(Invited) Red TiO2 and Ferroelectric Photocatalysts

Abstract

The strong band-to-band absorption of photocatalysts spanning the whole visible light region (400-700 nm) is critically important for solar-driven photocatalysis. Although it is actively and widely used as photocatalyst for various reactions in the past four decades, TiO2 has a very poor ability to capture the whole-spectrum visible light. Here, by controlling the spatially homogeneous distribution of boron and nitrogen heteroatoms in anatase TiO2 microspheres with a predominance of high-energy {001} facets, a strong visible light absorption spectrum with a sharp edge beyond 680 nm is achieved. The red TiO2 with the homogeneous doping of boron and nitrogen obtained shows no increase in defects like Ti3+ that are commonly observed in doped TiO2. More importantly, it has the ability to induce photocatalytic water oxidation to produce oxygen under the irradiation of visible light beyond 550 nm and also photocatalytic reducing water to produce hydrogen under visible light. Integrating a semiconducting light absorber with an appropriate co-catalyst appears almost indispensable for photocatalytic solar fuel generation. Although ferroelectric materials with spontaneous electrical polarization are considered promising light absorbers with the ability to induce oppositely directed transport of photogenerated electrons and holes in the bulk, their applications are intrinsically restricted by the large Schottky barrier at the interface of the ferroelectric material and the co-catalyst, which has a larger work function. Here, we demonstrate that, by selective chemical epitaxial growth of anatase TiO2 islands on the positively poled (00-1) facet of PbTiO3 single-crystal particles to form an atomically smooth interface with a small potential difference, the material shows significantly improved photocatalytic hydrogen and oxygen generation under both UV-visible and visible light, while the island-free PbTiO3 is inactive in visible light.