A red anatase TiO2 photocatalyst for solar energy conversion

Abstract

Narrowing the bandgap of wide-bandgap semiconductor photocatalysts (for instance, anatase TiO₂) by introducing suitable heteroatoms has been actively pursued for increasing solar absorption, but usually suffers from a limited thermodynamic/kinetic solubility of substitutional dopants in bulk and/or dopant-induced recombination centres. Here we report a red anatase TiO₂ microsphere with a bandgap gradient varying from 1.94 eV on its surface to 3.22 eV in its core by a conceptually different doping approach for harvesting the full spectrum of visible light. This approach uses a pre-doped interstitial boron gradient to weaken nearby Ti–O bonds for the easy substitution of oxygen by nitrogen, and consequently it substantially improves the nitrogen solubility. Furthermore, no nitrogen-related Ti³⁺ was formed in the red TiO₂ due to a charge compensation effect by boron, which inevitably occurs in common nitrogen doped TiO₂. The red anatase TiO₂ exhibits photoelectrochemical water splitting activity under visible light irradiation. The results obtained may shed light on how to increase high visible light absorbance of wide-bandgap photocatalysts.