Selective photo-reduction of p-nitrophenol to p-aminophenol by Au deposited CdS nanostructures of different shapes having large surface area.

The preparation and photocatalytic reductive ability of a new spongy flower or cotton bud like amorphous CdS microstructures (size = 200-300 nm) having intermediate crystal phase between cubic and hexagonal structure and possesses much larger surface area ca. 119 m2 g(-1) is demonstrated here. Structural analysis has been done by TEM, XRD, BET surface area, UV-Vis absorption, luminescence analysis, and photocatalytic study. The photoreactivity of as-prepared CdS for p-nitrophenol reduction to p-aminophenol conversion under visible light (150 W halogen lamp) irradiation has been found to be greatly enhanced from 62% to 94% (yield) and 81% to 100% (selectivity) after 1 wt% Au deposition. The obtained p-aminophenol yield is always better than 32% for CdS nanosphere (size 10-12 nm) and 40% for CdS nanorod (length/width in nm = 126/6). Surface passivation with a thin layer of SiO2 coating over this flower like spongy CdS appreciably increased the BET surface area to 158 m2 g(-1) and displayed stable photocatalytic activity for p-nitrophenol reduction up to 30 h of light exposure as compared to bare CdS of low activity because of its easy photodissolution. A good co-relation between the BET surface area and surface photoactivity of as-prepared CdS with the conventional cubic and hexagonal CdS nanoparticles of different dimensions is established here.