MINISTRY OF EDUCATION AND

TRAINING

VIETNAM ACADEMYOF

SCIENCE AND TECHNOLOGY

GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY

……..….***…………

Nguyen Vu Ngoc Mai

STUDY ON SYNTHESIS OF MANGANESE OXIDE,

IRON OXIDE ON REDUCED GRAPHENE OXIDE

NANOPARTICLES TO TREATMENT OF PIGMENTS

AND PESTICIDES IN THE AQUEOUS ENVIRONMENT

Major: Environmental Engineering

Code: 9 52 03 20

SUMMARY OF ENVIRONMENTAL ENGINEERING

DOCTORAL THESIS

Hanoi – 2020

The thesis was performed at Graduate University of Science and

Technology, Vietnam Academy Science and Technology

Supervisor 1: Assoc. Prof. Dr.Nguyen Quang Trung

Supervisor 2: Assoc. Prof. Dr. Dao Ngoc Nhiem

Reviewer 1: …

Reviewer 2: …

Reviewer 3: ….

The thesis will be defended at the doctoral thesis committee at the

Academy level, meeting at the Graduate University of Science and

Technology - Vietnam Academy of Science and Technology at

………… on………, 20…….

The thesis can be found in:

- The library of Graduate University of Science and Technology

- National Library of Vietnam

NEW FINDINGS OF THE THESIS

1. Successfully synthesized mixed oxide Fe2O3 – Mn2O3

nanoparticles using tartaric acid (AT), tartaric acid combined with

polyvinyl alcohol (PVA) as gel – forming agents. Nanostructured

Fe2O3-Mn2O3 mixed-oxides prepared by the combustion method that

used a mixture of tartaric acid and PVA (pH 4, the molar ratio of

Fe/Mn = 1/1, the molar ratio of AT/PVA = 1/1, the molar ratio of

(Fe/Mn)/(AT /PVA) = 1/3, the gel-forming temperature of 80 oC and

the calcination temperature at 450 oC during 2h) had uniform size

and specific surface area of their (63.97 m2/g) was larger than using

only tartaric acid as gel – forming agents (46.25 m2/g).

2. Studied the photocatalytic ability of Fe2O3 –Mn2O3 and

Fe2O3 –Mn2O3/rGO materials to decompose some pollutants such as

methyl orange , methylene blue, parathion, fenitrothion. For the first

time, mixed oxide Fe2O3 – Mn2O3/rGO nanoparticles were studied to

decompose parathion and fenitrothion. The results showed that

parathion was decomposed efficiency (after 90 minutes reaction

time, pH 7.5, the concentration after adsorption equilibrium is 1.5

ppm, the catalyst content of 0.05 g/L, the decomposition efficiency

of parathion is 77.32%). The decomposition efficiency fenitrothion

(after 90 minutes reaction time, pH 7.0, concentration after

adsorption equilibrium 1.4 ppm, catalyst content of 0.05 g/L) is

88.61%. Through modern analytical methods such as High-

performance liquid chromatography and Gas chromatography- mass

spectrometry, some intermediates formed during the decomposition

of methyl orange, methylene blue, parathion, fenitrothion are

proposed.

LIST OF WORKS HAS BEEN PUBLISHED

1. Nguyen Vu Ngoc Mai, Dao Ngoc Nhiem, Pham Ngoc

Chuc, Nguyen Quang Trung, Cao Van Hoàng, Synthesis of Fe2O3-

Mn2O3 nanostructured by tartaric acidand preliminary study on

methylene orange degradations, Vietnam Journal of Chemistry

(2017), 55 (3e12).

2. Nguyen Vu Ngoc Mai, Nguyen Thi Ha Chi, Nguyen

Quang Bac, Doan Trung Dung, Pham Ngoc Chuc, Duong Thi Lim,

Nguyen Quang Trung, Dao Ngoc Nhiem, Synsthesis of nano – mixed

oxides Fe2O3 - Mn2O3 and their applications to photocatalytic

degradation of Parathion from water, Proceedings The 3rd

International Workshop on Corrosion and Protection of Materials

(2018), Hanoi, Vietnam.

