Prepration Of TiO₂Doped With Nonmetal Elements And The Study Of Photocatalytic Activities And Degradation Mechanism

Titaniium dioxide(TiO2) has been recognized as one of the most promising semiconductor photocatalysts in various fields for its long-term stability,high efficiency, nontoxicity, and low cost.However,TiO2has a large relatively band gap of3.2eV and can only be activated under the conditions with ultrovoilet irradiation when λ less than387.5nm; Moreover, the recombining rate of electron and hole in the semiconductor is high and the quantum efficiency is low.Therefore,how to extend the photoresposes of TiO2into the visible region and improve quantum efficiency of TiO2by modification have become a hotspot in photocatalysis research.This dissertation summarized the mechanism of TiO2photocatalysis techniques,the methods for preparing TiO2,the influencing factors of TiO2photocatalytic acivity and the preparation of modified titaniium dioxide,and review the study on development and application of visible light-activated TiO2photocatalysts in detail. The nonmetal ions doped photocatalysts were prepared via the method by using tetrabutyl titanate (Ti(OC4H9)4) as precursor, boric acid (H3BO3) and ammonia (NH3·H2O) as doping angents.The photocatalysts were characterized by X-ray diffraction(XRD)analysis, X-ray photoelectron spectroscopy(XPS) and UV-vis diffuse reflectance spectrophotometer(UV-Vis DRS) in order to study the influence of different dopant. The photocatalytic activity was evaluated with photocatalytic effects of methyl orange dye (MO) undervisible light and UV-visible light irradiation in order to study the effects of the calcinations temperature and the doping content. On the base of preparation techniques,we put attention into the degradation mechanism of organic pollutants of TiO2doped by nonmetal.The results were summarized as follows:(1) The boron doped TiO2photocatalysts were prepared via the sol-gel method by using tetrabutyl titanate (Ti(OC4H9)4) as precursor, boric acid (H3BO3)) as doping angent. The photocatalytic activity of as-prepared B-doped TiO2powders in the ultraviolet light was improved obviously.When the molar ratio of B:Ti was5%, the calcination temperature was400℃,the degradation of MO were60%under UV light irritation2h.However, The B doped TiO2samples have not significanr photocatakytic visible light activity. When the molar ratio of B:Ti was10%, the calcination temperature was400℃,the degradation of MO were34%under UV light irritation8h. (2) The boron and ammonia co-doped TiO2photocatalysts were prepared via the sol-gel method by using tetrabutyl titanate (Ti(OC4H9)4) as precursor, boric acid (H3BO3) and ammonia (NH3·H2O) as doping angents. When the molar ratio of B:Ti was10%, the calcinations temperature was450℃,the degradation of MO were61%and73%under visibile light irritation8h and UV light irritation2h respectively.. The results showed that the synergistic effect of B and N enhances the photocatalytic activities of codoped TiO2.(3) Degradation mechanism:1)B or(and) N-doped can associated with the formation of B-O-Ti,Ti-O-N,Ti-O-B-N and O-Ti-B-N,both leading to locatized states in the TiO2band gap.These localized states can extend the photoresposes of TiO2.2)B2O3,Ti-O-B-N and O-Ti-B-N can facilitate the separation and transfer of charge carriers. The two aspects improve the photocatalytic activity.