Unravelling the Efficient Photocatalytic Activity of Boron-induced Ti3+ Species in the Surface Layer of TiO2

Ningdong Feng,Jun Xu,Feng Deng,Fen Liu,Anmin Zheng,Jie Fan,Gengyu Cao,Qiang Wang,Tiehong Chen,Min Huang

doi:10.1038/srep34765

Abstract

Ti3+ species are highly unstable in air owing to their facile oxidation into Ti4+ species, and thus they cannot concentrate in the surface layer of TiO2 but are mainly present in its bulk. We report generation of abundant and stable Ti3+ species in the surface layer of TiO2 by boron doping for efficient utilization of solar irradiation. The resultant photocatalysts (denoted as B-TiO2−x) exhibit extremely high and stable solar-driven photocatalytic activity toward hydrogen production. The origin of the solar-light activity enhancement in the B-TiO2−x photocatalysts has been thoroughly investigated by various experimental techniques and density functional theory (DFT) calculations. The unique structure invoked by presence of sufficient interstitial boron atoms can lead to substantial variations in density of states of B-TiO2−x, which not only significantly narrow the band gap of TiO2 to improve its visible-light absorption, but also promote the photogenerated electron mobility to enhance its solar-light photocatalytic activity.

Highlights

Driven by the decrease of fossil fuel resources and the environmental concerns, the search for new clean and renewable energy technologies is urgent on the research agendas of many research and development communities
To gain insight into the active center structures and plausible mechanisms associated with the photocatalysts, the results from density functional theory (DFT) calculations were correlated to those obtained from experimental studies, such as UV–vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS), electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spectroscopy etc
For the 10% B-TiO2−x samples, considerable visible-light absorption is still observable at ca. 1350 nm in the UV-Vis spectrum (Figure S2 in SI). All these experimental results suggest that rich mid-gap states should exist in the band gap of B-TiO2−x samples, and the B doping is responsible for the high visible-light absorption of B-TiO2−x photocatalysts

Summary

Introduction

Driven by the decrease of fossil fuel resources and the environmental concerns, the search for new clean and renewable energy technologies is urgent on the research agendas of many research and development communities. It was found that the low concentration of Ti3+ species formed in the TiO2−x would produce localized oxygen vacancy states with energies being 0.75 to 1.18 eV below the conduction band minimum of TiO2, which tends to deteriorate the electron mobility in the bulk region and eventually reduce the photocatalytic activity[5,20]. Many strategies, such as heating under vacuum or in reducing gas (i.e. H2), combustion, laser irradiation, and high-energy particle (such as electrons or Ar+ ions) bombardment[13,22], have been applied to synthesize TiO2−x These methods, started from pure TiO2, possess more or less limitations such as multiple steps, harsh synthesis conditions and expensive facilities. The exceptionally high photocatalytic activity observed for the B-TiO2−x is ascribed to the synergistic effect of the interstitial B and Ti3+ species

Methods

Results

Conclusion