MINISTRY OF EDUCATION AND TRAINING MINISTRY OF NATIONAL DEFENCE ACADEMY OF MILITARY SCIENCE AND TECHNOLOGY TRAN DINH TUAN STUDY ON SYNTHESIS OF THE METAL ORGANIC FRAMEWORKS Fe-MOFs MATERIALS AND USED AS PHOTOCATALYST FOR TREATMENT OF AROMATIC NITRO COMPOUNDS IN EXPLOSIVES PRODUCTION Specialization: Chemical engineering Code: 952 03 01 SUMMARY OF DOCTORAL THESIS Hanoi - 2019 This thesis has been completed at: Academy of Military Science and Technology, Ministry of Defence Scientific supervisors: Assoc Prof Dr Ninh Duc Ha Dr Do Huy Thanh Reviewer 1: Prof Dr Vu Thi Thu Ha Reviewer 2: Assoc Prof Dr Cao Hai Thuong Reviewer 3: Assoc Prof Dr Tran Van Chung The thesis was defended in front of the Doctoral Evaluating Council at Academy level held at Academy of Military Science and Technology at 8:30 AM, date … month … , 2019 The thesis can be found at: - The Library of Academy of Military Science and Technology - Vietnam National Library THE SCIENTIFIC PUBLICATIONS Tran Dinh Tuan, Ninh Duc Ha, Nguyen Thi Hoai Phuong, Nguyen Cong Thang (2015), “Synthesis and study reactive photocatalysis of Fe-BDC and Cr-BDC”, Vietnam Journal of Chemistry, No.53(5e1), p.43-47 Tran Dinh Tuan, Le Thanh Bac, Ninh Duc Ha, Do Huy Thanh (2015), “Study on synthesis of MIL-100(Fe) at low temperature and atmospheric pressure”, Vietnam Journal of Chemistry, No.53(6e4), p.322-325 Le Thanh Bac, Tran Dinh Tuan, Nguyen Thi Hoai Phuong, Nguyen Duy Anh, Tran Van Chinh, Doan Thi Ngai (2015), “Study synthesis on material metal organic framework based on Fe-BDC”, Vietnam Journal of Chemistry, No.53(4e1), p.33-36 Tran Dinh Tuan, Nguyen Thi Hoai Phuong, Ngo Hoang Giang, Nguyen Tien Hue, Do Huy Thanh, Ninh Duc Ha (2016), “Study on synthesis of Fe-BTC MOF material at low temperature and atmospheric pressure” Proceedings CASEAN-4, Bangkok, Thailand Tran Dinh Tuan, Nguyen Thi Hoai Phuong, Do Huy Thanh, Ninh Duc Ha (2016), “Synthesis and reactive photocatalysis of MOF material based on Fe-BTC”, Vietnam Journal of Catalysis and Adsorption, No.2, 91-96 Tran Dinh Tuan, Le Viet Ha, Nguyen Thi Hoai Phuong, Ninh Duc Ha (2017), “A new photocatalyst for the degredation of TNT by metal organic framework NH2-MIL-88B(Fe)” Journal of Military Science and Technology, Special Issue, No.51A, 71-76 INTRODUCTION The urgency of the thesis topic In Vietnam, defense industry factories produce a large amount of explosives for military and civil purposes every year This industry uses a range of aromatic nitro derivatives such as trinitro toluene (TNT), dinitro toluene (DNT), trinitro phenol (TNP) which results in a large amount of waste containing toxic aromatic compounds Meanwhile, the present technologies for handling military waste in general and aromatic ring nitro compounds in particular still exist many limitations Many catalysts have been used for treatment of aromatic ring nitro compounds Among them, the photocatalysis materials based on semiconductors such as TiO2, ZnO… are well-known which have proven their high effectiveness for degradation of toxic organic waste However, the disadvantagies such as the poor recyclibility, low light harvesting efficiency, fast charge recombination have limited their application in practical Metal-organic frameworks materials (MOFs) are known as hybrid inorganic-organic material, which metal-oxide units or metal ions joined by organic linkers through strong covalent bonds MOFs have unique crystal structure, large specific surface area, flexible structural frame, resizable size, porosity through synthetic methods Therefore, MOFs can be employed as best candidate for adsorption and catalysts application Many domestic and international scientists had been studied on the field of MOFs materials for few decade It must be emphasized that MOFs are very potential materials More research is needed to contribute to the database of the MOFs material synthesis and catalysis applications, especially as photocatalyst for environmental treatment In order to fulfill this task, the PhD student has proposed and implemented the thesis topic: "Study on synthesis of the metal organic frameworks Fe-MOFs materials and used as photocatalyst for treatment of aromatic nitro compounds in explosives production", with the aim is to contribute to the diversification of MOFs material synthesis techniques, characterize and evaluation of prepared materials and their potential application as photocatalyst for the degradation of toxic aromatic nitro waste in explosive production The contents - Study on the synthesis of Fe-BTC and Fe-BDC-NH2 by the refluxing method at low pressure and temperature - Study on the synthesis of Fe-BDC and Fe2Ni-BDC by the solvothermal method - Analyzing structure and characterization of synthesized materials - Investigate photocatalytic activity of the