Preparation And Photocatalytic Degradation Phthalate Esters Of Polyoxometalates-Titania Porous Materials

In this thesis, we focus on the vital scientific difficult problem in the TiO2 photocatalytic technology such as the lower quantum efficiency, the lower activity under visible light, and difficult separation of powder catalyst from catalysed system. H3PW12O40/TiO2 and H3PW12O40/Ag-TiO2 were prepared and well-characterized, and their catalytic activities were systematically studied. The photocatalytic degradates mechanism of DEP and DBP were studied.New and efficient heterogeneous photocatalytic material, H3PW12O40/TiO2 with anatase crystalline phase, was prepared by combination of the methods of sol-gel and hydrothermal treatment at a lower temperature. Composition, structure, optical absorption property, physicochemical properties, and surface morphology of the composite were characterized by test technologies. Under simulated-sunlight irradiation, we studied the photocatalysic activities of H3PW12O/TiO2 for phthalate acid esters (PAEs) in aqua, and tested the effects of the pH value of solution on photocatalysic degration efficiency. Research results indicated that the starting Keggin structure of H3PW12O40 in the as-synthesized composites was still remained intactly after immobilization of the unit into the TiO2 network. Hydrogen bonding and chemical interactions between the unit and the anatase network existed in the composite. Moreover, the BET area of this material with dual-pore structures, micro-and meso-porosity, was increased obviously. Under simulated-sunlight the photocatalytic activity of the composites was evaluated by degradation of aqueous phthalate esters. The results showed that the photocatalytic activity of H3PW12O40/TiO2 was higher than that of pure TiO2, In addition, the photocatalytic activity of H3PW12O40/TiO2 monotonically increased along of loadings H3PW12O40 from 0 to 19.8%. Under the simulated-sunlight irradiation, the degradation efficiency of H3PW12O40/TiO2-19.8 for PAEs was determined in sequence DBP>DEP>DMP. It is also observed that pH variations influence the photocatalytic activity of the H3PW12O40/TiO2 composite, and neuter or alkaline conditions can promote the photocatalytic degradation of H3PW12O40/TiO2 for DEP.HPLC-MS and IC were used to detect and analysis the intermediates generated during the DEP and DBP degradation process. Tests of TOC also were carried out. Based on the intermediates identified in the reaction system, the photocatalytic degradation pathway of DEP and DBP were put forward. DEP can realize mineralization by three path, and the main products among the degradation process is consist of hydroxyl DEP, phthalic acid,2-hydroxyl benzoic acid, maleic anhydride and phenol, etc. DBP can realize mineralization by four path, and the main products among the degradation process is consist of hydroxyl DBP, hydroxyl phthalic acid, butyl acrylate acid, etc. Both the intermediates generate formate, succinic acid, and acetic acid, etc. through degradation, further CO2 and H2O.H3PW12O40/Ag-TiO2 nanocomposites, H3PW12O40 and Ag co-doped TiO2 nanocomposites with enhanced photocatalytic activity, was successfully prepared by combination of the methods of sol-gel and hydrothermal treatment at a lower temperature. Composition, structure, optical absorption property, physicochemical properties, and surface morphology of the composite were characterized by test technologies. It was obsreved that the H3PW12O40/Ag-TiO2 show anatase crystalline phase, and metallic Ag particles well distributed on the surface. Also it was shown that the maximum absorption of composite material after introduction of Ag ion occured a obvious small shift toward longer wavelengths, and appeared not only at 200-380 nm but also at 400-600 nm; Compared with pure TiO2, the BET area of composite material with dual-pore structures, micro-and meso-porosity (0.45 nm and 4.2 nm) was slightly decreased. The photocatalysic activities of H3PW12O40/Ag-TiO2 was tested by degradation of aqueous DEP and Sulfamethoxazole (SMZ) under simulated-sunlight irradiation. The results showed that the photocatalytic activity of H3PW12O40/TiO2 was higher than that of pure TiO2. The photocatalytic activity of different composites are arranged as follows:H3PW12O40/Ag-TiO2>Ag/TiO2>H3PW12O40/TiO2>TiO2. The reasons of this enhanced photocatalytic activity were discussed logically.