nqu

Sor,c,*

340

i Ara

1. Introduction

Concerning the hazardous effects of dyes on ora and fauna anincreasing research has been going on worldwide to control or to

ease of operation, simplicity of the design and exibility are someof the merits of adsorption process. Currently, carbonaceousmaterials such as activated carbon are the most widely usedadsorbents. However, combustion at high temperature, pore

the demerits oftical applicability

ials are micropo-eight compoundssions are close toremoval of largeould have a well-0 nm). Moreover,

Journal of Industrial and Engineering Chemistry 21 (2015) 369377

Accepted 25 February 2014

Available online 2 March 2014

Keywords:

Mesoporous carbon coated monolith

Surfactant (F-127)

Methylene blue

Desorption

Regeneration

on coated monolith was used as an adsorbent for methylene blue (MB)

adsorption. Effects of pH, salt, contact time, initial dye concentrations and temperature on dye

adsorption were studied. Higher solution pH favoured MB adsorption. Furthermore, kinetics study

showed that the adsorption could be better represented by the pseudo-second-order model. Linear and

non-linear isotherm studies revealed better tting of Langmuirmodel to adsorption data withmaximum

monolayer adsorption capacity 388 mg/g. The adsorption was found to be spontaneous and

endothermic. Desorption studies indicate that 0.1 N HCl exhibits higher elution efciency (82.1%) with

appreciable quantitative MB recovery.

2014 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rightsreserved.

Contents lists available at ScienceDirect

Journal of Industrial and

journal homepage: www.ean upper hand over the aforementioned processes. Low initial cost,The treatment techniques for removing dyes include coagula-tion and occulation [4], oxidation or ozonation [5,6], membraneseparation [7], biosorption [8] and adsorption [9]. Adsorption has

powder carbonaceous adsorbents cannot be easily regenerated,and can escape through lters, causing handling problems.Therefore, an improved support is required to overcome theproblems related to clogging, dispersion of particles and highpressure drop. At the same time they have low mechanicalminimize them. Dyes even in very low concentrations in water areundesirable [1]. Characteristically dyes are stable molecules,resistant to light, heat and biodegradation [2]making conventional(primary and secondary) treatment techniques unsuitable forwater decontamination [3]. Methylene blue (MB), a cationic dye, isusually used as a colouring agent in paper and pulp and textileindustries. Although, MB is not regarded as a highly toxic dye, butstill MB can have various harmful effects on human beings andanimals.

blockage and hygroscopicity [10] are some ofcarbonaceous adsorbents restricting their pracfor dyes removal.

In addition, most of the carbonaceous materrous highly efcient to remove low molecular w[1113]. The dyes and pigments molecular dimenupper limit of micropore size. For efcientmolecules like dyes and pigments, adsorbents shdeveloped mesopore structure (pore size of 25Adsorption/desorption of cationic dye omesoporous carbon coated monolith: Ethermodynamic studies

Mohamad Rasool Malekbala a, Moonis Ali Khan b,Luqman Chuah Abdullah a,c, Thomas S.Y. Choong a

aDepartment of Chemical and Environmental Engineering, Universiti Putra Malaysia, 4bChemistry Department, College of Science, King Saud University, Riyadh 11451, Saudc INTROP, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia

A R T I C L E I N F O

Article history:

Received 27 August 2013

A B S T R A C T

Surfactant modied carb* Corresponding author at: Department of Chemical and Environmental

Engineering, Universiti Putra Malaysia, 43400 UPM, Seri Kembangan, Selangor,

Malaysia. Tel.: +60 3 89466293; fax: +60 3 86567120.

