Summary of doctor thesis: Research on synthesizing new composite materials system based on MOFs containing Fe and graphene oxide as photocatalysts in decomposing dyes in water environment

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Study the structural, morphological and physicochemical properties of synthetic materials by modern physical and chemical methods such as XRD, FTIR, SEM, TEM, XPS, EDX, BET, TG-DTA, UV -Vis; evaluation of photochemical catalyst using visible light in the decomposition of dyes RR-195, RY-145 on synthetic materials.

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Nội dung Text: Summary of doctor thesis: Research on synthesizing new composite materials system based on MOFs containing Fe and graphene oxide as photocatalysts in decomposing dyes in water environment

MINISTRY OF VIETNAM ACADEMY OF SCIENCE AND EDUCATION AND TRAINING TECHNOLOGY GRADATE UNIVERSITY OF SCIENCE AND TECHNOLOGY ------------------ VU THI HOA RESEARCH ON SYNTHESIZING NEW COMPOSITE MATERIALS SYSTEM BASED ON MOFS CONTAINING Fe AND GRAPHENE OXIDE AS PHOTOCATALYSTS IN DECOMPOSING DYES IN WATER ENVIRONMENT Major: Theoretical Chemistry and Physical Chemistry Code : 62.44.01.19 SUMMARY OF DOCTOR THESIS Ha Noi , 06- 2020
The thesis was completed at Institute of Chemistry, Vietnam Academy of Science and Technology. Supervisors: 1. Assoc. PhD. Vu Anh Tuan 2. Assoc. PhD. Vu Minh Tan Reviewer 1: Reviewer 2: Reviewer 3: The dissertation defended at Graduate University of Science and Technology, 18 Hoang Quoc Viet street, Hanoi. Time: hour, date /month/2020 The thesis could be found at: - National Library of Vietnam - Library of Graduate University of Science and Technology - Library of Institute of Chemistry
INTRODUCTION * The thesis necessity Today, along with the development of science and technology, industries have been developing strongly, positively affecting the social economy. However, besides that it also has negative effects leading to environmental pollution and public health. In the sewage industry of textile, printing, paper, cosmetics ... there are many environmental pollutants such as: reactive dyes, heavy metal ions ... reactive dyes in wastewater are difficult decomposes because they are highly resistant to light, heat and other oxidizing agents. In recent years, there have been many studies and using different methods to treat textile wastewater such as mechanical, biological and chemical methods (using oxidizing agents such as H2O2, O3, H2O2/O3) applies. However, some traditional methods of treating textile dyeing wastewater, such as mechanical methods, biological methods, etc., have limitations of not thoroughly treating these pollutants. The highly effective method to treat textile dyeing is an advanced oxidation process (AOPs) using photochemical catalysts such as semiconductors such as TiO2, ZnO, CdS ... [1], photo fenton catalyst. such as Fe2O3, FeOOH, Fe@Fe2O3 ... [2]. Under the action of light (photons), electrons from the valence band jump onto the conduction band to produce electrons (e-) and holes (h+), h+ hole acts with H2O to produce free radicals •OH and e- works with O2 to create free radicals O2• -. These free radicals have a high reduction potential, capable of oxidizing organic substances, organic pigments into CO2 and H2O, so it is possible to thoroughly treat organic pigments [1-4]. To enhance the processing efficiency, the use of photocatalytic catalysts combined with strong oxidizing agents such as H2O2 and O3 have been researched and developed strongly in recent years [3]. 1
