Study On The Preparation And Visible-light Photocatalytic Properties Of Ti³⁺ Self-doped Nano TiO₂

The excellent chemical stability, nontoxicity, and photoactivity of titanium dioxide (TiO2)has attracted much attention for its potential use as a solid photocatalyst for environmentalpurification and split water for the production of hydrogen. However, a major drawback thatimpedes the practical applications of pristine TiO2-based photocatalytic oxidation is the factthat the large band gap of TiO2(anatase TiO2~3.2eV，rutile TiO2~3.0eV). As a consequence,only UV light can be utilized to generate electron-hole pairs and to initiate the photocatalyticoxidation process. An effective approach to tackle this challenge is to dope TiO2with heteroelements, which acts as electron donor or acceptor in the forbidden band of TiO2and inducesabsorption in the visible region. Recently, reduced TiO2(TiO2-x), which contains the Ti3+oroxygen vacancy, has emerged as an effective approach to introduce visible photoactivity. Thepresence of Ti3+in non-stochiometric TiO2-ximproves the wet stability, which is important forphotocatalysis and superhydrophilic effects.In order to further enhance the TiO2photocatalyst activeness in visible-light range，thisdissertation research the Ti3+self-doped nanometer TiO2as photocatalytic materials. Theenhanced photocatalytic activity of as-prepared photocatalysts was probed by degradationreaction of methylene blue (MB) solution under visible-light irradiation and photocatalytic H2production from aqueous methanol solution. Specific work focused on the following aspects:1. Ti3+self-doped TiO2-xnanoparticles were synthesized by mild hydrothermal treatment ofTiH2in H2O2aqueous solution. The structure, crystallinity, morphology, and otherphysical-chemical properties of the samples were characterized by X-ray diffraction (XRD),transmission electron microscopy (TEM), high-resolution transmission electron microcopy(HRTEM), X-ray photoelectron spectroscopy (XPS). Methylene blue (MB) solutions wereused as model wastewater to evaluate the adsorption and photocatalytic activity of thesamples under natural sunlight and visible ligh. The formation mechanism of the nanoporouscomposites was extensively discussed. As the results show, under visible light irradiation, thesamples exhibit higher photocatalytic activity for hydrogen evolution and photooxidation ofmethylene blue than that of the commercial P25TiO2nanoparticles. The sample obtained at160C for27h showed9-fold enhancement for the visible light decomposition of methyleneblue and12.5times higher for H2production in comparison to P25TiO2. The samples alsoshowed an excellent cyclic stability of the photocatalytic activity. 2. Ti3+self-doped TiO2-xnanoparticles were synthesized by calcined treatment. Thestructure, crystallinity, morphology, and other physical-chemical properties of the sampleswere characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM),high-resolution transmission electron microcopy (HRTEM), X-ray photoelectronspectroscopy (XPS). Methylene blue (MB) solutions were used as model wastewater toevaluate the adsorption and photocatalytic activity of the samples under natural sunlight andvisible ligh. The formation mechanism of the nanoporous composites was extensivelydiscussed. As the results show, under visible light irradiation, the samples exhibit higherphotocatalytic activity for hydrogen evolution and photooxidation of methylene blue than thatof the commercial P25TiO2nanoparticles. The sample under calcined showed enhancementfor the visible light decomposition of methylene blue and H2production in comparison to P25TiO2. The samples also showed an excellent cyclic stability of the photocatalytic activity.3. Ti3+self-doped TiO2-xnanoparticles were synthesized by different precursor gels undermild hydrothermal treatment. The structure, crystallinity, morphology, and otherphysical-chemical properties of the samples are characterized by X-ray diffraction (XRD),transmission electron microscopy (TEM), high-resolution transmission electron microcopy(HRTEM), X-ray photoelectron spectroscopy (XPS). Methylene blue (MB) solutions wereused as model wastewater to evaluate the adsorption and photocatalytic activity of thesamples under natural sunlight and visible ligh. The formation mechanism of the nanoporouscomposites which prepared by yellow precursor gel was extensively discussed. As the resultsshow, TiH2content resulted in different status between precursor gels, which has importantinfluence on the material structure, size and type. The samples also showed an excellentcyclic stability of the photocatalytic activity.