solution.

Results showed that no dissolution of sorbent occurred, even in 1 M NaOH

solution.

Ming & Hsing (2002) investigated the adsorption of C.I Reactive

red 189 (RR189) on cross-linked chitosan beads, including the effects of

particle sizes on the isotherm, and the effects of the initial dye concentrations,

temperature, pH and the epichlorohydrin/chitosan weight ratio on the kinetics

of the adsorption processes. The cross-linked chitosan beads have a high

adsorption capacity to remove dye RR 189. The maximum monolayer

adsorption capacities of cross-linked chitosan beads with diameters 2.3–2.5,

2.5–2.7 and 3.5–3.8mm were 1936, 1686 and 1642 g/kg, respectively, at pH

3.0, temperature 30ºC and epichlorohydrin/chitosan weight ratio of 0.2.

A decrease in the pH of the solutions lead to a large increase in the adsorption

capacity of dye RR189 on the cross-linked chitosan beads.

Khraisheh et al (2002) studied the rate-limiting steps of reactive

dye adsorption onto FS-400 activated carbon, elucidated through the

investigation of adsorption kinetics. They revealed initially that only 20% of

the available adsorption capacity was achieved during the first 6 h. Kinetic

profiles showed that the adsorption process was mainly controlled by external

diffusion during the first 30 min of the reaction, after which internal diffusion

controlled the process. The interruption test method identified the rate-

limiting steps; the results showed that sorption of reactive dyes onto FS-400

were mainly controlled by internal diffusion. Furthermore, the external and

internal diffusion coefficients and the desorption rate decreased after the

interruption period. The same parameters increased when the solution

46

temperature was raised. The thermodynamic parameters studied showed that

the adsorption of reactive dyes onto activated carbon was endothermic and

was mainly controlled by internal diffusion with a minor effect of external

diffusion.

Daniela & Doina (2005) studied the adsorption capacity of

commercial powdered activated charcoal when used for the sorption of

reactive dye Brilliant Red HE-3B from aqueous solutions. The sorption of

reactive dye Brilliant Red HE-3B on activated carbon has an insignificant

variation with pH in the range 5–11, when the sulphonic acid groups of the

dye are completely deprotonated. Because the pH of the aqueous dye solution

is about 7. The dye amount sorbed increased with increasing dye

concentration but the percent of dye removal decreased. The amount of dye

sorbed increase with increasing temperature, suggesting an endothermic

process. Also they found high temperatures favor the dye molecule diffusion

in the internal porous structure of activated carbon.

Santhy & Selvapathy (2006) investigated the removal efficiency of

activated carbon prepared from coir pith towards three highly used reactive

dyes in textile industry C.I Reactive orange 12, C.I Reactive red 2 and C.I

Reactive Blue 4 in batch mode. Adsorption of dyes was found to follow the

Freundlich model. Kinetic studies indicated that the adsorption followed first

order and the values of the Lagergren rate constants of the dyes were in the

range of 1.77 10-2 to 2.69 10-2 min-1. The column experiments using

granular form of the carbon (obtained by agglomeration with polyvinyl

acetate) showed that adsorption efficiency increased with an increase in bed

depth and decrease of flow rate. The bed depth service time (BDST) analysis

carried out for the dyes indicated a linear relationship between bed depth and

service time. The exhausted carbon could be completely regenerated and put

47

to repeated use by elution with 1.0 M NaOH. They also found the adsorption

studies significantly reduced COD levels of the textile wastewater.

Senthilkumaar et al (2006a) investigated the adsorption of Reactive

red dye (RR) onto Coconut tree male flower carbon (CFC) and Jute fibre

carbon (JFC) from aqueous solution. Quantitative removal of Reactive red

dye was achieved at strongly acidic conditions for both the carbons studied.

The adsorption isotherm data fitted well to the Langmuir isotherm and the

adsorption capacity were found to be 181.9 and 200 mg/g for CFC and JFC,

respectively. By Elovich model to study the mechanism of adsorption,

calculated qe values agreed well with the qe experimental values, supporting

chemisorption. Analysis of mechanistic steps involved in the adsorption

process confirmed that the adsorption process was film-diffusion controlled.

Xiaoyan & Bushra (2005) studied the adsorption equilibrium and

kinetics of three reactive dyes from their single-component aqueous solutions

onto activated carbon in a batch reactor. The results show that the modified

pseudo-first-order kinetic model generates the best agreement with the

experimental data for the three single-component adsorption systems. The

adsorption equilibrium and kinetics of three adsorption systems (RN/F400,

RR/F400 and RY/F400) were studied. It was found that the adsorption

equilibrium of the three adsorption systems could be fitted by the four-

parameter Fritz–Schlünder isotherm model. Effects of the initial

concentration and adsorbent particle size on adsorption rate were investigated.

The rate constant of the modified pseudo-first-order kinetic model was found

to decrease with both increasing initial concentration and increasing adsorbent

size. It was also found that the rate constant of RY/F400 system was much

larger than that of RR/F400 system, which in turn was slightly larger than that

of RN/F400 system. This was attributed to the difference in molecular size

and polarity of the three reactive dyes.