Recently, a new generation of photocatalytic catalysts is based on MOFs (Metal-organic frameworks) containing Ti, Zn, Fe, etc. nano systems such as TiO2, P25 (Degussa), ZnO, Fe2O3 ... [5-6]. The advantage of this material system is its porous structure, large surface area. The structure and properties of materials can be "engineered" based on the change of Ligan and various metal ions, so these MOFs have unique properties, are particularly attractive and are able to High applicability such as gas storage materials, air separation, adsorbents, catalysts, sensors, electrode materials in sensors, carriers, etc. [7-9]. In order to enhance the functionality and applicability, new composite materials based on the mechanical metal frame material are of special interest. Recently, some nano-based composites of MOFs and nano carbon such as nano MIL53/rGO, MIL88/GO, MIL101/rGO as well as MIL53, MIL88 and MIL101 contain Fe/CNT. The role of carbon nanomaterials is not only to carry and disperse MOFs, but also to play an important role in the material: the electron conductor jumps from the valence band to the conduction band, reducing the ability to re combination of e- and h+ cavities. In addition, nano carbon has the ability to absorb visible light, increasing photochemical activity. Nowadays, the trend of application of green and clean technologies is specially focused and developed. The method of synthesizing traditional MOF materials is a solvent thermal method. In this method, it is necessary to use large quantities of solvents such as DMF, an expensive and very toxic chemical. A number of recent studies on synthesizing MOFs materials without using organic solvents (using water as a substitute for published solvents [12-13]). Another new step in synthesizing MOFs is to successfully synthesize a number of nano-sized MOFs (nano MOFs) in place of traditional micrometer-sized MOFs when using techniques such as ultrasound. , microwaves ... in the synthesis of MOFs [14]. In order to integrate with the new trend of metallic mechanical frame materials, in this thesis, we focus on synthesizing 2
MOFs materials without using organic, nano-structured solvents (nano Fe-BTC/GO) and Fenton photocatalyst application for the treatment of organic pigments (reactive dyes RR-195 and RY-145) in aqueous environment. The thesis title is “Research on synthesizing new composite materials system based on MOFs containing Fe and graphene oxide as photocatalysts in decomposing dyes in water environment” * Main research contents of the thesis: - Research on synthesizing some new nano composite materials, based on nano Fe-MIL-53, Fe-MIL-88B, Fe-BTC and GO (graphene oxide) by different methods such as solvent heat, hydrothermal , micro-hydropower and mechanical grinding. - Study the structural, morphological and physicochemical properties of synthetic materials by modern physical and chemical methods such as XRD, FTIR, SEM, TEM, XPS, EDX, BET, TG-DTA, UV -Vis. - Evaluation of photochemical catalyst using visible light in the decomposition of dyes RR-195, RY-145 on synthetic materials. - Comparison of the above catalytic systems to find the most effective catalyst in decomposition of RR-195 and RY-145 dyes. - Study the main influencing factors such as pH, H2O2 concentration, initial color concentration to decomposition efficiency of organic pigments. - Study on catalytic durability as well as regeneration and reuse potential of catalysts. - Proposing the path to decomposition of organic color through intermediate products formed during the decomposition process. * Thesis structure The thesis consists of 146 pages, 99 figures, 15 tables and 142 references. The thesis layout consists of the following sections: introduction, 3 chapters of content and conclusions. The new 3
