Preparation And Properties Of Non-metallic Element Co-doped Black TiO 2 Nanosheets

With the increasing environment issue and energy crisis,elimination of environmental pollutants and hydrogen production from water splitting via semiconductor photocatalysis have become a promising approach.Among various active photocatalyst materials,titanium dioxide?TiO₂?has received a lot of attention for pollutant degradation,photocatalytic hydrogen evolution,dye-sensitized solar cells,and other photocatalytic applications owing to its nontoxicity,superior photocatalytic activity,good stability,and low cost.However,the widespread application of pure TiO₂is greatly restrained by two major barriers.Firstly,the wide band gap?³.2 eV for anatase?restricts its photocatalytic activity in the visible region.Secondly,the fast recombination of photogenerated electron-hole pairs results in low efficiency of photoinduced chemical reactions.Thus numerous approaches have been proposed to narrow the band gap and restrain the photogenerated electron-hole pair recombination.Doping TiO₂ with nonmetal elements is an intelligent strategy to narrow the band gap and decrease the required activation energy.Therefore,doping TiO₂ with three kinds of nonmetal elements simultaneously improve the photocatalytic activity owing to the merits benefited from each dopant.Anatase TiO2 single crystal nanosheet with highly energetic{001}facet has attracted great interest because of its fascinating shape-dependent physicochemical properties.In addition to the above methods,the preparation of black TiO₂ by in-situ solid phase reduction is another advancing way to enhance the utilization of solar energy.In this paper,C-N-S-tridoped single crystal black Ti O₂ nanosheets with exposed{001}facets are fabricated through a hydrothermal method and an in-situ controllable solid-state reaction strategy.The crystal structure,crystallinity,morphology and composition of the as-prepared samples are investigated through X-ray diffraction,Raman,scanning electron microscopy,transmission electron microscopy,X-ray photoelectron spectroscopy,and UV-vis diffuse reflectance spectroscopy,respectively.Moreover,visible-light-driven photocatalytic activity and electrochemical performance of the prepared photocatalytic materials are evaluated.The results demonstrate that the prepared TiO₂ nanosheets photocatalytic material exhibit uniform nanosheet-like structure with exposed{001}facets,and the formation of trivalent titanium and oxygen vacancies in the TiO₂ crystal lattice are owing to the reduction of NaBH4.Therefore,black TiO2 nanosheets exhibit excellent photocatalytic activity.Under the visible light irradiation,the degradation efficiency of methyl orange,rhodamine B,and phenol reach 84.32%,84.91%and 85.17%,respectively.Meanwhile,the hydrogen production rate is as high as 100.30?mol h^-1 g^-1.In addition,the obtained black C-N-S-TiO₂ nanosheets exhibit excellent photocatalytic performance due to the presence of carbon,nitrogen,and sulfur.The visible-light photocatalytic degradation rate of methyl orange is up to 92.13%,and photocatalytic hydrogen evolution is 149.7?mol h^-1 g^-1.The excellent photocatalytic activity can be ascribed to the synergetic effect of surface heterojunction between{001}and{101}facets,the C-N-S-tridoping,and the formed Ti³⁺species in photocatalyst,which can not only favor the visible-light absorption but also facilitate the separation and transfer of photogenerated charges.