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MINISTRY OF EDUCATION VIETNAM ACADEMYOF AND TRAINING SCIENCE AND TECHNOLOGY GRADUATE UNIVERSITY SCIENCE AND TECHNOLOGY -NGUYEN THI MAI THO STUDY ON USING PHOTOTCATALYST BASED ON LAYERED DOUBLE HYDROXIDES ZnBi O /GRAPHIT AND ZnBi O /Bi S FOR TREATMENT OF ORGANIC DYES Major: Inorganic Chemistry Code: 9440113 SUMMARY OF CHEMISTRY DOCTORAL THESIS Ha Noi - 2021 The dissertation was completed at: Industrial University of Ho Chi Minh City, Korea Instite of Toxicology – Gajeong-ro, Yuseong-gu, Daejeon; The Department of Chemistry - Changwon National University; HoChiMinh City Institute of Resources Geography Graduate University of Sciences and Technology, Vietnam Academy of Science and Technology; Institute of Applied Materials Science Scientific Supervisors: Assoc Prof Dr Nguyen Thi Kim Phuong Dr Bui The Huy st Reviewer: 2nd Reviewer: rd Reviewer: The dissertation will be defended at Institute of Applied Materials Science, Graduate University of Science And Technology, Vietnam Academy of Science and Technology, 01A, Thanh Loc 29, Thanh Loc ward, 12 District, Ho Chi Minh City At … hour… date… month … 2021 The dissertation can be found in: - National Library of Vietnam and the library of Graduate University of Science And Technology - Vietnam Academy of Science and Technology INTRODUCTION The necessity of the thesis Currently, environmental pollution is at an alarming level, especially pollution of textile industry wastewater Therefore, the research and development of materials as well as the textile and dyeing wastewater treatment methods are essential requirements The removal of harmful organic pollutants through advanced oxidation processes (AOPs) photocatalytic oxidation is attracting an increasing attention Heterojunctions in photocatalysts has been proved to be one of the most promising ways for the preparation of advanced photocatalysts because of its feasibility and effectiveness for the spatial separation of electron–hole pairs Objectives Study on treatment of RhB (Rhodamine B) and IC (Indigo carmine) dyes by photocatalytic ZnBi2O4/x.0Graphite, ZnBi2O4/x.0Bi2S3 under visible light Research scope and content ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 composites signifcance to find cost-effective and advanced have heterojunction photocatalysts for environmental remediation Structure of the thesis The dissertation has 116 pages, including the Preface, Chapter 1: Overview, Chapter 2: Experiment, Chapter 3: Results and discussions, Conclusions, publications with 44 images, 32 tables and 153 references Chapter OVERVIEW A heterojunction, in general, is defned as the interface between two different semiconductors with unequal band structure, which can result in band alignments The heterojunction photocatalyst should fulft several requirements, such as visible-light activity, high solarconversion effciency, proper bandgap structure for redox reactions, high photostability for long-term applications, and scalability for commercialization Many semiconductors have been investigated and developed for various photocatalytic such as ZnO/Al-Mg-LDHs, RGO/Bi-Zn-LDHs,Ti/ZnO-Cr2O3 Recently, mixed-metal oxides, which are prepared by the calcination treatment of layered double