3. Nguyen Vu Ngoc Mai, Duong Thi Lim, Nguyen Quang

Bac, Nguyen Thi Ha Chi, Doan Trung Dung, Ngo Nghia Pham, Dao

Ngoc Nhiem, Fe2O3/Mn2O3 nanoparticles: Preparations and

applications in the photocatalytic degradation of phenol and

parathion in water, Journal of the Chinese chemical society (2019),

DOI : 10.1002/jccs.201900033

4. Nguyen Vu Ngoc Mai, Doan Trung Dung, Duong Thi

Lim, Dao Ngoc Nhiem, Study on synthesis of Mn3O4 nanoparticles

and their photocatalytic ability, Vietnam Analytical Sciences Society

(2019), 1, 24.

5. Nguyen Vu Ngoc Mai, Nguyen Thi Ha Chi, Duong Thi

Lim, Nguyen Quang Trung, Dao Ngoc Nhiem, Study on

photodegradation of methyl orange, dimethoate and parathion from

aqueous solution by nano iron – manganese oxide particles, Vietnam

Journal of Chemistry (2019), 57(4e1,2) 330-334.

6. Nguyen Vu Ngoc Mai, Doan Trung Dung, Nguyen

Quang Bac, Duong Thi Lim, Nguyen Quang Trung, Dao Ngoc

Nhiem, Synthesis of nano-mixed oxides Fe2O3-Mn2O3 and their

applications in phenol treatment, Vietnam Journal of Chemistry

(2019), 57(4e1,2) 330-334.

1

INTRODUCTION

The urgency of the thesis

Currently, environmental pollution is a great challenge to the globe

including Vietnam. Industrialization and modernization of the

economy are raised many persistent pollutants such as pigments,

phenol, antibiotics, …becoming more and more.

Viet Nam is a long-standing agricultural country. To meet the food

needs of the increasing number of people, the cultivated area is

increasingly shrinking, measures such as agricultural intensification,

seed improvement, the use of crop pesticides are implemented to

increase productivity. Organophosphorus with the advantage of a

wide range of prevention and rapid elimination of pests and diseases

are now widely applied. However, the widespread use of

organophosphorus during cultivation has left this chemical residue in

the environment very large, especially in the aqueous environment.

Thus, not only in industrial wastewater but also in agricultural

wastewater, durable and persistent organic substances should be

treated. Currently, many studies focus on completely mineralizing

these persistent pollutants into non-toxic substances. The advanced

oxidation method based on hydroxyl radical activity ●OH (with the

highest oxidation potential of 2.8 eV) is of interest to study on. The

formation of ●OH radicals during reaction occurs through a variety of

processes, including photocatalytic processes based on mixed oxide

Fe2O3 – MnOx nanoparticles. The efficiency of the photocatalytic

process increases with the dispersion of these nanoparticles on the

carrier (rGO). The object selected for treatment is persistent organic

pigments, including MO, MB, and pesticides which are represented

2

by fenitrothion and parathion. The photocatalytic process is applied

to treat these pollutants. From the above reasons, the topic “ Study on

synthesis of manganese oxide, iron oxide on reduced graphene oxide

nanoparticles to treatment of pigments and pesticides in the aqueous

environment” is selected to research and deal with these pollutants in

Vietnam.

The objectives of the thesis

Successfully synthesized nano – mixed oxide by different gelling

agents; compared, selected the appropriate gelling agent; researched

to evaluate the catalytic activity of mixed oxide nanoparticles formed

with pollutants methyl orange (MO), methylene blue (MB).

Successful dispersed mixed oxide nanoparticles on rGO; investigated

catalytic activity of material systems on parathion, fenitrothion.

