Abstract
Titanium dioxide is a promising photocatalyst for water splitting, but it suffers from low visible light activity due to its wide band gap. Doping can narrow the band gap of titanium dioxide; however, new charge-carrier recombination centres may be introduced. Here we report the design of sub-10 nm rutile titanium dioxide nanoparticles, with an increased amount of surface/sub-surface defects to overcome the negative effects from bulk defects. Abundant defects can not only shift the top of the valence band of rutile titanium dioxide upwards for band-gap narrowing but also promote charge-carrier separation. The role of titanium(III) is to enhance, rather than initiate, the visible-light-driven water splitting. The sub-10 nm rutile nanoparticles exhibit the state-of-the-art activity among titanium dioxide-based semiconductors for visible-light-driven water splitting and the concept of ultra-small nanoparticles with abundant defects may be extended to the design of other robust semiconductor photocatalysts.
Highlights
Titanium dioxide is a promising photocatalyst for water splitting, but it suffers from low visible light activity due to its wide band gap
Rutile TiO2 has a band gap ca. 0.2 eV lower than that of anatase (3.0 versus 3.2 eV), and this could be crucial to the band-gap narrowing to extend its working spectrum to the visible light region
Bulk rutile TiO2 can be obtained via the high temperature calcination of anatase TiO2 at temperatures higher than 773 K, while rutile TiO2 nanostructures can be prepared via a hydrothermal route[33,34] or a direct hydrolysis route[35,36,37]
Summary
Titanium dioxide is a promising photocatalyst for water splitting, but it suffers from low visible light activity due to its wide band gap. The sub-10 nm rutile nanoparticles exhibit the state-of-the-art activity among titanium dioxide-based semiconductors for visible-light-driven water splitting and the concept of ultra-small nanoparticles with abundant defects may be extended to the design of other robust semiconductor photocatalysts. Self-doping with Ti3 þ was further developed for narrowing the band of TiO2 without the introduction of unwanted carrier recombination centres from dopants[19,20,21], which exhibited good stability and considerable activity for photocatalytic hydrogen production under visible light[20,21]. The successful photocatalyst system should fulfill all the requirements simultaneously: (i) narrowed band gap for visible light response; (ii) delicately designed band edge positions to realize photocatalytic redox reaction; and (iii) high efficiency for chargecarrier separation to promote photocatalytic activity. The simple strategy leads to state-of-the-art photocatalytic activity among TiO2-based semiconductors, and the simplified rutile TiO2 semiconductor system can provide information on the essence of defect-induced visible light photocatalytic activity
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