Tuning the surface structure of nitrogen-doped TiO_2 nanofibres - An effective method to enhance photocatalytic activities of visible-light-driven green synthesis and degradation

摘要

Nitrogen-doped TiO_2 nanofibres of anatase and TiO_2(B) phases were synthesised by a reaction between titanate nanofibres of a layered structure and gaseous NH_3 at 400-700 °C, following a different mechanism than that for the direct nitrogen doping from TiO_2. The surface of the N-doped TiO_2 nanofibres can be tuned by facial calcination in air to remove the surface-bonded N species, whereas the core remains N doped. N-Doped TiO_2 nanofibres, only after calcination in air, became effective photocatalysts for the decomposition of sulforhodamineB under visible-light irradiation. The surface-oxidised surface layer was proven to be very effective for organic molecule adsorption, and the activation of oxygen molecules, whereas the remaining N-doped interior of the fibres strongly absorbed visible light, resulting in the generation of electrons and holes. The N-doped nanofibres were also used as supports of gold nanoparticle (Au NP) photocatalysts for visible-light-driven hydroamination of phenylacetylene with aniline. Phenylacetylene was activated on the N-doped surface of the nanofibres and aniline on the Au NPs. The Au NPs adsorbed on N-doped TiO_2(B) nanofibres exhibited much better conversion (80 % of phenylacetylene) than when adsorbed on undoped fibres (46 %) at 40 °C and 95 % of the product is the desired imine. The surface N species can prevent the adsorption of O_2 that is unfavourable for the hydroamination reaction, and thus, improve the photocatalytic activity. Removal of the surface N species resulted in a sharp decrease of the photocatalytic activity. These photocatalysts are feasible for practical applications, because they can be easily dispersed into solution and separated from a liquid by filtration, sedimentation or centrifugation due to their fibril morphology. Legal doping: Efficient visible-light photocatalysts for the degradation of organic compounds in water can be achieved by nitrogen-doped titanate nanofibres (NFs) produced by nitrogen doping and subsequent calcination in air. Gold nanoparticles (Au NPs) adsorbed on the N-doped nanofibres without calcination are superior visible-light photocatalysts for hydroamination (see figure). The surface properties of N-TiO_2 NFs significantly affect the performance of the photocatalysts.