Synthesis, characterization and photocatalytic activity of composite g c3n4 gan zno

VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY NGUYEN HA TRANG SYNTHESIS, CHARACTERIZATION AND PHOTOCATALYTIC ACTIVITY OF COMPOSITE G-C3N4/GAN-ZNO MASTER'S THESIS VIETNAM NATIONAL UNIVERSITY, HANOI VIETNAM JAPAN UNIVERSITY NGUYEN HA TRANG SYNTHESIS, CHARACTERIZATION AND PHOTOCATALYTIC ACTIVITY OF COMPOSITE G-C3N4/GAN-ZNO MAJOR: ENVIRONMENTAL ENGINEERING CODE: 85203202.01 RESEARCH SUPERVISOR: Dr TRAN THI VIET HA Dr NGUYEN MINH VIET Hanoi, 2020 MAJOR: ……………… CODE: ………………… (All cap, bold, font size 14, Times New Roman) ACKNOWLEDGMENTS I would like to express the sincerest gratitude to my supervisors Dr Tran Thi Viet Ha from the Department of Environmental Engineering in Vietnam Japan University and Dr Nguyen Minh Viet from VNU University of Science, who help me to broaden my view, my knowledge as well as support me a lot in both my career and life I have further to thank my willing teachers and colleagues in Vietnam Japan University and the University of Tokyo for supporting me a lot to perform this research and giving me an opportunity to approach the vast knowledge intensively Without your helps, I cannot complete this thesis i TABLE OF CONTENTS INTRODUCTION CHAPTER LITERATURE REVIEW 1.1 The situation of dye and antibiotics residue contamination 1.1.1 Organic dye contamination and their effects 1.1.2 Antibiotics residue contamination and their effects 1.2 Photocatalyst, photocatalysis mechanism 1.2.1 Definition 1.2.2 Mechanism of photocatalytic reaction 1.2.3 Photocatalytic material in photocatalytic reaction 10 1.3 Graphitic carbon nitride g-C3N4 12 1.3.1 Brief introduction of g-C3N4 12 1.3.2 Advantages and disadvantages of g-C3N4-based photocatalysts 15 1.4 GaN-ZnO based photocatalyst 18 1.5 Research objectives 19 CHAPTER EXPERIMENTS AND METHODOLOGIES 21 2.1 Chemicals, apparatus and instruments 21 2.1.1 Chemicals 21 2.1.2 Apparatus and instruments 21 2.2 Synthesis of materials 22 2.2.1 Synthesis of g-C3N4 22 2.2.2 Synthesis of GaN – ZnO 22 2.2.3 Synthesis of g-C3N4/GaN – ZnO composite 23 2.3 Characterization of materials 23 2.3.1 X-ray diffractometer (XRD) 23 2.3.2 Fourier-transform infrared spectroscopy (FTIR) 24 2.3.3 Energy dispersive X-ray (EDX) 25 2.3.4 Scanning Electron Microscope (SEM) 26 2.3.5 Brunauer–Emmett–Teller (BET) 26 2.3.6 Diffuse Reflectance UV-vis Spectrum (UV-Vis-DRS) 27 2.4 Photocatalytic activity evaluation of materials 29 2.4.1 Process of photocatalytic activity evaluation of materials 29 2.4.2 Determination of the kinetic of photocatalytic reaction 31 2.4.3 Determination of point zero charge of material (pzc) 32 CHAPTER RESULTS AND DISSCUSSION 33 3.1 Characterization and photocatalytic activity of g-C3N4 33 3.1.1 Characterization results of g-C3N4 33 3.1.2 Photocatalytic activity of g-C3N4 37 ii 3.2 Characterization and photocatalytic activity of GaN – ZnO 38 3.2.1 Characterization results of GaN – ZnO 38 3.2.2 Photocatalytic activity of GaN- ZnO 41 3.3 Characterization and photocatalytic activity of g-C3N4/GaN – ZnO composite 42 3.3.1 Characterization of g-C3N4/GaN – ZnO composite 42 3.3.2 Photocatalytic activity of g-C3N4/GaN-ZnO composite 53 CONCLUSION 66 REFERENCES 67 iii LIST OF FIGURES Figure 1.1 Sources and pathways of antibiotics in the environment Figure 1.2 The fundamental mechanism of heterogeneous photocatalysis Figure 1.3 Photocatalytic mechanism of denatured materials 11 Figure 1.4 Photocatalyst mechanism of g-C3N4/NiFe2O4 material 12 Figure 1.5 Synthesis of g-C3N4 by condensation of NH(NH2)2 14 Figure 