NGHIÊN CỨU CHẾ TẠO VẬT LIỆU TỔ HỢP NANO TiO2 DẠNG SỢI ỨNG DỤNG TRONG LĨNH VỰC QUANG ĐIỆN HÓA .TT LUẬN ÁN TIẾN SỸ VẬT LÝ

12 Fig 3.4 The SEM of samples Ti2+/PVP with different rate: ( a) 0.3 mL/h;(b) 0.4 mL/h; (c) 0.5 mL/h; (d) 0.6 mL/h Fabrication parameters: injection rate: 0.4 mL/h; electric field: 0.6 kV/cm, the TTiP / PVP mass ratio: 2:1, and the PVP solution has a mass percentage of 8% 3.1.2 The results of structural analysis and morphology of TiO2 nanofibers 3.1.2.1 XRD results Fig 3.6 XRD spectrum of samples Ti2+/PVP and TiO2 at 500 0C 3.1.2.2 SEM, TEM results Fig 3.7 The SEM (a), EDS spectrum (b) of fiber TiO2 at 500 0C 13 Fig 3.8 The TEM (a) and HR-TEM (b) of fiber TiO2 at 500 0C TiO2 has nanofibers with a diameter of 130 nm and has an anatase phase structure at 500 0C 3.1.3 XPS results Fig 3.9 XPS spectrum of Ti2p (b), and O1s (c) 3.2 RESULTS OF PROPERTIES ANALYSIS PHOTOELECTROCHEMICAL Highest efficiency was archieved with spraying time of 20 minutes The efficiency we calculated is 0.027% (at a voltage of 0.2 V corresponding to a current density of 80 A/cm  ) (Fig 3.10 (b)) 14 Fig 3.10 Optical current density dependence (a); conversion efficiency (b) according to the spray time of the photoelectrode Based on these results, we choose the spraying time of 20 minutes to coat the surface of the TiO2 fiber with the CdS semiconductor to enhance the working ability of the electrode in the visible light CHAPTER THE PHOTOELECTROCHEMIACL PROPERTIES OF THE FIBER NANOSTRUCTURED TiO2 NANOCOMPOSITES 4.1 PROPERTIES OF NANOCOMPOSITES CdS/TiO2 4.1.1 XRD Results Fig 4.1 XRD spectrums of CdS/TiO2-1h; CdS/TiO2-2h and CdS/TiO2-3h TiO2 has anatase phase and CdS has the hexagonal structure 4.1.2 The results of morphological analysis using SEM, TEM 15 Fig 4.2 (a) The SEM of CdS/TiO2 and (b) the diameter of fiber of its The TEM image (Figure 4.3 (a)) shows that the fiber diameter for the CdS/TiO2 sample is about 173  16 nm From the HR-TEM image: CdS has the hexagonal structure; TiO2 has the anatse phase Fig 4.3 TEM (a) and HR-TEM (b) images of CdS/TiO2-2h 4.1.3 The UV-Vis spectrum results Fig 4.4 UV-Vis spectrum (a) and (F(R)*h)1/2vs photon energy (h) ( b ) of samples CdS/TiO2 16 The presence of CdS nanoparticles surrounding TiO2 fibers increases the absorbance of the electrode in the visible light field 4.1.4 The XPS Results Fig 4.5 XPS spectrum of TiO2 CdS/TiO2-2h: (a) survey; (b) Ti 2p; (c)O 1s; (d) Cd 3d and (e) S 2p 4.1.5 The results of the photo-electrochemical analysis 17 Fig 4.6 Photocurrent density and conversion efficiency of CdS/TiO2 photoelectrode with different coating time CdS The efficiency reached a maximum value of 3.2% with an electrode with a CdS coating time of hours and decreased as the time of CdS coating increases We choose 2-hour hydrothermal time when coating CdS on TiO2 4.2 PROPERTIES OF Au/TiO2 NANOFIBER MATERIALS 4.2.1 The results of structural analysis Au has the Cubic phase and TiO2 has the anatase structure Fig 4.9 XRD pattern of Au/TiO2 samples with irradiation times of minutes, 10 minutes and 20 minutes 4.2.2 Analysis results SEM, TEM The average size of Au particles over 10 minutes, 15 minutes and 20 minutes was 16.1 ± 2.6 nm, 20.8 ± 1.9 nm and 28.5 ± 2.9 nm, respectively 18 Fig 4.10 (a-d) FE-SEM images with h irradiation times of 5, 10, 15, and 20 minutes, respectively Fig 4.11 (a)TEM image and (b)HR-TEM TEM image with irradiation time of 15 minutes 4.2.3 UV-Vis spectrum results The material has an absorption peak in the visible region between 500 nm and 620 nm due to the SPR effect of Au 19 Fig 4.11 UV-Vis spectrum with irradiation times of 0, 