48

Orfao et al (2005) studied that the surface chemistry of activated

carbons plays a key role in the performance of the reactive dye adsorption

process. The adsorption kinetics of the C.I. Reactive red 241 on the three

activated carbons (slightly basic - commercial, acid, and basic - prepared in

the context of this study) was well described by the second order model in the

wide pH range studied (2–12). Langmuir provides the best fit. Irrespective of

the solution pH, the adsorption of the reactive dye on basic activated carbons

was favoured, mainly due to the dispersive interactions between the

delocalized electrons in the carbon basal planes and the free electrons in the

dye molecules (aromatic rings and N=N bonds). In relation to reactive dyes,

the pH value must be lower than the pH of the activated carbon under

consideration in order to maximize adsorption.

Ponnusami et al (2007) investigated the biosorption of reactive red

RGB on rice husk treated with nitric acid. The efficiency of color removal

was determined after 60 min of treatment. They investigated that nitric acid

treated rice husk is effective in removal of reactive dye and could provide an

economical solution for removal of such dyes from aqueous solutions. For

50 mg/L solution maximum color removal of 96.33% was achieved with

pH 2, 5 g/L of adsorbent, and 40°C. Similarly for 250 mg/L solution

maximum color removal was achieved at pH 2, 50 g/L of adsorbent and 40ºC.

They found adsorbent dosage, initial concentration of dye and solution pH

were highly significant.

Chung (2007) examined the equilibrium and dynamic adsorption

of Procion Red MX-5B onto CNTs at various pHs and temperatures. The

adsorption capacity was highest when 0.25 g/L CNTs was added. The results

suggested that the adsorption of Procion Red MX-5B on CNTs decreased as

the pH but increased with temperature. RL lay between zero and unity,

revealing that the adsorption of Procion Red MX- 5B on CNTs was favorable.

49

The adsorption of Procion Red MX-5B onto CNTs was endothermic, the

result was supported by the increasing adsorption of Procion Red MX-5B

with temperature. The values of H , G and Ea all suggested that the

adsorption of Procion Red MX-5B onto CNTs was a physisorption process

and was spontaneous.

Yahya et al (2007) examined that the activated carbon with a large

surface area (820 m2/g) and a modest surface charge density (0.54 group/nm2)

was shown to be effective in removing anionic reactive dyes from solution. At

pH 7.0 and 298 K, the maximum adsorption values as described using the

Langmuir equilibrium isotherm model was 0.27, 0.24, and 0.11 mmol/g for

C.I. Reactive Blue 2, C.I. Reactive Yellow 2 and C.I. Reactive Red 4 dyes,

respectively. The formation of a complete monolayer was not achieved and

the fraction of surface coverage was calculated as 0.45, 0.42, and 0.22 for C.I.

Reactive Blue 2, C.I. Reactive Yellow 2 and C.I. Reactive Red 4 dyes,

respectively. The adsorption capacity of the dyes on activated carbon

increased in acidic solutions, but decreased in basic solutions.

Al-Degs et al (2009) examined a good removal of problematic

reactive dyes by fixed-bed activated carbon column. The characteristics of

MTZ of reactive yellow and black adsorption indicated that a better column

adsorber is achieved at longer bed-depth and diluted inlet dye concentration.

A service time of 36.5 h (at 90% exhaustion) was reported for reactive yellow

adsorption at carbon bed-depth 0.09 m, inlet dye concentration 0.19 kgm 3,

flow rate 5.0×10 6 m3min 1, pH 5, and particle diameter 600–710 m.

Analysis of reactive yellow adsorption data by BDST model revealed that

3.5 h was needed to exhaust 1.0 cm of carbon bed-depth at 50% break through

point.

50

Vijayaraghavan et al (2009) investigated the treatment of complex

Remazol dye effluent using sawdust and coal based activated carbon.

A complex Remazol dye effluent, comprised of four reactive dyes and

auxiliary chemicals, was decolorized using SPS-200 (sawdust-based) and

SPC-100 (coal-based) activated carbon and it was revealed that the pore

diameter plays a vital role in the adsorption of reactive dyes. The average pore

diameter of SPS-200 was higher than SPC-100 and thus, possess a high

adsorption capacity. This study also highlighted that the pore size of activated

carbon plays an important role in the uptake and adsorption kinetics of a dye.

Fernando et al (2011) studied that the multiwall carbon nanotube

(MWCNT) and powdered activated carbon (PAC) were good adsorbents to

remove Reactive Red M-2BE (RRM) textile dye from aqueous solutions. The

best condition was established with respect to pH and contact time to saturate

the available sites located on the adsorbent surface. Three kinetic models were

used to adjust the adsorption, and the best fit was the Avrami fractional

kinetic model. The equilibrium isotherm of the RRM dye was obtained, and

these data fit best to the Liu isotherm model. The maximum adsorption

capacities were 335.7 and 260.7 mg g 1 for MWCNT and PAC, respectively.

