Enhanced Photocatalytic Benzene Oxidation to Phenol over Monoclinic WO3 Nanorods under Visible Light

The photocatalytic oxidation of benzene to phenol driven by visible light (λ > 420 nm) at room temperature and under ambient pressure is a promising process. In particular, the application of heterogeneous catalysts to benzene photooxidation, where the catalyst and product are easily separated, facilitates the construction of practical processes. Here, we report that a Pt-loaded 1D monoclinic WO3 nanorod (Pt/m-WNR) exhibited higher activities than other Pt/WO3 catalysts with different crystal structures and morphologies in water under ambient conditions and visible light. Pt/m-WNR showed high stability in repeated reactions. Furthermore, other typical photocatalysts (TiO2, Bi2WO6, Bi2MoO6, BiOBr, and C3N4) showed negligible phenol formation using Pt as a cocatalyst. Both experimental results and density functional theory calculations show that the specific performance of Pt/m-WNR is due to the efficient reduction of O2 to produce hydroxyl radicals via H2O2 as an intermediate. Notably, m-WNR shows much higher phenol formation than h-WNR, although h-WNR has a higher surface area. The higher activity of m-WNR may be due to its lower work function to provide electrons for O2 reduction. A lower work function will favorably form a higher Schottky barrier with Pt nanoparticles to suppress the recombination of photogenerated charge carriers. The effect of the Schottky barrier is further confirmed by different activities using various metal particles as cocatalysts.