Fe-MOFs materials for degradation of TNT, TNP solutions in lab scale - Study on the mechanism of the photocatalytic behavior toward the TNT, TNP solutions of Fe-MOFs materials The research method The thesis used the solvothermal and the refluxing methods at low temperature to synthesize Fe-MOFs materials Modern physical and chemical analysis techniques are used to structure analysis and characterizration of synthesized materials such as: XRD, FT-IR, SEM, BET, TGA, EDX, XPS, UV-Vis DRS Furthermore, the qualitative and quantitative analysis techniques for content of TNT, TNP in the solutions after degradation reactions such as HPLC, TOC are also employed to determine photocatalysis treatment effectiveness Scientific significance and applicability of the thesis - Synthesis of several Fe-MOFs materials by solvothermal and refluxing methods and using physical and chemical analyzing techniques to contribute to the database of the materials - Study on the application of synthesized materials as the photocatalyst to removal of TNT, TNP out of wastewater in the explosive industry The results show that four synthesized materials have high efficiency and degradation rate The results of the thesis are primary for application of Fe-MOFs materials for treatment of wastewater containing nitro aromatic ring compounds The layout of thesis The thesis contains 119 pages which is constructed as following: Overview pages; chapter - Introduction, 31 pages; chapter Experiments, 18 pages; chapter - Results and Dicussion, 50 pages; Conclusion pages; List of published scientific reports, page and 106 references Chapter Introduction Overview about structural properties, synthesis methods and application of MOFs as well as Fe-MOFs materials Analysis and evaluation of research status on the application of photocatalytic properties and photocatalytic degradation mechanism of MOFs materials in Vietnam and around the world Overview about status of solutions for the removal of aromatic nitro compounds out of wastewater in propellant and explosive manufacture industry As a result, establishscientific basis and orientation for implementing of the research content of the thesis Chapter Experiments 2.1 Synthesis method 2.1.1 Materials Terephthalic acid (H2BDC), C8H6O4; Trimesic acid (H3BTC), C9H6O6; 2-Amino terephthalic acid (NH2-BDC), C8H7NO4; FeCl3.6H2O; Fe(NO3)3.9H2O; Ni(NO3)2.6H2O; Dimethyl formamide (DMF), C3H7NO; Hydro peroxide, H2O2; Trinitro toluene, C6H2(CH3)(NO2)3; Trinitro phenol, C6H2(OH)(NO2)3 2.1.2 Accessories and equpipments - Basic laboratorial accessories - 250 mL three - neck flask, gauge glass, reflux condenser - Analytic balance, measure range from 0,001 to 220 g - Mechanical stirrer with glass stirrer, IKA RW16, Germany - 200 mL Autoclave reactor 304 stainless with PTFE liner - Heating oven, 101 HU VUE, China - Centrifugal machine, EBA 21 Hettich, Germany, maximum speed 6000 rpm - Heating plate and magnetic stirrer, IKA C-MAGSH, Germany - Photocatalytic reactor 2.1.3 Synthesis of Fe-BTC 2.1.3.1 Synthesis process of Fe-BTC Fe-BTC was synthesized by refluxing method Typically, mixture of Fe(NO3).9H2O and acid H3BTC were dissolved in 50.4 mL distilled water and magnetic stirred for 30 minutes After that, the solution was poured into the three-neck flask and adjusted pH about and stirred in 15 minutes The refluxing condenser system was installed, magnetic stirring speed was adjusted about 300 rpm The system was heated to 100oC and and maintained for hours The product was washed many times by distilled water to remove impurities and washed by ethanol at 70oC Finally, the product was filtered and heated at 60oC for 10 hours 2.1.3.2 Study on the effect of factors on the synthesis Study on the effect of factors on the synthesis of Fe-BTC such as: percentage of reactants, reaction time, reaction temperature by adjusting mol ratio of H3BTC/Fe3+ from 0.5:2 to 2:2; reation time is 4, 6, 8, 10 hours; reaction temperature is 60, 80, 100oC 2.1.4 Synthesis of Fe-BDC-NH2 2.1.4.1 Synthesis process of Fe-BDC-NH2 Fe-BDC-NH2 was synthesized by refluxing method Typically, the mixture of FeCl3.6H2O and DMF were dissolved in glass cup, magnetic stirred for 30 minutes, added NH2-BDC acid and stirred continually for 15 minutes After that, the solution was poured into the three-neck flask and adjusted pH about and stirred for 15 minutes The refluxing condenser system was installed, magnetic stirring speed was adjusted about 300 rpm The system was heated to 100oC and and maintained for hours The product was washed many times by DMF to remove acid and washed by ethanol at 70oC to remove DMF Finally, the product was filtered and heated at 60oC for 10 hours 2.1.4.2 Study on the effect of factors on the synthesis Fe-BDC-NH2 Study on the effect of factors on the synthesis