hydroxides (LDHs), have been used as photocatalysts for the elimination of toxic organic compounds in aqueous solutions LDHs are two-dimensional layered anionic clays that are generally expressed as [M1-x 2+Mx3+ (OH)2]x+ (An-)x/n.yH2O as one of the simplest mixed-metal oxides derived from LDHs, ZnBi2O4 is a promising, highly efficient, visible-light active photocatalyst, with advantages of small optical band gap, high stability, and low conduction band edges There have been many studies of the photocatalysts application based on Bi3+ to remove organic pollutants Graphite is a carbon allotrope with a layered structure of stacked graphene sheets It is commonly available and widely used as an adsorbent for organic pollutants and several studies on the photocatalytic performance of graphite have been reported so far Bismuth sulfide (Bi2S3) has a typical lamellar structure with a narrow bandgap, especially as a potential visible light photocatalyst through combination with other semiconductors material In the present work, ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 composites were obtained through a simple co-precipitation method which exhibited effective photocatalysis for the decomposition of RhB and IC under visible light Chapter EXPERIMENT 2.1 Synthetic of ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 Synthesized ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 heterojunction by in-situ coprecipitation (Figure 2.1) The as-prepared materials were labeled as ZnBi2O4, ZnBi2O4/x.0Graphite (x = 1, 2, 5, 10, and 20), ZnBi2O4/x.0Bi2S3(x = 1, 2, 6, 12, and 20), x is the percentages of graphite and Bi2S3 in ZnBi2O4 Figure 2.1 The synthesis process a) ZnBi2O4/x.0Graphit and (b) ZnBi2O4/x.0Bi2S3 The ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 were characterized using various methods, including XRD, IR, XPS, UV-VIS, SEM, TEM, UV-Vis DRS 2.2 Applications of ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 photocatalytic systems The photocatalytic activity of the ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 was assessed using IC and RhB under visible light irradiation The catalytic process consists of two phases QT1: the dark adsorption equilibrium was established for 60 QT2: visible-light irradiation by A 300 W halogen lamp (Osram, Germany) was used to provide a full spectrum emission without the use of a filter Chapter RESULTS AND DISCUSSIONS 3.1 ZnBi2O4/x.0Graphite comsposite 3.1.1 Characterization of ZnBi2O4/x.0Graphite Figure 3.1 shows the XRD patterns of graphite, ZnBi2O4 and ZnBi2O4/x.0Graphite The XRD pattern of ZnBi2O4 showed several strong peaks corresponding to tetragonal zinc bismuth oxide and pure hexagonal zinc oxide Pristine graphite typically shows a strong diffraction peak at around 26.6° The diffraction pattern of ZnBi2O4/20.0Graphite was characterized by a new stronger peak at 27.3° as compared to that of pristine ZnBi2O4, indicating hybridization between graphite and ZnBi2O4 The main diffraction peaks of ZnBi2O4/xGraphite were similar to those of ZnBi2O4 and graphite Figure 3.1 XRD and IR patterns of the samples: ZnBi2O4 and ZnBi2O4/xGraphite (x = 1, 2, 5, 10 and 20) The ZnBi2O4/x.0Graphite sample exhibited characteristic vibrational peaks at 1480 cm-1 and 1028 