Comparative Study On The Preparation Processes Of Sm-N-P-TiO₂ Nanocomposite Photocatalyst

In order to improve solar energy utilization and efficiency of quantization nano-TiO2, comparative study of sol-hydrothermal and microwave-assisted hydrothermal preparation technology of Sm-N-P-tridoping nano-TiO2 was carried out, establishing new preparation process of Sm-N-P-TiO2(SNPTO)nano-composite photocatalyst.High-performance anatase phase Sm-N-P-TiO2 nano photocatalyst was prepared with sol-hydrothermal technology, using high content of titanium and economic TiCl4 as precursors, without organic solvent and subsequent high temperature calcination process.The optimal technological conditions was that hydrothermal temperature was 160 ℃, Sm doping amount was 0.1 wt%, P doping amount was 10 wt%, and N doping amount was 8.76 wt%. The physicochemical properties of as-prepared samples were characterized by X-ray diffraction, Transmission electron microscopy, N2 adsorption-desorption isotherm, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV-vis absorbance spectroscopy, Photoluminescence spectroscopy. Results showed that compared with SNPTO nano photocatalyst prepared by the sol-solvothermal technology, SNPTO prepared by sol-hydrothermal method exhibits a higher specific surface area(199.84 m2g-1)and a bigger pore volume(0.291 cm3g-1). Sm or N doping could narrow band gap of TiO2, effectively restraining the recombination of photogenerated electrons and holes. P doping could inhibit phase transformation from anatase to rutile phase, which played a key role in controling crystal growth, steadying surfacial structure properties of the sample and increasing the surface hydroxyl content. The photocatalytic activities of the samples were evaluated by degradation of 4-chlorophenol(4-CP)under simulated sunlight irradiation. SNPTO showed the highest photocatalytic activity(Kapp=0.032 min-1), which was 3.85 times of P25 TiO2(Kapp=0.012 min-1). Sm-N-P tridoping enhanced UV-light absorption ability, inhibited the recombination of the photogenerated carrier, increased the surface hydroxyl content, and improved the surfacial structure properties. As a result, SNPTO had a high photocatalytic performance due to cooperative effects of all above factors.Aiming at the problems in traditional hydrothermal process including large energy consumption and time-consuming, the influences of the microwave hydrothermal temperature and hydrothermal time on the photocatalytic performances of SNPTO using economic and environmental microwave-assisted hydrothermal technology were investigated, which established a new preparation technology of Sm-N-P tridoped nano-TiO2. The optimal technological conditions was that when Sm doping amount was 0.1 wt%, P doping amount was 10 wt%, and N doping amount was 8.76 wt%, hydrothermal temperature and time were 195 ℃ and 15 min. The physicochemical properties of as-prepared samples were characterized by X-ray diffraction, Transmission electron microscopy, N2 adsorption-desorption isotherm, UV-vis absorbance spectroscopy techniques. Results indicated that the SNPTO prepared using microwave-assisted hydrothermal method presented a larger specific surface area(214 m2g-1), a better dispersibility and a higher crystallization degree compared with that by sol-hydrothermal method.Among all samples, the photocatalytic activities of SNPTO(Kapp=0.0307 min-1) towards the degradation of 4-chlorophenol(4-CP)under simulated sunlight irradiation was best, which was 2.62 times of the commercial P25TiO2(Kapp=0.0117 min-1). Sm-N-P tridoping led to enhanced ultraviolet absorption ability, reduced photogenerated carrier recombination, and increased surface hydroxyl radicals, as well improved surfacial structure properties, thus improving the photocatalytic activity of the sample. The obtained SNPTO improved the practical application performance of nano-TiO2 photocatalyst.