of Fe-BDC-NH2 such as: percentage of reactants, reaction time, reaction temperature by adjustment mol ratio of NH2-BDC/Fe3+ from 0.5:1 to 2:1; reation time is 4, 6, 8, 10 hours; reaction temperature is 60, 80, 100oC 2.1.5 Synthesis of Fe-BDC, Fe2Ni-BDC 2.1.5.1 Synthesis technique of Fe-BDC Fe-BDC was synthesized by solvothermal method Typically, a mixture of FeCl3.6H2O, H2BDC and DMF were dissolved with mol ratio of which were 1:1:280, respectively A mixture of FeCl3.6H2O and 160 mL DMF were dissolved and then added gently 1.235 g H2BDC acid in the solution and stirred continually until the solution was transmisparent, yellow and pH of which was After that, the solution was poured into autoclave reactor and heated at 110oC for 10 hours The product was washed times by DMF and washed times by ethanol at 70oC Finally, the product was filtered and heated at 60oC for hours and maintained in vacuum condition 2.1.5.2 Synthesis of Fe2Ni-BDC Fe2Ni-BDC was synthesized by solvothermal method Typically, prepared a mixture of [FeCl3.6H2O + Ni(NO3)2.6H2O] and H2BDC and DMF with mol ratio were 1:1:280, respectively and mol ratio of FeCl3.6H2O/Ni(NO3)2.6H2O were 2:1 The mixture of FeCl3.6H2O, Ni(NO3)2.6H2O and 160 mL DMF were dissolved and then added gently 1.235 g H2BDC acid in the solution and strirred continually until the solution was transmisparent, yellow and pH=6 After that, the solution was poured into autocalve reactor and heated at 110oC in 10 hours The product was washed times by DMF at room temperature and washed times by ethanol at 70oC Finally, the product was filtered, heated at 60oC for hours and maintained in vacuum condition 2.2 Photocatalytic degradation of TNT/TNP solutions using FeMOFs materials Photocatalytic degradation tests were carried out by dispersion of MOFs materials in TNT/TNP solutions, the reacted solution were poured into a 250 mL glass beaker and magnetic stirred with speed of 300 rpm, the period temperature were controlled at room temperature, under simulated sunlight conditions (Philips LED lights, 40 W power, 1200 lux intensity, 440-415 nm wavelength, - 6% UV light) Experiments were performed with 100 mL of TNT / TNP solutions, Fe-MOFs catalytic dosage were 0.5 g / L, adding 0.4 mL of 30% H2O2 solution (0.05 M) for reaction times of 15, 30, 45, 60 minutes, after each period time took mL of sample, filted and analyzed HPLC, TOC to determine the concentration of TNT / TNP Determination of adsorption characteristics of synthesized materials was carried out the same in the dark condition 2.2.1 Study on the effect of factors on photocatalyst degradation TNT solution using Fe-BDC-NH2 materials Study on the effect of factors such as: content of catalyst, luminous intensity, initial concentration of TNT solution, pH, temperature and content of additive H2O2 2.2.2 Study on recyclability of catalytic materials The photocatalytic experiments were repeated several times with 100 mL of TNT solution of 50 mg/L, with pH = 7, a catalyst content of 0.5 g/L, adding 0.4 mL of 30% H2O2 solution Photocatalytic reactions were performed at room temperature and take samples for analysis every 60 minutes For the second, third and fourth experiments, the solution was regenerated and calculated to add a content of TNT so that concentration of TNT in solution is 50 ppm 2.3 Analysis techniques for investidation of photocatalytic activity 2.3.1 Analysis technique to characterization The modern physical and chemical analysis techniques were used to analyze and evaluate properties synthesized material consist of XRD, FT-IR, SEM, TGA, BET, EDX, XPS, UV-Vis-DRS 2.3.2 Analysis technique to evaluate treated wastewater samples The efficiency of photocatalytic degradation was determined by using HPLC and TOC technique Chapter RESULT AND DICUSSION 3.1 Synthesis of Fe-BTC 3.1.1 Study on the effect of some factors on the synthesis of Fe-BTC material 3.1.1.1 The effect of H3BTC/Fe3+ contents Fe-BTC materials were synthesized for hours, at 100oC, with mol ratio of H3BTC/Fe3+ in turn are: 0.5:2; 1:2; 1.5:2; 2:2 Synthesized reaction equation is followed: Fe(NO3)3.9H2O + H3BTC → Fe3O(H2O)2(OH)(BTC)2.nH2O + H2O + HNO3 XRD patterns in Figure 3.1 showed that sample M1.1-2 had peaks of Fe-BTC with high intensity, and position of the peaks at 2θ = 6.03o; 6.6o; 10.59o, 11.12o were similar to XRD patterns of MIL-100 in previous works, thus synthesized Fe-BTC material was MIL-100(Fe) When mol ratio of H3BTC/Fe3+ was 0.5:1 (M2.0,5-1 sample), acid concentration was not enough to form crystalline structure of Fe-BTC material XRD patterns of the samples with high molar ratio of H3BTC/Fe3+ (M1.1,5-2, M1.2-2) had low intensity of specific peaks, simultaneously the presence of other peaks were ascribed to diffracted peaks of H3BTC acid M1.1-2 sample was