Study on synthesis of TiO2- Fe2O3/GNP materials from ilmenite and graphite ore to orient Cr(VI) transformation in defense industrial wastewater - 2

Table 3.2. Effect of dissolution solution volume on average particle size of TFG0 81 composite material

Table 3.3. Elemental composition in TFG sample 0-8h 83

Table 3.4. Effect of GNP content on particle size of the material

2-oxide complex on GNP 87 base

Table 3.5. Effect of hydrothermal temperature on grain size 91

Table 3.6. Surface area of ​​two hydrothermal TFG20 samples in different environments 95

Table 3.7. Effect of mixing factors on particle size 98

Table 3.8. List of basic conditions for fabrication of TiO 2 - Fe 2 O 3 /GNP composite material 124

Table 3.9. Data table for evaluating technological stability with different batch sizes 125

Table 3.10. Results of measuring wastewater samples before treatment of the pyrotechnics production line at factory 2, Z121 126

Table 3.11. Table of actual wastewater sample data of factory Z121 128

LIST OF DRAWINGS

Page

Figure 1.1. Main methods of graphene synthesis [54] 5

Figure 1.2. Structure of graphene nanoplate 6

Figure 1.3. Crystal structure of the adsorbed forms of TiO2 15

Figure 1.4. Simulation of the photoreduction process of Cr(VI) [34] 42

Figure 1.5. Positions of the conduction and valence bands of TiO2 (anatase) in comparison

with reduction potential of metal ions at different pH values ​​[29] 43

Figure 2.1. Flow chart of GNP synthesis process 52

Figure 2.2. Flowchart of the synthesis process of precursor solution containing titanium and iron 52

Figure 2.3. Schematic diagram of synthesis of TiO2- Fe2O3 composite material 53

Figure 2.4. Schematic diagram of synthesis of TiO2- Fe2O3/GNP composite material 53

Figure 2.5. Raman transformation diagram 59

Figure 2.6. Types of adsorption - desorption isotherms 61

Figure 2.7. Determination of photocatalytic activity on photochemical testing equipment

................................................................ ................................................................ ......... 64

Figure 3.1. Image of graphite and GNP with the same weight of 0.1g 69

Figure 3.2. SEM images at 5,000 and 20,000 times magnification of the original graphite

(A and B) and the fabricated graphene nanoplatelets (C and D). 69

Figure 3.3. XRD patterns of the original graphite sample and the synthesized GNPs 70

Figure 3.4. Raman spectrum of GNP (large image) and of the magnified peak at 2683 cm-1 (small image) 71

Figure 3.5. EDX diagram of GNP material fabricated from graphite 72

Figure 3.6. XPS spectrum of synthesized GNP material 73

Figure 3.7. XPS spectrum of C 1s in GNP 73 material

Figure 3.8. Energy dispersive X-ray (EDX) spectrum of ilmenite 52% 74

Figure 3.9. XRD diagram of 52% ilmenite concentrate before and after 75% calcination

Figure 3.10. XRD pattern of the residue sample after dissolution 76

Figure 3.11. Sample of TiO2- Fe2O3 composite material (TFG0) 77

Figure 3.12. XRD patterns of hydrothermal TFG0 material in acidic (TFG0 (pH5)), neutral (TFG0 (pH7)) and alkaline (TFG0 (pH11)) environments 78

Figure 3.13. XRD patterns of Fe2O3 -TiO2 oxide composite samples with different hydrothermal times 79

Figure 3.14. SEM (a) and TEM (b) images of TFG0 82 composite material

Figure 3.15. Tauc-plot curve of sample TFG0 84

Figure 3.16. Sample of TiO2- Fe2O3/GNP 85 material

Figure 3.17. XRD patterns of TFG samples with different GNP contents 86

Figure 3.18. UV-DRS spectrum (a) and [F(R)hν]1/2 curve of TFG10 material (10 mg GNP) 88

Figure 3.19. UV-Vis DRS spectra of TFG composite samples with different GNP contents 88

Figure 3.20. Graph of the influence of GNP content on the Cr(VI) conversion capacity of TFG 89 material

Figure 3.21. XRD patterns of hydrothermal TFG20 samples at different temperatures 91

Figure 3.22. Diagram determining the influence of hydrothermal temperature on the Cr(VI) conversion capacity of TFG20 samples 93

Figure 3.23. XRD patterns of hydrothermal TFG20 samples in pH3, pH5, pH6, pH7 and pH11 environments 94

Figure 3.24. Comparison of band gap energy of hydrothermal TFG20 material in

different environments: pH11(a), pH7(b), pH5(c) 95

Figure 3.25. Comparison chart of Cr (VI) conversion capacity of hydrothermal TFG material in different environments 96

Figure 3.26. XRD spectrum of TFG composites with and without the presence of stirring element 97

Figure 3.27. Graph evaluating the influence of stirring factor on the Cr(VI) conversion capacity of TFG 98 material

Figure 3.28. Energy dispersive X-ray spectrum (EDX) of TFG20 100 material

Figure 3.29. XPS spectrum of TFG20-8h 100 composite material

Figure 3.30. XPS spectra of elements C1s (a), Fe2p (b), Ti2p (c) and O1s (.d) in TFG20-8h 101 composite material

Figure 3.31. FT-IR spectra of GNPs, Fe-Ti 2-component oxide mixtures and materials

TiO2- Fe2O3/GNP 103 composite

Figure 3.32. Raman spectrum of TFG20 and GNP 104 composites

Figure 3.33. SEM images of TFG20 composite materials with magnifications of 5,000 times (a) and 200,000 times (b) 105

