Titanate nanowires doping graphitic carbon nitride nanosheets enhanced visible light photoactivity for sulfamthoxazole degradation

THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURAL AND FORESTRY NGUYEN HOANG NAM TITANATE NANOWIRES DOPING GRAPHITIC CARBON NITRIDE NANOSHEETS ENHANCED VISIBLE LIGHT PHOTOACTIVITY FOR SULFAMETHOXAZOLE DEGRADATION BACHELOR THESIS Study Mode : Full-time Major : Environmental Science and Management Faculty : Advanced Education Program Office Batch : 2014-2018 Thai Nguyen, 25/9/2018 Thai Nguyen University of Agriculture and Forestry Degree Program Student name Bachelor of Environmental Science and Management Nguyen Hoang Nam Student ID DTN1454290020 Thesis Title Supervisor(s) Titanate nanowires doping graphitic carbon nitride nanosheets enhanced visible light photoactivity for sulfamthoxazole degradation - Prof Ruey-an Doong, National Chiao Tung University, Taiwan - Prof Phan Dinh Binh, Thai Nguyen University of Agriculture and Forestry, Vietnam Supervisor’s signature Abstract The presence of antibiotics in water bodies has received great attention since they are continuously introduced and detected in the environment and may cause unpredictable environmental hazards and risks Herein, Titanate nanowires (TNWs) decorated graphitic carbon nitride (g-C3N4) nanosheets has been successfully synthesized by a facile hydrothermal–assisted thermal polymerization approach for the degradation of sulfamethoxazole (SMX) TNWs are a promising material for photocatalytic applications such as hydrogen production, solar cells, water splitting and environmental treatment through the degradation of organic pollutants In addition the chemical and thermal stability, low cost, nontoxicity and high photocatalytic activity of TNWs This promise reflects the advantageous photo physical efficacy The g-C3N4 nanosheets, possess the suitable band gap as a photocatalyst, however the addition of TNWs on the surface and intercalated layers of g-C3N4 can enhance the photocatalytic degradation of organic pollutants The asprepared g-C3N4/TNWs photocatalysts were characterized by X-Ray diffraction (XRD), Scanning Electronic Microscope (SEM), Transmission electron microscopy (TEM), UV-visible Spectrophotometer (UV-vis), Thermogravimetric Analysis (TGA), Brunauer-Emmett-Teller (BET) The results showed that g-C3N4 and TNWs were successfully fabricated under optimal conditions The photocatalytic performances of g-C3N4/TNWs nanocomposites were investigated for the degradation of Sulfamethoxazole (SMX) under visible light irradiation The calcination temperature and the g-C3N4 ratio to TNWs are two important factors which enhance the SMX degradation 1:8 weight percentages of bulk g-C3N4 and TNWs polymerized at 500 °C under N2 atmosphere shows the best SMX degradation rate and reached to 60 % in h incubation time The enhanced photocatalytic performances could be mainly attributed to the modified band gap structure of g-C3N4/TNWs We expect that the g-C3N4/TNWs nanocomposites in specific fabrication ratios can serve as supervisor photocatalysts for antibiotics degradation under visible light i Keywords Titanate nanowires, g-C3N4 nanosheets, Photodegradation, Sulfamethoxazole, Antibiotics, Visible light, photocatalytic, degradation, Number of papers Date of submission 40 pages 25th September, 2018 ii ACKNOWLEDGEMENTS I am deeply indebted to my research supervisor Prof Ruey-An Doong, whose stimulating motivations and valuable ideas helped me to complete my thesis and I would like to offer my sincere gratitude Prof Phan Dinh Binh for his support throughout my thesis with his patience and knowledge whilst allowing me the room to work in my own way My special thanks go to Mrs Duong Thi Ngoc Anh (MSc) about the help dedicated of his during my studies and research in this laboratory She was hearted guidance, given the comments and the orientation in my experiment steps as well as the process of writing my report I would like to thank Jim, Micheal, Sharon, Luong and Ruben for their