The thermodynamic parameters of adsorption ( H°, S° and G°) were

calculated. For treatment of simulated industrial textile effluents, the

MWCNT adsorbent presented very good performance for removing at least

98.7% of the mixture of dyes in a medium containing high saline

concentrations.

51

Table 2.3 Summary of adsorption results in reactive dye adsorption

Adsorbent Adsorbate Adsorption result Reference Quarternized rice husk

Reactive Blue 2

Sorption capacity decreased with increasing concentration of NaOH.

Low & Lee (1997)

Cross-linked chitosan beeds

Reactive Red 189

The maximum monolayer adsorption capacities of cross-linked chitosan beads with diameters 2.3–2.5, 2.5–2.7 and 3.5–3.8mm were 1936, 1686 and 1642 g/kg, respectively

Ming & Hsing (2002)

FS-400 activated carbon

Reactive dye The thermodynamic parameters studied showed that the adsorption of reactive dyes onto activated carbon was endothermic and was mainly controlled by internal diffusion with a minor effect of external diffusion

Khraisheh et al (2002)

Powdered activated charcoal

Brilliant Red HE-3B

The amount of dye sorbed increase with increasing temperature, suggesting an endothermic process. Also they found high temperatures favor the dye molecule diffusion in the internal porous structure of activated carbon.

Daniela & Doina (2005)

Coir pith C.I Reactive orange12, C.I Reactive red 2 and C.I Reactive Blue 4

Adsorption of dyes was found to follow the Freundlich model. Kinetic studies indicated that the adsorption followed first order. The bed depth service time (BDST) analysis carried out for the dyes indicated a linear relationship between bed depth and service time. 1.0 M NaOH was found as a desorption agent. They also found the adsorption studies significantly reduced COD levels of effluent.

Santhy & Selvapathy (2006)

52

Table 2.3 (Continued)

Coconut tree male flower carbon and Jute fibre carbon

Reactive red dye

The adsorption isotherm data fitted well to the Langmuir isotherm and the adsorption capacity were found to be 181.9 and 200 mg/g for CFC and JFC, respectively.

Senthil kumaar et al (2006a)

Commerical Activated Carbon (F400)

Reactive Red, Reactive Yellow, Reactive N

It was found that the adsorption equilibrium of the three adsorption systems could be fitted by the four-parameter Fritz–Schlünder isotherm model.

Xiaoyan & Bushra (2005)

Commercial activated carbon (Slightly basic - commercial, acid, and basic)

C.I. Reactive Red 241

Langmuir provides the best fit. Irrespective of the solution pH, the adsorption of the reactive dye on basic activated carbons was favoured, mainly due to the dispersive interactions between the delocalized electrons in the carbon basal planes and the free electrons in the dye molecule

Orfao et al (2005)

Rice husk Reactive Red RGB

For 50 mg/L solution maximum color removal of 96.33% was achieved with pH 2, 5 g/L of adsorbent, and 40°C. They found adsorbent dosage, initial concentration of dye and solution pH were highly significant.

Ponnusami et al (2007)

Carbon Nano Tubes

Procion Red MX-5B

The adsorption of Procion Red MX-5B onto CNTs was endothermic, the result was supported by the increasing adsorption of Procion Red MX-5B with temperature. The values of H , G and Ea all suggested that the adsorption of Procion Red MX-5B onto CNTs was a physisorption process and was spontaneous.

Chung (2007)

53

Table 2.3 (Continued)

Commercial activated carbon

C.I. Reactive Blue 2, C.I. Reactive Yellow 2 and C.I. Reactive Red 4

The maximum adsorption values as described using the Langmuir equilibrium isotherm model was 0.27, 0.24, and 0.11 mmol/g for C.I. Reactive Blue 2, C.I. Reactive Yellow 2 and C.I. Reactive Red 4 dyes, respectively. The formation of a complete monolayer was not achieved and the fraction of surface coverage was calculated as 0.45, 0.42, and 0.22 for C.I. Reactive Blue 2, C.I. Reactive Yellow 2 and C.I. Reactive Red 4 dyes, respectively.

Yahya et al (2007)

Commercial activated carbon

Reactive Yellow

Analysis of reactive yellow adsorption data by BDST model revealed that 3.5 h was needed to exhaust 1.0 cm of carbon bed-depth at 50% break through point.

Al-Degs et al (2009)

Sawdust and coal based activated arbon

Complex Remazol dye

They highlighted that the pore size of activated carbon plays an important role in the uptake and adsorption kinetics of a dye

Vijaya raghavan et al (2009)

Multiwall carbon nanotube (MWCNT) and powdered activated carbon (PAC)

Reactive Red M-2BE

The maximum adsorption capacities were 335.7 and 260.7 mg g 1 for MWCNT and PAC, respectively

Fernando et al (2011)

54

2.14 REVIEW OF ADSORPTION OF ACID DYE

Soheil et al (2007) studied the removal of acid orange 7 from

aqueous solutions by using powdered activated carbon with an initial

concentration of 150 ppm to 350 ppm and initial pH values of 2.8, 5.8, 8.0

and 10.5 at 25ºC in batch mode. They found that in most cases, after 75 min

the removal of acid orange 7 is performed. They found the removal percent

of acid orange 7 decreases with increase in its initial concentration. The

maximum removal percent of acid orange 7 was 96.24% at a pHi of 2.8 and Ci

of 150 ppm and the minimum was 48.05% at pHi of 5.8 and Ci of 350 ppm.