contributions of the thesis are published in 05 specialized scientific journals, including 02 international scientific journals and 02 national scientific journals. Chapter 1. Literature review Chapter 1 is presented in 38 pages, including general introduction of MOFs, methods of synthesizing MOFs, and application of MOFs. In MOFs applications, catalyst applications are quite new and have not been studied much in Vietnam. MOFs act as catalysts in the decomposition reactions of toxic organic substances, pigments, dyes. In order to enhance the functionality and applicability, new composite materials based on the mechanical metal frame material are of special interest. Recently, a number of composite materials based on nano MOFs and nano carbon such as nano MIL53/rGO, MIL88/GO, MIL101/rGO as well as MIL53, MIL88 and MIL101 containing Fe/CNT have been synthesized and evaluated with optical activity. High catalyst in the decomposition reaction of organic substances, organic pigments in water environment [9-11]. Therefore, the use of MOFs/GO nanocomposite photocatalytic materials to treat dyes is practical and of high scientific significance. From the overview of the research situation on MOFs materials at home and abroad, we can see that nanostructured MOFs are a new generation of MOFs material superior to conventional MOFs because of special features. such as small particle size (nm), large capillary size (nm), large surface area, large porous volume increases heat transfer, mass transfer, speed diffusion of reaction substances to centers operating with high dispersion. The process of micro-hydrothermal crystallization creates particles of small size, acting as a catalyst with redox potential. Studies aimed at reducing the time to germinate and 4
develop MOFs are also a solution to synthesize nanoparticle-sized MOFs. Chapter 2. Experimental Chapter 2 is presented in 20 pages including: 2.1. Chemistry 2.2. Process of synthesizing materials - Synthesis of some Fe-BDC/GO composite materials (Fe-MIL- 53/GO, Fe-MIL-88B/GO) by solvent thermal method. - Synthesis of Fe-BTC/GO composite nanocomposite materials by solvent thermal method, hydrothermal (at 60oC, 90oC, 120oC), hydrothermal - microwave (at 90oC with periods of 10, 20, 30, 40) minute). - Synthesis of Fe-BTC material (at 20, 40, 60, 80 minutes) and Fe- BTC/GO composite material (60 minutes) by mechanical mechanical crushing. - Research photocatalytic process in the reaction of reactive dye decomposition of synthesized catalysts. - Studying RR-195 dye decomposition pathway on Fe-MIL-88B/GO catalyst through intermediate products determined by liquid-mass chromatography (LC-MS). 2.3. Characterisation Techniques - Material characteristics by modern physical methods, using equipment in Vietnam and Korea: XRD, XPS, EDX, SEM, TEM, BET, FT-IR, TGA, UV-Vis. 2.4. Method to assess photocatalytic ability of materials in photocatalytic process in decomposition of dyes - Develop a model to evaluate photocatalytic activity of materials in the decomposition reaction RR-195 and RY-145. 5
