Summary of Environmental engineering doctoral thesis: Study on synthesis of manganese oxide, iron oxide on reduced graphene oxide nanoparticles to treatment of pigments and pesticides in the aqueous environment

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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.

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Nội dung Text: Summary of Environmental engineering doctoral thesis: Study on synthesis of manganese oxide, iron oxide on reduced graphene oxide nanoparticles to treatment of pigments and pesticides in the aqueous environment

MINISTRY OF EDUCATION AND VIETNAM ACADEMYOF TRAINING 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 1.2. The molecular Figure 1.3. The molecular structure of MO structure of MB
5 Figure 1.4. The molecular Figure 1.5. The molecular structure of parathion structure of fenitrothion 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
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) String, heating Drying at 110 oC for 2h Gel- forming agents solution Mixture solution Fe2O3- Viscous Dry Mn2O3 gel gel Fe2+ solution adjust pH calcinating and Mn2+ solution Figure 2.1. Diagram of Fe2O3-Mn2O3 synthesis process using combustion method Gel- forming String, heating rGO agents solution Mixture Visc Visco solution ous us gel Fe2O3- gel /rGO Mn2O3 /rGO Fe2+ solution and Mn2+ solution 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 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 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: C0 − Cf H % = ∗ 100% 2.3 C0 2.4.2. Test of (Fe2O3 – Mn2O3)/rGO on pesticides treatment
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 Figure 3.1. TGA and DTA Figure 3.2. X-Ray diffractions at curves of the as - various calcination temperatures a) prepared gel 300 oC, b) 400 oC, c) 450 oC, d) 500 oC, e) 550 oC, f) 600 oC → The optimum temperature (500 C) was chosen o Figure 3.3. X-Ray diffractions at various pH a) pH 1, b) pH 2, c) pH 3, d) pH 4, e) pH 5 → The pH value chosen was pH 4 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 → The Fe/Mn mole ratio chosen was Fe/Mn = 1/1
12 Figure 3.5. X-ray diffraction of samples at various gel temperatures a) 40 oC; b) 50 oC; c) 60 o C; d) 80 oC; e) 100 oC → 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) Figure 3.6. TGA and DTA curves of the as - prepared gel (Fe-Mn)/ (AT+PVA) 3.1.2.2. The effect of calcination temperature on the formation of Fe2O3 - Mn2O3 phase (Figure 3.7) Figure 3.7. X-Ray diffractions at various calcination temperatures: a) 300oC, b) 400oC, c) 450oC, d)500oC, e) 550oC và f) 600oC
13 → The optimum temperature (450 oC) was chosen 3.1.2.3. The effect of pH on the formation of Fe2O3 – Mn2O3 phase Figure 3.8. X-Ray diffractions at various pH: a) pH 1, b) pH 2, c) pH 3, d) pH 4 → The pH = 4 was chosen. 3.1.2.4. The effect of Fe/Mn mole ratio on the formation of Fe2O3 – Mn2O3 phase 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 → 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 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 → The AT/PVA mole ratio chosen was AT/PVA = 1/1
14 3.1.2.6. The effect of gel-forming temperature on the formation of Fe2O3 - Mn2O3 phase Figure 3.12. X-ray diffraction of samples at various gel temperatures: a) 40 oC, b) 60 oC, c) 80 o C, d) 100 oC → 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 Calcination BET (m2/g) References o agents temperature ( C) PVA 550 68.5 [118] AT 500 46.25 This research PVA + AT 450 63.97 This research a) b) Figure 3.15, Figure 3.16. TEM images of Fe2O3 – Mn2O3 samples a) using tartaric acid b) using AT+PVA
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 Pore size 3 (cm /g) (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