The results indicated that the application of different initial pH values,

similar experimental conditions altered the acid orange 7 removal no more

than 90.6%.

Chan et al (2008) studied the adsorption of acid dye using bamboo

based activated carbon. Activated carbon of two different sizes like high

surface area and low surface area were prepared by thermal activation with

phosphoric acid impregnation. Two different acid dyes with varying

molecular sizes were used for adsorption namely Acid Yellow 117 and Acid

blue 25. The dye with smaller molecular size (Acid blue 25) was readily

adsorbed onto the carbon where as the larger size dye (Acid Yellow 117)

showed little adsorption. Thus by changing the conditions for AC preparation

it is possible to produce tailor-mode activated carbon for the adsorption of dye

mixtures in industrial applications, especially textile dyeing.

Mohamed et al (2004) compared the surfactant-modified

mesoporous FSM-16 with activated carbon for the removal of acid yellow and

acid blue. Activated carbon was prepared from rice husk with an

impregnation of H3PO4 at 773K. It was found that that the ultimate capacity of

55

the adsorbents varied in the order FSM-16 > modified FSM- 16 > Activated

carbon and it followed first order kinetics. As compared to activated carbon of

micro porous character, the CTAB/FSM-16 sample achieved higher

performance at low concentrations. This was due to the successful narrowing

of the pore opening of FSM-16 using CTAB but retaining a considerable

portion of the pore volume.

Malik (2003) prepared an activated carbon from low-cost

mahogany sawdust and rice husk which is used to remove the Acid yellow 36

from the aqueous solution. Study revealed that the pH value of 3 is favourable

for the adsorption of acid dye. Adsorption capacities of saw dust carbon and

rice husk carbon were found to be 183.8 mg and 86.9 mg/g. It was observed

that both the adsorbents could be employed as low-cost alternatives to

commercial activated carbon in wastewater treatment for the removal of acid

dyes.

Amina et al (2006) investigated the adsorption capacity of

commercial activated carbon was used as parent and heated products for the

removal of Acid Blue 74, Acid Red 73 and Acid Yellow 23 from aqueous

solution. Thermal treatment resulted in some enhancement in the porosity

characteristics (specific area and pore volume) particularly in micropores,

although insignificant changes appear in the surface chemical properties.

Evaluated capacity and affinity parameters demonstrated that the

uptake of the acid dyes decreased in the order of Acid blue > Acid Red > Acid

yellow, which may be due to chemical structure differences in substituents

and side chains leading to unavailable accessibility. Heated carbons exhibit a

reduction in uptake of Acid Blue, and an increase in case of Acid Yellow and

Acid Red dyes. Changes in surface chemical groups, under action of heat

56

probably influence the adsorbate/adsorbent, adsorbate/liquid and

adsorbent/liquid relationships leading to the apparent differences. Further they

found, thermal activation leads to a small enhancement in microporosity due

to the removal of adsorbed gases acquired during processing and storing.

Indra et al (2006) studied the removal of orange-G and methyl

violet dyes on low cost adsorbent derived from bagasse fly ash. Effective pH

for orange-G and methyl violet were 4 and 5 in which batch studies were

performed. Greater percentage of dye was removed with decrease in the initial

concentration of dyes, and increase in amount of adsorbent used. Physico-

chemical characteristics, surface area, pore volume and pore size observed

exhibit potential use of BFA as adsorbent. Thermogravimetric analysis

exhibited the thermal stability of BFA even at temperature up to 300ºC.

Shaobin & Huiting (2007) studied dye adsorption mechanism on

unburned carbon with kinetic modelling. Here adsorption method was

investigated using unburned carbon from coal combustion residue for the

decolourisation of typical acidic and basic dyes. Since higher solution pH

favoured the adsorption of basic dye while it reduced the adsorption in case of

acid dye. The adsorption of dye increased with increasing temperature but

decreased with increasing particle size. For Basic Violet, the adsorption

involves both physical and chemical processes while the adsorption is the

main process for the Acid Black. Finally it was found that the unburned

carbon showed high adsorption capacity of 1.97 10-4 and 5.27 10-4 mol/g for

Basic Violet 3 and Acid Black 1.