cm-1 corresponding to the stretching modes of C=C and C–O groups, respectively The bands at 1384 and 843 cm-1 in the pristine ZnBi2O4, ZnBi2O4/x.0Graphite samples are typically attributed to Bi–O and Bi–O–Bi stretching modes, respectively The C 1s XPS spectrum of graphite for the ZnBi2O4/1.0Graphite sample is shown in Figure 3.2 A dominant peak at 284.4 eV and a weak peak at 288.1 eV are observed in the graphite spectrum corresponding to C-C (or C=C) and C=O, respectively The binding energies decreasing Zn 2p (0.4 eV), Bi 4f (0.8eV) O 1s (0.3eV) compare the ZnBi2O4/1.0Graphite and ZnBi2O4 sample The strong electronic coupling between ZnBi2O4 and Graphite would likely accelerate the electron-hole separation Figure 3.2 XPS spectra of ZnBi2O4 and ZnBi2O4/1.0Graphite Figure 3.3 SEM image of asprepared samples (a) Graphite, (b) ZnBi2O4, and (c-f) ZnBi2O4/x.0Graphite (x = 1, 5, 10 and 20); (g) TEM image ZnBi2O4/1.0Graphite sample Figure 3.4 The absorption edges of the samples, and band gap energy of Graphite, ZnBi2O4, and ZnBi2O4/x.0Graphite The SEM of ZnBi2O4/x.0Graphite samples, ZnBi2O4 tends to grow on the graphite sheet Figure 3.3 shows the typical TEM images of the ZnBi2O4/1.0Graphite composite; it was found that the graphite sheets were densely covered by the ZnBi2O4 plates Bảng 3.1 Band gap energy Eg of ZnBi2O4, Graphit, ZnBi2O4/x.0Graphit Graphit 768 1.5 400 2.9 535 2.2 ZnBi2O4/x.0Graphit 400 2.9 (x = 1, 2, 5, 10) 535 2.2 ZnBi2O4/20.0Graphit 420 3.10 ZnBi2O4 The pristine ZnBi2O4 material exhibited visible-light response with the absorption edges at 400 and 535 nm, indicating the presence of a small amount of the ZnO phase, while graphite showed intense absorption over the visible range that extended even to the infrared region (Figure 3.4) The absorption edges of ZnBi2O4/x.0Graphite (x = 1, 2, 5, 10) were similar to that of ZnBi2O4 and blue-shifted in comparison with those of graphite However, the ZnBi2O4/20.0Graphite composites exhibited a mixed absorption at 420 nm This change indicated a strong interaction between graphite and ZnBi2O4 in the resulting ZnBi2O4/x.0Graphite photocatalysts, which strongly affected the light energy absorption region 3.1.2 Photocatalytic Degradation of IC by ZnBi2O4/x.0Graphite Effect of Graphite content in ZnBi2O4/x.0Graphite composites The order of the RhB degradation rate for as-prepared photocatalysts was ZnBi2O4/1.0Graphite (0.0141 min–1) > ZnBi2O4/2.0Graphite (0.0077 min–-1) > ZnBi2O4/5.0Graphite (0.0074 min–1) –1 > –1 ZnBi2O4/10.0Graphite (0.0043 ) > ZnBi2O4 (0.0032 ) > ZnBi2O4/20.0Graphite (0.0018 min–1) The kinetic data of the photodegradation were a good approximation to pseudo-first-order kinetic behavior (r2 = 0.9121–0.9945) The photodegradation rate of RhB on ZnBi2O4/1.0Graphite was significantly higher (~4.5-fold) than that of ZnBi2O4 Thus, ZnBi2O4/1.0Graphite structure increased the rate of RhB oxidation in comparison with pristine ZnBi2O4 (figure 3.5) Figure 3.5 Photodegradation of RhB using ZnBi2O4/xGraphite catalysts under visible light irradiation Effect of the loading of ZnBi2O4/1.0Graphite When the concentration of ZnBi2O4/1.0Graphite was increased from 0.5 to 1.0 g/L, the rate constant k of RhB degradation increased significantly from 0.0053 to 0.0141 min–1 (Figure 