guidance to use a variety of important machinery serving my experiment, David and Bin for their impressive help in perform analysis of TEM and XRD samples I would also like to thank all members ofthe ECCL Lab, Institute of Environmental Engineering, National Chiao Tung University, Taiwan, who provided their ongoing support, questions and suggestions Finally, I would like to express to my classmates and gratitude to my beloved parents, their always support me during the time I study in Taiwan Student Nguyen Hoang Nam iii TABLE OF CONTENTS LIST OF FIGURES vi LIST OF TABLES viii LIST OF ABBREVATIONS ix PART I INTRODUCTION 1.1 Research rationale 1.2 Research objective 1.3 Research questions 1.4 Limitations 1.5 Definitions PART II LITERATURE REVIEW 2.1 Overview of Titanate nanowires 2.1.1 Titanium oxidation structures and properties 2.1.2 Titanate nanowires 2.1.3 The photocatalytic activity of Titanate nanowires 2.2 Overview of Graphitic carbon nitride nanosheets 2.2.1 Graphitic carbon nitride nanosheets structures and properties 2.2.2 Graphitic carbon nitride nanosheets highlights and limitations 2.2.3 Application of Graphitic carbon nitride nanosheets 2.3 Overview of g-C3N4/ TNWs nanocomposites 10 2.3.1 g-C3N4/ TNWs nanocomposites properties 10 2.3.2 Fabrication of g-C3N4/ TNWs nanocomposites 10 2.4 Overview of sulfamethoxazole 11 2.5 Overview of research and application of nanomaterial 14 iv 2.6 The Antibiotics Sulfamethoxazole in Vietnam 15 PART III METHODS 16 3.1 Material 16 3.2 Methods 16 3.2.1 Synthesis of titanate nanowires 16 3.2.2 Synthesis of g-C3N4nanosheets 17 3.2.3 Synthesis of g-C3N4/TNWs composites 17 3.2.4 Characterization 17 PART IV RESULTS 24 4.1 XRD spectra 24 4.2 UV-Vis analysis 25 4.3 TGA analysis 26 4.4 BET analysis 27 4.5 SEM analysis 28 4.6 TEM analysis 31 4.7 Photocatalytic activity 32 PART V DISCUSSION AND CONCLUSIONS 35 5.1 Discussion 35 5.2 Conclusions 35 REFERENCES 37 v LIST OF FIGURES Figure 2.1 Photo-degradation reduction of humic acid (HA) at TNW10 and TNW20 Figure 2.2 Schematic illustration of the synthesis process of g-C3N4by thermal polymerization of different precursors Figure 2.3 (a) s-triazine and (b) tri-s-triazine (heptazine) structures of g-C3N4 Figure 2.4 Schematic representation of the charge generation, migration and hydrogen production mechanism at the g-C3N4/TiO2 nanowires heterostructures 11 Figure 3.1 Schematic diagram of ultraviolet-visible spectrometer 18 Figure 3.2 Schematic diagram of transmission electron microscope 22 Figure 3.3 The process TEM characterization 22 Figure 4.1 XRD patterns of the samples calcined (a) in air and (b) in N2 atmosphere 24 Figure 4.2 The XRD pattern of g-C3N4/TNWs nanocomposite in different ratio 25 Figure 4.3 UV-Vis DRS of g-C3N4, g-C3N4nanosheets, pre-TNWs, TCN-4 and TCN-8.26 Figure 4.4 UV-Vis plots of (αhv)2various photon energy (hv) 26 Figure 4.5 TGA curves of N-TNWs, g-C3N4 and g-C3N4/TNWs nanocomposite (ratio 1:8) 27 Figure 4.6 BET specific surface areas and pore size distribution of g-C3N4/TNWs nanocomposite 28 Figure 4.7.SEM images of (a,b) N-TNWs 400, (c,d) N-TNWs 500, (e.f) N-TNWs 600 29 Figure 4.8 SEM images of a) A-TNWs 400, b) A-TNWs 500, c) A-TNWs 600 30 Figure 4.9 TEM images of TNWs at difference calcined temperature 31 Figure 4.10 TEM image of g-C3N4/TNWs nanocomposite 32 vi Figure 4.11 The photodegradation of mgL-1 SMX 33 Figure 4.12 The photodegradation at various concentrations under visible light 33 vii LIST OF TABLES Table 2.1 Properties of sulfamethoxazole (SMX) 13 Table 4.1 P25-TiO2, TCN-4 and TCN-8 reacted with SMX (pH =7) 34 viii LIST OF ABBREVATION Abbreviations Full text content XRD X-Ray Diffraction TEM Transmission electron microscopy SEM Scanning electronic microscope UV Ultra-violet Vis Visible BET Brunauer-Emmett-Teller TGA Thermogravimetric analysis g-C3N4 Graphitic carbon nitride nanocomposite TNWs Titanate Nanowires SMX Sulfamethoxazole TCN g-C3N4/TNWs nanocomposite ix Figure 4.3 UV-Vis DRS of g-C3N4, g-C3N4nanosheets, pre-TNWs, TCN-4 and TCN-8 Figure 4.4 