(Luận văn thạc sĩ) study on development of visible light active photocatalyst g c3n4 comoo4 for removal of antibiotic and inactivation of antibiotic resistant bacteria

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY NGUYEN THI THU HUONG STUDY ON DEVELOPMENT OF VISIBLE LIGHT ACTIVE PHOTOCATALYST g-C3N4/CoMoO4 FOR REMOVAL OF ANTIBIOTIC AND INACTIVATION OF ANTIBIOTIC RESISTANT BACTERIA h MASTER’S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY NGUYEN THI THU HUONG h STUDY ON DEVELOPMENT OF VISIBLE LIGHT ACTIVE PHOTOCATALYST g-C3N4/CoMoO4 FOR REMOVAL OF ANTIBIOTIC AND INACTIVATION OF ANTIBIOTIC RESISTANT BACTERIA MAJOR: ENVIRONMENTAL ENGINEERING CODE: 8520320.01 RESEARCH SUPERVISORS: Dr TRAN THI VIET HA Associate Prof Dr NGUYEN MINH PHUONG Hanoi, 2022 Hanoi, 2022 COMMITMENT I have read and understood the plagiarism violations I pledge with personal honor that this research result is my own and does not violate the Regulation on prevention of plagiarism in academic and scientific research activities at VNU Vietnam Japan University (Issued together with Decision No 700/QD-ĐHVN dated 30/9/2021 by the Rector of Vietnam Japan University) Author of thesis Nguyen Thi Thu Huong h ACKNOWLEDGEMENTS Doing science research is a long journey that I am so grateful that I have received a great deal of support and assistance First and foremost, I would like to express my deepest thank to my supervisor - Dr Tran Thi Viet Ha for her thoughtful orientation, valuable advice, continuous support, and encouragement This research could not have been possible without her persistent guidance and indispensable support I would also like to extend my sincere gratitude to my co-supervisor – Associate Professor Nguyen Minh Phuong for her precise advice and feedback during my research progress Her insightful suggestions have contributed greatly to this master’s thesis I would like to convey my special appreciation to Associate Professor Kasuga Ikuro, who also guided me through this research with critical suggestions and provided me with his connections so I could conduct my bacterial study h I must also thank Dr Takemura Taichiro for providing me the chance to carry out molecular biology experiments at NIHE-Nagasaki Friendship Laboratory I must also thank all the staff at NIHE-Nagasaki Friendship Laboratory, especially Duong san for their guidance and useful advice during my internship there This work is fully supported by the project with the code number of VJU.JICA.21.03, from VNU Vietnam Japan University, under the Research Grant Program of Japan International Cooperation Agency I would like to acknowledge lecturers at the Master’s Program in Environmental Engineering - VNU Vietnam Japan University for giving constructive criticism to improve the quality of my research Last but not least, the warmest thanks also go to my classmates, my lab mates, as well as staff at Vietnam Japan University, with whom I have the pleasure to work while doing the thesis Sincerely thank TABLE OF CONTENTS h LIST OF TABLES i LIST OF FIGURES ii LIST OF ABBREVIATIONS iii CHAPTER 1: INTRODUCTION 1.1 Research background .1 1.2 Research significance 1.3 Research objectives 1.4 Thesis structure CHAPTER 2: LITERATURE REVIEW .4 2.1 Issue of antibiotic and antibiotic-resistant bacteria residues in wastewater 2.1.1 Issue of antibiotic residues in wastewater .4 2.1.2 Tetracycline antibiotic 2.1.3 Issue of antibiotic-resistant bacteria residues in wastewater 2.1.4 Escherichia coli (E coli) antibiotic-resistant bacteria 2.2 Technologies to remove antibiotics and inactivate antibiotic-resistant bacteria residues in wastewater .9 2.2.1 Physical technologies .9 2.2.2 Biological technologies 10 2.2.3 Chemical technologies 11 2.3 g-C3N4 and CoMoO4 photocatalyst .14 2.3.1 g-C3N4 photocatalyst 14 2.3.2 CoMoO4 photocatalyst 16 2.4 Development of g-C3N4/CoMoO4 heterostructure photocatalyst 17 CHAPTER 3: MATERIALS AND METHODOLOGY .19 3.1 Chemicals and apparatus .19 3.2 Photocatalyst preparation .19 3.2.1 Synthesis