- Analysis and evaluation of intermediate products formed during the RR-195 decomposition process on Fe-Mil-88B/GO excavator. Calculate the efficiency of the decomposition process. Chapter 3. Results and Discussions Chapter 3 is presented in 80 pages including: 3.1. Characteristics of structure and morphology of catalytic systems 3.1.1. X-ray diffraction (XRD) 3500 Fe-MIL-88/GO 3000 Intensity (a.u) 2500 Fe-MIL-88 Cường độ (a.u) 2000 1500 Fe-MIL-53/GO 1000 500 Fe-MIL-53 0 5 10 15 20 25 30 Góc 2 độ 2θ (degree) Fig. 3.2. XRD patterns of Fe-MIL-53, Fe-MIL-88B, Fe-MIL-53/GO and Fe-MIL-88B/GO The XRD patterns of Fe-MIL-53/GO, Fe-MIL-88B/GO materials appear all the same pic as those of Fe-MIL-53, Fe-MIL-88B materials. However, the peak intensity at 2θ~11o characteristic of GO structure sharply decreased and almost no appearance was observed. This can be explained by the fine dispersion of Fe-MIL-53, Fe-MIL- 88B crystals on the surface of GO layers. The XRD patterns of Fe- BTC/GO materials synthesized by different methods appears peaks with the intensity at 2θ ~ 5.8o; 7,8o; 12o; 13.7o; 17,6o and 22,1o are corresponding to the diffraction planes (012); (104); (110) characteristic of Fe-BTC structure [125]. However, the 2θ~11o peak that characterizes GO structure plummeted and almost no occurrence. 6
This is explained by the dispersion, and alternation of Fe-BTC material on the surface of GO layers. Intensity (a.u) 2θ (degree) 2θ (degree) Intensity (a.u) 2θ (degree) 2θ (degree) Intensity (a.u) 2θ (degree) Fig.3.6. XRD patterns of Fe-BTC NDM, Fe-BTC/GO were synthesized by different methods In the sample Fe-BTC/GO-30 synthesized by hydrothermal- microwave (30 minutes) has a peak intensity at 2θ ~12o, more 7
balanced than Fe-BTC/GO samples synthesized by solvent thermal, hydrothermal, and mechanical mechanical methods. The XRD pattern show that Fe-BTC/GO materials synthesized by hydrothermal - microwave (30 minutes) have a stable crystal phase structure, high crystallinity. 3.1.2. Scanning electron microscopy (SEM) and Transmission electron microscopy (TEM) In Figure 3.10, TEM image of Fe-MIL-88B material shows small pseudo-Fe nanoparticles of size 5-8 nm, fastened on the surface of Fe-MIL-88B crystals. On the TEM image of Fe-MIL-88B/GO composite material, Fe nanoparticles tend to cluster to form larger particles (the size increases from 5-8 nm to 10-20 nm. ). This may be due to the interaction between Fe ions with hydroxyl and carboxylic groups in GO to form Fe complex. Fig.3.10. TEM image of GO (A), Fe-MIL-88B(B) and Fe-MIL- 88B/GO(C) 8
Fig. 3.14. SEM image of Fe-BTC/GO tổng hợp bằng các phương pháp khác nhau (a) Fe-BTC/GO –NDM; (b) Fe-BTC/GO-90oC; (c) Fe-BTC/GO VS- 30; (d) Fe-BTC/GO NC-60 As shown in Figure 3.14 (a), the material Fe-BTC/GO-NDM has Fe-BTC nanoparticles unevenly dispersed on the surface layers of GO, the particles are uneven in size and tend to contract. Clustered together to form large crystals of about 120-150 nm. Figure 3.14 (b) of Fe-BTC/GO-90oC material found that Fe-BTC particles are dispersed evenly on the surface layer of GO, Fe-BTC nanoparticle size is in the range of 60 - 80 nm. Some Fe-BTC particles tend to cluster in sizes between 80 and 100 nm. Fe-BTC/GOVS-30 material (Figure 3.14 c) has Fe-BTC particles of uniform size and evenly distributed over the surface of GO, the particle size is about 40-50 nm. Fe-BTC/GO materials synthesized by mechanical grinding (Figure 3.14d) have a particle size of 100-150 nm and Fe-BTC particles are unevenly dispersed on the GO layers. Thus, SEM image of Fe-BTC/GO materials synthesized by different methods show that Fe-BTC/GOVS-30 materials (synthesized by hydrothermal- microwave) have Fe- BTC is evenly dispersed on GO carriers and has a nanoparticle size of about 40 -50 nm. This is explained by the rapid germination and development of Fe-BTC crystals, so the crystallization process takes place quickly to help control the size of the crystal particle. 3.1.3. Energy-dispersive X-ray spectroscopy (EDX) Table 3.1. Composition of elements in materials Fe-MIL-53/GO and Fe-MIL-88B/GO Materials Fe-MIL-53/GO Fe-MIL-88B/GO Element % wt % atomic % wt % atomic C 64.54 73.60 63.93 73.52 O 28.95 24.76 28.56 24.63 Fe 6.51 1.64 7.51 1.85 Table 3.1 shows that the Fe content in Fe-MIL-53/GO and Fe-MIL- 88B/GO materials accounts for 6.51% and 10.02%, respectively (according to Fe theory, 10.02%, 7.51% by weight, respectively). 9
