Synthesis And Photocatalytic Activity Of La ^{3 +} TiO 2 Powders

As a kind of important inorganic functional materials, nano titanium dioxide has been used in many fields, such as otocatalytic water splitting for H2 production, eliminate water pollution, purify the air, UV coating and so on. Metal ion doping is a simple and effective method to improve the photocatalytic performance of TiO2. Different types of metal ions with different doping principle and different ways of action. In this paper, a kind of transition metal ions Cr3+ and a kind of rare earth metal ions La3+ were respectively doped into titanium dioxide, and the titanium dioxide photocatalyst was prepared by polymer network gel method. The process parameters of preparation of TiO2 powder by polymer network gel method were studied, and studied the factors influencing the body structure of titanium dioxide powder with all kinds of ways, such as orthogonal test, infrared spectrum, BET, XRD and UV-VIS spectroscopy. The change regulatio was also clear. The photocatalytic effect of TiO2 was evaluated by the degradation of methyl orange, The factors influencing the photocatalysis performance of doped powders were also discussed. The following conclusions were obtained:The orthogonal experimental results showed that the optimum formula of raw material was monomer dosage 7%, the proportion of monomer crosslinking agent was 3:1, initiator dosage was 6%, and the catalyst dosage was 6%. Infrared spectrum analysis showed that the C=C double bond has been opened and connected together when the gel has been polymerized, free radical polymerization reaction has been completely finished. The dry gel has begun to break down at 200℃, organic matter has serious carbonation at 250 ℃, when the temperature reached 400 ℃, carbon has been burned out and the titanium dioxide has been generated. The orthogonal experiment determined the best combination experiments of Cr3+ doped TiO2 with Cr3+ doped amount is 1.5mol%, calcination temperature is 600 ℃, holding time is 30min. Cr3+ ions doping can significantly improve the TiO2 visible light absorption ability; Cr3+ ion pair can accelerate transformation, while inhibiting the growth of crystals. Improve the powder specific surface area; with the increase of temperature. Cr3+-doped TiO2 crystal type into the rutile, crystal growth, specific surface area is reduced. The orthogonal experiment determined the best combination experiments of La3+-doped TiO2 with La3+ doped amount is 0.5mol%, calcination temperature is 800℃, holding time is 30min; La3+ incorporation did not effectively improve the ability of visible light absorption of TiO2; La3+ ions inhibits the phase transformation, hinder the crystal growth, improves the powder specific surface area; with the increase of temperature, La3* doped TiO2 crystal type into the rutile, crystal growth, specific surface area is reduced.The experiment of methyl orange photocatalytic degradation by doped TiO2 showed that, TiO2 photocatalytic degradation of methyl orange is zero-order reaction, doping does not change the types of photocatalytic reaction; Cr3+ doping reduces the photocatalytic activity of TiO2 with the increase of Cr3+ concentration, the degradation efficiency gradually weak with the increase in Cr3+ doped titanium dioxide heat treatment temperature, La3+ions can improve the catalytic efficiency of titanium dioxide, ion doping amount exists an optimum value, low and high temperature is not conducive to improving the La3+ doped TiO2 photocatalytic efficiency and photocatalytic activity exist has an optimal temperature. Crystal type ratio, specific surface area, visible light absorption efficiency, the effect of the incorporation of ions on the carrier recombination are all affected the final photocatalytic effect of titanium dioxide. Cr3+ ions in solid solution doped into TiO2 lattice. La3+ elements was not be doped into the lattice of TiO2, but at the grain boundary and the surface of the titanium dioxide in the form of the second phase. The action mechanisms of the two ions were different, which result in the difference of the photocatalytic effect.