A novel visible-light-active BiOCl/BiVO 4 photocatalyst with a p−n heterojunction structure was prepared using a hydrothermal method. The photocatalytic activity of the heterojunction was investigated by monitoring the change in methyl orange (MO) concentration under visible-light irradiation. The results reveal that the composite exhibited markedly improved efficiency for MO photodegradation in comparison with pure BiVO 4 , BiOCl, and Degussa P25. This is ascribed to the Btype heterojunction structure with a strong oxidative ability and efficient charge separation and transfer across the BiOCl/BiVO 4 p−n junction. The highest activity was obtained in the BiOCl/BiVO 4 heterojunction using a composite of 13 mol % BiOCl and 87 mol % BiVO 4 . The removal of MO was mainly initiated by valence-band holes, but dissolved oxygen also played a crucial role in consuming the conductionband electrons. This was verified by the effects of scavengers and N 2 purging.

Photocatalytic reduction of carbon dioxide can activate chemically inert carbon dioxide by the use of renewable energy. In the present work, the main products of photocatalytic reduction of CO 2 in aqueous TiO 2 suspensions were found to be methane, methanol, formaldehyde, carbon monoxide, and H 2 . Anatase TiO 2 catalysts with various morphologies, such as nanoparticle, nanotube, and nanosheet, were synthesized through a hydrothermal method. The TiO 2 nanosheets were more active than the nanotubes or nanoparticles in the reduction of CO 2 in aqueous solution. This is because the photogenerated carriers prefer to flow to the specific facets. The TiO 2 sheet with high-energy exposed {001} facets facilitates the oxidative dissolution of H 2 O with photogenerated holes, leaving more photogenerated electrons available for the reduction of CO 2 on {101} facets. Moreover, surface fluorination promotes the formation of Ti 3+ species, which is helpful in the reduction of CO 2 to CO 2 − and in extending the lifetime of photogenerated electron−hole pairs. The optimum ratio of exposed {001} to {101} facets for surface-fluorinated TiO 2 nanosheets was found to be ∼72:28, which corresponds to an initial F/Ti ratio of 1. From our analysis of the effect of adding of known intermediates on the photocatalytic reduction of CO 2 , we propose that the photocatalytic reduction of CO 2 with H 2 O on surface-fluorinated TiO 2 nanosheets proceeds via a mechanism involving generation of hydrogen radicals and carbon radicals.

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