E-mail addresses: tsyc2@yahoo.co.uk, csthomas@upm.edu.my

(Thomas S.Y. Choong).

http://dx.doi.org/10.1016/j.jiec.2014.02.047

1226-086X/ 2014 The Korean Society of Industrial and Engineering Chemistry. Publissurfactant modiedilibrium, kinetic and

aya Hosseini a,

0 UPM Serdang, Selangor, Malaysia

bia

Engineering Chemistry

l sev ier .com/ locate / j iecstrength that limits their application in certain areas. Studiesshowed use of carbonaceous materials for dyes removal fromaqueous phase [14,15]. However, in some cases the adsorptioncapacity of these adsorbents due to their low mesopore volumewas not high.

hed by Elsevier B.V. All rights reserved.

M.R. Malekbala et al. / Journal of Industrial and Engineering Chemistry 21 (2015) 369377370Cordierite monoliths could be utilized to overcome theselimitations as these materials shows a high mechanical strength,good thermal stability, a relatively uniform porosity, uniformow distribution and low pressure drop [1618]. Recently,amphiphilic molecules, such as surfactants, have been exten-sively employed for the synthesis of porous carbons. The uniquenature of this category of chemicals allows synthesizingmesoporous materials with large surface areas and uniformpore sizes that are suitable for numerous potential applications.Due to its surface properties, carbonaceous materials synthe-sized by using surfactant provides marked advantages overtypical activated carbon during the adsorption and diffusionprocess [19].

Considering the aforementioned merits of surfactants in thisstudy we had modied cordierite monoliths by using non-ionicsurfactant (F127). The surfactant modied mesoporous carboncoated monolith (MCCM) was then utilized for MB removal formaqueous system. To check the economic feasibility, desorptionstudies were also carried out. The equilibrium and kineticparameters were studied to justify the results.

2. Materials and methods

2.1. Chemical and reagents

Ceramic monoliths (diameter 25 mm and length 100 mm)were supplied from Beihai Huihuang Chemical packing Co. Ltd.,GuangXi, China. The chemical composition of monolithic substrateused during the study were SiO2 50.9 1%, Al2O3 35.2 1%, MgO13.9 0.5%, and others

2.5. Desorption and regeneration studies

Batch process was employed for MB desorption and regenera-tion. A MCCM was loaded with 250 mL MB solution of 200 mg/Linitial concentration at pH: 10 and contact time 48 h. The MBloaded MCCM was washed several times with distilled water toremove unadsorbed MB traces on the surface. Desorptionexperiment was performed at 25 8C for 24 h by using 250 mL of0.05 N each of HCl, H2SO4, H3PO4, ethanol (ETOH), NaCl and NaOHas an eluent. Desorption ratio was calculated from the amount ofMB initially loaded on MCCM and nal MB concentration in theeluent. Regeneration studies were conducted by using the sameadsorbent.

3. Results and discussion

3.1. Characterization of MCCM

Fig. 1 showed FT-IR spectra of MCCM before and after MBadsorption, and after MB desorption. The CH stretching bandswere appeared between 2900 and 2700 cm1. The vibration peaksat 2991 and 2784 cm1 assigned to asymmetric and symmetricstretching of CH2 groups belong to saturated CH in alkane andaldehyde groups [22,23], respectively were observed. Aromaticbands show absorptions in the regions 16001550 cm1 and15001400 cm1 due to CC stretching vibrations in the aromaticring. The bands at 1567 and 1416 cm1 belongs to ring stretchingvibrations [24]. An intense peak was observed at 1182 cm1

is very low [26,27]. In addition, after the loading of MB onMCCM anew peak appeared at 683 cm1 and it disappeared afterdesorption. This peak is due to CN or CS groups of MBconrming the attachment of dye on the MCCM. Differentmechanisms are proposed for MB adsorption; (1) the cationiccentre N+ of MB can make favourable interactions with the p-electron cloud of aromatic side chains (2) pp interactionsbetween p aromatic ring donors of MB and p acceptor groups inthe adsorbent [28].