of g-C3N4 .19 3.2.2 Synthesis of CoMoO4 20 3.2.3 Synthesis of g-C3N4/CoMoO4 20 3.3 Photocatalyst characterization .21 3.3.1 Scanning electron microscopy (SEM) 21 3.3.2 Energy-dispersive X-ray analysis (EDX) 22 3.3.3 Brunauer-Emmett-Teller analysis (BET) 24 3.3.4 X-ray powder diffraction analysis (XRD) 25 3.3.5 Fourier transform infrared spectroscopy (FTIR) 26 3.3.6 UV–vis diffuse reflectance spectroscopy (UV-DRS) 28 3.3.7 Photoluminescence spectroscopy (PL) 29 3.4 Experimental setup 31 3.4.1 Photocatalytic removal of tetracycline antibiotic 31 h 3.4.2 Photocatalytic inactivation of E coli antibiotic-resistant bacteria 32 3.4.3 Determination of photocatalyst's pH point of zero charge 34 3.4.4 Reactive oxygen species trapping experiments 34 3.5 Statistical analysis 34 CHAPTER 4: RESULTS AND DISCUSSION 36 4.1 Optimization of photocatalyst synthesis conditions 36 4.2 Characterization of synthesized materials 37 4.2.1 Scanning electron microscopy (SEM) 37 4.2.2 Energy-dispersive X-ray analysis (EDX) 38 4.2.3 Brunauer-Emmett-Teller (BET) analysis 39 4.2.4 X-ray powder diffraction analysis (XRD) 40 4.2.5 Fourier transform infrared spectroscopy (FTIR) 41 4.2.6 UV–vis diffuse reflectance spectroscopy (UV-DRS) 42 4.2.7 Photoluminescence spectroscopy (PL) 43 4.3 Removal efficiency of synthesized materials with tetracycline antibiotic 44 4.3.1 Enhancement of tetracycline removal efficiency of g-C3N4/CoMoO4 composite 44 4.3.2 Effect of photocatalyst dosage on tetracycline removal efficiency .45 4.3.3 Effect of pH on tetracycline removal efficiency 46 4.3.4 Effect of initial pollutant concentration on tetracycline removal efficiency 48 4.4 Inactivation efficiency of synthesized materials with E coli bacteria 49 4.5 Proposed photocatalytic mechanism 50 CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 53 5.1 Conclusion 53 5.2 Recommendations 54 REFERENCES 55 LIST OF TABLES Table 2.1 g-C3N4 and CoMoO4-based heterojunction photocatalyst 18 Table 3.1 Optimization of preparation conditions of g-C3N4/CoMoO4 composite .21 Table 4.1 Surface area and total pore volume of the synthesized materials 39 h i LIST OF FIGURES h Figure 2.1 (a) Structure and (b) speciation diagram of tetracycline antibiotic Figure 2.2 Schematic diagram of the photocatalytic oxidation process of organic pollutants in the aqueous environment 13 Figure 2.3 Structure of graphitic carbon nitride 15 Figure 2.4 Crystal structure of cobalt molybdate 16 Figure 3.1 SEM instrument 22 Figure 3.2 EDX instrument 24 Figure 3.3 BET instrument 25 Figure 3.4 XRD instrument 26 Figure 3.5 FTIR instrument 28 Figure 3.6 UV-DRS instrument 29 Figure 3.7 PL instrument .30 Figure 3.8 Standard calibration curve of Tetracycline 32 Figure 4.1 Change in tetracycline removal efficiency of synthesized materials at different preparation conditions 36 Figure 4.2 Effect of pristine mixing ratio on antibiotic removal efficiency 37 Figure 4.3 SEM image of the synthesized a) g-C3N4, b) CoMoO4 and .38 Figure 4.4 EDX spectrum of the synthesized a) g-C3N4, b) CoMoO4 and c) gC3N4/CoMoO4 composite 39 Figure 4.5 EDX elementary mapping of the synthesized a) g-C3N4, b) CoMoO4 and c) g-C3N4/CoMoO4 composite 39 Figure 4.6 XRD patterns of the synthesized g-C3N4, CoMoO4, and g-C3N4/CoMoO4 composite .40 Figure 4.7 FTIR spectra of the synthesized g-C3N4, CoMoO4, and g-C3N4/CoMoO4 composite .41 Figure 4.8 UV-vis diffuse reflectance absorption spectra of the synthesized g-C3N4, CoMoO4, and g-C3N4/CoMoO4 composite 42 Figure 4.9 Tauc plot of the synthesized g-C3N4, CoMoO4, and g-C3N4/CoMoO4 composite .43 Figure 4.10 PL spectra of the synthesized g-C3N4, CoMoO4, and g-C3N4/CoMoO4 composite .44 Figure 4.11 Tetracycline removal efficiency of the synthesized g-C3N4, CoMoO4, and g-C3N4/CoMoO4 composite 45 Figure 4.12 Effect of photocatalyst dosage on tetracycline removal efficiency 46 Figure 4.13 Effect of pH condition on tetracycline removal efficiency 47 Figure 4.14 pH point of zero charge of the synthesized g-C3N4/CoMoO4 composite 47 Figure 4.15 Effect