This is explained by the amount of Fe does not react with H2BDC ligand so the washing process is washed out into the environment. Table 3.4. Composition of elements in Fe-BTC/GO materials synthesized by different methods Samples Element C O Fe Cl Total Fe-BTC-NDM % wt 62.99 30.69 6.20 0.12 100 % atomic 72.07 26.36 1.53 0.04 100 Fe-BTC/GO % wt 66.76 28.91 4.21 0.12 100 NDM % wt 74.66 24.29 1.01 0.04 100 Fe-BTC/GO 90oC % wt 62.48 30.42 7.02 0.08 100 % atomic 71.94 26.29 1.74 0.03 100 Fe-BTC/GO-30 %wt 61.75 31.25 6.93 0.07 100 % atomic 71.09 27.17 1.71 0.03 100 Fe-BTC/GO-NC %wt 68.74 27.66 3.49 0.11 100 % atomic 76.13 23.00 0.83 0.04 100 Table 3.4 shows the main components of Fe-BTC/GO materials including C, O Fe, Cl. However, Fe content depends on different synthesis methods. By various synthetic methods such as solvent heat, hydrothermal, microwave, and mechanical grinding, the percentage of iron mass 4.21%, 7.02%, 6.93%, 3.49%, respectively. 3.1.4. N2 adsorption–desorption isotherms (BET) Table 3.5 shows the surface area and total capillary volume, the average capillary width of materials Fe-MIL-53/GO, Fe-MIL- 88B/GO increases compared to Fe-MIL-53, Fe -MIL-88B. This is explained by the uniform distribution of Fe-MIL-53, Fe-MIL-88B on the GO layers to help improve the porosity and size of Fe-MIL-53, Fe-MIL-88B crystals [117]. Moreover, the crystals of Fe-MIL-53, Fe-MIL-88B are dispersed on GO layers smaller than the original Fe- MIL-53, Fe-MIL-88B crystals, this is explained. by the epoxy groups on the GO layers preventing the clumping and agglomeration of the crystals Fe-MIL-53, Fe-MIL-88B, resulting in the formation of Fe- 10
MIL-53, Fe-MIL-88B nanoparticles on the GO carrier. This also contributes to the specific surface of the material. In Table 3.5 Fe- MIL-88B/GO materials have the largest surface area (99 m2/g). Table 3.5. Textual characteristics of Fe-MIL-53, Fe-MIL-88B, Fe- MIL-53/GO and Fe-MIL-88B/GO Samples SBET (m2/g) Vpore (cm3/g) DBJH (nm) Fe-MIL-53 62 0.14 4.1 – 7.2 Fe-MIL-53/GO 80 0.21 10.2 – 20.3 Fe-MIL-88B 89 0.15 3.2 – 7.4 Fe-MIL-88B/GO 99 0.23 12.2 – 21.3 Table 3.9. Textual characteristics of Fe-BTC and Fe-BTC/GO synthesized by different methods Samples SBET (m2/g) Vpore (cm3/g) DBJH (nm) Fe-BTC-NDM 349 0.55 2.2 – 3.2 Fe-BTC/GO-NDM 376 1.33 12.5 – 23.7 Fe-BTC/GO-90oC 786 0.82 5.9 -7.2 Fe-BTC/GO-30 1015 1.13 6.5-8.2 Fe-BTC/GO-NC 60 849 0.65 7.4-18.4 Table 3.9 shows that Fe-BTC/GO material has a high specific surface area (376 - 1015 m2/g) and a large total capillary volume (0.82-1.33 cm3/g) compared to the material. Fe-BTC. Fe-BTC/GO materials have an average increase in capillary width compared to Fe-BTC samples, which is favorable for adsorption and diffusion processes. This is explained by the dispersion of Fe-BTC crystals on the GO carrier (GO has a layered structure). Fe-BTC/GO-30 material (synthesized by microwave hydrothermal method for 30 minutes) has the largest surface area and a large total capillary volume. This is explained by the fact that Fe-BTC/GO is synthesized by micro- hydrothermal method with small particle size of about 40-50 nm, 11