3.6a) Beyond the ZnBi2O4/1.0Graphite loading of 1.0 g/L, the value of k decreased (0.0137–0.0059 min–1), which may be due to the excessive catalyst causing opacity of the solution, there by hindering light passing through the solution and consequently interfering with the RhB degradation reaction Effect of initial RhB concentration The effect of initial RhB concentration on the degradation kinetics was investigated in range 15–60 mg/mL It can be seen that the rate constant k of RhB degradation was greatly decreased from 0.0519 to 0.0089 min–1 with the increasing initial RhB concentration from 15 to 60 mg/L This might be explained by the fact that a high concentration 11 The mechanism for photodegradation of RhB by the ZnBi2O4/1.0Graphite catalyst under visible-light irradiation can be described by the following reactions: ZnBi2O4+ h ZnBi2O4 (e–, h+) RhB + h RhB+ + e– ZnBi2O4 (h+) + RhB/RhB+ CO2 + H2O Graphite + e– Graphite (e–) Graphite (e–) + O2 O2– O2– + RhB/RhB+ CO2 + H2O O2– + 2H2O 2OH + 2OH– ZnBi2O4 (h+) + 2H2O OH + H+ OH + RhB/RhB+ CO2 + H2O h+ + e– (e–, h+) (negligible recombination) 3.1.3 Photocatalytic Degradation of IC by ZnBi2O4/x.0Graphite The order of the rate constants of the IC decomposition of the catalysts is as follows: ZnBi2O4/5.0Graphite (0.0032 min-1)> ZnBi2O4/2.0Graphite (0.0027 min-1)> ZnBi2O4/1.0Graphit (0.0021 min-1)> ZnBi2O4/10.0Graphit (0.0016 min-1)> ZnBi2O4 (0.0012 min1 )> ZnBi2O4/20.0Graphit (0, 0007 min-1) Figure 3.8 Photodegradation of IC over ZnBi2O4/x.0Graphite (1, 2,5, 10, 20) under visiblbe light 12 It can be seen that the ZnBi2O4/1.0Graphite hasn't an good photocatalytic activity for the degradation of RhB under visible light irradiation, on which more than 42,5% of IC had been degraded within 180 3.2 ZnBi2O4/x.0Bi2S3 comsposite 3.2.1 Characterization of ZnBi2O4/x.0Bi2S3 The XRD pattern of pristine ZnBi2O4 sample is in good accordance with the standard card of tetragonal ZnBi2O4 (JCPDS No 043-0449) and the formation of pure hexagonal ZnO (JCPDS No 0790207) The main diffraction peaks of ZnBi2O4/x.0Bi2S3 composites were similar to those of the ZnBi2O4 samples However, the patterns of the ZnBi2O4/x.0Bi2S3 composites showed a low-intensity and wide diffraction peaks, especially the peak at 2 = 28.1, indicating the presence of an amorphous phase after coupling took place between Bi2S3 and ZnBi2O4 Figure 3.9 XRD and FT- IR patterns of the samples: ZnBi2O4 and ZnBi2O4/x.0Bi2S3 (x = 1, 2, 6, 12 and 20) The peak at 3460, 1630 cm-1 in the ZnBi2O4, ZnBi2O4/x.0Bi2S3 spectrum can be referred to OH bonding (FT-IR) The bands at 1384 and 13 843 cm-1 in the pristine ZnBi2O4, ZnBi2O4/x.0Bi2S3 samples are typically attributed to Bi–O and Bi–O–Bi stretching modes, respectively The higher the amount of Bi2S3 in ZnBi2O4/x.0 Bi2S3, the more obvious the shift in the number of Bi-O bonds at the 832 cm-1, proving that there is a chemical interaction that changes the number of characteristic waves of the bond Figure 3.10 XPS spectra of ZnBi2O4 and ZnBi2O4/12.0 Bi2S3 Figure 3.11 UV-Vis spectra, and band gap energy of pristine ZnBi2O4, pristine Bi2S3, and ZnBi2O4/Bi2S3 composites 14 XPS spectra of Zn 2p, O 1s, 4f5/2 and Bi 4f7/2 two samples ZnBi2O4 and ZnBi2O4/12.0Bi2S3 showed difference in energy level The