An optical image of MCCM for bare monolith and carbon coatedmonolith are illustrated in (Fig. 2a,b), respectively. SEM images for

[(Fig._1)TD$FIG]

Fig. 1. FT-IR spectra of MCCM.

us carbon; SEM images of (c, d) inside channels, (e) high resolution of network carbonic

M.R. Malekbala et al. / Journal of Industrial and Engineering Chemistry 21 (2015) 369377 371assigned to CO stretching vibrations of phenolic group [22,23].Peaks in region 956770 cm1 ascribed to the vibration of CH outof plane mode which further conrms the existence of aromaticstructures of carbon basal plane [25]. Metal oxide stretching bandswas also revealed at low frequency of the spectrum [26]. The FT-IRspectrum of MCCM after MB adsorption showed nearly the samecharacteristics as presented in FT-IR spectrum of MCCM beforeadsorption. As shown, the adsorption is probably a physicalprocess or, if it is chemical, the adsorbentadsorbate bond energy[(Fig._2)TD$FIG]

Fig. 2. Optical images, (a) bare cordierite, (b) cordierite after coating with mesoporomaterials of MCCM adsorbent.mesoporous carbon coated on honeycomb cordierite aftercarbonization show relatively uniform surface and the coverageof carbonic materials inside channels (Fig. 2c, d). High magnica-tion image (Fig. 2e) revealed the network of carbonaceousmaterials which linked together making an interconnectedworm-like framework of porous structures. Surface studies ofMCCM showed surface area (BET) and total pore volume 849 m2/gand 0.3 cm3/g, respectively. N2 adsorption/desorption isothermplot (Fig. 3) revealed applicability of type IV isotherm for the

conditions, H+ may compete with MB ions (cationic dye) foroccupying adsorption sites on absorbent surface, thereby decreas-ing MB adsorption. Also, a change in solution pH affects the natureof the surface charge on the adsorbent. A negative chargedeveloped on the surface oxides of adsorbent in basic mediumresulting in comparatively higher cationic dye adsorption than inbasic solution [29,30]. OptimumMB adsorption under highly basicconditions on various adsorbents was reported by other research-ers [31,32]. The observed MCCM pHzpc was 5.5 (Fig. 6). AtpH < pHPZC, MCCM surface is positively charged while, atpH > pHPZC, the surface is negatively charged. This observation

[(Fig._3)TD$FIG]

Fig. 3. Nitrogen adsorption/desorption isotherm plot of MCCM.

Table 1Surface active sites on MCCM.

Active sites Values (milliequiv./g)

Total acidic sites 0.6612

Carboxylic 0.1651

Lactonic 0.1277

Phenolic 0.3684

Total basic sites 0.0205

M.R. Malekbala et al. / Journal of Industrial and Engineering Chemistry 21 (2015) 369377372synthesized sample according to IUPAC classication. This typereports on the bimodal materials with micro/mesopores. Thehorizontal branch near the saturation pressure (p/po = 0.9)indicates all the mesoporous are lled with liquid adsorbate.Fig. 4 exhibited pore-size distribution of MCCM determined usingthe BJH-methods. The pore-size distributions of sample revealed abroad distributionwith amean size of 21 nm. The Boehm acid basetitration experiment showed dominance of total acidic sites overthe MCCM surface (Table 1).

3.2. Effect of pH

The pH is an important parameter affecting both aqueouschemistry and surface charge of the adsorbent. The effect of pH onMB adsorption onto MCCM was studied within pH range 211under the specied experimental conditions (Fig. 5). The MBadsorption on MCCM from aqueous phase was highly dependenton solution pH. The adsorption capacity was minimum at pH: 2(92 mg/g) and attaining optimum value (240 mg/g) at pH: 10. Theincrease in pH leads to increase the number of OH ions in aqueous

phase enhancing MB adsorption capacity. Under highly acidic pH

[(Fig._4)TD$FIG]

Fig. 4. Pore size distribution of MCCM.also conrms optimum MB adsorption at higher pH values.