The main contents of the thesis

- Synthesis of metal oxide nanomaterials by a gel - forming agent as

tartaric acid and a combination of tartaric acid and PVA, thereby

comparing and selecting the appropriate gel - forming agent.

- Evaluation of the photocatalytic ability of system Fe2O3 – Mn2O3

in decomposition process MO and MB of the synthesized material

system.

- Dispersion of mixed oxide nanoparticles Fe2O3 – Mn2O3 on a

carrier rGO. Survey to evaluate the photocatalytic ability of material

system Fe2O3 – Mn2O3/rGO in the process of decomposition

parathion and fenitrothion.

- Evaluation of the reusability of the catalyst.

3

Chapter 1. OVERVIEW

1.1. General introduction about pesticides

1.1.1. Definitions of pesticides

Pesticides which are substances or mixtures work to:

prevent, stop, repel, induce, destroy or control crop pests;

regulate crop or insect growth;

preserve crops; increase safety and effectiveness when using

the pesticides.

1.1.2. Classification of pesticides: four main groups

1.1.2.1. Organochlorines

1.1.2.2. Organophosphorus: is the ester of phosphoric acid and its

derivatives [7].

1.1.2.3. Carbamates

1.1.2.4. Pyrethroids

1.1.3. Current situation of pesticide use in Vietnam

How to use pesticides in our country today

Using pesticides which has been banned

Increasing using dosage

Spraying pesticides at anytime

Using the wrong manual

Organophosphorus are more durable than those in the pyrethroids

group. Carbamates have a fairly common use rate in many

agricultural areas. Organochlorines are mostly banned from use.

1.1.4. Negative effects of organophosphorus pesticides

1.1.4.1. Soil pollution

1.1.4.2. Air pollution

1.1.4.3. Water polution

4

In the Northern of Viet Nam [16], fenitrothion (0,06 và 0,04

mg/L), dichlorvos (0,02 and 0,03 mg/L) were detected.

In groundwater: dichlorvos was found in 45% of all samples

taken, fenitrothion was found in all samples [16].

In the Mekong Delta, in 2008, Carvalho and etc. [17]

showed that concentration of diazinon was 3,5 – 42,8 ng/L, that of

fenitrothion was 3,3 – 11,9 ng/L found in 5/8 samples.

Organophosphorus pesticides residues were detected in soil, air,

surface water, and groundwater. The commonly used peticides are

fenitrothion, diazinon, quinalphos, dichlorvos. Comparing with

Limited standard EC, residues concentration of pesticides exceeds

the allowed level (0.5 µg/L).

1.1.4.4. Impact on human, plants and animals

In addition to the environment pollution by pesticide residues, the

pollution by pigments should also be treated. These substances are

very toxic and dangerous to human health and the ecosystem [19,

20]. In the thesis, MO, MB which are the pigments and pesticides

which are parathion, fenitrothion are selected to research and

treatment with these pollutants in Vietnam.

1.2. General introduction about some research pollutants

1.2.1. Physical and chemical properties of some organic pigments

Hình

Figure 1.3. The molecular

structure of MB

Figure 1.2. The molecular

structure of MO

5

1.3. Methods for treating pigments and organophosphorus in

agricultural wastewater

1.3.1. The adsorption method

The main disadvantage of this method is that the adsorbent must be

reconstituted, and the hazardous solid waste which is a saturated

adsorbent containing the high concentrations of pollutants after

treatment must be generated.

1.3.2. The biological treatment methods

The drawbacks of the method are research local available

microorganism, long decomposition time, low decomposition

efficiency.

1.3.3. Decomposes by oxidizing agents

Using strong oxidizing agents to oxidize persistent organic

compounds in wastewater are applied.

1.3.4. The advanced oxidation process

The advanced oxidation process decomposes organic pigments and

pesticides by producing hydroxyl radicals with the highest oxidative

potential (2.8 eV) during the reaction.