lower binding energy shift of Zn 2p that reduces the charge density of Zn is due to the chemical interaction of ZnBi2O4 and Bi2S3 that stimulates the electron transfer between Zn and Bi via an oxygen (Zn-O-Bi) The energy difference Bi-O at 4f5/2 and Bi 4f7/2 also changes with chemical interaction between Bi2S3 and ZnBi2O4 in ZnBi2O4/12.0B Bi2S3 The pristine ZnBi2O4 material exhibited visible light response with the absorption edges at 400 and 535 nm while Bi2S3 showed intense absorption over the visible range that extended even to the infrared region However the ZnBi2O4/x.0Bi2S3 (x = 6, 12) composites exhibited a mixed absorption edge between Bi2S3 and ZnBi2O4 and were significantly red shifted as compared to that of ZnBi2O4 This change was attributed to the strong interaction between Bi2S3 and ZnBi2O4 in the resulting ZnBi2O4/x.0Bi2S3 photocatalysts, which strongly affected the energy profile The band gap energy (E g) of the as-prepared materials was estimated in Table 3.2 Table 3.2: Band gap energy (Eg) of the as-prepared materials max (nm) Eg (eV) 900 400 535 1,20 2,9 2,2 ZnBi2O4/x.0Bi2S3 (x = 1, 2) 400 2,9 ZnBi2O4/x.0Bi2S3 (x = 6, 12, 20) 400 900 2,9 1,39 Material Bi2S3 ZnBi2O4 The SEM micrographs revealed that as-prepared ZnBi2O4 and Bi2S3 consisted of stacked particles with an irregular morphology because 15 of the collapse of the layered structure The individual plates of ZnBi2O4 were flat and the edges of the plates appeared rounded Another interesting observation was made in the case of the ZnBi2O4/x.0Bi2S3 composites; the SEM images showed that Bi2S3 tended to grow on the plates of ZnBi2O4 in the composites Figure 3.12 SEM image of as-prepared samples ZnBi2O4/x.0Bi2S3 (x = 1, 2, 6; 12 and 20); (g) TEM image ZnBi2O4/x.0Bi2S3 sample 3.2.2 Photocatalytic Degradation of IC by ZnBi2O4/x.0Bi2S3 Effect of Bi2S3 content in ZnBi2O4/x.0Bi2S3 composites The efficacy of the photocatalysts under visible light was evaluated by comparing the values of k and followed the decreasing order of ZnBi2O4/12.0Bi2S3 (0.0540 min–1) > ZnBi2O4/20.0Bi2S3 (0.0266 min– ) > ZnBi2O4/6.0Bi2S3 (0.0254 min–1) > ZnBi2O4/2.0Bi2S3 (0.0203 min–1) > ZnBi2O4/1.0Bi2S3 (0.0180 min–1) > ZnBi2O4 (0.0028 min–1) The values of r2 ranged from 0.9562 to 0.9920 and indicated that the 16 photocatalytic experimental results were a good approximation to first-order kinetic behavior Figure 3.13 Photocatalytic IC degradation efficiencies of the ZnBi2O4-xBi2S3 catalysts under visible-light irradiation Effect of the loading of ZnBi2O4/12.0Bi2S3 Figure 3.14a illustrates the degradation of 50 mg/L of IC under visible light irradiation with various loads of ZnBi2O4/12.0Bi2S3 at pH 6.3 When the concentration of ZnBi2O4/12.0Bi2S3 was increased from 0.2 to 1.0 g/L, the rate constant k of IC degradation was greatly increased from 0.0059 to 0.0540 min–1 Beyond the ZnBi2O4/12.0Bi2S3 loading of 1.0 g/L, the value of k decreased to 0.0198 min–1 Effect of initial IC concentration The rate constant k of IC degradation by ZnBi2O4/12.0Bi2S3 was greatly decreased from 0.0854 to 0.0380 min–1 with increasing initial Indigo carmine concentration from 15 to 60 mg/L Effect of pH solution Figure 3.14a shows that the maximum degradation of 50 mg/L of Indigo carmine over ZnBi2O4/12.0Bi2S3 