Ewa & Grazyna (2007) found that the adsorption characteristics of

Congo Red on bituminous coal-based mesoporous activated carbon. The

mesopore contribution to the total pore volume ranged from 52 to 83%. The

57

adsorption tests were performed under static conditions at solution pH 7.8-

8.3. Activated carbon at the point of zero charge pH 10 was maintained. It

was found that higher the fraction of mesopores with a size between 10 and

50 nm, the shorter the time to achieve the equilibrium stage for Cango Red

adsorption. The activated carbon were characterized by mesopore volume

between 0.271 and 0.471 cm3/g and high mesopore contribution to the porous

texture, ranging from 53.4 to 82.1%. The monolayer adsorption capacity of

activated carbon was found to increase with increase in both the mesopore

volume and the mesopore contribution to their porous texture.

Purkait et al (2005) investigated the performance of activated

carbon on eosin dye in which adsorption study was conducted in batch and

column mode. The effects of various operating conditions like pH, initial dye

concentration and temperature were investigated for the batch operation and

also the effect of changing the bed depth was studied for column adsorption.

Breakthrough curves for column adsorption were also studied. It has been

experimentally investigated that the regeneration of spent carbon by

desorbing the dye by means of applying a surfactant enhanced carbon

regeneration technique using both cationic and anionic surfactants. It was

observed that the desorption of the dye was favoured at highly basic pH

(desorption was 46% at a pH of 12).

They also studied use of cationic surfactant resulted in about 23%

desorption but significantly higher desorption (about 70 and 63%) were

obtained using the anionic surfactants with 2000 mg/L of surfactant

concentration after 40 min of operation. It was found that the comparison

between the model and the experimental results were satisfactory.

58

Table 2.4 Summary of adsorption results in acid dye adsorption

Adsorbent Adsorbate Adsorption Results Reference

Powderedactivated carbon

Acid

Orange 7

The maximum removal percent of acid orange 7 was 96.24% at a pHi

of 2.8 and Ci of 150 ppm and the minimum was 48.05% at pHi of 5.8 and Ci of 350 ppm.

Soheil et al (2007)

Bamboo basedactivated carbon

Acid Yellow117 and Acid blue 25

They found changing the conditions for activated carbon preparation it is possible to produce tailor-mode activated carbon for the adsorption of dye mixtures in industrial applications, especially textile dyeing

Chan et al (2008)

Rice husk Acid Yellow

They found found that that the ultimate capacity of the adsorbents varied in the order FSM-16 > modified FSM- 16 > Activated carbon and it followed first order kinetics.

Mohamedet al (2004)

Mahogany sawdust and rice husk

Acid yellow 36

Adsorption capacities of saw dust carbon and rice husk carbon were found to be 183.8 mg and 86.9 mg/g

Malik(2003)

Commercial activated carbon

Acid Blue 74, Acid Red 73 and Acid Yellow 23

Evaluated capacity and affinity parameters demonstrated that the uptake of the acid dyes decreased in the order of Acid blue > Acid Red > Acid yellow, which may be due to chemical structure differences in substituents and side chains leading to unavailable accessibility.

Amina et al (2006)

59

Table 2.4 (Continued)

Bagasse fly ash

Orange-G andMethylviolet

Greater percentage of dye was removed with decrease in the initial concentration of dyes, and increase in amount of adsorbent used. Physico-chemical characteristics, surface area, pore volume and pore size observed exhibit potential use of bagasse fly ash activated carbon.

Indra et al (2006)

Coalcombustion residue

Acid black 1

They found that the unburned carbon showed high adsorption capacity of 5.27 10-4 mol/g

Shaobin & Huiting (2007)

Bituminous coal

Congo Red

The monolayer adsorption capacity of activated carbon was found to increase with increase in both the mesopores volume and the mesopores contribution to their porous texture

Ewa & Grazyna(2007)

Commercial activated carbon

Eosin dye adsorption study was conducted in batch and column mode. The effects of various operating conditions like pH, initial dye concentration and temperature were investigated for the batch operation and also the effect of changing the bed depth was studied for column adsorption. cationic surfactant resulted in about 23% desorption but significantly higher desorption.

Purkait et al (2005)

2.15 REVIEW OF ADSORPTION OF BASIC DYE

Tan et al (2007) showed that oil palm fibre was a promising

precursor to be used in the preparation of activated carbon for the removal of

60

methylene blue dye from aqueous solutions over a wide range of

concentrations. The equilibrium data was best described by Langmuir

isotherm model, with maximum monolayer adsorption capacity of

277.78 mg/g at 30°C. The kinetics of the adsorption process was found to

follow the pseudo-second order model and the process was endothermic in

nature.

Karagozoglu et al (2007) studied sepiolite, fly ash and apricot

stone activated carbon (ASAC) as adsorbents for the investigation of the

adsorption kinetics, isotherms and thermodynamic parameters of the Astrazon

Blue FGRL from aqueous solutions and various concentrations (100–300 mg/L),

adsorbent doses (3–12 g/L) and temperatures (303–323 K). The result showed

that the adsorption capacity of the dye increased with increasing initial dye

concentration, adsorbent dose and temperature. The kinetics of adsorption of

the basic dye followed pseudo-second-order kinetics. The adsorption

capacities calculated from the Langmuir isotherm were 181.5 mg/g for

ASAC, 155.5 mg/g for sepiolite and 128.2 mg/g for fly ash at 303 K.