5, 10, and 20 minutes, respectively 4.2.4 XPS Results Fig 4.13 XPS spectrum of TiO2 and Au/TiO2 with irradiation time of 15 minutes: (a) survey; (b) O 1s; (c) Ti 2p; (d) Au 4f 4.2.5 The results of the photo-electrochemical analysis 20 Fig 4.14 Photocurrent density and conversion efficiency of CdS/TiO2 photoelectrode with different with irradiation times Fig 4.15 The photocurrent density dependence on the electrolysis time (a) and the photoelectric current density of the TiO2 and Au/TiO2 electrodes under LED excitation The efficiency for the Au/TiO2 nanofibers structure was 0.52% (at 0.5 V, corresponding to a current density of 0.9 mA/cm2) with a UV irradiation time of 15 minutes 4.3 PROPERTIES OF CdS/Au/TiO2 NANOFIBER MATERIALS 4.3.1 The results of structural analysis Sample CdS/Au/TiO2 shows the complete phases of the component materials in the structure (TiO2 has anatase; CdS has hexagonal phase and Au has cubic phase) 21 Fig 4.17 XRD pattern of TiO2; Au/TiO2 and CdS/Au/TiO2 samples 4.3.2 SEM results Fig 4.18 (a) FE-SEM and (b) cross - section images of CdS/Au/TiO2 4.3.3 UV-Vis spectra results Fig4.22 Uv-Vis spectrum of TiO2, Au/TiO2 and CdS/Au/TiO CdS/Au samples The absorption spectrum of the CdS/Au/TiO /Au/TiO2 sample extended from the ultraviolet to the visible 700 nm region region 4.3.4 The results of the photo-electrochemical electrochemical analysis 22 Fig 4.23 Photocurrent density and conversion efficiency of Au/TiO2, CdS/TiO2, Au/CdS/TiO2 CdS/Au/TiO2 photoelectrodes Conversion efficiency increases corresponding to the above structures and reaches a maximum value of 4% (at 0.3V) corresponding to the CdS/Au/TiO2 structure electrode 4.3.5 Charge transfer mechanism of the structure of CdS/Au/TiO2 in PEC model Fig 4.25 Charge transfer mechanism of the structure of CdS/Au/TiO2 4.3.5 Design of hydrogen gas capture system through PEC model Fig 4.27 Volume of hydrogen gas obtained over time under illumination 23 CONCLUSION TiO2 material with fiber structure has been synthesized successfully by the electrospinning method SEM image results and X-ray diffraction analysis showed that TiO2 has a nanofiber form and an anatase structure at 500 0C The photoelectrochemical properties of water splitting have been investigated with samples with different spray times The results showed that under the illumination of a 150W Xenon light source (P = 100 mW.cm-2), photoelectrode corresponding to a 20-minute spray time gave an efficiency of 0.027%, the optical current density of 80 A/cm2 CdS nanoparticles were direct grown on the fibrous TiO2 nanofibers by the wet chemical method CdS have a hexagonal structure TEM images showed that CdS particles had an average size of about 10 nm The material is capable of absorbing light in the wavelength region less than 520 nm The conversion efficiency achieved for CdS/TiO2 nanofibers was 3.2% corresponding to the CdS coating time of hours The plasmonic Au nanostructured material is decorated to the TiO2 fiber surface by the Au3+  Au reduction method under the support of ultraviolet light The results of measurements: XRD, SEM, TEM, HR-TEM, XPS showed that Au attached to TiO2 fiber had a face-centered cubic structure, crystal size about 15 nm The material has an absorption peak in the visible region between 500 nm and 620 nm due to the SPR effect of Au The water-separating photoelectric properties were also determined after Au was attached to the TiO2 nanofibre structure, the results showed that the efficiency obtained for the Au/TiO2 nano-fiber structure was 0.52% (at 0.5 V, corresponding to a current density of 0.9 mA/cm2) corresponding to a