was more than 97% in h at 17 pH 6.3 (k=0.0540 min–1), while the degradation of IC at pH 4.0 and pH 7.0 was 90% (k=0.0385 min–1) and 82% (k= 0.0262 min–1), respectively Approximately 94.1% of IC was degraded after four runs, indicating that the loss in photocatalytic performance of ZnBi2O4/12.0Bi2S3 was insignificant after four recycling runs These results indicate that O2– radicals are the major active species responsible for the complete photocatalytic degradation/mineralization of IC The TOC removal reached 81.1% in the presence of ZnBi2O4/12.0Bi2S3 catalyst after visible light irradiation for h, which confirmed that the outstanding mineralization performance of composite under visible light Figure 3.14 Photodegradation of IC over ZnBi2O4/12.0Bi2S3 under visiblbe light (a) Effect of the loading of ZnBi2O4/12.0Bi2S3, (b) Effect of initial IC concentration, (c) Effect of pH solution, and (d) Reusability of ZnBi2O4/12.0Bi2S3 catalyst under visible light 18 Thus, the likely mechanism for the photodegradation of IC using the ZnBi2O4/12.0Bi2S3 catalyst under visible light irradiation can be described by the following reactions: ZnBi2O4/12.0Bi2S3 + h ZnBi2O4/12.0Bi2S3 (e–, h+) ZnBi2O4/12.0Bi2S3 (e–) + O2 O2– O2– + IC CO2 + H2O ZnBi2O4/12.0Bi2S3 (h+) + IC CO2 + H2O ZnBi2O4/12.0Bi2S3 (h+) + 2H2O OH + H+ OH + IC CO2 + H2O h+ + e– (e–, h+) (negligible recombination) This strong synergistic effect is ascribed to the promotion of heterogeneous catalysis in ZnBi2O4/12.0Bi2S3 by the irradiation of visible light as a result of improved transfer of the photogenerated electron and h+ at the heterojunction interface between ZnBi2O4 and 0Bi2S3, which reduces the recombination of e- and h+ pairs Figure 3.15 Photodegradation of Indigo carmine over ZnBi2O412.0Bi2S3 under visible light with addition of h+; O2–, and OH radical scavengers; Proposed mechanism of the photodegradation over ZnBi2O4/12.0Bi2S3 under visible light 3.2.3 Photocatalytic Degradation of RhB by ZnBi2O4/x.0Bi2S3 Effect of Bi2S3 content in ZnBi2O4/x.0Bi2S3 composites IC 19 It can be seen that there was no significant change in the concentration of RhB under visible light After 90 visible light irradiation, the degradation percentage is calculate ZnBi2O4/12.0Bi2S3 (71,%) > ZnBi2O4/6.0Bi2S3 (53,3%) > ZnBi2O4/2.0Bi2S3 (54,7%) > ZnBi2O4/1.0Bi2S (38,1%) > ZnBi2O4 /20.0Bi2S3 (35,6%) Figure 3.16 Photocatalytic RhB degradation efficiencies of the ZnBi2O4/xBi2S3 catalysts under visible-light irradiation Effect of pH solution Figure 3.16 shows that the maximum degradation of 50 mg/L of RhB over 12Bi2S3/ZnBi2O4 catalyst was more than 89.2 % in 90 at pH 2.0 (with k = 0.0212 min–1), while the degradation of RhB at pH 4.5 and pH 7.0 was ~ 71.0 % (k = 0.0118 min–1) and 49.0 % (k = 0.0065 min–1), respectively Effect of the loading of ZnBi2O4/12.0Bi2S3 When the concentration of ZnBi2O4/12.0Bi2S3 was increased from 0.2 to 1.0 g/L, the rate constant k of RhB degradation increased significantly from 0.0071 to 0.0212 min–1 (Figure 3.17b) Effect of initial IC concentration Figure 3.16c shows that the maximum degradation of 50 mg/L of RhB over ZnBi2O4/12Bi2S3 catalyst was more than 89.2% in 90 at pH 2.0 20 Stability and reusability of ZnBi2O4/1.0Graphite ZnBi2O4/12Bi2S3 hybrid catalyst was