A novel method of synthesis of small band gap SnS nanorods and its efficient photocatalytic dye degradation.

A facile one pot method has been developed for synthesis of stable (ξ=-37.5 mV), orthorhombic structured SnS nanorods capped with mercaptoacetic acid by precipitation method. The SnS nanorods were measured to be about 45 nm long with a diameter of 20 nm, as studied by transmission electron microscopy (TEM). The band gap of the MAA capped SnS nanorods was 1.81 eV, measured by diffused reflectance spectroscopy and was larger than the bulk SnS. The relative positions of highest valence band and lowest conduction band were determined from theoretical band structure calculation as 1.58 eV and -0.23 eV, respectively. The UV-Visible-NIR fluorescence emission spectrum of the SnS nanorods revealed intense emission peak at 1000 nm (1.239 eV) and weaker peaks at 935 nm, 1080 nm, 1160 nm which is likely to be due to Sn(2+) vacancies. The as-synthesized SnS nanorods exhibited more than 95% sunlight induced photocatalytic degradation of trypan blue in 4 h, following first order kinetics with high rate of degradation (k) (0.0124 min(-1)). The observed dye degradation is attributable to generation of reactive oxygen species (ROS), confirmed from terephthalic acid assay. The ROS generation has been explained on the basis of interaction between photoexcited electrons from conduction band with molecular oxygen adhered to the surface of nanorods owing to favourable redox potentials of O2/O2(-) (-0.20 eV) in normal hydrogen electrode (NHE) scale.