| Environment and energy issues are still the bottle neck for the continual development of human being. Semiconductor photocatalysis is an advanced technology which can convert solar energy into chemical energy. Pollutants can be removed and hydrogen can be obtained via water-splitting in the presence of converted chemical energy. The focus of semiconductor photocatalysis is to develop visible light induced photocatalysts with high catalytic activity. Visible-light-induced activity is the base of exploiting solar energy. High efficiency makes its application to be possible. In this paper, we focus on developing visible light drived photocatalysts with high catalytic activity and exploring the controllable mechanism of photocatalytic activity by using material characterization and density functional theory (DFT).TiO2 and LaBO3 (B= Cr, Mn, Fe, Co and Ni) powders with perovskite structure have been prepared by sol-gel technique. The photocatalytic activity of the as-prepared samples has been evaluated by degradation of methyl orange solution under UV-light and Vis-Light irradiation. The results showed that the photocatalytic activities increased with the order:TiO2, LaNiO3 and LaCoO3 under UV light irradiation. Compared investigation of photocatalytic activities between the as-synthesized powders under visible light irradiation showed that the LaFeO3, LaCoO3 and LaNiO3 were visible-light-driven photocatalyst. Based on the DFT, the energy band structure of LaBO3 series oxidation has been calculated by CASTEP code. The results showed that LaCrO3 own large band gap and high discreteness valence band (VB) and conduction band (CB). DFT calculations of LaMnO3 showed the metal character, resulting high recombination of photo induced carrier. The splitting of CB for LaFeO3 and LaCoO3 degrade the transportation of electron. LaNiO3 own high discreteness VB and CB. The band potentials of LaNiO3 shift downwards, which indicates that photogenerated holes have stronger oxidative power. In the series oxidation, LaCoO3 and LaNiO3 stabilize in the rhombohedral structure. Compared with the LaMnO3, LaFeO3 and LaCrO3, which stabilize in orthorhombic structure, the BO6 octahedra own higher distortion. Because the internal dipole moments promote the charge separation, the LaCoO3 and LaNiO3 exhibited higher photocatalytic activity. The band structure, crystal structure and the degradation of MO solution indicate that LaNiO3 is the best efficient visible light induced photocatalyst in the series perovskite oxidation.The preparation, characterization and photocatalytic activity of LaNiO3 have been investigated. The results showed that the formation temperature of LaNiO3 phase is 600℃. The sample synthesized by solution combustion synthesis (SCS) and subsequent calcined at 600℃for 4 h own highest photocatalytic activity. The degradation percentage of methyl orange solution (MO,10 mg/L) after 5 h on the sample is 74.9%. The photocatalyst exhibits good stability and precipitation performance in aqueous solution. The XPS spectra of LaNiO3 showed that there are oxygen vacancies existing in the LaNiO3 lattice, which can promote the segregation of electron/hole pairs. In addition, the adsorption oxygen which induced by the oxygen vacancy can be transformed to high-activity substance such as HO·, HO2·,etc under light irradiation. The MO molecule can be degradated into CO2 and H2O in the presence of holes and such high-activity substance under visible light irradiation.The perovskite LaNi1-xTixO3 powder has been prepared by SCS. The synthesis process and structure characterization have been investigated. The results showed that the synthesis process of Ti-doped sample is more persistent and less acute exothermal than undoped sample. Crystalline LaNi1-xTixO3 with fined structure can be prepared after calcined at 650℃for 4 h. MO degradation test showed that the photocatalytic activity of Ti-doped samples first increased and then decreased with the Ti contents. The highest efficiency is observed when the sample calcined at 650℃for 4 h with 3 wt% Ti content. The degradation percentage of MO solution (10 mg/L) on the sample is as high as 92.2% after 5 h visible light irradiation. Combined with the results of PL and XPS spectra, the origin of enhanced performance of the Ti-doped oxidation is the effective separation of charge carriers. The kinetic study on the MO concentration (Co) and the addition concentration of LaNi0.97Ti0.03O3 (C') have been performed. The results showed that, for 2 g/L LaNi0.97Ti0.03O3, the kinetic equation is a first-order reaction when C0=5 mg/L and zero-order reaction when C0>10 mg/L. The rate constant k decreased with the increasing of Co. For 10 mg/L MO solution, the kinetic equation is zero-order reaction when C'> 2g/L.The preparation, characterization and photocatalytic performance of LaNiO3 modified TiO2 composite have been investigated. The TiO2 is raw material, and LaNiO3-TiO2 composite have been prepared by using sol-gel technique. The crystal, morphology and optical properties have been characterized by DTA-TG, XRD, TEM, DRS and BET. The results showed that the crystal LaNiO3-TiO2 composite can be synthesized by sol-gel technique at 700℃. TEM showed that nano-size LaNiO3 particles dispersed on the surface of TiO2 particles. The surface area of the composites is large than TiO2. MO degradation test showed that the MO solution can be degradated in the presence of LaNiO3-TiO2 composites under visible light irradiation. The highest efficiency sample can be obtained when the LaNiO3 content is 10 wt%. The degradation of MO reaches to 55% after 6 h visible light irradiation. Compared with LaNiO3 (about 10%), the photocatalytic activity increased drasticly. Based on the DFT calculation, The CB and VB of LaNiO3 and TiO2 have been estimated by absoluted electronegativity. The origin of enhanced performance of the composite is the effective separation of electron/hole pairs caused by the P-N heterounction electric field and the electric potential difference between the CB of P-type LaNiO3 and N-type TiO2.
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