1.4. The photocatalysis decomposes organic pigments and

organophosphorus

1.4.1. Introduction to photocatalysis

Figure 1.4. The molecular

structure of parathion

Figure 1.5. The molecular

structure of fenitrothion

6

Figure 1.6. Schematic representation of semiconductor

photocatalytic mechanism

1.4.2. Introduction to Fe2O3 – Mn2O3 materials

Mixed oxide Fe2O3 – Mn2O3 nanoparticles are mainly used for

decomposing colored pollutants and high treatment efficiency. The

pesticides that belong to the organophosphorus group, namely

parathion and fenitrothion have not been studied for decomposition

by photochemical processes using this catalyst.

rGO that has a multilayered structure has many functional groups in

its molecule, so it is easy to form bonds with transition metal ions.

With the above advantages, rGO is suitable for dispersing metal

oxide Fe2O3 – Mn2O3 nanoparticles.

1.4.3. The situation of researching on the treatment of pigments

and organophosphorus in Vietnam

Studies to treat organic pigments such as MO and MB have been

widely conducted in Vietnam. Many methods are applied such as

adsorption, coagulation and flocculation,biodegradation,…especially

advanced oxidation processes, including photocatalytic processes.

7

In Vietnam, research on treating residues of organophosphorus is

limited, the main subjects of study are organochlorines such as DDT,

Dioxin. Studies of decomposition by biological, physical, and

chemical methods have also been conducted. However, in Vietnam,

there have been no specific studies on the decomposition of

pesticides, including organophosphorus, particularly parathion and

fenitrothion using a photochemical process with a catalyst of mixed

oxide Fe2O3 – Mn2O3 nanoparticles.

1.5. Methods of synthesizing Fe2O3 - Mn2O3 materials

1.51. Hydrothemal method

1.5.2. Co - precipitation

1.5.3. Sol gel method

1.5.4. Combustion method

The combination of organic acids and PVA as a gel - forming agent

help metal ions easily formed complexes of the metal ion with gel -

forming agents which are organic acids. These complexes which are

disperse evenly in polymers help to prevent phase separation. The

combination of PVA and organic acids increases the process of

complex creation, the metal complexes are evenly distributed in the

polymer network of PVA, reduced the calcination temperature

needed for the synthesis of mixed oxide Fe2O3 – Mn2O3

nanoparticles.

8

Chapter 2. EXPERIMENT

2.1. Materials

2.2. Synthesis of materials

2.2.1. Methods of synthesis of mixed oxide Fe2O3 – Mn2O3

nanoparticles (Figure 2.1)

2.2.2. Methods of synthesis of mixed oxide Fe2O3 – Mn2O3/rGO

nanoparticles (Figure 2.2)

Gel-

forming

agents

solution

Fe2+

solution

and Mn2+

solution

Mixture

solution Viscous

gel

String, heating

adjust pH

Drying at 110 oC for 2h

calcinating

Fe2O3-

Mn2O3 Dry

gel

Figure 2.1. Diagram of Fe2O3-Mn2O3 synthesis process using

combustion method

Fe2+

solution

and Mn2+

solution

Gel-

forming

agents

solution

Mixture

solution

Visc

ous

gel

Visco

us gel

/rGO

Fe2O3-

Mn2O3

/rGO

rGO String, heating

adjust pH

string heating, calcinating

Figure 2.2. Diagram of Fe2O3-Mn2O3/rGO synthesis process

using combustion method

9

2.3. Characterization of materials

2.3.1. Thermal Analysis method (TGA - DTA)

2.3.2. X – ray diffraction method (XRD)

2.3.3. Energy-dispersive X-ray spectroscopy method (EDS)

2.3.4.Scanning Electron Microscope Method (SEM) and

Transmission Electron Microscope Method (TEM)

2.3.5. Brunauer-Emmet-Teller Method (BET)

2.3.6.The method of determining the point of zero

charge of materials

2.4. Catalyst activity testing

2.4.1. Decomposion efficiency of MO, MB of photocatalyst mixture

material by Fe2O3 – Mn2O3 nanoparticles

The photodegradation efficiency of each sample was calculated by

the following expression:

2.4.2. Test of (Fe2O3 – Mn2O3)/rGO on pesticides treatment

Figure 2.3. Equipment of Ace

Photochemical UV Power Supply &

Mercury Vapor Lamps (USA)

V: 500 mL

Lamp Watts: 450W, 135 V, Arc –

length:11,4 cm, lamp is the use of

a light source to simulate sunlight

H % = C0 − Cf

C0∗ 100% 2.3

10

2.4.2.1. Equilibrium adsorption process of pesticides

2.4.2.2. Effect of reaction time on the degradation of pesticides

2.4.2.3. Effect of catalyst dosage on the degradation of pesticides

2.4.2.4. Effect of pH on the degradation of pesticides

2.4.2.5. Effect of inital pesticides concentration

2.5. The methods used to analyze pollutants in the study

2.5.1. The photometric method was determined the content of MO

and MB in the sample

2.5.2.The liquid chromatographic method was identified

intermediates formed during the decomposition of MO and MB

2.5.3.The GC/MS method was determined the concentrations of

parathion and fenitrothion in the sample

Chapter 3. RESULTS

3.1. Study on synthesizing nano mixed oxide Fe2O3 - Mn2O3

particles

3.1.1. Study on synthesizing nano mixed oxide Fe2O3 – Mn2O3

particles with tartaric acid as gel – forming agents

3.1.1.1. TGA – DTA analysis of pre - sample with tartaric acid as gel

– forming agents (Figure 3.1)

3.1.1.2. The effect of calcination temperature on the formation of

Fe2O3 - Mn2O3 phase (Figure 3.2)

3.1.1.3. The effect of pH on the formation of Fe2O3 - Mn2O3 phase

(Figure 3.3)

3.1.1.4. The effect of Fe/Mn mole ratio on the formation of Fe2O3 -

Mn2O3 phase (Figure 3.4)

3.1.1.5. The effect of gel-forming temperature on the formation of

Fe2O3 - Mn2O3 phase (Figure 3.5)

11

→ The optimum temperature (500 oC) was chosen

→ The pH value chosen was pH 4

→ The Fe/Mn mole ratio chosen was Fe/Mn = 1/1

Figure 3.3. X-Ray

diffractions at various pH

a) pH 1, b) pH 2, c) pH 3,

d) pH 4, e) pH 5

Figure 3.4. X-ray

diffraction of samples with

various mole ratios of

Fe/Mn a) 9/1; b) 3/1; c) 2/1;

d) 1/1; e) 1/3; f) 1/9

Figure 3.1. TGA and DTA

curves of the as -

prepared gel

Figure 3.2. X-Ray diffractions at

various calcination temperatures a)

300 oC, b) 400

oC, c) 450

oC, d)

500 oC, e) 550

oC, f) 600

oC

12

→ The gel-forming temperature was chosen at 80 oC

3.1.2. Study on synthesizing nano mixed oxide Fe2O3 – Mn2O3

particles with tartaric acid combined with PVA as gel – forming

agents

3.1.2.1. TGA – DTA analysis of pre - sample with tartaric acid

combined with PVA as gel – forming agents (Figure 3.6)

3.1.2.2. The effect of calcination temperature on the formation of

Fe2O3 - Mn2O3 phase (Figure 3.7)

Figure 3.5. X-ray

diffraction of samples at

various gel temperatures

a) 40 o

C; b) 50 o

C; c) 60

oC; d) 80

oC; e) 100

oC

Figure 3.6. TGA and

DTA curves of the as

- prepared gel

(Fe-Mn)/ (AT+PVA)

Figure 3.7. X-Ray

diffractions at various

calcination temperatures: a)

300oC, b) 400

oC, c) 450

oC,

d)500oC, e) 550

oC và f) 600

oC

13

→ The optimum temperature (450 oC) was chosen

3.1.2.3. The effect of pH on the formation of Fe2O3 – Mn2O3 phase

→ The pH = 4 was chosen.

