Heterogeneous photocatalysis that employs photo-excited semiconductor materials to reduce water and oxidize toxic pollutants upon solar light irradiation holds great prospects for renewable energy substitutes and environmental protection. To utilize solar light effectively, the quest for highly active photocatalysts working under visible light has always been the research focus. Layered BiOX (X = Cl, Br, I) are a kind of newly exploited efficient photocatalysts, and their light response can be tuned from UV to visible light range. The properties of semiconductors are dependent on their morphologies and compositions as well as structures, and this also offers the guidelines for design of highly-efficient photocatalysts. In this review, recent advances and emerging strategies in tailoring BiOX (X = Cl, Br, I) nanostructures to boost their photocatalytic properties are surveyed.

The efforts to produce photocatalysts operating efficiently under visible light have led to a number of plasmonic photocatalysts, in which noble metal nanoparticles are deposited on the surface of polar semiconductor or insulator particles. In the metal–semiconductor composite photocatalysts, the noble metal nanoparticles act as a major component for harvesting visible light due to their surface plasmon resonance while the metal–semiconductor interface efficiently separates the photogenerated electrons and holes. In this article, we survey various plasmonic photocatalysts that have been prepared and characterized in recent years.

We developed a facile in situ method of preparing noble-metal plasmonic photocatalysts M@TiO₂ (M = Au, Pt, Ag). In this method, the UV irradiation of TiO₂ powder dispersed in absolute ethanol generates some Ti³⁺ ions on the surface of TiO₂ particles and these Ti³⁺ ions, upon addition of a noble-metal salt in the dark, reduce the metal cations to deposit metal nanoparticles on the TiO₂ surface. This Ti³⁺-ion-assisted synthesis leads to a homogeneous loading of noble-metal nanoparticles on the surface of TiO₂ particles, which allows photocatalytic reactions to take place under visible-light on the whole TiO₂ surface. Among the three photocatalysts M@TiO₂ (M = Au, Pt, Ag), Au@TiO₂ exhibits a high yield (63%) and selectivity (91%) for the oxidation of benzene to phenol in aqueous phenol. For this photocatalytic reaction, our study suggests a mechanism in which the visible-light absorption by the Au nanoparticles causes electron transfer from the Au nanoparticles to the TiO₂ particle, and the electron-depleted Au oxidizes phenoxy anions to form phenoxy radicals that oxidize benzene to phenol.