Study On Preparation, Characterization And Binary Synergistic Mechanism Of Nitrogen Doping And Oxygen Defective Tio2 Visible Photocatalyst

With the growing environmental problems, the photocatalytic oxidationtechnology based on TiO2, which can completely decompose most of organicpollutants, was one of the most potential green oxidation technologies. However,there are some important problems unsolved towards TiO2photocatalysis, such aslower utilization of solar energy (~3%) and low quantum efficiency ofphotocatalytic reaction (~4%), which seriously restrict the application ofphotocatalytic oxidation technology.To solve the two scientific problems, nitrogen-doped and oxygen-deficient TiO2,an efficient visible-light-driven photocatalyst, was prepared by using commercialTiO2-P25, hydrogen gas, ammonia gas and dicyandiamide as starting materials in thispaper. Characterization was carried out by using XRD, BET, XPS, ESR, UV-VisDRS and PL to investigate the properties of the as-prepared samples includingcrystallization phase, specific surface area, surface chemical state, oxygen-deficientspecies, optical absorption and separation of photogenerated carrier. Thephotocatalytic measurement was carried out by the degradation of gas-phase benzeneunder visible light irradiation (λ>400nm).The results show that the N-doped TiO2and oxygen-deficient TiO2, prepared at500℃in NH3or H2atmosphere, followed by postcalcination at400℃in O2atmosphere, exhibit obvious visible-light activity. After photocatalytic oxidation for5h, the conversion rates of benzene are42.0%and12.2%at steady state,simultaneously, the concentration of carbon dioxide are113ppmv and32ppmv,respectively. Compared with the N-doped TiO2-xand the oxgen-deficient TiO2, thephotocatalytic activity of the N-doped and oxgen-deficient TiO2is much higher.Under the similar conditions, the conversion rate of benzene and the yielded CO2are 66.0%and180ppmv, respectively. The photoactivity of the N-doped andoxgen-deficient TiO2is higher than the sum of the single-doped catalysts. Theefficient visible-light activity is originated from a synergistic effect of thesubstitutional N dopant and the oxygen vacancy in TiO2matrix. The effect ofpostcalcination on the N-doped and oxgen-deficient TiO2is found to be positive byremoving surface oxynitrides (i.e. Ti-N-O existed in bulk), reducing surface oxygenvacancy and facilitating the generation of oxygen radical (O2) on the catalyst,resulting in an enhanced separation efficiency of photoinduced carriers, improvedinterface transfer of photoinduced election and high visible-light activity towardbenzene degradation.Combined with results mentioned above, the synergistic effect of the N-dopedand oxgen-deficient TiO2active in gas-solid phase photocatalysis is studied. It ishopeful to reveal the nature of the interactions between the N-doped unit and theoxygen-deficient unit, the information of matched heterojunctions, the separation andtransfer of photoinduced carriers. The aim is to clarify the synergistic mechanism ofthe binary active centers, stimulated by visible light, in photocatalytic process. It alsoprovides a theoretical basis for the development of novel, efficient and stablephotocatalysts active in visible light.