UV-Vis plots of (αhv)2various photon energy (hv) 4.3 TGA analysis To support the presence of g-C3N4 and thermal stability of the nanocomposite, TGA experiment was carried out at different temperature from room temperature shown in the Figure 4.5 All the samples show good stability at 550 ºC, which suggest 26 the formation of stable heptazine structure in g-C3N4 From ambient temperature to 200 °C, small weight loss was observed This is attributed to desorption of the physically adsorbed and intercalated water The main weight loss appears at the range of 500 to 685 °C due to the combustion of g-C3N4 Pure g-C3N4 shows 100 % degradation at 685 °C which, however, prove the complete removal of g-C3N4The second weight loss stage indicates the weight percent of g-C3N4 in the composites gC3N4/TNWs show around 83 % degradation after heating up to 700 ºC and remaining 17 % weight representing the stable titanium nanotubes This weight loss clearly demonstrates the presence of g-C3N4 in the nanocomposite 100 Weight (%) 80 60 40 TNWs g-C3N4 20 g-C3N4/TNWs 100 200 300 400 500 600 700 Temperature (C) Figure 4.5 TGA curves of N-TNWs, g-C3N4 and g-C3N4/TNWs Nanocomposite (ratio 1:8) 4.4 BET analysis Figure 4.6 shows the N2 adsorption−desorption isotherms of as-received gC3N4/TNWs nanocomposite show a typical type I isotherm with a hysteresis loop in the relative pressure (P/P0) range of 0.8−1.0, and clearly indicating the macro-porous 27 nature of as-received g-C3N4/TNWs nanocomposite The BET surface area of the gC3N4/TNWs nanocomposite was calculated to be approximately15.3670 m²/g1 and the pore distribution shows several modal distributions Pore size distribution calculated from the desorption isotherm using the Barrett–Joyner–Halenda (BJH) method The pore size around 36.12487 nm is mainly attributed to the macro-porous adsorption desorption 80 0.0015 60 40 dv/dW (cm3g-1nm-1) Volume adsorbed (cm3STP/g) 100 20 0.0010 0.0005 0.0000 20 40 60 80 100 Pore Diameter (nm) 0.0 0.2 0.4 0.6 0.8 1.0 Relative Pressure (P/P0) Figure 4.6 BET specific surface areas and pore size distribution of g-C3N4/TNWs nanocomposite 4.5 SEM analysis For the fabrication of TiO2 nanowire in different synthesis conditions, figure 4.7 (a, b) shows the SEM image for the morphologies of N-TNW, which synthesized by hydrothermal method at 180 oC in 12 hours The N-TNW was successfully obtained from the precursor Degussa P25 through the thermal treatment After calcined under 400 oC in hours, the morphologies of TNWs was one step converted from H2Ti3O7 nanotubes However, when the temperature increase for the calcination 28 of N-TNW after hydrothermal method, the SEM images shows at figure 4.7 (c ,d), we investigated that the size of N-TNW increase dramatically into micro-scale as well The N-TNW transferring to titanium oxide nanowire was found under the heating at 500oC in hrs In the figure 4.7 (e, f), the morphology of N-TNW comprehensively became TiO2-based nanoparticles, when the temperature of calcination uplift at 600 oC in hours Figure 4.7 SEM images of (a,b) N-TNWs 400, (c,d) N-TNWs 500, (e.f) N-TNWs 600 29 It eases to see the change of morphologies when TNWs was calcined in air atmosphere compared with TNWs calcined in N2 atmosphere When calcined in air, organics confined in the TNTs were burned out in the calcination process by the reaction with oxygen in the air When calcined in N2 atmosphere, however, the decomposed products could not be burned out due to the lack of oxygen It is clear that the presence of N doped in these samples is the cause of the difference in morphologies between samples calcined in air and N2 We also found that these samples have very different colors For samples calcined in air, they are pure white For samples calcined in N2 atmosphere, however, all three samples have similar dark color a) b) c) Figure 4.8 SEM images of a) A-TNWs 400, b) A-TNWs 500, c) A-TNWs 600 30 4.6 TEM analysis The morphological study of nanoparticles has been done by transmission electron microscopy (TEM) It’s clearly