Study On The Preparation And The Photocatalytic Property Of LaFeO₃ Perovskite Oxides

LaFeO₃ perovskite(ABO₃) composite oxide is a new type of inorganic non-metallic materials with wide range of special physical and chemical properties, recent studies show that they have significant promise in the field of environment problem.In our present work,LaFeO₃ catalysts were prepared by citric acid complexation,infrared-assisted sol-gel,citric acid-ethyleneglycol complexation and coprecipitation methods,respectively,to explore the effects of preparation methods on structure and performance of LaFeO₃ catalyst.The samples were characterized by X-ray diffraction,UV-visible diffuse reflectance spectrum,photoluminescence spectrum,scanning electron microscopy and N₂-adsorption.The photocatalytic activities of different catalysts were investigated by utilizing rhodamine B as degradation agent under visible light irradiation.The results show that the sample prepared by coprecipitation method exhibits the highest activity and has the largest crystallite size,and after reaction for 140 min,53.6%of rhodamine B is decolored; while for catalyst prepared by the citric acid complexation,the decoloration ratio is only 9.0%,though the latter has a higher surface area and smaller crystallite size than the former.The results suggest that smaller crystallite size and higher surface area are not always favorable to photocatalytic activity of a catalyst,other factors,such as large crystallite size and regular morphology,also play a crucial role.To discuss the Preparation of catalysts detailedly,We have done a series of experiments.The results showed that,using 50%of excess precipitant and 400-800-6h calcined way we can get the sample more faster,cheaper and good reproducibility. solution pH value of the dispersion impact the suspended particles,which relate to the efficiency of photocatalytic degradation.The results show that the isoelectric point of the sample prepared by coprecipitation method is pH=4.2.For negatively charged molecules dye,the pH value of the the dye solution was adjusted to pH＜4.2.In this case,there is high degree of hydroxylation on the catalyst surface with positive charge, both of them are easy to attract.A large number of dye molecules were adsorbed on the catalyst surface.Under the light radiation,the dye molecules are adsorbed first and then completely degraded to CO₂ and H₂O,there was the higher catalytic efficiency.The visible-light photocatalytic activity of LaFeO₃ can be enhanced by simple treating in molten salt.The visible light photocatalytic activity is evaluated by measuring the decoloratation of acid red R aqueous solution.It can be seen that the photoactivity of catalysts was remarkably enhanced by the post-treatment of nitrate molten salts and all LaFeO₃ catalysts had much higher photoactivty than P25 TiO₂,which has higher activity under ultraviolet irradiation.The photoactivity of the samples obeys the following order:LaFeO₃-K＞LaFeO₃-Na＞LaFeO₃-Li＞LaFeO₃-K₀＞LaFeO₃＞P25.The catalyst LaFeO₃-K exhibited the highest activity of 0.061 min^-1 and after 60 min visible-light irradiation,98%Acid Red R was decolorized,whereas LaFeO₃ and P25 had a constant of 0.016min^-1 and 0.002 min^-1,respectively.The enhancement of the photocatalytic activity is attributed to surface modification of LaFeO₃ by treating in molten salt.