Highly enhanced photocatalytic activity of Au nanorod–CdS nanorod heterocomposites

Abstract

This paper signifies the importance of different shapes of Au and CdS-nanoparticles for fabricating Au–CdS heterocomposites {prepared by mixing or impregnation of Au-nanosphere (9.1nm), Au-nanorod (20nm×8.6nm; L×W), CdS-nanosphere (10–12nm) and CdS-nanorod (126nm×5.5nm)} onto the photoluminescence and photocatalytic study. Second derivative absorption spectra's exhibit precise onset at 441nm (CdS-nanosphere) and 469.5nm (CdS-nanorod) that are significantly red-shifted to 509nm (Au-nanosphere–CdS-nanosphere), 485nm (Au-nanosphere–CdS-nanorod), 520nm (Au-nanorod–CdS-nanosphere) and 485.5nm (Au-nanorod–CdS-nanorod) depending upon interfacial contact-area. XRD patterns reveal the hexagonal phase of pure and Au–CdS nanocomposites. Photoluminescence of CdS nanorods has been effectively inhibited by modifying its surface with Au-nanoparticles (0.002–0.04wt%). Relaxation lifetime of photoexcited charge-carriers found to be improved ca. 12.5μs for Au-nanosphere–CdS-nanorod and 34μs for Au-nanorod–CdS-nanorod due to effective charge transfer kinetics at the interface, in contrast to prompt charge-recombination (2.7μs) in CdS. Under UV light (10.4mW/cm2) irradiation, Au-nanorod–CdS-nanorod exhibits the best photocatalytic activity for the oxidation of salicylic acid (86%, k=9×10−3min−1) and reduction of p-nitrophenol to p-aminophenol (53%) as a function of improved stability and better current–voltage (I–V) characteristics suitable for rapid charge transfer process during photoreaction.