considerred as the most similar to MIL-100(Fe) reported previously Therefore, the H3BTC/Fe3+ molar ratio of 1:2 was chosen as optimized ratio to synthesize Fe-BTC material Figure 3.1 XRD patterns of synthesized Fe-BTC material with the different molar ratios of H3BTC/Fe3+ 3.1.1.2 Effect of temperature on the MOF formation Formation of Fe-BTC materials was investigated at various temperatures such as 60oC, 80oC and 100oC The reaction time of the 10 BET result of Fe-BTC material showed that surface area was 1777 m2/g, volume of porous hole was 0.85 cm3/g TGA result indicated that synthesized material was resisted the elevate temperature of 346oC 3.2 Synthesis of Fe-BDC-NH2 3.2.1 Study on the effect of reaction conditions on the synthesis of Fe-BDC-NH2 The thesis studied on the optimal conditions to synthesize Fe-BDCNH2 by refluxing approach 3.2.1.1 Effect on the molar ratio of NH2-BDC to Fe3+ The materials were synthesized at 80oC for hours, with molar ratios of NH2-BDC/Fe3+ were 0.5:1; 1:1; 1.5:1; 2:1 Reaction equation was showed as following: FeCl3.6H2O + H2N-BDC → Fe3O(H2O)2(OH)(H2N-BDC)3.nH2O + HCl + H2O Figure 3.11 XRD patterns of resultant Fe-BDC-NH2 compounds with different molar ratios of NH2-BDC/Fe3+ Figure 3.11 show the XRD patterns of MOFs materials obtained with various molar ratios When molar ratio between NH2-BDC/Fe3+ is 0.5:1 (M2.0,5-1 sample), acid concentration was not enough to form crystalline structure of Fe-BDC-NH2 material, thus obtained product showed amorphous nature XRD patterns of the samples with high molar ratio of NH2-BDC/Fe3+ (M2.1,5-1, M2.2-1) had low intensity of specific peaks which characterize for Fe-BDC-NH2 material, moreover the presence of impurity peaks were characteristic difraction peaks of NH2-BDC acid M2.1-1 sample with NH2-BDC/Fe3+ molar ratio 1:1 had specific peak of Fe-BDC-NH2 at 2θ = 9.12o; 9.74o; 18.90o with high intensity The result was consistent with previous reports Therefore, the 11 NH2-BDC/Fe3+ molar ratio of 1:1 was chosen as optimal ratio to synthesize Fe-BDC-NH2 material 3.2.1.2 Effect of DMF contents Figure 3.12 XRD patterns of synthesized Fe-BDC-NH2 materials with different content of solven XRD patterns in Figure 3.12 showed that DMF content significantly affected crystalline intensity of Fe-BDC-NH2 materials It has been known that DMF was suitable solvent for the synthesis of Fe-BDC-NH2 material This could be explained that DMF was polarized solvent which have high dissolving ability toward the organic acids As a result, the process of crystalline development of Fe-BDC-NH2 occurred facily However, when content of DMF solvent was higher than the optimized condition, crystalline intensity of synthesized material would decrease The highest crystalline of Fe-BDC-NH2 was obtained M2-140dm sample with NH2-BDC : Fe3+ : DMF molar ratio of of 1:1:140 3.2.1.3 Effect of temperature of refluxing condensation on the synthesis of Fe-BDC-NH2 material XRD patterns of the synthesized materials at different refluxing temperatures were shown in Figure 3.13: The result indicated that the refluxing temperature greatly affected to crystalline nature of Fe-BDC-NH2 materials At low temperature, the crystallisation occurred slowly When the refluxing temperature increased, crystalline structure increase At 80oC, synthesized material had the high crystalline intensity Thus, the high temperature promoted formation and development of crystall However, the refluxing condensation required the continuous stirring to increase possibility of the reaction, therefore the low temperature was more suitable for crystallization of this MOFs The chosen refluxing temperature was 80oC 12 Figure 3.13 XRD patterns of synthesized Fe-BDC-NH2 materials at different refluxing temperatures 3.2.1.4 Effect of the refluxing time on the synthesis of Fe-BDC-NH2 material The refluxing time was an important factor that affected to the synthesis of Fe-BDC-NH2 material XRD patterns in 3.14 showed that M1-4h sample had the lowest intensity specific peaks, while M1-8h and M1-10h had the highest intensity peaks All samples are without the presence of impurity peaks Therefore, the refluxing time was selected to be hours The result is consistent with published reports Figure 3.14 XRD patterns of Fe-BDC-NH2 materials synthesized in the different refluxing times 3.2.2 Synthesized procedure of Fe-BDC-NH2 material The investigations of the influencing factors has established a following synthesized procedure of Fe-BDC-NH2 material in lab scale by refluxing method with NH2-BDC: Fe3+: DMF molar ratio of 1:1:140 A mixture of 0.72 g FeCl3.6H2O is dissolved in 28 mL DMF The solution is homogenised on magnetic stirred in 30 minutes, added 0.48g NH2-BDC, poured into three neck flask and sitrred in 15 minutes Install 13 reflux