3.3. Effect of ionic strength

Wastewater streams containing dyes generally containssignicant quantities of salts, thus, the effect of electrolyte onMB removal needs to be investigated. The effect of ionic strengthon MB adsorption was studied at 200 mg/L initial MB concentra-tion at 25 8C and pH: 10. As revealed in Fig. 7, MB adsorption onMCCM increased on addition of small molar quantities of NaCl. Thepresence of electrolyte such as NaCl, MgCl2, CaCl2 may havedifferent effects in aqueous solution. These salts dissociates inwater to provide positive and negative ions (Na+, Mg2+,Ca2+ andCl). The neutralization of MCCM surface charge may occur due tocompeting of the resulted ions with MB for surface adsorption. Atlow salt concentrations, electrostatic repulsions are predominantso that high salt retentions are obtained. The retention factor ofNaCl is low when NaCl concentration is high with reduction inelectrostatic interactions. This can be explained by the screeningeffect due to addition of NaCl. Theoretically, the electrostatic forcesbetween the adsorbent surface and adsorbate ions are attractive[(Fig._5)TD$FIG]Fig. 5. Effect of pH on MB adsorption onto MCCM.

t 12 t (3)

[(Fig._6)TD$FIG] [(Fig._8)TD$FIG]M.R. Malekbala et al. / Journal of Industrial and Engineering Chemistry 21 (2015) 369377 373and an increase in ionic strength will decrease the adsorptioncapacity. Conversely, when the electrostatic forces are repulsive,an increase in ionic strength will increase adsorption [33,34]. Fig. 7shows the adsorption of positively charged dye molecules onnegatively charged mesoporous carbon increased with increase inNaCl concentration. The higher NaCl concentration created a lowretention factor that decreases MB dissociation to their ionic formsfor adsorption, therefore, the adsorption capacity would beconstant at higher NaCl concentrations.

3.4. Effect of contact time at various initial MB concentrations

Contact time studies for MB adsorption on MCCM at variousinitial concentrations were carried at pH: 10 and temperature 298 K. The MB adsorption on MCCM was initially fast as largenumbers of vacant surface sites were available for MB adsorption[35,36] and then became slower attaining equilibrium as near theequilibrium the remaining vacant sites were difcult to beoccupied probably due to slow pore diffusion of the solutemolecules on the solid phase from bulk phase (Fig. 8). The amountof MB adsorbed at equilibrium (qe) increased from 95 to 381 mg/gas the initial concentration increased from 50 to 400 mg/L. This

Fig. 6. Point of zero charge (pHpzc) of MCCM.indicates that the initial MB concentration plays an important rolein the MB adsorption onto MCCM. Hence, higher initial MBconcentration will enhance MB uptake. The equilibration timeranged between 660 and 4180 min with increase in MBconcentration from 50 to 400 mg/L. Similar equilibration time[(Fig._7)TD$FIG]

Fig. 7. Effect of ionic strength on MB adsorption (Co of MB 200 mg/L).(4000 min) forMB adsorption onmesoporous carbonwas reportedelsewhere [37].

3.5. Adsorption kinetics

Kinetic models, pseudo rst-order [38] and pseudo-second-order [39] were used to determine the adsorption behaviour suchas adsorption type, rate and adsorption capacity of the system. Thebest model was selected by the determination of R2 and comparingadsorption capacity values at equilibrium (qe,exp) and calculated(qe,cal).

The pseudo rst-order model expressed as:

logqe qt log qe k1t

2:303(2)

where, k1 is a pseudo-rst-order rate constant determined byplotting log(qe qt) versus t (gures not given).

The pseudo second-order kinetic is given as:

Fig. 8. Effect of contact time onMB adsorption at various initial concentrations ontoMCCM.qt k2qe qe

where, k2 is a pseudo-second-order rate constant determined fromthe intercept and the slope of plot between t/qt versus t (gures notgiven).