quite stable and RhB degradation was approximately 81.6 % after four consecutive reuse, indicating that the ZnBi2O4/12Bi2S3 hybrid catalyst has pretty good stability and reuseability Figure 3.17 Photodegradation of RhB over ZnBi2O4/12.0Bi2S3 under visiblbe light (a) Effect of pH ; (b) Effect of the loading of ZnBi2O4/12.0Bi2S3, (c) Effect of initial RhB concentration, and (d) Reusability of ZnBi2O4/12.0Bi2S3 catalyst under visible light As shown in Figure 3.18 a scavenging experiments indicated that photoinduced h+ are the major species responsible for complete RhB degradation, whereas the contributions of O2– and OHradicals are moderate and minor, respectively Based on the results of the scavenging experiment, the proposed mechanism for synergistic effects between Bi2S3 and ZnBi2O4 within 21 12Bi2S3/ZnBi2O4 hybrid catalyst is shown in Figure 3.18 The likely mechanism for the photodegradation of RhB using the hybrid catalyst under visible light irradiation can be described by the following reactions ZnBi2O4/12.0Bi2S3 + h ZnBi2O4/12.0 Bi2S3 (e–, h+) RhB + h RhB+• + eZnBi2O4/12.0Bi2S3 (h+) + RhB/RhB+ CO2 + H2O ZnBi2O4/12.0Bi2S3 (e–) + O2 O2– O2– + RhB/RhB+• CO2 + H2O ZnBi2O4/12.0Bi2S3 (h+) + 2H2O OH + H OH + RhB/RhB+• CO2 + H2O h+ + e– (e–, h+) (negligible recombination) Figure 3.18 The comparison Figure 3.19 The proposed of RhB photodegradation mechanism for RhB using 12Bi2S3/ZnBi2O4 hybrid photodegradation process using catalyst with addition of 12Bi2S3/ZnBi2O4 different scavengers hybrid catalyst 3.3 Comparision of photocatalytic decomposition of IC anf RhB by ZnBi2O4/x.0Graphit ZnBi2O4/x.0Bi2S3 22 The comparison results showed that ZnBi2O4 /x.0Graphite was able to decompose RhB of much better than decomposition IC under visible light ZnBi2O4/12.0Bi2S3 hybrid catalyst is capable of degrading both IC and RhB dyes However, the catalyst ZnBi2O4/12.0Bi2S3 is more able to decompose IC than RhB Both the ZnBi2O4 /1.0Graphite and ZnBi2O4/12.0Bi2S3 catalysts were highly reactive for the decomposition of RhB dyes under visible light Table 3.3 Comparision of photocatalytic decomposition of IC and RhB by ZnBi2O4/x.0Graphit under visible light Organic pollutants RhB Material ZnBi2O4/1.0Graphit ZnBi2O4/5.0Graphit pH 2.0 6.3 50 50 1.0 0.5 150 150 93.8 42.5 77.7 - h+ O2– - 0.0141 0.0032 Initial concentration (mg/L) The loading material (g/L) Times of visible-light irradiation Degradation percentage Mineralization ability of catalyst IC Active species in the photocatalytic process Constant k of firstorder kinetics (min-1) 23 Tabble 3.4 Comparision of photocatalytic decomposition of IC and RhB by ZnBi2O4/x.0Bi2S3 under visible light Organic pollutants Material pH Initial concentration (mg/L) The loading material (g/L) Times of visible-light irradiation Degradation percentage Mineralization ability of catalyst IC RhB ZnBi2O4/12.0Bi2S3 ZnBi2O4/12.0Bi2S3 6.3 2.0 50 50 1.0 1.0 60 90 97.4 89.2 82.6 81.6 O2– h+ 0.0540 0.0212 Active species in the photocatalytic process Constant k of firstorder kinetics (min-1) CONCLUSION The novel ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 photocatalyst were synthesized by co-precipitation method The photocatalytic activity of the ZnBi2O4/1.0Graphite/Vis system composite was greatly enhanced as