Simultaneous Oxidation of p-Chlorophenol and Reduction of Cr(VI) on Fluorinated Anatase TiO2 Nanosheets with Dominant {001} Facets under Visible Irradiation

A series of fluorinated anatase TiO2 nanosheets with dominant {001} facets were synthesized to oxidize p-chlorophenol (PCP) and reduce Cr(VI) simultaneously under visible light. The {001}/{101} surface facets ratio of TiO2 was controlled by varying the initial HF concentration, and fluorine-free samples were obtained by alkaline-washing. A synergistic effect among TiO2, Cr(VI), and PCP was observed, which is ascribed to effective trapping of photogenerated electrons and holes by Cr(VI) and PCP, respectively. A maximum synergistic effect was obtained at a molar ratio of [PCP] to [Cr(VI)] of one. Using X-ray diffraction, X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, and Brunauer-Emmett-Teller analyses, the optimum ratio of exposed {001} to {101} facets for TiO2 was determined to be 80:20 because of selective transfer and charge balance of photogenerated carriers. Surface fluorination facilitates the formation of oxygen vacancies and unsaturated Ti atoms, which is useful for visible light activity induction, extending the lifetime of photogenerated electron-hole pairs, and enhancing the rate of PCP oxidation and Cr(VI) reduction.