Exploring the Origin of Enhanced Activity and Reaction Pathway for Photocatalytic H2 Production on Au/B-TiO2 Catalysts

Abstract

Gold-embedded boron-doped TiO2 (Au/B-TiO2) photocatalysts were synthesized by a sol–gel hydrothermal method. The TEM images display that the gold nanoparticles were embedded into the B-TiO2 framework. Hydrogen evolution under light irradiation showed that doping of boron into TiO2 enhanced the photocatalytic activity. A further remarkable improvement of the activity was observed over the Au/B-TiO2. Evidenced by B 1s XPS and 11B MAS NMR spectra, the embedment of Au nanoparticles contributes to the formation of more interstitial boron species in B-TiO2. In turn, it gives rise to surface or near-surface states facilitating the embedment of Au nanoparticles, as demonstrated by the Au 4f XPS spectra, which indicates the strong interaction between gold and the B-TiO2 framework. This specific synergy significantly contributes to the enhancement of photocatalytic activity. For the first time, the isotopic tracer studies using a gas chromatograph isotope ratio mass spectrometer along with a series of control experiments reveal that the produced hydrogen originated mainly from water rather than methanol, whereas the direct oxidation of methanol did not lead to hydrogen generation. Acting as a sacrificial reagent, methanol could be oxidized to formaldehyde by protons/water under oxygen-free conditions.