3.1.2.4. The effect of Fe/Mn mole ratio on the formation of Fe2O3 –

Mn2O3 phase

→ The Fe/Mn mole ratio chosen was Fe/Mn = 1/1

3.1.2.5. The effect of AT/PVA mole ratio on the formation of Fe2O3 -

Mn2O3 phase

→ The AT/PVA mole ratio chosen was AT/PVA = 1/1

Figure 3.8. X-Ray

diffractions at various

pH: a) pH 1, b) pH 2,

c) pH 3, d) pH 4

Figure 3.9. X-ray diffraction

of samples with various

mole ratios of Fe/Mn: a)

Fe/Mn = 6/1, b) Fe/Mn =

3/1, c) Fe/Mn = 1/1, d)

Fe/Mn = 1/3, e) Fe/Mn = 1/6

Figure 3.11. X-ray diffraction of samples with various mole ratios of AT/PVA: a) AT/PVA = 6/1, b) AT/PVA = 3/1, c) AT/PVA = 1/1, d) AT/PVA = 1/3, e) AT/PVA = 1/6

14

3.1.2.6. The effect of gel-forming temperature on the formation of

Fe2O3 - Mn2O3 phase

→ The gel-forming temperature was chosen at 80 oC

3.2. Compare and select gel – forming agents to synthesize mixed

oxide Fe2O3 – Mn2O3 nanoparticles

Table 3.8. The results of samples with different gel-forming agents

Gel-forming

agents

Calcination

temperature (oC)

BET (m2/g) References

PVA 550 68.5 [118] AT 500 46.25 This research

PVA + AT 450 63.97 This research

Figure 3.15, Figure 3.16. TEM images of Fe2O3 – Mn2O3 samples

a) using tartaric acid b) using AT+PVA

Figure 3.12. X-ray

diffraction of samples at

various gel temperatures:

a) 40 oC, b) 60

oC, c) 80

oC, d) 100

oC

a) b)

15

The synthesized mixed oxide Fe2O3 – Mn2O3 nanoparticles had a

spherical shape, the nanoparticle size synthesized by gel AT agent

combined with PVA is smaller and has a higher uniformity than

those by the only agent as AT. Moreover, the material surface was

more porous, the specific surface area is bigger, increasing the

adsorption capacity, creating more favorable conditions for the

photocatalytic process to decompose pollutants later.

→ The gel – forming agent which was AT + PVA was chosen to

synthesize mixed oxide Fe2O3 – Mn2O3 nanoparticles

To further clarify the formation of mixed oxide Fe2O3 – Mn2O3,

mixtures of AT and PVA were applid to synthesize metal oxide

singles of iron and manganese under conditions suitable for gel-

forming agents.

Table 3.6. Characteristics of the synthesized materials using AT +

PVA

Materials Morphology BET (m2/g) Vpore

(cm3/g)

Pore size

(nm)

Fe2O3 Stick 18.313 0.071 19.962

Mn2O3 Sphere 9.169 0.003 18.195

Fe2O3 - Mn2O3 Sphere 63.971 0.103 10.939

Figure 3.17. FE – SEM

images of Fe2O3, Mn2O3,

Fe2O3 – Mn2O3

16

The mixed oxide nanoparticles were porous, small in size, uniform

with a specific surface area many times larger than the synthetic

single oxide nano (these properties are not available in the case of

mixtures of two oxides Fe2O3 and Mn2O3).

3.3. Photocatalytic degradation of MO, MB by synthesized

catalysts of mixtures of AT and PVA using gel – forming agents

3.3.1. Photocatalytic degradation of MO by Fe2O3, Mn2O3, Fe2O3 –

Mn2O3

The formation of intermediates in a convenient way for the

decomposition process to produce the final product as CO2 , H2O

continued these intermediates [120, 121].

