Study On Preparation Of LaBO₃ (B=Fe, Mn, Co) And Their Photocatalytic Activity For TNT Wastewater

Nanostructure perovskite-type LaFeO₃, LaMnO₃ , LaCoO₃ and oxideα-Fe2O₃ were successfully synthesized by Stearic Acid Gel Combustion, where the stearic acid was used as chelating agent and fuel. The obtained samples were characterized by FTIR, XRD, SEM and BET techniques and their photocatalytic activities for TNT degradation were studied.The experimental results showed that LaFeO₃ andα-Fe2O₃ were directly obtained by combustion of stearic acid gel, but LaMnO₃ and LaCoO₃ were obtained by additio- nal calcinations treatment. The particle sizes of LaFeO₃, LaCoO₃ andα-Fe2O₃ are about 50nm, 40nm and 30nm, respectively, and their specific surface areas are 48.34m2/g, 22.23m2 /g and 63.4m2/g, respectively, which are higher than that recorded in literatures prepared by citrate acid or chemical coprecipitation method. But the particle diameter of LaMnO₃ is 0.5μm that is lager than those of LaFeO₃, LaCoO₃ andα-Fe2O₃.In addition, taking LaFeO₃, LaMnO₃ and LaCoO₃ as catalysts, we obtained the optimal reaction conditions. Adsorptive equilibrium time is about 30 minutes and the amounts of all used catalysts'amounts are 0.001mol. Compared with the other perovskite-type oxides (i.e. LaMnO₃ and LaCoO₃), LaFeO₃ has the best photocatalytic activity which was further proved by UV-Vis DRS spectrogram.For LaFeO₃ catalyst, a variety of the factors that influenced in TNT degradation progress were investigated. Of all the initial concentrations of TNT, 20mg/L TNT could be rapidly degradaed in the alkaline conditions, the optimal reaction time was 60 minutes, and the photocatalytic reaction could be expressed as the first order kinetics. After reusing, LaFeO₃ still had good photocatalytic activity.A comparision of LaFeO₃ withα-Fe2O₃ showed that the oxygen and hydroxyl absorbed were probably the main active sites of LaFeO3 catalyst. Through the UV spectrogram, the possible pathway of TNT degradation was disscussed. First, methyl group was removed from TNT, then the nitro group which was difficult to oxide was reduced to amine group, finally, the aromatic compounds degraded into small organic molecules.