1.6 Polymerization pathway from dicyandiamide to g-C3N4 15 Figure 1.7 The advantages and disadvantages of g-C3N4 based photocatalyst 15 Figure 1.8 GaN and ZnO structure 18 Figure 1.9 Chemical structure of (a) TC and (b) DB71 20 Figure 2.1 Vacuum Rotatable Tube Furnace 23 Figure 2.2 The reflection on the crystal surface 24 Figure 2.3 Schematic diagram of the photocatalytic activity 29 Figure 2.4 Calibration curve of DB71 30 Figure 2.5 Calibration curve of TC 31 Figure 3.1 g-C3N4 samples at different conditions 33 Figure 3.2 XRD patterns of g-C3N4 at different heating conditions (a) temperature (b) time 33 Figure 3.3 FTIR spectrum of g-C3N4 34 Figure 3.4 SEM image of g-C3N4 35 Figure 3.5 EDX spectrum of (a) g-C3N4-550-3 (b) g-C3N4-500-3 (c) g-C3N4-450-3 (d) g-C3N4-500-2 (e) g-C3N4-500-4 36 Figure 3.6 Degradation of DB71 (10 mg/L) by g-C3N4 at different conditions 37 Figure 3.7 GaN – ZnO sample at different heating temperature 38 Figure 3.8 XRD pattern of GaN – ZnO at different heating temperature 38 Figure 3.9 FTIR spectrum of GaN – ZnO at different heating temperature 39 Figure 3.10 SEM image of GaN – ZnO 40 Figure 3.11 EDX spectrum of GaN – ZnO at different heating temperature 40 Figure 3.12 Degradation of DB71 (10 mg/L) by GaN – ZnO at different heating temperature 41 Figure 3.13 XRD patterns of g-C3N4-550-3, GaN-ZnO-900and composite g-C3N4/GaNZnO 42 Figure 3.14 FT-IR spectrum of g-C3N4-550-3, GaN-ZnO-900and composite gC3N4/GaN-ZnO 43 Figure 3.15 SEM image of composite g-C3N4/GaN-ZnO 44 Figure 3.16 SEM image of g-C3N4-550-3, GaN-ZnO-900and composite g-C3N4/GaNZnO 44 iv Figure 3.17 EDX spectrum of g-C3N4-550-3, GaN-ZnO-900 and composite gC3N4/GaN-ZnO 48 Figure 3.18 Nitrogen adsorption−desorption isotherm of (a) g-C3N4-550-3, (b) GaNZnO-900 and (c) composite g-C3N4/GaN-ZnO 51 Figure 3.19 UV-Vis-DRS spectra of GaN-ZnO-900 and g-C3N4/GaN-ZnO 52 Figure 3.20 The energy band gap of GaN-ZnO-900 and g-C3N4/GaN-ZnO 53 Figure 3.21 Degradation of (a) DB71 and (b) TC at different catalyst dosage by composite gC3N4/GaN-ZnO 54 Figure 3.22 Degradation of (a) DB71 and (b) TC at different initial concentration by composite gC3N4/GaN-ZnO 55 Figure 3.23 Degradation of (a) DB71 and (b) TC at different pH by composite gC3N4/GaN-ZnO 56 Figure 3.24 The plot of initial pH value versus delta pH value 57 Figure 3.25 Cycling test for the degradation of DB71 by g-C3N4/GaN-ZnO sample 58 Figure 3.26 Cycling test for the degradation of TC by g-C3N4/GaN-ZnO sample 58 Figure 3.27 Degradation of DB71 by different materials 59 Figure 3.28 Degradation of TC by different materials 60 Figure 3.29 First-order rate constant of g-C3N4-550-3, GaN-ZnO-900 and composite gC3N4/GaN-ZnO for DB71 degradation 61 Figure 3.30 First-order rate constant of g-C3N4-550-3, GaN-ZnO-900 and composite gC3N4/GaN-ZnO for TC degradation 61 Figure 3.31 Mechanism of DB71 and TC decomposition by g-C3N4/GaN-ZnO composite 63 Figure 3.32 PL spectra of GaN - ZnO and g-C3N4/GaN-ZnO composite 64 v LIST OF TABLES Table 1.1 GaN and ZnO parameters 18 Table 2.1 List of chemicals 21 Table 2.2 Lists of instruments and apparatus 21 Table 3.1 Elemental composition of g-C3N4-550-3, GaN-ZnO-900 and gC3N4/GaNZnO 46 Table 3.2 Specific surface area, pore volume, and average pore radius 49 Table 3.3 kapp values of g-C3N4, GaN-ZnO and composite g-C3N4/GaN-ZnO 62 Table 3.4 Photocatalytic activity for the degradation of TC and DB71 65 vi LIST OF ABBREVIATIONS BET CB DB71 EDX FT-IR SEM TC UV-Vis-DRS VB XRD Brunauer–Emmett–Teller Conduction band Direct Blue 71 Energy Dispersive X-ray Fourier-transform infrared spectroscopy