The parameters obtained from the models are presented inTable 2. The pseudo-rst-order model did not showed goodregression coefcient (R2) results for the entire concentrationrange while, pseudo-second order model showed higher R2 valuesfor the entire concentration range. Moreover, the qe,exp and qe,calvalues for MB on MCCM were nearer (Table 2) conrming theapplicability of pseudo-second-order model for the entire concen-tration range. The applicability of pseudo-second-order modelpredicts chemisorption process.

The pseudo-rst-order and pseudo-second-order kinetic mod-els could not identify the diffusion mechanism. Thus, the kineticresults were then analyzed by using Weber and Moris intra-particle diffusion model [40]. The plot of qt versus t

1/2 usuallyshowsmore than one linear portion (Fig. 9). As observed, the intra-particle diffusion plots were not linear over the whole time range,implying that more than one process affecting the adsorption. Thisstudy was in good agreement with previously reported study onMB adsorption [41].

3.6. Adsorption isotherm

Adsorption isotherms are used to illustrate the distribution ofadsorbate between solid and solution phase at equilibrium. Anoptimized data of adsorption process design can be achieved withthe help of isotherm studies. Freundlich [42] and Langmuir [43]isotherm models were applied to evaluate the adsorption data.

Freundlich model is an empirical equation that describesadsorption on heterogeneous surface through a multilayeradsorption mechanism [44]. Freundlich model in linearized formis given as:

showed better tting of the model to experimental data. Thisconrms monolayer coverage of MB on to MCCM surface and also

Table 2Kinetics parameters for MB adsorption onto MCCM.

Pseudo-rst-order Pseudo-second-order

Co (mg/L) qe,exp (mg/g) qe,cal (mg/g) k1104 (1/min) R2 qe,cal (mg/g) k2104(g/mg-min) R2

50 95.7 81.5 108.2 0.99 97.1 2.7 0.99

100 193.6 174.5 85.2 0.98 196.1 0.9 0.99

200 279.7 228.6 32.2 0.96 285.7 0.3 0.99

300 345.4 283.5 20.7 0.93 357.1 0.2 0.99

400 381.5 308.2 18.4 0.90 400.0 0.1 0.99

Table 3Isotherm parameters for MB adsorption onto MCCM.

Langmuir constants Freundlich constants

b (L/g) qm (mg/g) R2 KF (mg/g)(L/mg)

1/n 1/n R2

24.4 388.4 0.99 64.4 0.36 0.91

M.R. Malekbala et al. / Journal of Industrial and Engineering Chemistry 21 (2015) 369377374log qe logKF 1

nlogCe (4)

Langmuir model assumes a monolayer adsorption onto theadsorbent surface. Furthermore, it has a free-energy change for alladsorption sites considering no adsorbateadsorbate interaction.In linearized form Langmuir model is given as:

Ceqe 1

bqm 1qm

Ce (5)

where, Ce (mg/L) and qe (mg/g) are the equilibrium concentrationand the adsorption capacity at equilibrium state, respectively. Theparameters KF [(mg/g) (L/mg)

1/n] and n are Freundlich constantsobtained by plotting log qe versus log Ce (Figure not given). TheLangmuir isotherm constants b (L/mg) and qm (mg/g) are obtainedfrom the intercept and slope of the plot between Ce/qe versus Ce(Figure not shown).

Table 3 summarized the results obtained by apply Freundlichand Langmuir isotherm models to the isotherm data. Compara-tively higher regression coefcient (R2) value for Langmuir model[(Fig._9)TD$FIG]Fig. 9. Intra-particle diffusion plot for MB adsorption on MCCM at various initialconcentrations.homogeneous distribution of active sites on the adsorbent surface.The applicability of Lagmuir model was further conrmed by non-linear isotherm plot (Fig. 10). The observed maximum monolayersaturation capacity (qmax) was 388 mg/g which was comparativelyhigher than that reported qmax values for MB adsorption ofmodied clay [45].