uniformly distributed on the GO carrier layer and stable phase structure, high crystallinity (Figure 3.6). 3.1.5. Fourier transform infrared spectroscopy (FTIR) Transmitance (%T) Wavenumber (cm-1) Fig. 3.24. FTIR spectra of Fe-MIL-53, Fe-MIL-88B, Fe-MIL-53/GO and Fe-MIL-88B/GO FTIR spectrum of Fe-MIL-53/GO and Fe-MIL-88B/GO is almost identical to Fe-MIL-53 and Fe-MIL-88 except for two low-intensity oscillations occurring at 2339-2360 cm-1 relates to the saturated and unsaturated CH oscillations, showing the interaction between MIL53, MIL-88B and GO. The absorption band at the top of 759-711 cm-1 is characteristic related to the oscillation of the BTC ligands. The peaks at 750 cm-1 correspond to the C-H strain variation of benzene. High strength peaks of 624 cm-1 characterize the oscillation of the Fe - O bond [140]. 12
Transmitance (%T) (%T) Số sóng (cm )(cm-1) Wavenumber -1 Fig. 3.27. FTIR spectra of Fe-BTC/GO synthesized by different methods 3.1.6. X-ray Photoelectron Spectroscopy (XPS) Complete survey of XPS, C1s, O1s and Fe2p spectra for Fe-MIL- 88B, Fe-MIL-88B/GO is shown in Figure 3.30. Figure 3.30a and c show optoelectronic currents with binding energies of 284 eV, 530 eV, and 711 eV corresponding to C1s, O1s and Fe2p. In Figures 3.30b and d show four vertices at about 284.9; 286.2; 288.1 and 289.5 eV correspond to the C-C, C-O, C=O and O-C=O links [141]. In addition, the shift of the C1s band to higher binding energies shows the interaction of carbon in H2BDC and carbon in GO. Moreover, the increase in peak intensity of the C-C group, and the decrease of the peak intensity of the C-O groups, C=O and O-C=O of Fe-MIL-88B/GO compared to Fe-MIL-88B, showing the interaction between Fe-MIL-88B and GO in Fe-MIL-88B/GO materials. In the 13
XPS spectrum of O1s (Figure 3.30e), there are 2 peaks at 531.7 and 533.7eV corresponding to Fe-O-C bonds. In Fe2p spectrum of Fe- MIL-88B/GO (Figure 3.30f), there are two peaks at 711.9 and 725.7eV corresponding to Fe2p3/2 of Fe2O3 and Fe2p1/2 of α-FeOOH [126-129 ]. a b d Hình 3.30. Phổ XPS củacFe-MIL88B (c, d) và compozit Fe- MIL88B/GO (a) (b) C1S; (e) O1S; (f) Fe2p e f Fig. 3.28. XPS of Fe-MIL88B (c, d) và compozit Fe-MIL88B/GO (a) (b) C1S; (e) O1S; (f) Fe2p 3.1.7. Results of TGA analysis of Fe-BTC/GO materials As shown in Figure 3.37, Fe-BTC/GO materials synthesized by different methods have high thermal stability (300oC). The higher this temperature, the combustion of thermal decomposition occurs. 14
% wt Temperture (oC) Fig. 3.30. TGA of Fe-BTC/GO samples 3.1.8. Results of UV-vis solid analysis of Fe-BTC/GO materials (ahv)1/2(eV)1/2 hv (eV) Fig. 3.31. Energy gap of Fe-BTC/GO materials is synthesized by different methods The energy of the Eg region of Fe-BTC/GO material synthesized by hydrothermal-microwave method (30 minutes) is 2.2eV; FeBTC/GO synthesized by hydrothermal method is 2.4 eV; Fe- BTC/GO synthesized by mechanical grinding method is 2.48 eV which is less than the band gap energy of Fe-BTC material (2.5 -2.7 eV) [132]. The presence of the external GO carrier helps disperse the Fe-BTC crystals evenly, creating small sized particles, the GO carrier is very important to receive electrons from the conduction area of photocatalyst MOFs, minimizing recombination between electrons 15
