Promotion of Phenol Photodecomposition over TiO₂ Using Au, Pd, and Au–Pd Nanoparticles

Noble metal nanoparticles (Au, Pd, Au-Pd alloys) with a narrow size distribution supported on nanocrystalline TiO(2) (M/TiO(2)) have been synthesized via a sol-immobilization route. The effect of metal identity and size on the photocatalytic performance of M/TiO(2) has been systematically investigated using phenol as a probe molecule. A different phenol degradation pathway was observed when using M/TiO(2) catalysts as compared to pristine TiO(2). We propose a mechanism to illustrate how the noble metal nanoparticles enhance the efficiency of phenol decomposition based on photoreduction of p-benzoquinone under anaerobic conditions. Our results suggest that the metal nanoparticles not only play a role in capturing photogenerated electrons, but are strongly involved in the photocatalytic reaction mechanism. The analysis of the reaction intermediates allows us to conclude that on M/TiO(2) undesired redox reactions that consume photogenerated radicals are effectively suppressed. The analysis of the final products shows that the reusability performance of the catalyst is largely dependent on the pretreatment of the catalyst and the identity of the metal nanoparticle. Interestingly, the as-prepared Pd and Au-Pd decorated TiO(2) materials exhibit excellent long-term photoactivity, in which ~90% of the phenol can be fully decomposed to CO(2) in each cycle.