that the morphologies change when the calcined temperature increase At 400 °C the morphologies were nanotube At 500 °C the morphologies changed to form nanowires and it continuous changed to form nanoparticles when the temperature increased to 600 °C The results indicated that the morphologies of TNWs depend on the calcined temperature Figure 4.9 TEM images of TNWs at difference calcined temperature 31 Figure 4.10 shows the morphology of g-C3N4/TNWs nanocomposites It’s easy to see g-C3N4nanosheets doped onto the surface of TNWs, it illustrated that the composites successful fabricated Figure 4.10 TEM image of g-C3N4/TNWs nanocomposite 4.7 Photocatalytic activity The visible-light-driven photocatalytic activity of g-C3N4/TNWs toward SMX degradation was evaluated by the visible light irradiation Figure 4.11 shows the photodegradation efficiency of mgL-1 by P25 and TNWs/g-C3N4 nanocomposite in difference ratio (1:4, 1:8) Only around % of the original SMX are removed within 120 mins when P25 TiO2 is irradiated with 465 nm visible light The photocatalytic activity of TCN-4 and TCN-8 can be enhanced under visible light irradiation and the degradation efficiency of SMX is around 25 % and 60 %, respectively Figure 4.12 shows the photodegradation efficiency of various initial concentrations of SMX by TCN-8 under 465 nm visible light irradiation at 25°C and at pH It is evident that the photodegradation efficiency of SMX decrease in the increase in initial SMX concentrations at mgL-1 and 10 mgL-1 Around 60% of SMX mgL-1 was 32 degradation while only 29 % of SMX 10 mgL-1 was removed after 120 mins In this result indicates that the formation between g-C3N4nanosheets and TNWs plays a decisive role in enhancing the visible-light-sensitive photocatalytic activity of gC3N4/TNWs prepared by calcined method Figure 4.11.The photodegradation of mgL-1 SMX Figure 4.12 The photodegradation at various concentrations under visible light 33 Table 4.1 P25-TiO2, TCN-4 and TCN-8 reacted with SMX (pH =7) Photocatalyst SMX Catalyst Wavelength Irradiation Degradation (mg/L) (g/L) (nm) time(min) (%) P25- TiO2 10 465 120 TCN-4 10 465 120 25 TCN-8 10 465 120 60 34 PARTV DISCUSSION AND CONCLUSIONS 5.1 Discussion To summary, the study has developed g-C3N4/TNWs nanocomposite of the potential for waste water purification through utilization of solar energy In this study, TNWs andg-C3N4/TNWs were synthesized by hydrothermal method with the aim of extending the light absorption spectrum toward the visible light Their characteristic was evaluated by TEM, XRD and UV-Vis spectroscopy TEM image revealed the structural morphology of the synthesized material This result indicated that g-C3N4 doping could decrease the particle size of TNWs nanoparticles The XRD pattern result point out that g-C3N4 doping TNWspromotes the phase transformation of TiO2 from anatase to rutile The UV-Vis spectroscopy analysis was helped calculate band gap of TiO2 and it also show that the absorption of g-C3N4/TNWshas moved to the visible spectrum Band gap of g-C3N4/TNWs was smaller than band gap of pure TiO2 this demonstrates that g-C3N4doping helped shrink the band gap of pure TiO2 This indicated why TiO2 can absorb visible light Experimental results obtained in this study clearly demonstrate that gC3N4/TNWs nanocomposite was an effective adsorbent for organic pollutant in water The photocatalytic degradation of methyl orange indicates that g-C3N4/TNWs powders can effectively photodegrade methyl orange under visible light irradiation and UV light The maximum degradation of methyl orange under UV irradiation is 90% The photoactivity of g-C3N4/TNWs was higher than photocatalyst of pure TiO2 5.2 Conclusion The various fabrications of g-C3N4/TNWs were successfully synthesized by simple facile hydrothermal method led calcination for the degradation of SMX The 35 TNWs was synthesized by the TNTs modified synthesized methods, the hydrothermal method under 180 °C in 12 hrs and calcined 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