Figure 3.19. MO

decomposition using

various materials

Figure 3.24. MO

decomposition

pathway using

Fe2O3 – Mn2O3

catalyst

17

3.3.2. Photocatalytic degradation of MB by Fe2O3, Mn2O3, Fe2O3 –

Mn2O3

3.4. Synthesis of Fe2O3-Mn2O3/rGO material

Figure 3.25. MB

decomposition using

various materials

Figure 3.32. X-ray

diffraction of

samples: a) rGO, b)

Fe2O3-Mn2O3, c)

Fe2O3-Mn2O3 /rGO

Figure 3.31. MB decomposition

pathway using Fe2O3 – Mn2O3

catalyst

18

Results of XRD of the Fe2O3-Mn2O3 /rGO sample appear typical

peaks of rGO, Fe2O3-Mn2O3

Table3.13. Structural parameters of synthesized materials

Materials BET (m2/g) Vpore (cm

3/g) Pore size (nm)

rGO 200.682 0.352 8.789

Fe –Mn 63.972 0.103 10.939

Fe –Mn/rGO 131.984 0.418 14.422

.

There was a connection between metal ions into rGO layers. The

increased hole size, pore size created more activity centers on the

material surface than those on the original Fe2O3-Mn2O3, rGO

materials.

3.5. Effects of parameters on the degradation of fenitrothion and

parathion using Fe2O3-Mn2O3/rGO photocatalytic material

3.5.1. Effects of parameters on the degradation of parathion

3.5.1.1. Equilibrium adsorption process of parathion

3.5.1.2. Effect of reaction time on the degradation of parathion

3.5.1.3. Effect of catalyst dosage on the degradation of parathion

3.5.1.4. Effect of pH on the degradation of parathion

3.5.1.5. Effect of inital parathion concentration

3.5.1.6. Proposed oxidative degradation route of parathion

Figure 3.35. FE – SEM

images of rGO, Fe2O3 –

Mn2O3, Fe2O3 – Mn2O3/rGO

19

Figure 3.37.

Parathion adsorption ability

using Fe2O3 – Mn2O3/rGO in

the dark for 24h

Figure 3.38.

Parathion decomposition ability

using Fe2O3-Mn2O3 /rGO at

various reaction times

Figure 3.39. Parathion

decomposition ability using

Fe2O3-Mn2O3/rGO at various

catalyst content a) 0,05 g/L; b)

0,025 g/L; c) 0,01 g/L; d) 0,1 g/L

Figure 3.40. Parathion

decomposition ability using Fe2O3-

Mn2O3/rGO at various pH

Figure 3.42. Parathion removal

efficiency on Fe2O3-Mn2O3 /rGO

catalyst at different catalyst initial

parathion concentrations a) 1,5

ppm; b) 5 ppm; c) 10 ppm

20

3.5.2. Effects of parameters on the degradation of fenitrothion

3.5.2.1. Equilibrium adsorption process of fenitrothion

3.5.2.2. Effect of reaction time on the degradation of fenitrothion

3.5.2.3. Effect of catalyst dosage on the degradation of fenitrothion

3.5.2.4. Effect of pH on the degradation of fenitrothion

3.5.2.5. Effect of inital fenitrothion concentration

3.5.2.6. Proposed oxidative degradation route of fenitrothion

Figure 3.46. Parathion

decomposition pathway

using Fe2O3-Mn2O3/rGO

nanocomposite catalyst

21

Figure 3.47.

Fenitrothion adsorption ability

using Fe2O3 – Mn2O3/rGO in

the dark for 24h

Figure 3.48.

Fenitrothion decomposition ability

using Fe2O3-Mn2O3 /rGO at

various reaction times

Figure 3.49. Fenitrothion

decomposition ability using

Fe2O3-Mn2O3/rGO at various

catalyst content a. 0,01 g/L; b.