Thermodynamical parameters were also evaluated for the dye–adsorbent

systems and revealed that the adsorption process was endothermic in nature.

Demirbas et al (2008) prepared activated carbon from apricot stone

with H2SO4 activation and its ability to remove astrazon yellow 7GL, from

aqueous solutions was studied. The optimum conditions for removal of the

basic dye were found to be pH 10, 6 g/L of adsorbent dosage and equilibrium

time of 35 min, respectively. The basic dye adsorbent system showed that the

removal rate was heavily dependent on diffusion controlled kinetic models.

The adsorption isotherm data were fitted well to Langmuir isotherm and the

capacity was 221.23 mg/g at 50oC. Thermodynamics parameters were also

evaluated. The values of enthalpy and entropy were 49.87 kJ/mol and

31.93 J/mol K, respectively, indicating that this process was spontaneous and

endothermic.

61

Hameed et al (2008) studied the ability of coconut bunch waste

(CBW) activated carbon to remove methylene blue from aqueous solution by

Batch mode. The adsorption isotherm data were fitted well to Langmuir

isotherm and the monolayer adsorption capacity was found to be 70.92 mg/g

at 30oC. The experimental data fitted very well to the pseudo-second-order

kinetic model.

Meral (2008) studied the simultaneous analysis and adsorption of

Basic Yellow 28 and Basic Red 46 dyes in binary mixture onto bentonite in

batch mode. First order derivative spectrophotometric method was used for

simultaneous analysis of BY28 and BR46 in binary mixtures. The monolayer

coverage capacities of bentonite for BY28 and BR46 dyes in single solution

system were found as 256.4 mg/g and 333.3 mg/g, respectively. It was

observed that the equilibrium uptake amounts of BY28 and BR46 dyes in

binary mixture onto bentonite decreased considerably with increasing

concentrations of the other dye resulting in their antagonistic effect. The

adsorption equilibrium data fitted more adequately to mono-component

Langmuir isotherm model than mono-component Freundlich isotherm model,

while the extended Freundlich isotherm model adequately predicted the multi-

component adsorption equilibrium data at moderate ranges of concentration.

Thermodynamic parameters showed that adsorption of BR46 and BY28 were

endothermic and spontaneous in nature.

Wang et al (2010) prepared low cost activated carbon from

Polygonum orientale Linn by phosphoric acid activation. Its ability to remove

the basic dyes, malachite green (MG) and rhodamine B (RB) were evaluated.

The surface area of P. orientale Linn activated carbon (PLAC) was found to

be 1398 m2/g. Alkaline pH was more favorable for MG adsorption, whereas

acidic pH was better for RB uptake. Adsorption of dyes on PLAC were

weakly dependent on ionic strength. The adsorption kinetics was found to be

best represented by the pseudo-second-order kinetic model. The mechanism

62

of the adsorption process was determined from the intraparticle diffusion

model. The equilibrium adsorption data was well described by the Langmuir

model. Thermodynamic study showed that the adsorption was spontaneous

and endothermic process.

Eren & Eren (2010) studied the adsorption behavior of crystal

violet (CV+) from aqueous solution onto a manganese oxide-coated (MCS)

sepiolite sample. The Langmuir monolayer adsorption capacity of MCS was

estimated as 319 mg/g. The pseudo-first-order, pseudo-second-order kinetic

and the intra-particle diffusion models were used to describe the kinetic data

and rate constants were evaluated. The values of the energy (Ea), enthalpy

H°) and entropy of activation ( S°) were 56.45 kJ/mol, 53.90 kJ/mol and

117.26 J/ (mol K), respectively, at pH 6.5. The quite high adsorption

capacity and high adsorption rate of MCS was an important advantage for use

of this material in basic dye solutions.

Dalia et al (2012) prepared adsorbent from kenaf fibre using HCl as

activating agent (3 M). The highest percentage removal of Methylene blue

dye (MB) was found to be 95 wt% at a concentration of 50 mg/L. At a pH of

8.5, the sorption of dye was favorable. The equilibrium data was best

represented by the Langmuir isotherm model and the reaction followed

pseudo- second-order model. Thermodynamic studies indicated that the

adsorption was endothermic in nature.

Kumar et al (2013) studied the adsorption kinetics of Acid Blue 113

(AB), Basic Red 5 (BR) and Reactive Yellow 81 (RY) textile dyes. They

determined the influence of the initial dye concentration of aqueous solutions

on the adsorption kinetics. The experiments, carried out in a batch reactor,

allowed the determination of the equilibrium times ( 1 h for RY and AB and

4 h for BR). The adsorption results were perfectly fitted to the pseudo-

second order, predicting a significant intra-particle diffusion stage in the

63

controlling of the adsorption process. Moreover, the fit to Elovich equation,

confirms that the process is ensured by chemisorption on a highly

heterogeneous material.

