Facile photochemical synthesis of gold nanoparticles graphitic carbon nitride aug c3n4 for 4 nitrophenol reduction

THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURE AND FORESTRY TRAN THI LE VAN TOPIC TITLE: FACILE PHOTOCHEMICAL SYNTHESIS OF GOLD NANOPARTICLESGRAPHITIC CARBON NITRIDE (Au@g-C3N4) FOR 4-NITROPHENOL REDUCTION BACHELOR THESIS Study Mode : Full-Time Major : Environmental Science and Management Faculty : International Programs Office Batch : 2013 – 2017 Thai Nguyen, 20/08/2017 Thai Nguyen University of Agriculture and Forestry Degree Program Bachelor of Environmental Science and Management Student name Tran Thi Le Van Student ID DTN1353110296 Thesis Title Facile photochemical synthesis of gold nanoparticles- graphitic carbon nitride (Au@g-C3N4) for 4-nitrophenol reduction Supervisor(s) Prof Dr Ruey- an Doong- National Chiao Tung University, Taiwan Assoc Prof Dr Tran Quoc Hung - Thai Nguyen University of Agriculture and Forestry, Vietnam Abstract: In this study, we have demonstrated that Au/g-C3N4 nanocomposite with different Au contents has been fabricated via facile one-step synthesis as photodeposition of Au ions onto g-C3N4 nanosheets Au NPs with average diameter of 5-15 nm were deposited onto the surface of g-C3N4 The as-prepared Au/g-C3N4 nanocomposites exhibit excellent catalytic activity toward 4-nitrophenol reduction and is highly dependent on reactant concentration, metal loading and pH The apparent rate constant for 4-NP reduction by wt% Au/g-C3N4 is 0.902 min-1, respectively The wt% loading amount of Au NPs onto the g-C3N4 performs the highest conversion and can be reused for 10 consecutive catalytic cycles without a considerable loss in catalytic activity The possible mechanism of binary catalyst for enhanced conversion efficiency of 4-nitrophenol was also investigated based on the experimental results Our results clearly demonstrate that the combination of low mass of Au NPs and g-C3N4 is a reliable green chemistry with great potential applications for catalytic transformation in the field of environmental remediation Keywords Gold- carbon nitride, nanocomposite, 4-nitrophenol, NaBH4 , hole scavenger, reduction Number of pages 49 Date of submission 20th September, 2017 Supervisor’s signature ACKNOWLEAGEMENT With all my heart, I would like to express my deepest appreciation to the cooperation between Thai Nguyen University of Agriculture and Forestry and University System of Taiwan, especially National Chiao Tung University for providing me an amazing opportunity to complete this thesis Foremost, I would like to say my sincere gratitude and deep regards to my Taiwanese supervisor: Prof Dr Ruey- an Doong whose guided and gave me suggestions wholeheartedly when I implemented this research Besides my Taiwanese supervisor, I would like to say thankful my second supervisor: Assoc Prof Dr Tran Quoc Hung for his supervision, encouragement, advice, and guidance in writing this thesis My special thanks go to Mr Nguyen Thanh Binh (Ph.D) who offered me a warmly welcome, assisted me in the synthesis of nanoparticles and various other techniques Besides, he was not so patient with my knowledge gaps only, but he also was very enthusiastic for providing me suggestions and methods to successful complete my experiments Furthermore, it was really fortunate for me to worked in Prof Ruey-an Doong’s lab, I want to deeply thanks to all the members in Professor Doong’s laboratory special: Mrs Nguyen Thi Ngoc Anh, Ms Khuat Thi Thanh Huyen, Ms Duong Thi Ngoc Anh who helped me a lot during the time that I did my research in Taiwan My sincere thanks also go to my classmates – k45 AEP especially: Trung, Pim, Manh, Lam, Noy for supporting me when I stayed in Taiwan Last but not the least, I would like to thank all of my family members who always encourage and back me up unceasingly Hsinchu – Taiwan, May 2017 Tran Thi Le Van TABLE OF CONTENT PART I INTRODUCTION 1.1 Research rationale: 1.2 Research’s objectives 1.3 Research questions 1.4 Limitations PART