condenser, adjust magnetic stirring speed about 300 rpm, heat to 80oC and maintain in hours The product is washed three times use distilled water and three times use ethanol at 70oC Finally, the product is filtered and heated at 60oC in 10 hours Obtained Fe-BDC-NH2 material is pink, the yield of the synthesis process was 58% Figure 3.15 Diagram of synthesized procedure of Fe-BDC-NH2 material 3.2.3 Characteration of synthesized Fe-BDC-NH2 material Structural characteristic of synthesized Fe-BDC-NH2 material was analyzed by IR spectrum IR spectrum of synthesized Fe-BDC-NH2 materials was showed in Figure 3.16 Some main vibrations include: - The band at wave number 520 cm-1 corresponds to Fe-O valence vibration in FeO6 octahedra - The strong band at 768 cm-1 corresponds to bending vibration of C-H bond in benzene ring - The strong band at 1255 cm-1 corresponds to vibration of C-N bond - The stronger band at 1381 represents C-O valence vibration in carboxyl group 14 - The present of the band at 1578 cm-1 results from the stretching vibration of C=C bond - Finally, the other band at 3334 cm-1 corresponds to stretching vibration of N-H bond in amin group IR spectrum of synthesized Fe-BDC-NH2 are consistent with previous works XRD pattern of Fe-BDC-NH2 exhibits four peaks at 2θ = 9.12o; 9.74o; 18.90o; 28.36o with high intensity, which are similar to NH2-MIL88B reported previously [67], therefore resultant Fe-BDC-NH2 was NH2-MIL-88B(Fe) In addition, XRD pattern also indicates that the obtained MOFmaterial is highly crystalline without the presence of impurity This result exhibit that the synthesized material was relative pure The result was consistent with previous reports Figure 3.16 IR spectrum of Fe-BDC-NH2 Figure 3.18 XRD pattern of synthesized Fe-BDC-NH2 Morphology of the material was determined by SEM analysis The crystals of Fe-BDC-NH2 were hexagonal shape with the length of 1.5 µm and the width of 0.3 µm 15 Figure 3.19 SEM image of synthesized Fe-BDC-NH2 The porosity of synthesized material including surface area and porous volume was analysed by Quantachrome equipment The porosity of prepared material was determined by BET technique The result showed that the material had a relative high surface area of 560 m2/g The result of TGA analysis indicated that the material is stable at high temperature, only decompose after 346oC 3.2.4 The stability of synthesized Fe-BDC-NH2 3.2.4.1 The stability of the material in ambient conditions The result showed that synthesized Fe-BDC-NH2 was stable in ambient condition and the structure of the material was not changed after three months exposure Thus, prepared Fe-BDC-NH2 had a good resistance to the ambient condition and can be stored in room temperature for long time 3.2.4.2 The stability of the material in salty medium and dilute H2O2 solution The result showed that synthesized Fe-BDC-NH2 was quite stable in salty medium and diluted H2O2 solution in period of time Thus, synthesized Fe-BDC-NH2 can be employed as a photocatalyst in salty medium 3.3 Synthesis of Fe-BDC, Fe2Ni-BDC 3.3.1 Synthesis and characterizer of Fe-BDC The material based on Fe-BDC was synthesized by solvothermal method with FeCl3.6H2O : H2BDC : DMF molar ratio of to 1:1:280 FT-IR and XRD patterns of synthesized Fe-BDC material were showed n Figure 3.23, 3.24, the peaks were consistent with published samples SEM image showed that synthesized Fe-BDC material has granular shape of octagon or polyhedron, with dimension in range of from 500 nm to µm BET image showed that surface area of synthesized materialis approximately 259 m2/g with pores volume of 0.1 cm3/g corresponding to mesoporous material The result of TGA analysis 16 indicated that the decompose of material only occurs at temperature of higher than 410oC Figure 3.23 XRD pattern of Fe-BDC material Figure 3.24 FT-IR pattern of Fe-BDC material 3.3.2 Characterisation of synthesized Fe2Ni-BDC material Results from FT-IR and XRD patterns of synthesized Fe2Ni-BDC are consistent with the published reports Element compositions in synthesized Fe2Ni-BDC material was determined by using EDX spectroscopy The result indicated atomic percentage of elements in synthesized Fe2Ni-BDC material consist of 57.54% C; 35.32% O; 4.86% Fe and 2.28% Ni These results were in agreement with theory component in assumption molecular formula of synthesized material Thus, it can be concluded that Fe and Ni were involved into construction of Fe2Ni-BDC crystals The SEM image showed the synthesized Fe2Ni-BDC material has uniform octagonal shape with dimension in range of from 200 to 300 nm The BET result indicated that the material has surface area of about 589 m2/g and pore volume of about 0.45 cm3/g corresponding to mesoporous material The result of TGA analysis indicated that the material had heat