of tetracycline's initial concentration on the removal efficiency 48 Figure 4.16 E coli inactivation efficiency with different dosages of photocatalyst 49 Figure 4.17 Effect of different scavengers on the photocatalytic efficiency of the synthesized 50 Figure 4.18 The proposed photocatalytic mechanism for degradation of antibiotics and antibiotic-resistant bacteria .51 ii LIST OF ABBREVIATIONS Antimicrobial resistance AOP: Advanced Oxidation Processes ARB: Antibiotic-resistance bacteria ARGs: Antibiotic-resistance genes BET: Brunauer-Emmett-Teller CB: Conduction Band EDX: Energy dispersive X-ray E coli: Escherichia coli FTIR: Fourier transform infrared spectroscopy HOMO: Highest occupied molecular orbital LUMO: Lowest occupied molecular orbital PL: Photoluminescence spectroscopy SEM: Scanning electron microscopy UV-DRS: UV–vis diffuse reflectance spectroscopy VB: Valence band WHO: World Health Organization WWTP: Wastewater treatment plants XRD: X-ray powder diffraction analysis h AMR: iii CHAPTER 1: INTRODUCTION 1.1 Research background Antibiotics are one of the crucial discoveries of the last century that changed the treatment of a variety of infections in a significant way However, in recent years, the unprecedented issue of antibiotic residues in environmental matrices has been receiving great attention from both academia and the public Several studies reported critical resistance of several kinds of antibiotics in surface and groundwater, sediments, soils, and even foodstuffs (Bombaywala et al., 2021; Daghrir & Drogui, 2013; K Wang et al., 2021) These residues may cause various consequences in the ecological system such as antibiotic-resistant bacteria and human health effects e.g allergy, mutation, and reproductive disorder (Monahan et al., 2021) Most critically, the abuse of antibiotics has directly resulted in the prevalence of antibiotic-resistant bacteria and antibiotic-resistant genes The rapid growth of antibiotic-resistant bacteria threatens the efficiency of medicines, which have revolutionized medicine and saved millions of lives In 2021, World Health Organization (WHO) listed antimicrobial resistance h (AMR) as one of ten global health issues that urgently need collective efforts to tackle (WHO, 2020) However, reports have shown that both antibiotics and antibiotic-resistant bacteria can not be completely removed by conventional wastewater treatment plants (WWTP), which mostly deploy physical and biological technologies (Baquero et al., 2008; Manoharan et al., 2022; K Wang et al., 2021) Hence, it is vital to develop supplement treatment technologies for the efficient removal of those critical pollutants in wastewater 1.2 Research significance In recent years, photocatalytic materials have emerged as a highly efficient and economic strategy for both antibiotic treatment and disinfection in the water environment Many photocatalysts such as TiO2, ZnO2, In2O3, and CdSe have been studied for the treatment of organic pollutants in the environment (Manaia et al., 2018; Noor et al., 2021; Philippopoulos & Nikolaki, 2010) Figure 4.12 Effect of photocatalyst dosage on tetracycline removal efficiency 4.3.3 Effect of pH on tetracycline removal efficiency h Furthermore, different pH conditions were examined to determine the optimal one to remove tetracycline in the solution The results in Figure 4.13 shows that acidic and neutral conditions facilitate better treatment efficiency of antibiotic At pH=7, the removal efficiency of the synthesized g-C3N4/CoMoO4 was recorded to be optimal at 92.88% To further understand the effect of pH conditions on the photocatalyst’s performance, the composite’s pH point of zero charges was determined to be 8.16 (Figure 4.14) It means that at a pH higher than 8.16, the material’s surface is positively charged, and it is negatively charged at a pH lower than 8.16 46 Figure 4.13 Effect of pH condition on tetracycline removal efficiency h Figure 4.14 pH point of zero charge of the synthesized g-C3N4/CoMoO4 composite 47 