II LITERATURE REVIEW 2.1 4-nitrophenol: 2.1.1 Definition and sources of 4-nitrophenol: 2.1.2 Characteristics of 4-nitrophenol: 2.1.3 4-nitrophenol pollution in the world and Vietnam 2.1.4 Effecting of 4-nitrophenol to environment and human’s health 2.1.5 The characteristics and health effects of Sodium Borohydride (NaBH4) 2.1.6 Method for treament 4-nitrophenol in aqueous solutions 2.2 Nanomaterials: 2.2.1 Gold Nanoparticle: (Au@g) 10 2.2.2 Overview of Graphitic carbon nitride: (C3N4) 11 2.2.3 Overview of nanocomposite 12 PART III MATERIALS AND METHODS 15 3.1 Materials 15 3.1.1 Chemical materials 15 3.1.1 Instruments: 15 3.2 Methods: 17 3.2.1 The synthesis of C3N4 17 3.2.2 The synthesis of Au@g-C3N4 17 3.2.3 Reduction Experiment: 18 3.2.4 The methods for determining the characteristics of material 19 3.2.4.1 X-Ray Diffraction (XRD) 19 3.2.4.2 Scanning Electron Microscopy ( SEM) 21 3.2.4.3 Transmission Electron Microscopy ( TEM) 22 3.2.4.4 High-resolution Transmission Electron Microscopy (HRTEM) 23 3.2.4.5 Zeta potential (ZP) 24 3.2.4.5 UV-vis spectrophotometer ( UV- vis) 25 PART IV RESULTS 27 4.1 X-ray diffraction of g-C3N4 and Au@g-C3N4 nanocomposite 27 4.2 Morphology of g-C3N4 and Au@g-C3N4 nanocomposite 28 4.3 Zeta potential 30 4.4 Application of Au@g-C3N4 for reduction of 4-nitrophenol 31 4.5 Effect of the concentration of NaBH4 on the catalytic activity of Au/g-C3N4 32 PART V DISCUSSION AND CONCLUSION 34 5.1 Discussion 34 5.2 Conclusion 35 REFERENCES 37 LIST OF FIGURES Figure 2.2.1.1: the crystal structure of the three forms of gold nanoparticle 11 Figure 2.2.2 the crystal structure of graphitic carbon nitride, g-C3N4 12 Figure 3.1.1: Some instruments used for this study 16 Figure 3.2.1 Schematic of the synthesis g-C3N4 17 Figure 3.2.2 Schematic of the synthesis Au@g-C3N4 17 Figure 3.2.4.1: Schematics of X-ray diffractometer technique used for crystal structure analysis 21 Figure 3.2.4.2: Schematic diagram of SEM 22 Figure 3.2.4.3: Schematic diagram of TEM 23 Figure 3.2.4.4: The effect of pH on Zeta potential 24 Figure 3.2.4.5 Schematic of UV – vis 26 Figure 4.1: XRD patterns of g-C3N4 and Au@g-C3N4 nanocomposite 27 Figure 4.2 A : SEM images of the synthesis a) g-C3N4 and b) Au@ g-C3N4 composites 28 Figure 4.2 B : TEM images of the synthesis g-C3N4 and Au@ g-C3N4 (a,b) composites, c) HRTEM image of the prepared Au@g-C3N4 29 Figure 4.3 : The effect of pH to zeta potential of g-C3N4 and Au@g-C3N4 30 Figure 4.4 : The reduction 4-nitrophenol by Au@g-C3N4 nanocomposite at pH=4 in aqueous solution at room temperature 31 Figure 4.5 : (a) Effect of the NaBH4 concentration on the reduction of 4-NP by Au/g-C3N4 nanocomposite and (b) k values for 4-NP reduction as a function of NaBH4 concentration 32 Figure 5.1: Proposed mechanism for 4-NP reduction by NaBH4 in the presence of Au/g-C3N4 34 LIST OF TABLES Table 2.1: Physical and Chemical Properties of 4- nitrophenol Table 3.1.1: Sources of chemical materials 15 LIST OF ABBREVIATIONS g-C3N4 Graphitic carbon nitride nanocomposite Au@g-C3N4 Gold- Carbon nitride nanocomposite C6H5NO3 4-nitrophenol NaBH4 Sodium borohydride XRD X-Ray Diffraction SEM Scanning Electron Microscopy TEM Transmission Electron Microscopy ZP Zeta Potential UV- vis Ultravioliet- visible and visible spectrophotometer PART IV RESULTS 4.1 X-ray diffraction of g-C3N4 and Au@g-C3N4 nanocomposite The XRD results for the crystal structures of g-C3N4 and Au@g-C3N4 Intensity (a.u.) nanocomposite were shown in Figure 4.1 as below Au/g-C3N4 g-C3N4 10 20 30 40 50 60 70 80 2 (degreee) Figure 4.1: XRD patterns of g-C3N4 and Au@g-C3N4 nanocomposite Figure 4.1 shows the XRD pattern of the g-C3N4 and Au@g-C3N4 nanocomposite obtained by the hole scavenger method It reveals the pure g-C3N4 shows one diffraction peak at about 2θ = 13.10 with respect to the characteristic interlayer structural packing, and another diffraction peak at 27.20 corresponding to the interpanar stacking peaks of the aromatic systems As the figure 4.1, it was seen that compared with pure