Scanning Electron Microscope Tetracycline Diffuse Reflectance UV-vis Spectrum Valence band X-ray diff ractometer vii INTRODUCTION Nowadays, the development of the industry depends strongly on fossil fuels However, this fossil fuel sources may be exhausted in the future, and that has been announced by scientists and the governments Therefore, renewable energy sources are considered as an excellent alternative fuel source with advantages such as being available and being clean energy, without affecting the environment when exploited Solar energy is a popular renewable energy source today, and the uses of sunlight-based environmental treatment techniques have become one of the most potential and environmentally friendly techniques Another concern is the water pollution caused by textile dyes, antibiotic residues and organic contaminants These pollutants have big impacts on the life of species and environment Therefore, the removal of these pollutants is extremely necessary In recent years, a sustainable treatment technology by using semiconductor photocatalytic has been introduced because of various potential advantages such as lowcost, environmental friendly, available to oxidize and remove the organic compounds and microorganisms and thus suitable for water/wastewater industry In chemistry, photocatalysis is the acceleration of a photoreaction in the presence of a catalyst According to theory, the structure of matter consists of a region of molecular orbitals that are packed with enough electrons, called valence band (VB) and a region of molecular orbitals and electron drums, called conduction band (CB) These two regions are separated by an energy gap called the band gap energy, which is the energy difference between the VB and the CB The difference between conductive, non-conductive and semi-conductive materials is the difference in the energy band gap value Semiconductor material is an intermediate material between conductive material and non-conductive material When excited enough by the energy (greater than the forbidden energy of E g), electrons in the VB of the semiconductor material can pass the banding gap to the CB, becoming the semiconductors All semiconductors can be the photocatalysts (Jie Xu et al., 2013) Therefore, to achieve an ideal photocatalyst, a semiconductor photocatalyst need to have a suitable band gap to harvest sufficient solar energy However, the using Comparison the photocatalytic activity and photocatalytic mechanism of g-C3N4/GaN-ZnO composite Based on the synthesis of types of materials examined, g-C3N4, GaN – ZnO solid solution and g-C3N4/GaN-ZnO composites, a best representative sample in each type was selected to compare the photocatalytic activity The samples selected were g-C3N4550-3, GaN-ZnO-900 and g-C3N4/GaN-ZnO composites The results were shown in Figure 3.27 and 3.28 Figure 3.27 Degradation of DB71 by different materials 59 Figure 3.28 Degradation of TC by different materials The photocatalytic activity of material samples in visible light area was assessed based on the DB71 and TC degradation under optimum conditions using the lamp of a 60W 220V In this experiment, 0.05g of catalyst was added into 100mL solution with the concentration of 10mg/L For DB71 degradation, the pH was For TC degradation, the pH was The results are shown in Figure After 180min of irradiation, the degradation efficiency of the materials increased in the following order: sample GaN-ZnO-900 reached 45.1% of DB71 and 40.7% of TC; g-C3N4 reached 56.8% and 47.9% of TC, gC3N4/GaN-ZnO reached 90.1% of DB71 and 94.3% of TC This