Hassani et al (2014), using response surface methodology (RSM)

studied the effects of operational parameters on the removal of two dyes (C.I.

Basic Blue 3 (BB3) and C.I. Basic Yellow 2 (BY2)) using coal as the low-

cost and available adsorbent. Quadratic central composite design (CCD) was

used for experiments designing, process modeling and optimization. The

investigated variables were initial concentration of dye (10–50 mg/L),

adsorbent dosage (0.4–2 g/L), temperature (12–60°C) and contact time

(5– 45 min). The significance of the model and regression coefficients were

tested by the analysis of variance (ANOVA), residuals analysis and t-test

statistics. For both dyes, the adsorption process was mainly influenced by the

initial concentration of the dyes and adsorbent dosage, whereas the other

factors showed lower effects. Different color removal efficiencies were

obtained for the dyes with different chemical structures. The optimum initial

concentration of dye, adsorbent dosage, temperature and contact time were

found to be 30 mg/L, 1.5 g/L, 25°C and 10 min. Under optimal conditions,

high removal efficiency of dyes (97.08% and 91.29% respectively for BY2

and BB3) were obtained.

Mohamed et al (2013) investigated that the adsorption of basic

yellow from aqueous solution by natural stevensite, having 104 m2/g specific

surface area. They found an alkaline pH favoured basic yellow adsorption and

the adsorption reached equilibrium in about 20 min. They concluded that the

adsorption process was governed by the electrostatic interaction. The

isothermal data were fitted by means of Langmuir and a monolayer

adsorption capacity of 454.54 mg/g was calculated. Finally, a good agreement

was found between the pseudo-second order model and the experimental data.

64

A high maximum adsorption capacity was obtained (526 mg/g) and a

maximum surface density of ~9 dye molecules/nm2 was estimated, involving

a column arrangement of the adsorbed molecules.

Emad et al (2008) compared the adsorption capacity of different

types of activated carbons produced by steam activation. Equilibrium

behavior of the activated carbons was investigated by performing batch

adsorption experiments using bottle-point method. Basic dyes (methylene

blue (MB), basic red (BR) and basic yellow (BY)) were used as adsorbate. It

was found that PAC2 (activated carbon produced from New Zealand coal

using steam activation) has the highest adsorptive capacity towards MB dye

(588 mg/g) followed by F400 (commercial activated carbon) (476 mg/g) and

PAC1 (Activated carbon Produced from Venezuelan bituminous coal in a

laboratory scale using physical activation) (380 mg/g). BR and BY showed

higher adsorptive affinity towards PAC2 and F400 than MB. Under

comparable conditions, adsorption capacity of basic dyes, MB, BR and BY

onto PAC1, PAC2 and F400 increased in the order of MB < BR< BY.

Redlich–Peterson model was found to describe the experimental data over the

entire range of concentration under investigation.

Lei & Yong (2014) studied the removal of anionic (methyl orange,

MO) and cationic dyes (methylene blue, MB) using Jerusalem artichoke stalk

based mesoporous activated carbon (MAC) as adsorbent. In batch adsorption

experiments they found that the adsorption data of both dyes fitted well to the

Langmuir model and pseudo second-order kinetic model. MB and MO

adsorbed by MAC were of endothermic and exothermic nature, respectively.

Acidic condition promotes the anionic dye molecules moving onto MAC

surface by electrostatic attraction, while it limits the initial adsorption rate of

cationic dye. The intra-particle diffusion was involved in the whole diffusion

process, but not the sole rate-controlling step. They calculated film diffusion

65

coefficient (Df) values 10-6 – 10-8 cm2/s, as two orders of magnitude higher

than intra-particle diffusion coefficient (Di) values, indicating the film

diffusion controls the whole diffusion rates of the dye molecules moving from

aqueous solution onto solid surface. Moreover, the Di values for both dyes

obtained in present study were superior to many reported carbon adsorbents.

This higher Di values were the result of more developed internal surface of

MAC as higher mesoporosity, which promotes the diffusion rate.

Table 2.5 Summary of adsorption results in basic dye adsorption

Adsorbent Adsorbate Adsorption Results Reference

Oil palm fibre Methyleneblue

The equilibrium data was best described by Langmuir isotherm model, with maximum monolayer adsorption capacity of 277.78 mg/g at 30°C.

Tan et al (2007)

Sepiolite, fly ash and apricot stone activated carbon(ASAC)

Astrazon Blue FGRL

The adsorption capacities calculated from the Langmuir isotherm were 181.5 mg/g for ASAC, 155.5 mg/g for sepiolite and 128.2 mg/g for fly ash at 303 K.

Karagozoglu et al (2007)

Apricot stone with H2SO4

activation

Astrazon yellow7GL

The basic dye adsorbent system showed that the removal rate was heavily dependent on diffusion controlled kinetic models. The adsorption isotherm data were fitted well to Langmuir isotherm and the capacity was 221.23 mg/g at 50oC.