0,025 g/L; c. 0,05 g/L; d. 0,1 g/L

Figure 3.50. Fenitrothion

decomposition ability using Fe2O3-

Mn2O3/rGO at various pH

Figure 3.51. Fenitrothion removal

efficiency on Fe2O3-Mn2O3 /rGO

catalyst at different catalyst initial

parathion concentrations a) 1,4

ppm; b) 5 ppm; c) 11 ppm

22

3.5.3. Comparison of photocatalytic activity of Fe2O3 – Mn2O3

and Fe2O3 – Mn2O3/rGO synthesized materials

Fe2O3 – Mn2O3 nanoparticles were not able to adsorb contaminants,

parathion removal efficiency was 93 %.

Only 5% Fe2O3 – Mn2O3 on the rGO carrier catalysts, parathion

adsorption ability were over 20%, parathion removal efficiency was

77.32%.

Figure 3.54. Fenitrothion

decomposition pathway

using Fe2O3-Mn2O3/rGO

catalyst

Figure 3.57. Parathion

removal efficiency on

Fe2O3 – Mn2O3 and

Fe2O3 – Mn2O3/rGO

catalyst after different

reaction times

23

3.5.4. The reusability of the Fe2O3 –Mn2O3/rGO catalyst

The photocatalytic ability of parathion and fenitrothion to decompose

has been changed after four times using, but this reduction was

almost negligible (after the fourth use: reduce only 3.5% for

parathion and 1.8% for fenitrothion).

CONCLUSIONS

Synthesis of mixed oxide Fe2O3 – Mn2O3 using various gel -

forming agents, including tartaric acid, and the combination of

tartaric acid and PVA by combustion method had been studied.

- Optimum conditions to make Fe2O3-Mn2O3 powder when

using tartaric acid were pH 4, temperature of gel formation 80oC,

mole ratio of Fe/Mn = 1/1, mole ratio of KL/PVA =1/3 calcinating

temperature 500oC during 2h, the nanostructured Mn2O3-Fe2O3

powder had specific area 46.20 m2/g.

- Optimum conditions to make Fe2O3 – Mn2O3 powder when

using tartaric acid and PVA were pH 4, temperature of gel formation

80oC, mole ratio of Fe/Mn = 1/1, mole ratio of KL/PVA =1/3, mole

ratio of AT/PVA = 1:1, calcinating temperature 450oC during 2h, the

nanostructured Mn2O3 – Fe2O3 powder had specific area 63.97 m2/g.

The efficiency of decomposition MO, MB of the

photocatalytic process using single oxides of iron, manganese, and

mixed oxide nano of Mn2O3 – Fe2O3 was compared. The results

showed that decomposition MO by using oxide nanoparticles Mn2O3

– Fe2O3 was almost double that of using single oxides. Whereas for

MB, single-phase oxide iron proved ineffective, the efficiency of

treatment using manganese oxide was nearly 2 times lower than that

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using the nano - mixed oxide Mn2O3 – Fe2O3. Some intermediates as

well as decomposition MO, MB pathway was also proposed.

Oxide Mn2O3 – Fe2O3 nanoparticles on carrier rGO and

investigated and decomposition ability of parathion of the material

had been successfully dispersed. The results showed that the

decomposition efficiency parathion was high (after 90 reaction

minutes, ph 7.5, the concentration after equilibrium was adsorbed 1.5

ppm, the decomposition efficiency was 77.32% when the catalyst

content of 0.05 g/L was used). For fenitrothion after 90 reaction

minutes, pH 7.0, the concentration after equilibrium was adsorbed

1.4 ppm, the decomposition efficiency was 88.6% when the catalyst

content of 0.05 g/L was used. After a 180 reaction minutes for

parathion and 120 minutes for fenitrothion, no organic substances

were detected in the sample. Several intermediates and degradation

pathways for these substances were also proposed. The reusability of

oxide Mn2O3 – Fe2O3 nanomaterials on carriers rGO was also studied

after 4 times, the decomposition efficiency was not significantly

reduced (only reduced by 3.5% for parathion and 1.8% for

fenitrothion).