Research On Preparation And Optical Property Of La2CuO4Powders Synthesised By Sol-gel Process

La2CuO4is a A2BO4-type mixed oxide with perovskite-like structure, which is composed of alternating layers of ABO3and the AO along c-axis with the ratio of1:1. It is a p-type anti-ferromagnetic semiconductor, and also the matrix material of La2-xMxCuO4-δ (M=Ba, Sr, Ca) and La2CuO4+δ superconductor. Due to the mechanism of high-temperature superconductor has not been fully revealed, the La2CuO4, which has simple structure and chemical composition, wide doping range, is an ideal material to study it and get more and more regards. In addition, with good catalytic activity and thermal stability, it can replace the precious metals as a cheap catalyst, which will achieve natural gas efficient combustion and ultra-low emission process. Furthermore, La2Cu04has a good application prospect in sensor, automobile exhaust catalytic purification, the nitrogen oxide catalytic eliminate, as well as intermediate temperature solid oxide fuel cell.The undoped and doped La2CuO4act as electrode material for the photocatalytic splitting of water, until now, the studies on La2CuO4and La2-xMxCuO4-δ are more in superconductivity and catalytic performance for harmful gas, few literature had concerned about the photocatalytic splitting of water.So it is of great significance to research the optical property and band gap of undoped and doped La2CuO4for the preparation of green non-pollution hydrogen energy.In this paper, the La2Cu04crystallites were prepared in a relatively low temperature using inorganic salt sol-gel preparation technology. The effects of the preparation technical parameters, the reaction mechanism and the reaction kinetics on the product and the optical property in the UV-Vis-NIR range of La2CuO4and La2-xMxCuO4-δ were studied.Pure La2CuO4nano-crystallites can be prepared after calcining at600℃using analytical grade La(NO3)3·nH2O and Cu(NO3)2·3H2O as the raw materials, distilled water as solvent and citric acid as complexing agent. The influence of process factors such as the calcination temperature, copper source and the addition amount of citric acid on the preparation of La2CuO4crystallites was systematic studied. The products were characterized by X-ray diffraction analysis (XRD), thermogravimetry-differential scanning calorimetry (TG-DSC), field emission scanning electron Microscope (FESEM), infrared spectroscopy (IR), microscopy transmission electron microscopy (TEM) and UV-Vis-NIR spectroscopy (UV-Vis-NIR). The results show that when the calcination temperature is700℃(for2h), the grain distributes uniformly and the size is about100-120nm. With the rise of calcination temperature, the increase in grain size is obvious, and the band gap decreases gradually from600℃(1.37eV) to800℃(1.28eV). Based on the analysis of reactive material and products, the best reactant to synthesize La2CuO4is copper nitrate among the copper sources of copper sulfate, copper chloride and copper nitrate. Different addition amount of citric acid has different affects on the purity and particle size of product and the synthetic activation energy. According to Arrhenius equation, it can be calculated that the synthetic activation energy decreases with the increases of the addition amount of citric acid.The effects of the doping of alkaline earth elements and the calcium ion concentration on the compositon and optical property of product was studied by La-site doping (A-site doping) in La2CuO4. The results show that single phase La2-xMxCuO4-δ (M=Ca, Sr, Ba) crystallites can be obtained after calcining at700℃for2h. The red shift phenomenon of the absorption edge occurs with the increase radius of doping ions Ca2+, Sr2+and Ba2+, the band gap is1.43eV,1.30eV and1.28eV respectively. With the increase of Ca2+content, the band gap of La2-xCaxCuO4-δ first increases and then decreases. The band gap is1.35eV,1.38eV,1.43eV,1.46eV,1.13eV and1.10eV for x value is0.05,0.08,0.10,0.12,0.15and0.20, respectively.