Role of surface defects on visible light enabled plasmonic photocatalysis in Au-ZnO nanocatalysts

Visible light photocatalytic activity of the plasmonic gold-zinc oxide (Au-ZnO) nanorods (NRs) is investigated with respect to the surface defects of the ZnO NRs, controlled by annealing the NRs in ambient at different temperatures. Understanding the role of surface defects on the charge transfer behaviour across a metal-semiconductor junction is vital for efficient visible light active photocatalysis. Au nanoparticles (NPs) are in situ deposited on the surface of the ZnO NRs having different surface defect densities, demonstrating efficient harvesting of visible light due to the surface plasmon absorption. The surface defects in the ZnO NRs are probed by using photoluminescence (PL) spectroscopy, X-ray photoemission spectroscopy (XPS), and photo-electro-chemical current-voltage measurements to study the photo-generated charge transfer efficiency across the Au-ZnO Schottky interface. The results show that the surface situated oxygen vacancy sites in the ZnO NRs significantly reduce the charge transfer efficiency across the Au-ZnO Schottky interfaces lowering the photocatalytic activity of the system. Reduction in the oxygen vacancy sites through annealing the ZnO NRs resulted in the enhancement of visible light enabled photocatalytic activity of the Au-ZnO plasmonic nanocatalyst, adding vital insight towards the design of efficient plasmonic photocatalysts.