چكيده به لاتين
Photocatalytic conversion of CO2 is an efficient and advanced technology to photoreduction of CO2 into hydrocarbons such as CH4 or CH3OH, etc. However, various catalysts were used in this process. In this study, the TiO2 was selected as the primary photocatalyst due to its chemical stability, low coast, non-toxicity and availability. However, TiO2 comes with its own limitations including weak CO2 adsorption and wide bandgap. Thus, various techniques like coupling with other semiconductors, doping metals and non-metals, and surface modification have been employed to reduce the bandgap of TiO2, limit the electron-hole recombination rate and thus enhance the photoactivity in visible light region. The first part of this research was related to the study of series of Bi2WO6/TiO2 composite photocatalysts with different ratios of Bi2WO6 nanosheets to TiO2 nanobelts (1, ½, ⅓ and ¼) synthesized by hydrothermal method and evaluated for CO2 photoreduction. The results showed that loading Bi2WO6 nanosheets on TiO2 nanobelts leads to formation a heterojunction, which enhances the photocatalytic visible light performance by decreasing the recombination rate of photoinduced electron-hole pairs. The maximum CH4 production of 18.95 μmol/gcat in 8 h has been reported for composite with Bi2WO6/TiO₂ ratio of ½, which is 3 times higher than that of bulk Bi2WO6 and pure TiO2. In second part of this investigation, a series of BiVO4/TiO2 photocatalysts with different molar ratios of BiVO4 to TiO2 (1, ½, ⅓ and ¼) was constructed, and evaluated for photocatalytic CO2 reduction. The results exhibit that fabrication a heterojunction structure between BiVO4 and TiO2 semiconductors can improve optical properties and electron-holes separation efficiency. The CO2 absorption capacity of TiO2 increases by loading BiVO4 on TiO2. The composite photocatalysts exhibit much higher photocatalytic performance than pure BiVO4 and TiO2 photocatalysts due to formation heterojunction structure between BiVO4 nanosheets and TiO2 nanobelts. BVT2 sample with ½ molar ratio of BiVO4 to TiO2 shows maximum CH4 production (28 µmol/g) in 8 h, which is about 7 times higher than pure TiO2. The third part of this study is dedicated to study of Bi2MoO6/ TiO2 composite with different molar ratios of Bi2MoO6 to TiO2 (1, 1/2, 1/3, 1/4, 1/5 and 1/6), which show enhanced photocatalytic activity comparison to pure Bi2MoO6 and TiO2. In compared to bulk Bi2MoO6 and TiO2, the formation of a heterojunction between Bi2MoO6 and TiO2 leads to enhanced CO2 adsorption. Bi2MoO6/TiO2 composite with ¼ molar ratio had the best performance in 8 h (36.4 µmol/gcat), which was about 10 and 3 times higher than TiO2 and Bi2MoO6 photocatalysts, respectively. In forth part of this study, the influence of the loading different co-catalyst on Bi2MoO6/TiO2 composite was investigated. M-Bi2MoO6/TiO4 samples with different cocatalysts (M: Ni, Ce, Co, Mo, Cu) were prepared by a deposition-ultrasound assistant method. The catalyst with different cocatalysts shows different photocatalytic performances for CO2 reduction. The highest CH4 production was related in Ni-BT sample resulting from the good dispersion of cocatalyst on the support surface, enhanced visible light absorption efficiency, efficient charge migration, and low recombination rate of electron-holes. Furthermore, the effect of platin and copper additions to Bi2MoO6/TiO4 catalyst using the chemical reduction method was investigated. The surface of optimum Bi2MoO6/TiO2 composite was decorated with cooper and/or platinum co-catalyst nanoparticles. Under UV-visible light irradiation, Pt-Cu@BMT4 sample produced highest methane (83.6 µmol/gcat) during CO2 photoreduction. At the last part of study, the effect of nickel concentration in TiO2 photocatalytic properties and effect of nitrogen-nickel co-doping in TiO2 structure was investigated to methane production. Furthermore, effect of construction heterojunction structure between modified TiO2 and Bi2MoO6 semiconductors was investigated in photocatalytic performance. The BM/Ni-N-T photocatalyst exhibits excellent photocatalytic performance for CO2 conversion (67.9 µmol/g), which is several times higher than that of pure TiO2 (3.2 µmol/g). The enhanced composite photocatalytic performance is mainly attributed to nitrogen and nickel co-doping in TiO2 and heterojunction structure, which improve light absorption capacity and charge carrier separation efficiency. The novel Bi2MoO6/W-N-TiO2 catalyst was synthesized and exchibited multiple advantages, such as the combination of incorporation of tungsten and nitrogen into TiO2 lattice and the formation of a heterojunction structure, which can enhance the optical properties and are favorable for photocatalytic conversion of CO2.
