Influence of Au Photodeposition and Doping in CdS Nanorods: Optical and Photocatalytic Study

Au-modified CdS nanorods (100-200nmx5-10nm) are synthesized via two different techniques, namely photodeposition and doping. The prepared samples are characterized by x-ray powder diffraction, transmission electron microscopy (TEM), and UV-vis and fluorescence spectroscopy. X-ray diffraction study confirmed the hexagonal phase of bare and Au-CdS samples, whereas, 5wt% Au3+ doping into CdS resulted in a slight distortion in the crystal structure toward higher degree side. TEM images revealed the fine distribution of Au nanodeposits of size in the range of 2.5-4.5nm on to the CdS surface in the photodeposited sample. The optical spectrum shows a significant red-shift in absorption onset (485nm -> 515nm) and band-edge emission (505nm -> 512nm) of CdS nanorods with the replacement of certain Cd2+ ions with Au3+. The influence of Au photodeposition and doping in CdS nanorods was comparatively tested by photooxidation of RhB (50ppm) dye aqueous solution under direct sunlight irradiation (35-40mWcm(-2)). Our results point out that 5wt% Au3+ doping into CdS nanorods remarkably improved its activity and stability due to homogeneous dispersion of charge throughout the crystal, quick Fermi level equilibration, and an improvement in ionic bond formation.