Meanwhile, as presented in the literature review, tetracycline, with three pKa values (3.3, 7.7, and 9.7), exists as a cationic, zwitterionic, and anionic species under acidic, curcumin-neutral, and alkaline conditions, respectively (McCormick et al., 1957) Based on this explanation, the acidic and neutral conditions with pH ranging from 3.3 to 7.7 mostly facilitate the adsorption of tetracycline on the photocatalyst’s surface This agrees with the significantly low performance of the material at base conditions such as pH=9 and pH=11 Therefore, this result aligned with the observation in Figure 4.13, and pH=7 was the optimized condition for the tetracycline removal process 4.3.4 Effect of initial pollutant concentration on tetracycline removal efficiency h Figure 4.15 Effect of tetracycline's initial concentration on the removal efficiency Figure 4.15 shows the effect of initial tetracycline concentration on the removal efficiency The removal efficiency of the synthesized composite increases from 80.50% to 95.53% as the tetracycline initial concentration decreases As the initial concentration of the tetracycline increases, pollutant molecules are more likely to be adsorbed on the surface of the photocatalyst and a significant amount of light is absorbed by the antibiotic molecules rather than the material particles Hence, the 48 penetration of light to the surface of the photocatalyst decreases, leading to a poorer result in pollutant removal efficiency To sum up, the highest removal efficiency of 95.93% was obtained with the gC3N4/CoMoO4 photocatalyst dose of g/L for mg/L tetracycline solution at pH=7 4.4 Inactivation efficiency of synthesized materials with E coli bacteria h Figure 4.16 E coli inactivation efficiency with different dosages of photocatalyst Figure 4.16 shows the inactivation efficiency of the inactivation of g-C3N4/CoMoO4 bateria in PBS solution containing E coli antibiotic-resistant bacteria at the concentration of 1.4 × 108 CFU/L In the blank experiment, i.e no photocatalyst was added to the reactor, barely change was observed in the reduction of the bacteria concentration This confirms that the presence of the synthesized photocatalyst lead to the inactivation of E coli in other experiments When varying the photocatalyst dosage from to g/L, the synthesized 6:4wt gC3N4/CoMoO4 composite shows optimal inactivation efficiency (log 2.3) with E coli at g/L This reduction was also caused by the adsorption phenomenon and 49 photocatalytic activity of the material The photocatalytic process slightly outweighs the former one in the causation of the bacteria disinfection efficiency 4.5 Proposed photocatalytic mechanism In this research, the characterization and investigation of the composite’s performance in the removal of tetracycline antibiotics proved that the coupling of CoMoO4 significantly addressed the drawback of g-C3N4 due to its wide bandgap The narrowed bandgap of the composite enables the g-C3N4/CoMoO4 to easily absorb photons from the visible light source and catalyze the degradation process of tetracycline Figure 4.17 illustrates the effect of scavengers, namely 1,4-benzoquinone (BQ) specifically reacts with hydroxyl radical (•OH) and isopropanol (IPA) specifically reacts with superoxide radical (•O2–) on the removal efficiency These scavenger experiments showed that superoxide radical (•O2–) played a key role in oxidizing the tetracycline in the solution h Figure 4.17 Effect of different scavengers on the photocatalytic efficiency of the synthesized 50 With the experimental results, the ability of the synthesized material to remove tetracycline was attributed to both adsorption and photocatalytic oxidation process The photocatalytic mechanism of the synthesized material in the degradation of the target pollutant is illustrated in Figure 4.18 h Figure 4.18 The proposed photocatalytic mechanism for degradation of antibiotics and antibiotic-resistant bacteria In the photocatalytic oxidation process, under the illumination of visible