Mechanistic insight into the interaction between a titanium dioxide photocatalyst and Pd co-catalyst for improved photocatalytic performance

Understanding the cocatalyst/semiconductor interaction is of key importance for the design and synthesis of next generation photocatalytic materials for efficient hydrogen production and environmental cleanup applications. Here we investigate preformed Pd nanoparticles (NPs) supported on a series of anatase TiO2 having well-controlled but varying degrees of crystallinity and crystallite size, and explore their photocatalytic performance for H2 production and phenol decomposition. While tuning the anatase crystallite size significantly influences the photocatalytic performance, varying the TiO2 crystallinity shows a negligible effect. Interestingly, the optimum quantum efficiency (∼78%) for H2 evolution is achieved with anatase having medium crystallite size (∼16 nm), whereas for phenol decomposition, a promotional effect is only observed for anatase with larger crystallite sizes (>20 nm). Surface radical species and radical densities study reveal that the photogenerated charge carriers have been trapped at different sites depending on the crystallite size of anatase. While the excited electrons are only trapped in bulk lattice sites in small anatase (