Synergism of oxygen vacancies, Ti3+ and N dopants on the visible-light photocatalytic activity of N-doped TiO2

Abstract

N-doped TiO2 photocatalyst with abundant oxygen vacancies (N-TiO2-x) has been fabricated by a novel solvothermal route (using HNO3 as a nitrogen source) combined with a solid-state chemical reduction method for the first time. Using this combined technology, high-quality N-TiO2-x photocatalyst with small mean particle size (around 7.1 nm) and high surface area (181.7 m2/g) can be acquired. The electron paramagnetic resonance and X-ray photoelectron spectrometer results indicate that oxygen vacancy and Ti3+ are produced in N-TiO2-x during solid-state chemical reduction process. Control experiments show that compare to pristine N-doped TiO2 and pure TiO2, the reduction activated N-TiO2-x catalyst has a great improvement in both optical absorption and photocatalytic performance. It suggests that the N-TiO2-x band-gap narrowing results from synergetic effect of Ti3+ and oxygen vacancies defect energy state belts, as well as N2p midgap state. These energy levels result in enhanced visible light absorption and serve to trap the photogenerated electrons, consequently improving both charge separation and the quantum efficiencies of N-TiO2-x catalysts.