resistance at 455oC 17 Figure 3.28 FT-IR spectrum Fe2Ni-BDC material Figure 3.29 XRD pattern of Fe2Ni-BDC material 3.4 Study photocatalytic performance of synthesized Fe-MOFs materials as photocatalyst for degradation of TNT, TNP 3.4.1 Adsorption behavior of the synthesized Fe-MOFs In order to determinate adsorption behavior, tests were performed in dark condition with initial concentration of TNT 50 ppm and Fe-MOFs dose 0.5 g / L The results showed that, in the first 15 minutes, the concentration of TNT in all solutions decreased quickly, proving that in this period all materials have high adsorption capacity for TNT and saturated adsorption obatained for hour, concentration of TNT decreased from 72 to 83% Among them, Fe2Ni-BDC has the lowest adsorption capacity (72%), Fe-BDC-NH2 has the best adsorption capacity (83%) for TNT This may be explained that because iron can form complexes with some organic compounds to increase the adsorption capacity of Fe-MOFs materials These results are consistent with other studies when using MOFs base on Fe as adsorbent 3.4.2 Photocatalytic performance of the synthesized Fe-MOFs In order to study the photocatalytic characteristic of Fe-MOFs materials, optical properties of materials were measured by UV-VisDRS method and energy band gap of the materials determined by the Tauc-Plot method The results showed that the light absorption area of Fe-MOFs materials stretched from the UV region to the visible area 18 Using Tauc - plot and Kubleka - Munk function, the energy band gap of synthesized Fe-MOFs materials were also determined respectively: FeBDC (2.65 eV), Fe2Ni-BDC (2.6 eV), Fe-BTC (2.8 eV), Fe-BDC-NH2 (2.1 eV) These values are consistent with other studies Thus, all synthesized materials can have photocatalytic acitivity in visible light areas or simulated sunlight with energy of ≥ 2.8 eV, equivalent wavelengths from 440 nm For this thesis, in order to ensure the accuracy and stability of the studies, all photocatalyst experiments were performed with simulated solar light source (40 W capacity, wavelength 440 -415 nm) Concentration of TNT in degraded solution using various MOFs materials were analyzed HPLC and the results were shown in Figure 3.36 Figure 3.36 Photocatalytic degradation of TNT using synthesized FeMOFs materials (100 mL initial concentration of TNT 50 ppm; 0.5 g/L catalyst dose; 0.4 mL H2O2 30%; room temperature; pH7) Figure 3.36 show that photocatalytic degradation of TNT using FeMOFs catalytic materials in simulated light condition with the presence of H2O2 were quickly and different from adsorption reaction of TNT After 15 minutes, transformed ratio of TNT obtained from 40 to 61% and after 60 minutes, transformed ratio obtained respectively: 96,5% (Fe-BTC); 97,8% (Fe-BDC); 99% (Fe2Ni-BDC) and 100% (Fe-BDCNH2) 3.4.3 Compararison TNT photocatalytic degradation performance of synthesized MOFs materials with commercial TiO2 Photocatalytic degradation of TNT by synthesized Fe-MOFs materials were studied in comparison with photocatalytic degradation using commercial TiO2 (P25 grade) Figure 3.37 show that in UV light 19 condition, degradation rate of TNT were 62% (TNT/TiO2/UV) and 84% (TNT/TiO2/H2O2/UV) for hour and after hours for TiO2 and the 75% (TNT/TiO2/UV) and 98% (TNT/TiO2/H2O2/UV) for the prepared MOFs material This indicats that the synthesized Fe-MOFs materials has higher photocatalytic activity than that of TiO2 3.4.4 Study on the effect of factors on photocatalytic degradation of TNT Fe-BDC-NH2 was employed to study the effect of various factors on the photocatalytic degradation of TNT Through the study on the factors affecting TNT treatment efficiency, we selected the optimal conditions for photocatalytic degradation of 100 mL of 50 ppm TNT solution: 0.05 g Fe-BDC-NH2 materials dose; 0.4 mL of 30% H2O2 solution, pH 7, at room temperature Conversion efficiency of TNT obtained nearly 100%, mineralization obtained 99% for hour Fe-MOFs materials have high catalytic activity, stability and can be reused many times 3.4.5 Study on the photocatalytic degradation of TNP in aqueous medium using the synthesized Fe-MOFs materials Fe2Ni-BDC and Fe-BDC-NH2 were employed to investigate of the photocatalytic degradation of TNP Experiment was carried out with TNP solutions of 50 ppm, 0.5 g /L Fe-MOFs dose, added 30% H2O2 solution, in simulated sunlight conditions Photocatalytic experiments were performed after the material was saturated The results are shown that the photocatalytic degradation of TNP when using Fe-MOFs catalysts is similar to TNT but with faster performance After 60 minutes, the degradation reaction of TNP is almost complete for both Fe2Ni-BDC and Fe-BDC-NH2 Thus, photocatalytic materials based on Fe-MOFs can remove thoroughly toxic aromatic nitro compounds