light, both CoMoO4 and g-C3N4 can be excited to generate electron-hole pairs The photogenerated electrons in the conduction of CoMoO4 tend to transfer and recombine with the photogenerated holes in the valence band of g-C3N4 In this way, the larger number of photogenerated electrons accumulated in the conduction band of g-C3N4 can reduce the adsorbed O2 to form more •O2– Meanwhile, the photo-generated holes left behind in the valence band of CoMoO4 can oxidize the adsorbed H2O to give •OH Therefore, the photocatalytic activity of the gC3N4/CoMoO4 heterojunction is significantly increased, and the organic compound is by •O2– and •OH reactive species, and •O2– plays the key role in the photocatalytic process The enhanced photodegradation of organic pollutants is elaborated in the following equations: 51 (i) Photo-excitation: CoMoO4/g-C3N4 + hv → CoMoO4/g-C3N4 (e− + h+) (i)Photo-reduction: O2 + e − → • O2 − • O2− + e− + 2H+ → H2O2 H2O2 + e− → •OH + OH− (Chang et al.) Photo-oxidation: 2h+ + H2O → 2H+ + •OH (iii) Photo-degradation • O2−, •OH + organic pollutants → CO2 + H2O + byproducts In the current case, during the illumination process, superoxide (•O2−) is the predominant active species formed by the synthesized heterojunction photocatalyst h responsible for the removal of tetracycline 52 CHAPTER 5: CONCLUSION AND RECOMMENDATIONS 5.1 Conclusion In this research, the g-C3N4/CoMoO4 heterostructure photocatalyst was successfully synthesized through a simple hydrothermal – calcination method, which has significantly improved the photocatalytic activity of g-C3N4 in terms of tetracycline removal under visible light irradiation Among the synthesized photocatalysts, the gC3N4/CoMoO4 sample consisting of 60% mass CoMoO4, going through hours hydrothermal at 180 oC, followed by calcination at 500 oC for hours, displayed superior photocatalytic performance for tetracycline removal under visible light The synthesized materials were characterized by several analytical methods The physical and chemical properties of the g-C3N4/CoMoO4 composite were significantly improved due to the coupling of the two pristine, providing an in-depth understanding of the enhanced performance in its application in antibiotic and antibiotic-resistant bacteria treatment in the aqueous environment h The optimally prepared material was applied to treat tetracycline antibiotic and E coli antibiotic-resistant bacteria With antibiotic, at the optimal operating parameters with g/L photocatalyst the mg/L tetracycline solution at pH = 7, the g-C3N4/CoMoO4 composite showed the highest removal efficiency with tetracycline antibiotic (95.93%) With bacteria, the highest E coli inactivation efficiency was observed at the photocatalyst dosage of g/L, at the initial concentration of 1.4 × 108 CFU/L E coli Based on experiment results, the removal mechanism of synthesized composite with tetracycline was proposed, in which •O2− plays the most important role in the degradation process This holistic study on the synthesis and optimization of g-C3N4/CoMoO4 heterostructure photocatalyst provides insights into the effects of preparation conditions on the material’s characteristics and performance, as well as the application of the effectively designed photocatalyst in the removal of antibiotics and bacteria, which can potentially be deployed for purifying wastewater 53 5.2 Recommendations With the critical of the issues, the potential of this research theme, and the findings obtained in this study, several research directions can be implemented to explore the application of the g-C3N4/CoMoO4 composite photocatalyst Further research on topics such as the optimization parameters and experiment conditions of the composite with E coli bacteria could be conducted For example, control experiments without irradiation time could be implemented to investigate the direct impact of photodegradation on the inactivation of E coli bacteria Besides, the material’s recycling 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