g-C3N4 and Au@g-C3N4 samples exhibit three additional peaks at 27 44.40 and 38.20 Such observations indicated that the Au NPs were successfully loaded on the g-C3N4 after irradiation 4.2 Morphology of g-C3N4 and Au@g-C3N4 nanocomposite Figure 4.2 A, 4.2 B were shown the SEM and TEM images of g-C3N4 and Au@g-C3N4 composite The morphology of the g-C3N4 nanosheet and Au@g-C3N4 nanocomposite were shown in Figure 4.2 A presents the SEM images of exfoliated g-C3N4 and Au@gC3N4, respectively Typical 2D interconnected wrinkling g-C3N4 nanosheets could be observed, suggesting that all the large bulk layers are successfully split into small and thin nanosheets via thermal exfoliation On the other hand, the exfoliated g-C3N4 nanosheets exhibited a severe restacking, whereby it is difficult to identify an individual nanosheet With the loading of wt% AuNPs on the surface of g-C3N4 layer, many small particles of Au were found to adhere to the nanosheet surface, indicating the formation of Au@g-C3N4 composite a) b) Figure 4.2 A : SEM images of the synthesis a) g-C3N4 and b) Au@ gC3N4 composites 28 a) g-C3N4 Au (111) d= 0.236 nm Au b) nm c) Figure 4.2 B : TEM images of the synthesis g-C3N4 and Au@ g-C3N4 (a,b) composites, c) HRTEM image of the prepared Au@g-C3N4 The TEM image of pure g-C3N4 shown in Figure 4.2B a) appears to be a lamellar structure, which was formed by the accumulation of the graphitic-like planes In the occurrence of Au NPS, the TEM image composite shows poor transparence since the Au NPs uniformly covered the entire surface area of the g-C3N4 sheet From the histogram analysis shows that the average diameter of approximately spherically shaped Au NPs are in the range 5−15 nm (Figure 4.2 B a) According to the ICP elemental analysis, the content of Au in the composite is estimated to be wt%, which is consistent with the starting ratio HRTEM image of the corresponding Au@g-C3N4 (Figure 1c) typically exhibits the characteristic lattice fringes with crystal plane 29 distances of 0.236 nm, which correspond to the (111) plane of face centered cubic (fcc) Au NPs The formation of the interface between Au NPs and g-C3N4 layer is also presented in Figure 1c revealing the strong interfacial interaction which is highly beneficial for electron migration process 4.3 Zeta potential Zeta potential (mV) 10 g-C3N4 Au/g-C3N4 -10 -20 -30 -40 10 pH Figure 4.3 : The effect of pH to zeta potential of g-C3N4 and Au@g-C3N4 It can be seen that the if zeta potential of g-C3N4 is always negative from about 15 mV to -40 mV belong to pH ≈ 3-9 So, there is no the isoelectric point- IEP On the other hand, the zeta potential of Au@g-C3N4 is positive from 11 mV to mV belong to pH ≈ 3.5–4, however, if the pH of the system has pH between and 9.3, the zeta potential is negative from to -28mV The zeta potential is about mV, pH reach to around pH ~4 (the isoelectric point- IEP) in the pH range from to 10 30 4.4 Application of Au@g-C3N4 for reduction of 4-nitrophenol Remaining ratio (Ct/C0) 1.0 0.8 0.6 g-C3N4 0.4 Au Au@g-C3N4 0.2 0.0 10 Time (min) Figure 4.4 : The reduction 4-nitrophenol by Au@g-C3N4 nanocomposite at pH=4 in aqueous solution at room temperature The reduction capacity 4-nitrophenol by Au@g-C3N4 nanocomposite was examined There was a significant increase in the reduction capacity 4-nitrophenol by Au@g-C3N4 nanocomposite at pH=4 in the different times The results presented in figure 4.4 above At the beginning, 100% 4-nitrophenol was contained in an aqueous solution In the first minute, the separation efficiency 4-nitrophenol out of aqueous solution increased and reached to 40% And the second minute, the reduction 4nitrophenol out of aqueous solution went up to 10% But the fourth minute, 100% 4nitrophenol was reduced by Au@g-C3N4 nanocomposite in aqueous solution and did not show changes in the remaining minutes It is clearly demonstrated that the synthesized Au@g-C3N4 nanocomposite with the linkage of gold on g-C3N4 surface area, as well as surface functionality, that are very