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 TiO2 (M/TiO2) have been synthesized via a sol-immobilization route. The effect of metal identity and size on the photocatalytic performance of M/TiO2 has been systematically investigated using phenol as a probe molecule. A different phenol degradation pathway was observed when using M/TiO2 catalysts as compared to pristine TiO2. We propose a mechanism to illustrate how the noble metal nanoparticles enhance the efficiency of phenol decomposition based on photoreduction of p-benzoguinone 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/TiO2 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 TiO2 materials exhibit excellent long-term photo-activity, in which similar to 90% of the phenol can be fully decomposed to CO2 in each cycle.