shows that the composite sample gave the best results in the samples For further study, to compare the degradation reaction rates of DB71 and TC of materials, the Langmuir-Hinshelwood kinematic model was also used The result is shown in Figure 3.29 and 3.30 60 Figure 3.29 First-order rate constant of g-C3N4-550-3, GaN-ZnO-900 and composite g-C3N4/GaN-ZnO for DB71 degradation Figure 3.30 First-order rate constant of g-C3N4-550-3, GaN-ZnO-900 and composite g-C3N4/GaN-ZnO for TC degradation 61 Figure 3.29 and 3.30 showed that the relationship ln (C0/Ct) with irradiation time (t) is linear This showed that the reaction follows the Langmuir - Hinshelwood kinematic model with a high correlation coefficient (R2 ≥ 0.99) From this relationship, kapp values and regression coefficients were calculated (Table 3.3) Table 3.3 kapp values of g-C3N4, GaN-ZnO and composite g-C3N4/GaN-ZnO Pollutant DB71 Sample Equation R2 kapp g-C3N4-550-3 y = 0.0051x + 0.0282 0.991 0.0051 GaN-ZnO-900 y = 0.0037x – 0.0069 0.993 0.0037 g-C3N4/GaN- y = 0.0163x + 0.0914 0.991 0.0163 g-C3N4-550-3 y = 0.0063x + 0.031 0.990 0.0063 GaN-ZnO-900 y = 0.0042x + 0.0246 0.995 0.0042 g-C3N4/GaN- y = 0.0204x – 0.0562 0.993 0.0202 ZnO TC ZnO The DB71 and TC decomposition mechanism by synthesized g-C3N4/GaN-ZnO composite material is proposed in Figure 3.31 In this figure, after receiving visible light, the electron – hole separation occurs simultaneously on g-C3N4 and GaN – ZnO material, the electron moves to the conduction band (CB) and leaving the holes h+ on the valence band (VB) In the conduction band, electrons from g-C3N4 will move to the GaN – ZnO of the composite, while in the valence band, the hole from GaN – ZnO will move to gC3N4 This process significantly reduces electron-hole recombination occurring in composites The reduction will occur in the conduction band of GaN-ZnO and the oxidation will occur in the valence band of g-C3N4 The following equations were used to determine conduction and valence band potentials of the synthesized samples 𝐸𝑉𝐵 = χ − 𝐸𝑒 + 0.5𝐸𝑔 𝐸𝐶𝐵 = 𝐸𝑉𝐵 − 𝐸𝑔 62 χ = [(χ𝐺𝑎 χ𝑁 )(1−𝑥) (χ𝑍𝑛 χ𝑂 )𝑥 ]1/2 where χ is semiconductor’s electronegativity, the χ value for Ga, N, Zn, and O are 3.21 7.27; 4.7 and 7.54 eV respectively; and its values for GaN – ZnO was calculated as 5.03 eV Ee is the free electron energy (4.5 eV) on hydrogen scale, Eg is the band gap energy, ECB and EVB are conduction and valence band potentials and have values -0.82 eV for CB potential and 1.86 eV for VB potential of GaN – ZnO The ECB and EVB for g-C3N4 are -1.13 eV and 1.57 eV as reported in many previous researches Figure 3.31 Mechanism of DB71 and TC decomposition by g-C3N4/GaN-ZnO composite g-C3N4/ GaN-ZnO + hν → g-C3N4/ GaN-ZnO (eCB- / hVB+) g-C3N4/ GaN-ZnO (eCB- / hVB+) → g-C3N4 (eCB- / hVB+) + GaN-ZnO (eCB- / hVB+) ℎ𝑣 − 𝑒𝐶𝐵 + 𝑂2 → 𝑂2∙− 𝑂2∙− + 𝐻 + + 2𝑒 → 𝐻𝑂∙ + 𝐻 + + ℎ𝑉𝐵 + 𝐻2 𝑂 → 𝐻𝑂∙ + 𝑂𝐻 − 𝑂2∙− + 𝑇𝐶 → 𝐻2 𝑂 + 𝐶𝑂2 + 𝑑𝑒𝑔𝑟𝑎𝑑𝑎𝑡𝑖𝑜𝑛 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 63 𝐻𝑂 ∙ + 𝑇𝐶 → 𝐻2 𝑂 + 𝐶𝑂2 + 𝑑𝑒𝑔𝑟𝑎𝑑𝑎𝑡𝑖𝑜𝑛 𝑝𝑟𝑜𝑑𝑢𝑐𝑡 For g-C3N4/ GaN-ZnO composites, g-C3N4 acts as a photosensitive agent, improving the ability to absorb visible light of composite materials With this proposal mechanism, the photocatalytic activity of g-C3N4/GaN-ZnO composite was significantly improved compared to the separate semiconductors g-C3N4 and GaN-ZnO To further prove the possible photocatalytic mechanism, the PL spectra of g-C3N4/GaNZnO composite were obtained From previous researches, PL intensity is associated with the photo-generated carrier recombination in semiconductors As shown in Figure 3.32, the