Enhanced photocatalytic activity of CdS/SnS nanocomposite with highly-efficient charge transfer and visible light utilization for selective reduction of 4-nitroaniline.

Photocatalytic reduction can be an effective and promising technology for the selective reduction of aromatic nitro organics. In this paper, a novel Z-scheme CdS/SnS photocatalyst was well-designed and fabricated via simple in-site reaction process containing thioacetamide as a sulfur sources and cubic CdSnO as template. The resulting CdS/SnS composite has well-constructed cubic nanostructure of strong adhesion between CdS and SnS, presenting high absorption to visible light. Importantly, strong charge transfer between the contacting regions of CdS and SnS through the intermediate sulfur atoms combined with both metals was generated, which speeds up separation of photogenerated electron and hole. The advantageous combination of high light-harvesting and effective charge transfer is responsible for the excellent photocatalytic activity at the CdS/SnS heterointerface. Resultantly, the prepared CdS/SnS composites exhibit high conversion efficiency and selectivity on 4-nitroaniline (4-NA) reduction in the aqueous solution containing ammonium formate under visible light irradiation, which can reduce almost all 4-NA within 12 min. Trapping experiments and ESR analysis demonstrated that ammonium formate not only can effectively decrease recombination of photogenerated charge carriers but also react with holes to generate CO radicals possessing strong reduction ability. The 4-NA are effectively photo-reduced by the synergistic effect of electrons and CO radicals. According to the experimental results, a possible Z-scheme charge transfer mechanism was proposed. Besides, the photo-reduction of aromatic nitro organics possessed different para-groups (p-nitrophenol, nitrobenzene, and p-nitrobenzaldehyde) was also investigated. It is found that the electron-drawing group can decrease the electron density of its para-position nitryl, which quickens the nitro reduction.