Demirbas et al (2008)

66

Table 2.5 (Continued)

Coconutbunch waste (CBW)

Methyleneblue

The adsorption isotherm data were fitted well to Langmuir isotherm and the monolayer adsorption capacity was found to be 70.92 mg/g at 30oC. The experimental data fitted very well to the pseudo-second-order kinetic model.

Hameed et al (2008)

Binarymixture onto bentonite

BasicYellow 28 and Basic Red 46

The monolayer coverage capacities of bentonite for BY28 and BR46 dyes in single solution system were found as 256.4 mg/g and 333.3 mg/g, respectively. It was observed that the equilibrium uptake amounts of BY28 and BR46 dyes in binary mixture onto bentonite decreased considerably with increasing concentrations of the other dye resulting in their antagonistic effect.

Meral(2008)

Polygonum orientale Linn by phosphoric acidactivation

The basic dyes,malachite green (MG) and rhodamine B (RB)

The adsorption kinetics was found to be best represented by the pseudo-second-order kinetic model. The mechanism of the adsorption process was determined from the intraparticle diffusion model. The equilibrium adsorption data was well described by the Langmuir model.

Wang et al (2010)

67

Table 2.5 (Continued)

Manganese oxide-coated(MCS) sepiolitesample

Crystalviolet (CV+)

The Langmuir monolayer adsorption capacity of MCS was estimated as 319 mg/g. The pseudo-first-order, pseudo-second-order kinetic and the intra-particle diffusion models were used to describe the kinetic data and rate constants were evaluated. The values of the energy (Ea),enthalpy ( H°) and entropy of activation ( S°) were 56.45 kJ/mol, 53.90 kJ/mol and

117.26 J/ (mol K), respectively, at pH 6.5.

Eren & Eren (2010)

Kenaf fibre using HCl as activating agent

Methyleneblue

The highest percentage removal of Methylene blue dye (MB) was found to be 95 wt% at a concentration of 50 mg/L. At a pH of 8.5, the sorption of dye was favorable.

Dalia et al (2012)

Commercial activated carbon

Acid Blue 113 (AB), Basic Red 5 (BR) and Reactive Yellow 81 (RY)

The adsorption results were perfectly fitted to the pseudo-second order, predicting a significant intra-particle diffusion stage in the controlling of the adsorption process. Moreover, the fit to Elovich equation, confirms that the process is ensured by chemisorption on a highly heterogeneous material.

Kumar et al (2013)

68

Table 2.5 (Continued)

Coal Basic Blue 3 (BB3) and Basic Yellow 2 (BY2)

The optimum initial concentration of dye, adsorbent dosage, temperature and contact time were found to be 30 mg/L, 1.5 g/L, 25°C and 10 min. Under optimal conditions, high removal efficiency of dyes (97.08% and 91.29% respectively for BY2 and BB3) were obtained.

Hassani et al (2014)

Naturalstevensite

Basicyellow

The isothermal data were fitted by means of Langmuir and a monolayer adsorption capacity of 454.54 mg/g was calculated. Finally, a good agreement was found between the pseudo-second order model and the experimental data. A high maximum adsorption capacity was obtained (526 mg/g) and a maximum surface density of ~9 dye molecules/nm2 was estimated, involving a column arrangement of the adsorbed molecules.

Mohamed et al (2013)

69

Table 2.5 (Continued)

Differenttypes of activated carbons

Basic dyes (methylene blue (MB), basic red (BR) and basicyellow(BY)

It was found that PAC2 (activated carbon produced from New Zealand coal using steam activation) has the highest adsorptive capacity towards MB dye (588 mg/g) followed by F400 (commercial activated carbon) (476 mg/g) and PAC1 (Activated carbon Produced from Venezuelan bituminous coal in a laboratory scale using physical activation) (380 mg/g).

Emad et al (2008)

Jerusalem artichoke stalk based mesoporous activated carbon(MAC)

Methylorange, Methyleneblue

In batch adsorption experiments they found that the adsorption data of both dyes fitted well to the Langmuir model and pseudo second-order kinetic model. MB and MO adsorbed by MAC were of endothermic and exothermic nature, respectively. The intra-particle diffusion was involved in the whole diffusion process, but not the sole rate-controlling step. The higher Di values were the result of more developed internal surface of MAC as higher mesoporosity, which promotes the diffusion rate.

Lei & Yong (2014)

70

2.16 SUMMARY OF LITERATURE SURVEY

Activated carbon is prepared by different methods both physical

and chemical activation as well as combination of both physical and chemical

activation. The drawback of physical activation is that the yields are relatively

poor while also required higher temperature for the activation process. A

number of literature is available for the chemical activation process using the

different chemical activating agent. Chemical activation gives higher yields of

carbon as well as larger pore size in the carbon is created. Mesopores

development is normally desired in treatment of effluents. As the activated

carbon produced is highly dependent on the raw materials used as well as the

activation procedure. In order to optimize parameters for the activation

process information from literature though in plenty cannot be directly

applicable to a particular biomass chosen leading to extensive experimental

work for its optimization as carried in the further studies.