compared to that of pristine 24 ZnBi2O4, as evident by the 4.5 times higher photocatalytic degradation rate of RhB with the ZnBi2O4/1.0Graphite /Vis system in comparison to that with pristine ZnBi2O4 The result shows the excellent functionality of ZnBi2O4/1.0Graphite as an efficient visible-lightactive photocatalyst for 77%TOC removal in 150 The photocatalytic degradation rate of IC on ZnBi2O4/12.0Bi2S3 was 0.0540 min–1, which is 19.3 times higher than that of pristine ZnBi2O4, with 1% of TOC removed upon irradiation for 60 The photocatalytic degradation rate of RhB on ZnBi2O4/12.0Bi2S3 is 19.3 times higher than that of pristine ZnBi2O4, with 80.1% of TOC removed upon irradiation for 90 ZnBi-LDH/x.0Graphite and ZnBi2O4/x.0Bi2S3 composites have signifcance to find cost-effective and advanced heterojunction photocatalysts, for environmental remediation THE NEW CONTRIBUTIONS OF THE THESIS The photocatalytic activity of the ZnBi2O4/1.0Graphite/Vis system and ZnBi2O4/12.0Bi2S3/Vis system composites were greatly enhanced as compared to that of pristine ZnBi2O4 The roles of Graphite and Bi2S3 in catalysis ZnBi2O4/x.0Graphite and ZnBi2O4/x.0Bi2S3 have been elucidated through the study of reaction mechanism and kinetics The ZnBi2O4/1.0Graphite and ZnBi2O4/12.0Bi2S3 hybrid catalyst exhibited stable performance, indicating the potential application of this photocatalyst for water purification 25 LIST OF WORKS HAS BEEN PUBLISHED Nguyen Thi Mai Tho, Bui The Huy, Dang Nguyen Nha Khanh, Ho Nguyen Nhat Ha, Vu Quang Huy, Ngo Thi Tuong Vy, Do Manh Huy, Duong Phuoc Dat Nguyen Thi Kim Phuong, Facile synthesis of ZnBi2O4-Graphit composites as highly active visible-light photocatalyst for the mineralization of rhodamine B Korean Journal of Chemical Engineering, 2018 35(12): p 2442-2451 Nguyen Thi Mai Tho, Bui The Huy, Dang Nguyen Nha Khanh, Nguyen Quoc Thang, Nguyen Thi Phuong Dieu, Bui Dai Duong Nguyen Thi Kim Phuong Mechanism of Visible-Light Photocatalytic Mineralization of Indigo Carmine Using ZnBi2O4-Bi2S3 Composites Chemistry Select 2018, 3, 9986–9994 Nguyen Thi Mai Tho, Dang Nguyen Nha Khanh, Nguyen Thanh Tien, Vu Quang Huy, Nguyen Quoc Thang, Nguyen Thi Phuong Dieu, Do Trung Sy, Nguyen Thi Kim Phuong, Self-assembly of a sonicate Graphit-ZnBi2O4 composite with enhanced visible light photocatalytic degradation of Rhodamine B, Viet Nam Journal of Chemistry 2018,56 (4e)83-90 Nguyen Thi Mai Tho, Dang Nguyen Nha Khanh, Nguyen Quoc Thang, Nguyen Lu Ngoc Hue, Nguyen Thi Kim Phuong, Visible-light driven Bi2S3/ZnBi2O4 hybrid catalysts for efficient photocatalytic degradation of Rhodamine B, Viet Nam Journal of Chemistry 2019, 57(4e1,2) 358-365 ... oxidation processes (AOPs) photocatalytic oxidation is attracting an increasing attention Heterojunctions in photocatalysts has been proved to be one of the most promising ways for the preparation... calcination treatment of layered double hydroxides (LDHs), have been used as photocatalysts for the elimination of toxic organic compounds in aqueous solutions LDHs are two-dimensional layered anionic... opacity of the solution, there by hindering light passing through the solution and consequently interfering with the RhB degradation reaction Effect of initial RhB concentration The effect of initial