out of wastewater in explosive production 3.5 Mechanism of photocatalytic degradation of organic compounds using Fe-MOFs materials 3.5.1 Mechanism of photocatalytic degradation of organic compounds The mechanism of photocatalytic reaction has also been studied Because Fe-MOFs contain Fe-oxo clusters, they have semiconductor properties Thus, Fe-MOFs materials have been studied and used as photocatalytic materials to effectively remove several organic compounds 20 In order to confirm this claim, some authors have used free radical quenchers to stop photocatalytic reaction Based on this idea, we chose some free radical quenchers to investigate the effect of these agents on the photocatalytic degradation of TNT degradation with the precense of Fe-BDC-NH2 catalytic material Firstly, mL these free radical quenchers were added to 100 mL of 50 ppm TNT solution with 0.5 g/L Fe-BDC-NH2 dose The next steps are similar to the testing process of photocatalytic activity The results are shown in Figure 3.46 Figure 3.46 Photocatalytic degradation of TNT using Fe-BDC-NH2 with the presence of free radical quencher The results showed that when using free radical quenching agents, TNT conversion rate decreased significantly Specifically, when using AO and DMSO, the degradation efficiency of TNT decreased significantly to 30% and 36%, respectively Therefore, it can be concluded that free radicals play an important role in the photocatalytic degradation of TNT In particular, photogenerated electron-hole pairs are the two main factors that determine the formation of free radical The results demonstrated that degradation reaction of TNT is characterized by free radical mechanism of Fe-MOFs materials which have photocatalytic acitivity And the reaction is not under any other process such as adsorption or thermal decomposition Thereby, we suggest the mechanism of photocatalytic decomposition of TNT, TNP by Fe-MOFs materials with the presence of H2O2 is as follows: in which, H2O2 plays a role as a photogenerated electron trapper which help to prevent the recombination of electron (e-) and hole (h+) and form more free radicals and improve effiecncy of photocatalytic process Fe-MOFs + hν → e-(MOFs) + h+(MOFs) 21 e-(MOFs) + O2 → MOFs + •O2h+(MOFs) + H2O → •OH + H+ + MOFs  eCB + H2O2 → OH- + •OH • O2-+ H2O2 → OH- + •OH + O2 • OH + TNT/TNP → non toxic product • O2- + TNT/TNP → non toxic product 3.5.2 Diagram of photocatalytic degradation of TNT using FeMOFs materials The concentration of TNT in solution was deteminated by HPLC method at certain time points (30 and 60 min) which are shown on Figure 3.47 Figure 3.47 HPLC diagram of TNT’s concentration in photocatalytic degradation of TNT/Fe-BDC-NH2/H2O2 system: initial sample (a), after 30 minutes (b) and afer 60 minutes (c) The results showed that TNT peaks at 4.1 retentive minutes After 30 minutes of treatment, intensity of TNT’s peak decreases and new peaks appear at tR (retention time) = 1.6 minutes; 2.3 minutes; 3.4 minutes with different intensities which are peaks of organic intermediate productsof photocatalytic degradation of TNT After 60 minutes of treatment, on the HPLC diagram, only trace amounts of 22 substances were observed which indicated that TNT and intermediate products were degradated completely and releasing non toxic inorganic products This result is consistent with the TOC value which is shown in section 3.4 Thus, it can be affirmed that the photocatalytic process is under radical mechanism and the main agent of this reaction is •OH which is a very strong oxidizing radical and can participate in a non-selective decomposition of organic compounds For TNT, the decomposition process can form many new intermediate compounds, however, regardless of any degradation diagram, the final products are non-toxic inorganic substances: CO2, H2O , NO3- 3.6 Study on the photocatalytic treatment of actual wastewater samples and suggestion of photocatalytic reaction equipment model From the obtained results of photocatalytic degradation of TNT and TNP samples, the experiments are carried out with industrial wastewater samples from production line of TNT at Z113 factory The results showed that the conversion and mineralization efficiency of aromatic nitro compounds by the photocatalytic degradation were higher than 99% Based on the results of lab-scale studies, pilot-scale photocatalytic reaction equipment model was suggested to treat wastewater directly which was contaminated with nitro aromatic compounds * Recommended treatment process for actual wastewater treatment using Fe-MOFs: Wastewater is collected into a collection tank, then pumped to a detension tank Here, the pH of the solution is adjust to pH of a neutral environment (pH = 7) with NaOH solution and amount of coagulant add flocculant