good for the reduction capacity of 4-nitrophenol in aqueous solution 31 4.5 Effect of the concentration of NaBH4 on the catalytic activity of Au/g- C3 N4 (b) 1.0 1.0 0.8 0.8 0.5 mM mM mM mM mM 0.6 0.4 kobs (min-1) 4-NP fraction (Ct/C0) (a) 0.2 0.6 0.4 0.2 0.0 0.0 10 NaBH4 concentration (mM) Time (min) Figure 4.5 : (a) Effect of the NaBH4 concentration on the reduction of 4-NP by Au/g-C3N4 nanocomposite and (b) k values for 4-NP reduction as a function of NaBH4 concentration The effect of the NaBH4 concentration on the reduction activity of the Au/gC3N4 nanocatalysts was further examined As shown in Figure 4,5a, the removal efficiency of 4-NP increased with increasing NaBH4 concentration, and a nearly complete reaction was observed within 10 at 0.5−7 mM NaBH4 The kobs value for 4-NP reduction increased from 0.258 min−1 at 0.5 mM NaBH4 to 0.949 min−1 at mM NaBH4 (Figure 4.5b) It is noteworthy that the relationship between the kobs value for 4-NP reduction and the NaBH4 concentration was found to follow the Langmuir−Hinshelwood kinetic mode k  bs KC dC k dt 1 K C F NaBH (1) max F NaBH 32 where is the aqueous concentration of NaBH4, kmax is the intrinsic maximum rate constant for 4-NP reduction, and KF is the Langmuir adsorption coefficient of Au/g-C3N4 A good linear relationship between the initial NaBH4 concentration and the kobs value for 4-NP reduction with KF and kmax values of 0.538 mM and 1.232 min−1, respectively, was obtained (r2 = 0.997), clearly showing that the reduction of 4-NP is a surface-mediated reaction and that BH4- can readily diffuse into the magnetite shell to reach the surface of the Au core nanoparticles 33 PART V DISCUSSION AND CONCLUSION 5.1 Discussion H2O - BH4 - - e e Au g-C3N4 Au Figure 5.1: Proposed mechanism for 4-NP reduction by NaBH4 in the presence of Au/g-C3N4 Based on the above experimental results and related published literature, we propose the following possible reaction mechanism for Au/g-C3N4 catalyzing 4-NP reduction in the presence of NaBH4, as shown Figure 5.1 When Au/g-C3N4 nanocatalysts are used for catalytic reduction, BH4- and 4-NP are first diffused from aqueous solution to the Au surface, especially, g-C3N4 sheets have adsorption capacity for 4-NP via π-π stacking interactions As a consequence, high concentration of 4-NP 34 is present near the bare Au NPs on g-C3N4, serving as catalysts to transfer electrons from BH4- to 4-NP The intimate Au/g-C3N4 contact system accelerates more electrons being generated from the oxidation of BH4-, resulting in the enhanced catalytic activity of Au/g-C3N4 At last, the amino derivative 4-AP is the only product of the sixelectron of 4-NP in the presence of catalyst and excess NaBH4 in accordance with other published results […] Especially, we previously found that the amine (-NH2) group in aminophenols has a strong binding ability with Au NPs and, therefore, adsorbs onto the surface of Au NPs, resulting in the block of reactive sites on Au NPs The outstanding physicochemical properties of the Au@g-C3N4 nanocomposite will play a very important role in environmental pollution management in the future 5.2 Conclusion In conclusion, nanocomposites have gained much interest recently Significant efforts are underway to control the nano structures via innovative synthetic approaches The successful combination of waste display panel glass which contains a large of Au with g-C3N4 which has confirmed by the characteristics of nanocomposite, the pore structure, the specific surface area and Au@g-C3N4 nano composite was formed The synthesized Au@g-C3N4 nanocomposite by thermal method was determined, examined and analyzed through the XRD, SEM, TEM, Uv-vis, Zeta potential With crystalline anatase phase of Au mixed with amorphous g-C3N4 matrix, the good dispersion of Au nanoparticles on the nanocomposite, Au@g-C3N4 linkage was formed to enhance the pore structure and surface area of nanomaterial, the zeta potential was about mV and pH reach to 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