and h+ holes and effectively increasing catalytic activity as well as catalytic durability [129]. The results of solid UV-Vis analysis showed that Fe-BTC/GO materials synthesized by hydrothermal- microwave method (30 minutes) had the smallest value (2.2 eV), so it had the best catalytic activity. 3.2. Evaluation of photocatalytic activity of synthesized materials 3.2.1. Evaluate catalytic activity of dye decomposition RR-195 of Fe-BDC/GO catalyst 3.2.1.1. Comparison of dye decomposition activity of RR-195 dye on Fe-BDC and Fe-BDC / GO catalysts C/Co Time (min) Fig. 3.33. Catalytic activity of Fe-MIL-53, Fe-MIL-88B, Fe-MIL-53/ GO, Fe-MIL-88B/GO in dye decomposition RR-195 To compare the catalytic activity of synthetic catalyst systems include: Fe-MIL-53, Fe-MIL-53/GO, Fe-MIL-88B, Fe-MIL-88B/GO during RR-195 was performed under conditions: initial RR-195 concentration was 100 mg/L; the amount of catalyst is 0.3g/L; H2O2 concentration is 136 mg/L; pH = 5.5; temperature T = 25oC and together lighting. From the results obtained, we can see that Fe-MIL-53/GO and Fe- MIL-88B/GO are much more photochemical than Fe-MIL-53 and Fe- MIL-88B. This proves the synergistic effect of Fe-MIL-53, Fe-MIL- 16
88B with GO. From Figure 3.33, the catalytic activity of Fe-MIL- 88B/GO is much higher than that of Fe-MIL-53/GO. This can be explained by the higher surface area of Fe-MIL-88B/GO (99 m2/g) than that of Fe-MIL-53/GO (80 m2/g). 3.2.1.3. Study on factors affecting RR-195 dye decomposition ability of Fe-MIL-88B/GO catalyst materials Effect of pH: To investigate the effect of pH, we performed RR- 195 decomposition reaction on Fe-MIL-88B/GO composite material at different pH values. The experiments were conducted at three different pH values: 3.0; 5.5 and 8.0 under the same conditions: H2O2 (30%) 136 mg/L, catalyst content of 0.3g/L, RR-195 concentration of 100 ppm, temperature t = 25oC and lighting for 25 minutes. The results showed that, with pH = 3.0, the rate of RR-195 decomposition took place quickly, when increasing pH = 5.5, the rate of RR-195 decomposition was slower but still achieved a conversion efficiency of 98% after 25. minute (same as at pH = 3). When pH> 6 efficiency decomposition process sharply reduced. Therefore pH=5.5 is selected for the next research process. Effect of H2O2 concentration: Similar experiments were conducted at different H2O2 concentrations: 68 mg/L; 136 mg/L and 204 mg/L with the same reaction conditions. Results showed that the decomposition process RR-195 increased as the concentration of H2O2 increased. When H2O2 concentration increased from 68 to 136 mg/L after 25 minutes, process efficiency increased sharply and reached 98%. This is because the •OH radicals from H2O2 are highly generated which promotes the reaction process leading to increased speed and degradation efficiency. However, when continuing to increase the amount of H2O2 (6mL/L) in the solution, this excess 17
H2O2 will work with the •OH radical to form the HOO• reduce the efficiency of the decomposition process. 3.2.1.3. Evaluate the activity of Fe-MIL-88B/GO catalyst materials under different conditions Figure 3.37A shows that under the condition of oxidation reaction under sunlight and without catalyst, the conversion of RR-195 is negligible. In Figure 3.37B, the adsorption process takes place quickly and reaches equilibrium after 25 minutes of reaction. The adsorption efficiency of RR-195 on catalyst reaches 25%. During Fenton reaction (in the presence of catalyst, H2O2), after 25 minutes of reaction, the efficiency reached 75% (Figure 3.37C). However, in the Photo-Fenton process (in the presence of catalysts, H2O2 and lighting) the efficiency reached 98% (Figure 3.37D). From these results, we found that the Fe-MIL-88B/GO composite has a high RR- 195 decomposition efficiency. Time (min) Fig. 3.37. Decomposition process RR-195 on Fe-MIL-88B/GO catalyst under different conditions 18