Figure 3.34. TEM image (a) and HRTEM image (b) of TFG20 106 composite material

Figure 3.35. PL spectra of TFG20 and TFG0 107 materials

Figure 3.36. Adsorption isotherm curve of sample TFG 20-8h 108

Figure 3.37. TGA diagram of sample TFG 20-8h 109

Figure 3.38. Graph of pH effect on Cr(VI) 110 treatment capacity

Figure 3.39. Graph of the influence of initial Cr(VI) concentration on the conversion efficiency 111

Figure 3.40. Effect of initial concentration on the relationship - Ln(C/C0) and time 112

Figure 3.41. Graph of the influence of hole accepting agent on the photocatalytic conversion of Cr(VI) 113

Figure 3.42. Graph of the influence of TFG20 catalyst amount on the conversion capacity of Cr(VI) 115

Figure 3.43. Graph of the influence of light intensity on the ability to transform Cr(VI) 116

Figure 3.44. Graph of the influence of light wavelength on photocatalytic ability

Cr(VI) transformation effect of TiO2- Fe2O3/GNP composite material 117

Figure 3.45. Graph evaluating the efficiency of the photocatalytic conversion of Cr(VI) of the composite material TiO2- Fe2O3/GNP 118

Figure 3.46. Relationship -ln(Co/Ct) with time of photocatalytic process

Cr(VI) treatment of TiO2- Fe2O3/GNP composites 119

Figure 3.47. Simulation of photocatalytic mechanism of Cr(VI) conversion using materials

TiO2- Fe2O3/GNP 121 composite

Figure 3.48. Graph of Cr(VI) treatment efficiency evaluation after 5 reuses 122

Figure 3.49. Technological diagram for manufacturing TiO2- Fe2O3/GNP 123 oxide composite material Figure 3.50. Diagram for treating wastewater from explosives production using composite materials

TiO2- Fe2O3/GNP 128

INTRODUCTION

1. Urgency of the thesis topic

The development of industries, especially the chemical industry, has been causing pollution and damaging the living environment. Therefore, the treatment of environmental pollution is a matter of special concern on a global scale.

Meanwhile, defense explosives manufacturing facilities, due to their specific nature, use many types of hazardous chemicals in both inorganic and organic compounds such as aromatic organic compounds or heterocyclic nitramines containing one or more nitro radicals, organic solvents and heavy metals such as Pb, Cr, Hg, etc. These are highly toxic chemicals that cause cancer and even death if contaminated with high concentrations. During the use and cleaning of equipment and production tools, these chemicals have penetrated into wastewater sources, with concentrations exceeding the permissible level, requiring treatment measures before being discharged into the environment. Research and application of new science and technology to establish measures to control, analyze and treat hazardous waste generated from the activities of defense manufacturing facilities (especially explosive and flammable waste) has been and is being paid attention to and studied.

Graphene is a new two-dimensional (2D) material in the carbon material family [91], this material has outstanding properties such as high flexibility, mechanical strength, high electrical and thermal conductivity and a large surface area of ​​2600 m 2 /g [26]. Graphene nanoplatelets or graphene nanoplate (GNP) is a type of material in the graphene family, extracted from graphite by chemical methods, the extraction process does not use strong oxidizing agents so the surface has few defects and few steps (because it does not have to go through the intermediate step of forming GO), so the material has great potential for industrial-scale production, low cost and is more suitable for application in the field of environmental treatment.

Due to the characteristics of explosives production wastewater containing many toxic organic and inorganic components, the advanced oxidation method in general and the photocatalytic method in particular have many advantages. In addition to the ability to convert toxic organic substances into CO2 and H2O , photocatalytic materials also have the ability to convert heavy metal ions into lower toxicity forms. On the other hand, the photocatalytic process is a "green" treatment process because the photocatalytic materials are non-toxic materials, so the process will avoid chemical residues or the formation of

toxic by-products. Photocatalytic materials based on TiO 2 are popular photocatalytic materials that are widely used, however, due to the limitation of high band gap energy and only show activity in the ultraviolet region. To overcome this disadvantage, different methods are used, but the most common is doping with transition metals, the most common of which is Fe. Ilmenite (FeTiO 3 ) is a natural mixture of TiO 2 and Fe 2 O 3 , with large reserves in our country. If the above mixture can be utilized, a composite material based on TiO 2 with photocatalytic ability in the visible light region will be obtained.

Composite materials have long been of interest to scientists, technologists and managers in many different fields. The combination and supplementation to overcome the limitations of single materials in composite materials helps to increase the features, efficiency and diversity of properties and applications of this type of material. Vietnam is a country with many minerals such as coal, graphite, bauxite, ilmenite, rare earth ..., which are mainly exported in the form of raw materials with low value. Therefore, deep processing of mineral resources into high-quality products with good features and increased economic value is the policy of the Party and the State. The fabrication of composite materials based on TiO 2 oxide , Fe 2 O 3 and graphene nanoplatelets (GNP) from graphite and ilmenite will contribute to creating a direction of photocatalytic materials with strong photocatalytic activity in the visible light region, with the ability to be widely applied on an industrial scale. Research on the synthesis process of materials, determining the optimal parameters of the process and evaluating the ability of the materials to transform heavy metals will have practical and scientific significance, contributing to enriching and finding suitable treatment methods for wastewater from the production of defense explosives.

From the above scientific and practical requirements, the topic: "Research on synthesis of TiO 2 -Fe 2 O 3 /GNP materials from ilmenite and graphite ores to orient the transformation of Cr(VI) in defense industrial wastewater" is urgent.

2. Objectives of the thesis

- Testing and evaluating photocatalytic activity and Cr (VI) conversion ability in defense production wastewater.

3. Research objects and scope