Exploring the Origin of Enhanced Activity and Reaction
Pathway for Photocatalytic H<sub>2</sub> Production on Au/B-TiO<sub>2</sub> Catalysts
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Abstract
Gold-embedded boron-doped TiO<sub>2</sub> (Au/B-TiO<sub>2</sub>) photocatalysts were synthesized by
a sol–gel hydrothermal
method. The TEM images display that the gold nanoparticles were embedded
into the B-TiO<sub>2</sub> framework. Hydrogen evolution under light
irradiation showed that doping of boron into TiO<sub>2</sub> enhanced
the photocatalytic activity. A further remarkable improvement of the
activity was observed over the Au/B-TiO<sub>2</sub>. Evidenced by
B 1s XPS and <sup>11</sup>B MAS NMR spectra, the embedment of Au nanoparticles
contributes to the formation of more interstitial boron species in
B-TiO<sub>2</sub>. 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-TiO<sub>2</sub> 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