Novel synthesis of C, N doped rice grain shaped ZnS nanomaterials – towards enhanced visible light photocatalytic activity for aqueous pollutant removal and H2 production

Abstract

Novel single step syntheses of visible active C, N doped zinc sulfide (ZnS) photocatalysts with rice grain morphology have been achieved without using expensive surfactants, capping agents and inert atmospheric conditions by using solution combustion synthesis in an energy and time efficient manner. Several ZnS samples such as ZnS (1 : 2), ZnS (1 : 3), ZnS (1 : 4), ZnS (1 : 5) and ZnS (1 : 6) have been synthesized by varying the metal and sulfur precursor ratio in order to obtain ZnS with desirable characteristics for visible light activity. X-ray diffraction indicated the nanocrystalline size and hexagonal ZnS phase, whereas, transmission electron microscopy confirmed the nanocrystalline size and also revealed the rice grain morphology for ZnS (1 : 5). Diffuse reflectance UV-Vis spectra indicated a red shift in the absorption maxima, possibly due to the decreasing band gap by C, N-doping, which was further confirmed by the elemental analysis and X-ray photoelectron spectroscopy. The visible light photocatalytic activity of the ZnS nanomaterials was assessed by high H₂ production (up to 10 000 μmol h⁻¹ g⁻¹ for ZnS (1 : 5)) by water splitting in the presence of Na₂S and Na₂SO₃ sacrificial reagents, whereas, the simultaneous oxidation of MB and reduction of Cr(VI) under natural sunlight complemented the activity of ZnS.