One-Step in Air Synthesis of Visible-Light-Active SnS2/SnO2 Nanocomposite for Photocatalytic Reduction of Aqueous Cr(VI)

Composition-tunable synthesis of SnS2/SnO2 nanocomposites was achieved simply via heating the mixture of Sn, S and NH4Cl powders in air at 320 degrees C for different times. The structures, compositions, BET specific surface areas and optical properties of the as-synthesized SnS2/SnO2 nanocomposites were characterized by X-ray diffraction, wavelength dispersive X-ray fluorescence spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy, N-2 adsorption/desorption isotherms and UV-vis diffuse reflectance spectra. The photocatalytic activities of the as-synthesized SnS2/SnO2 nanocomposites were tested in the reduction of aqueous Cr(VI) under visible-light (lambda > 420 nm) irradiation, and compared with that of SnS2 nanoflakes. Besides, the effects of the dosage of photocatalyst, the coexistence of organic compounds (phenol, rhodamine B and methyl orange) and the initial concentration of Cr(VI) aqueous solution on the photocatalytic efficiency were also investigated. It was observed that (i) all the as-synthesized SnS2/SnO2 nanocomposites (SnS2/SnO2-2 h, SnS2/SnO2-3 h and SnS2/SnO2-4 h) exhibited higher photocatalytic efficiencies than SnS2 nanoflakes, with SnS2/SnO2-3 h being the most efficient one; (ii) the coexistence of phenol and rhodamine B enhanced the photocatalytic reduction of Cr(VI), whereas the coexistence of methyl orange retarded the photocatalytic reduction of Cr(VI) over SnS2/SnO2-3 h; and (iii) the photocatalytic efficiency increased with the increase of the dosage (333-1667 mg/L) of SnS2/SnO2-3 h, but decreased with the increase of the initial concentration of Cr(VI) aqueous solution. The possible reasons accounting for the photocatalytic results were also discussed.