The essential feature of Langmuir isotherm can be expressed byseparation factor (RL), a dimensionless constant, can be repre-sented as:

RL 11 bC0 (6)

where, C0 is the initial MB concentration (mg/L). In general, anisotherm can be irreversible (RL = 0), favourable (0 < RL < 1), linear(RL = 1), or unfavourable (RL > 1) [46]. For MB adsorption onMCCM, RL falls in range of favourable adsorption process (i.e.0 < RL < 1).

3.7. Adsorption thermodynamics

The temperature has a pronounced effect on the adsorptioncapacity of the adsorbents [47]. Increasing the temperature is[(Fig._10)TD$FIG]Fig. 10. Non-linear isotherm plots.

The thermodynamic parameters are listed in Table 4. Thenegative values of DG8 indicate that the adsorption of MB ontoMCCM is spontaneous and the positive value of DH8 conrms thatthe adsorption process is an endothermic. The positive value ofDS8

[(Fig._11)TD$FIG]

Table 4Thermodynamic parameters for MB adsorption onto MCCM.

DS8 (J/molK) DH8 (kJ/mol) DG8 (kJ/mol)

293K 303K 313K

50.8 21.9 22.5 24.6 25.9

M.R. Malekbala et al. / Journal of Industrial and Engineering Chemistry 21 (2015) 369377 375known to increase the rate of diffusion of the adsorbate moleculesacross the external boundary layer and in the internal pores of theadsorbent particle, decrease the viscosity of the solution andchange the equilibrium capacity of the adsorbent for a particularadsorbate [48]. Fig. 11 depicted MB adsorption at variousconcentrations (50400 mg/L) on MCCM at different temperatures(298, 308 and 318 K). An increase inMB adsorption onMCCMwithincrease in temperature was observed. The adsorption capacity at400 mg/L initial MB concentration increased from 388 to 440 mg/gwith increase in temperature from 298 to 318 K, indicatingendothermic nature of process. Similarly at various MB concen-trations the increment in adsorption capacity was observed(Fig. 11). The enhancement in the adsorption capacity might bedue to possibility of an increase of number of active sites for theadsorbent as well as an increase in the mobility of the adsorbatemolecules [49].

Various thermodynamics parameters such as standard enthal-py change (DH8), standard entropy change (DS8) and Gibbs freeenergy change (DG8) were evaluated. Vant Hoff equationwas usedto determine DH8 and DS8 values. The equation is given as:

Fig. 11. Effect of temperature on MB adsorption onto MCCM at various initialconcentrations.ln b DS

RDH

RT(7)

where, R (8.314 J/mol K) is the universal gas constant, T (K) is theabsolute temperature and b is the Langmuir constant. A plot of ln bagainst 1/Twas used to obtainDS8 andDH8 (Figure not shown). TheDG8 can be calculated using the relation below:

G RT ln b (8)

Table 5Comparison of the maximum adsorption capacity of MB onto various adsorbents.

Adsorbent Experimental conditions

Co (ppm) pH

MCCM (F127) 50400 10

Anaerobic granular sludge 20300

Multiporous palygorskite 100 6.5

MCCM (PEG) 50480 10

Acid Activated Algerian Bentonite 10100 4.7

Carbon nanotubes 40 7

Poly NAN ospheres 3070 7

Clay honeycomb monoliths 10100 reecting the afnity of the adsorbent material towards dyes [50].Similar observations were reported for MB adsorption on differentadsorbents [51,52]. The adsorption capacities of various adsor-bents used for MB removal were compared and given in Table 5.From Table 5, it can be seen that the capacities of adsorbents foradsorbingMB range from3 to 388 mg/g. The adsorption capacity ofMCCM (PEG) is less compared to MCCM (F127) synthesized in thiswork. An increase of 3 fold in MB adsorption capacity by usingMCCM (F127) indicated the positive effect of surfactant on thetextural properties of MCCM for other applications.

