| Titanium dioxide has numerous advantages, but the low quantum yield and lowefficiency in solar energy utilization restrict its applications. Therefore, improving thereactivity and extending its absorption into visible region become the focus ofTiO2-based photocatalytic materials in recent years. In this article, we prepared TiO2with different microscopic structures and single crystals with a specific exposedcrystal face through the desigh of crystal faces and doping halide anions (mainlychoridion). It was found that surface chlorination can improve greatly thephotocatalytic activity of TiO2-based materials in both UV and visible regions.Meanwhile the modification process prouduced oxygen vacancies rendering TiO2withprominent visible light activity.In addition, we studied the photocatalytic behaviors of TiO2with different facesfor typicl gas phase probe molecules, and discussed the ralationship between faceenergy and photocatalytic activity. For new {001}TiO2single crystal, heterostructuresdesign and anionic doping (Cl and F) can expand further its absorption into visibleregion. This paper demonstrated a general and versatile route for modifyingTiO2-based photocatalysts through surface chlorination, making the chlorinatedphotocatalysts work efficiently in both UV and visible region. Especially, it possessedhigh minerlization effciency for aromatic molecules. The main conculsions arepresented as follows:(1) Using a facile hydrothermal route for sysnthesis of sheet-like anatase TiO2with the highly reactive {001}facets. Three composites were obtained by in-situ growAu, Cu2O, In2O3on {001}TiO2. We also prepared two other TiO2crystals withexposed {100} and {101}facets respectively. Gas phase degradation experimentsshowed that surface energy of different facet can be one of the important factorsinfluencing the photocatalytic activity of TiO2.(2) The photocatalytic activities of TiO2, TiO2-XNX, LaVO4/TiO2and BiOBr/TiO2before and after chlorination were investigated in UV and visible light regions. The results showed that the surface chlorinated photocatalysts exhibited an remarkablyincreased efficiency about several times for degradation and minerlization of olefin,linear alkanes and aromatic molecules. Surface chlorination process prouducedoxygen vacancies, rendering TiO2with excelent visible light activity and adsorptionability for molecular oxygen.(3) The corresponding reaction mechanism was discussed. First, the hydroxylgroups on the surface of TiO2-based photocatalysts were replaced by Cl, formingTi-Cl bond. Under suitable wavelength light excitation, the surface-bond chloridegroups could be converted to chlorine radicals by photogenerated holes, and attackorganic substances having weak bound branch hydrogen and effectively destruct theminto inorganic small molecules by a chain transfer oxidation which is faster than thecorresponding reaction with hydroxyl radicals. Additionally, the H2O was one of thefinal products in the photocatalytic reaction and could be adsorbed and converted tosurface hydroxyl groups by dissociating on acidic sites. As a result, partial HClmolecules generated from the chain transfer reaction were re-chemisorbed andcirculated into the reaction again, resulting in a good stability. The acidic sites on thesurface of solid catalysts may be one factor accelerating the photocatalytic reaction.From the comparision experiment, it was confirmed that the above enhancedreactivity primarily originated from the anions (Cl-). Under irradiation with light ofdiffernet wavelengths, the reaction mechanism is differnent due to the differences inthe numbers of photogenerated electron-hole pairs. |
PDF Full Text Request