are added before the solution is pumbed to settling tank The sediment is settled, the solution is fed to the mixing tank and then photocatalyst and H2O2 agent are added at here before the solution is pumbed to the photocatalyst reactor The reaction is carried out for 60 minutes The treated wastewater is brought to the outlet tank, if it is qualified, it can be fed into the environment Another batch will continue to carry out After many reaction cycles, if the catalyst activity is decreased, it will be filtered and recycled to be used for subsequent processing 23 CONCLUSION * Outcomes of the thesis: Through the review of the literature, we select photocatalytic materials based on Fe-MOFs and raw materials to synthesize the materials The method of synthesizing Fe-MOFs materials and the techniques for performing photocatalytic reactions of nitroaromatic compounds in the laboratory have been selected Fe-BTC and Fe-BDC-NH2 materials were synthesized successfully by refluxing method, the optimal conditions for synthesizing reaction were at 80oC temperature for hours The characteristic investigation shows that the obtained materials had a large surface area and large pore volume, those values were 1777 m2/g and 0.85 cm3/g for Fe-BTC; 560 m2/g and 0.41 cm3/g for Fe-BDC-NH2, respectively Fe-BDC, Fe2Ni-BDC materials were synthesized successfully by thermalsolvent approach The synthesized materials were characterized by modern physicochemical techniques such as X-ray diffraction, N2 adsorption (BET), SEM, FT-IR, TGA, EDX The results show that synthesized materials can be used as silmutaneously for both adsorbent and photocatalyst Study on the photocatalytic activity of Fe-MOFs materials toward degradation of TNT, TNP in lab-scale The results show that all types of synthesized materials had photocatalytic acitivity in visible light condition, with low energy band gap values The efficiency of TNT and TNP decomposition reached to 97 - 98% (Fe-BTC, Fe-BDC) and almost completely (Fe2Ni-BDC, Fe-BDC-NH2) for hour Study on effect of various factors and selecting the optimal conditions for lab-scale photocatalytic degradation of TNT (100 mL TNT solution 50 ppm) using Fe-BDC-NH2 material is as: 0.05 g catalyst dose; 0.4 mL of 30% H2O2 solution, at pH and at room temperature The results showed that conversion efficiency of TNT reached nearly 100%, mineralization reached 99% for hour Fe-MOFs materials have high catalytic activity and can be reused many times Study on the mechanism of photocatalytic degradation of TNT, TNP using Fe-MOFs materials The results of photocatalytic degradation is consistent with Langmuir - Hinshelwood kinetics model with high correlation coefficient (R2 ≥ 0.958) The mechanism of the reaction is of heterogeneous photocatalyst reaction and light radiation promote both Fe-oxo clusters and organic bridges of the MOF materials 24 and the main reaction agent is free radicals: •OH, •O2, e-, h+ By HPLC and TOC quantitative method, in colusion, the final products of the photocatalytic degradation of nitroaromatic compounds are non-toxic and environmentally friendly inorganic substances The thesis also employed the obtained MOFs materials to treat wastewater samples from TNT production line in practical The results showed that these materials can completely remove TNT out of wastewater Furthermore, the pilot-scale photocatalyst reaction equipment model is also proposed to treat wastewater contaminated with toxic nitroaromatic compounds using Fe-MOFs materials * New contributions of the thesis: Fe-BTC and Fe-BDC-NH2 materials were synthesized successfully by refluxing method and optimal conditions for synthesis of materials were proposed Investigate the photocatalytic performance of Fe-MOFs materials toward TNT and TNP in the laboratory scale The results show that all synthesized materials show high efficiency and quick degradation for aromatic nitro compounds The mechanism of TNT and TNP photocatalytical removal using Fe-MOFs materials has been studied, which exhibits that Fe-MOFs materials act as heterogeneous catalyst for TNT and TNP degradation, the final products of this process consists of non-toxic inorganic substances ... XRD pattern of Fe- BDC material Figure 3.24 FT-IR pattern of Fe- BDC material 3.3.2 Characterisation of synthesized Fe2 Ni-BDC material Results from FT-IR and XRD patterns of synthesized Fe2 Ni-BDC... as following: FeCl3.6H2O + H2N-BDC → Fe3 O(H2O)2(OH)(H2N-BDC)3.nH2O + HCl + H2O Figure 3.11 XRD patterns of resultant Fe- BDC-NH2 compounds with different molar ratios of NH2-BDC /Fe3 + Figure 3.11... NH2-BDC /Fe3 + molar ratio of 1:1 was chosen as optimal ratio to synthesize Fe- BDC-NH2 material 3.2.1.2 Effect of DMF contents Figure 3.12 XRD patterns of synthesized Fe- BDC-NH2 materials with different