3.8. Desorption of MB

3.8.1. Effect of various eluents on MB desorption

Fig. 12 revealed the amount of MB desorbed by variouschemical agents as eluents. TheMB elution by using 0.05 NHClwasoptimum (39%) followed by H2SO4 (0.05 N), H3PO4 (0.05 N), ETOH(0.05 N), NaOH (0.05 N) and NaCl (0.05 N). The elution efciencywas further investigated at various HCl concentrations (Fig. 13).The maximum MB elution (82.1%) was obtained with 0.1 N HClsolution. Further increase in HCl concentration leads to decrease inelution efciency. This might be due to deterioration of adsorptionsite on MCCM surface at higher HCl concentrations.

3.8.2. Regeneration studies

Regeneration of MCCM is an important step in order to checkthe economic feasibility of adsorption process. The regenerationstudies were carried out using 0.1 N HCl solution as it givesoptimum MB elution (82.1%). The regeneration studies werecarried out in batch mode for ve successive cycles (Fig. 14).Results showed 21% drop in the adsorption capacity for secondcycle. This decrease in adsorption capacity might be caused due tothe decomposition or damage caused by acidic solution to certainadsorption sites or functional groups present over MCCM surface[54]. The decrease in the adsorption capacity was about 15% for thethird cycle. The adsorption capacity remains almost stagnant(250 mg/g) for the consecutive cycles (up to fth cycle) showingthat the adsorbent could be reused without any further lose inadsorption capacity.Adsorption capacity (mg/g) References

T (8C)

25 388 This work

25 212.77 [3]

25 134.77 [2]

30 121 [17]

20 56.34 [53]

25 46.2 [12]

25 20 [9]

3 [16]

[(Fig._14)TD$FIG]

Fig. 14. Regeneration studies of MCCM.

[(Fig._12)TD$FIG]

Fig. 12. Desorption of MB from MCCM by various eluents.[(Fig._13)TD$FIG]

Fig. 13. Desorption of MB from MCCM by using HCl as an eluent.

M.R. Malekbala et al. / Journal of Industrial and Engineering Chemistry 21 (2015) 3693773764. Conclusions

The present investigation showed that MCCM mesoporousitycould enhance MB adsorption capacity. Initial MB concentration,solution pH and temperature showed profound inuence onadsorption process. Optimum MB adsorption was observed at pH:10. The adsorption of MB onMCCMwas amonolayer adsorption asconrmed by the applicability of Langmuir model. The kineticsstudies suggested applicability of pseudo-second-order model.Adsorption of MB on the MCCM is favourably inuenced by anincrease in the temperature of the operation. The free energy (DG8),enthalpy (DH8), and entropy (DS8) termswere determined, and thenegative values of DG8 indicated that MB adsorption process is aspontaneous and the positive DH8 value conrmed that theadsorption process was endothermic in nature. The elution of MBform MCCM was optimum with 0.1 N HCl conrming occurrenceion-exchange mechanism. The regeneration studies by 0.1 N HClshowed 21 and 15% loss in MB adsorption capacity for rst andsecond cycle thereafter, the adsorption capacity remain almoststagnant.

Acknowledgements

The authors would like to gratefully acknowledge Ministry ofEducation (MOE), Malaysian Government and Universiti PutraMalaysia (UPM) for the nancial support of this work (via vot:9416900).

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M.R. Malekbala et al. / Journal of Industrial and Engineering Chemistry 21 (2015) 369377 377

Adsorption/desorption of cationic dye on surfactant modified mesoporous carbon coated monolith: Equilibrium, kinetic and thermodynamic studiesIntroductionMaterials and methodsChemical and reagentsPreparation of adsorbentCharacterization of adsorbentAdsorption studiesDesorption and regeneration studies

Results and discussionCharacterization of MCCMEffect of pHEffect of ionic strengthEffect of contact time at various initial MB concentrationsAdsorption kineticsAdsorption isothermAdsorption thermodynamicsDesorption of MBEffect of various eluents on MB desorptionRegeneration studies

ConclusionsAcknowledgementsReferences