Precursor-directed synthesis of well-faceted brookite TiO2 single crystals for efficient photocatalytic performances

Abstract

Brookite-TiO₂ is a promising next-generation semiconductor material for solar energy conversion, but it suffers from difficulty in achieving high quality and phase purity due to its metastable characteristics. Long-chain fatty acid modification or surfactant assisted methods could orient the growth of brookite; however, purifying the products is complicated and the surface reactivity is invariably undermined. Herein, we demonstrate the design and tuneable synthesis of brookite nanostructures with geometric features of quasi-octahedral (QO), ellipsoid-tipped (ET) and wedge-tipped (WT) nanorods that are exposed primarily with {210} facet via water-soluble titanium precursors. When tested as a photocatalyst for hydrogen evolution from water or for the degradation of organic pollutants, QO brookite nanocrystals exhibited the highest catalytic activity compared to ET and WT nanorod counterparts. This observation could be due to the redox facets that form a “surface-heterojunction” and promote the separation of photogenerated carriers. The precursor-directed method reported here may usher in a new phase for the synthesis of novel metastable nanocrystals with specific facet exposure that are highly useful for applications in energy conversion and environment protection.