UV exposure time of 15 minutes Electrodes have a high response, less electrochemical corrosion during electrolysis The photoelectrode with the CdS/Au/TiO2 multilayer composite structure has been successfully fabricated Fabricated electrodes are capable of working in the region with excitation wavelengths less than 680 nm This structure gives a maximum 24 efficiency of 4% at 0.3V (for Ag / AgCl electrode) when excited by Xenon light The electrode has a good response and high electrochemical strength The mechanism of charge transfer in the above structures has also been discussed A system to capture hydrogen gas generated in a watersplitting photo-electrochemical reaction on a laboratory scale was successfully designed The volume of hydrogen gas obtained after hour is 35 ml corresponding to an area of cm2 electrode The results of hydrogen gas obtained from this system are quite promising for practical application The results of the thesis on optical current density and optical conversion efficiency are rather close to some previously published works LIST OF PUBLICATIONS [1] Van Nghia Nguyen, Minh Thuy Doan, Minh Vuong Nguyen (2018), "Photoelectrochemical water splitting properties of CdS/TiO2 nanofiers-based photoanode", Journal of Materials Science: Materials in electronics, Vol 2018(1), DOI: https://doi.org/10.1007/s10854-018-0363-8 [2] Van Nghia Nguyen, Minh Vuong Nguyen, Thi Hong Trang Nguyen, Minh Thuy Doan, Loan Le Thi Ngoc, Ewald Janssens, Anupam Yadav, Pin-Cheng Lin, Manh Son Nguyen and Nhat Hieu Hoang (2020), " Surface-Modified Titanium Dioxide Nanofibers with Gold Nanoparticles for Enhanced Photoelectrochemical Water Splitting", Catalysts, Vol.10(261); doi:10.3390/catal10020261 [3] Van Nghia Nguyen, Manh Son Nguyen, Minh Thuy Doan, Nhat Hieu Hoang (2019), "Fabrication of Electrode TiO2 Nanofibers for Hydrogen Generation from Photoelectrochemical Water Splitting", Journal of Nanoscience and Nanoengineering, Vol.5(1), pp 1-6 [4] Van Nghia Nguyen; Manh Son Nguyen and Minh Thuy Doan (2020), "Fabrication CdS/Au/TiO2 sandwich nanofibers for enhanced photoelectrochemical water-splitting efficiency", Hue University Journal of Science: Natural science, Vol.129(1B), pp 15-23 [5] Nguyen Van Nghia; Hoang Nhat Hieu; Nguyen Minh Vuong; Doan Minh Thuy, "Photocatalytic Activity of TiO2 Nanofiber Prepared By Electrospinning Method", Proceedings of IWAMSN 2016, pp 170 - 174 [6] Nguyen Van Nghia; Hoang Nhat Hieu; Nguyen Minh Vuong; Doan Minh Thuy, "Water-separating photoelectrochemical properties of nano-fiber TiO2/CdS electrodes", Proceedings of the SPMS 2017 conference, p 686-689 [7] N V Nghia; N T T Huyen; N T H Trang; N M Vuong; D M Thuy, H N Hieu and L T N Loan, "A facile method of TiO2 nanofiber surface modification by Au nanoclusters for enhanced photoelectrochemical water splitting performance", Proceedings of IWAMSN 2018, pp 399 - 403 [8] Nghia Nguyen Van; Dai Nguyen Xuan; Khanh Nguyen Quang; Vuong Nguyen Minh; Thuy Doan Minh and Hieu Hoang Nhat, "Optimization TiO2 nanofibers electrode for hydrogen generation from photoelectrochemical water splitting", Proceedings of IWAMSN 2018, pp 334 - 338 [9] Nguyen Van Nghia, Hoang Nhat Hieu, Nguyen Duc Toan, Nguyen Phi Hung, Doan Minh Thuy (2017), "Photocatalytic properties and activity of ZnO materials made by electrospinning method", Scientific Journal and Technology of Hue University of Science, volume (No 1), pp 47-54 [2] H N Hieu, N V Nghia, N M Vuong and H Van Bui (2020), " Omnidirectional Au embedded ZnO/CdS core/shell nanorods for enhanced photoelectrochemical water-splitting efficiency", Chem Commu., Vol.56, pp 3975-3978