PL spectra of g-C3N4/GaN-ZnO composite were obtained with an excitation wavelength of 365 nm at room temperature It can be seen that GaN – ZnO had high PL intensity as compared to g-C3N4/GaN-ZnO composite due to higher recombination rate of charge carriers In contrast with the g-C3N4/GaN-ZnO composite, the intensity of this emission peak was decreased significantly, which illustrated that the recombination of the photo-generated carriers was limited The PL results further confirmed the discussion on the photocatalytic mechanism and photocatalytic activity The efficiently separated electrons and holes will greatly contribute to the photocatalytic reaction Figure 3.32 PL spectra of GaN - ZnO and g-C3N4/GaN-ZnO composite 64 The obtained results have been compared with previous reports are shown in Table 3.4 It is clear to see that the TC and DB71 degradation results in this research reach a high efficiency under visible light by g-C3N4/GaN-ZnO composite Table 3.4 Photocatalytic activity for the degradation of TC and DB71 Sample Dye/ Antibiotics TiO2 DB71 Light %Degradation Ref 74% Ertugay et source UV light al., 2016 TC UV light 84% Safari et al., 2015 Visible light 56% Suqing et al., 2020 Previous FeNS/TiO2 DB71 Visibile 88% light work ZnO DB71 UV light Nguyen et al., 2016 90% Tabata et al., 2012 CdS/NC TC Visible light 83% Cao et al., 2019 g-C3N4/ TC Visible light 78% al., 2016 CdWO4 Present work Huang et g-C3N4/ DB71 GaN-ZnO TC Visible light 91% 94% 65 CONCLUSION In this thesis, several types of material were successfully synthesized, including: (i) g-C3N4 material by a simple calcination method from urea The optimum condition for synthesis g-C3N4 is heating at 5500C for hours (ii) GaN and ZnO material has been successfully synthesized by a new method by heating the mixture of Ga2O3, ZnO and urea in a nitrogen atmosphere The optimum condition for obtaining GaN - ZnO is heating at 9000C for hours (iii) The novel g-C3N4/ GaN-ZnO composites were successfully prepared by a simple calcination method With this process, the material can be prepared in large quantities in a short time According to XRD pattern, IR spectrum, EDX, BET result and SEM images, the presence of g-C3N4 and GaN-ZnO in the composite was observed The resulting gC3N4/GaN-ZnO composites showed an efficiency photocatalytic activity for degradation of DB71 and TC under visible light irradiation The composite sample also showed good repeatability and this makes this material reusable many times when applied in practice Under the optimum experiment, the DB71 and TC degradion of g-C3N4/ GaN-ZnO is much higher than g-C3N4 and GaN-ZnO 90% of DB71 and TC was degraded by composite g-C3N4/GaN-ZnO in 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Maeda, K., Domen, K., Liu, P., Antonietti, M., Wang, X., 2011 Sulfur-mediated synthesis of carbon nitride: band-gap engineering and improved functions for photocatalysis Energy & Environmental Science, 4(3), 675-678 72 73 ... g- C3N4- 550-3, GaN- ZnO- 90 0and composite gC3N4 /GaN- ZnO 43 Figure 3.15 SEM image of composite g- C3N4/ GaN- ZnO 44 Figure 3.16 SEM image of g- C3N4- 550-3, GaN- ZnO- 90 0and composite g- C3N4/ GaNZnO... and (c) composite g- C3N4/ GaN- ZnO 51 Figure 3.19 UV-Vis-DRS spectra of GaN- ZnO- 900 and g- C3N4/ GaN- ZnO 52 Figure 3.20 The energy band gap of GaN- ZnO- 900 and g- C3N4/ GaN- ZnO 53 Figure 3.21... temperature 41 3.3 Characterization and photocatalytic activity of g- C3N4/ GaN – ZnO composite 3.3.1 Characterization of g- C3N4/ GaN – ZnO composite The synthesis of g- C3N4 and GaN – ZnO material obtained