Non-stoichiometric SnS microspheres with highly enhanced photoreduction efficiency for Cr(VI) ions

Self-doped semiconductors have recently attracted extensive interest as highly efficient photocatalytic materials because the electronic properties can be modulated without sacrificing the chemical stability of the parent material. In this report, we report the facile synthesis of Sn2+ self-doped SnS microparticles via a simple template-free hydrothermal route. Because of the ability to successfully tune the band structure while minimizing defect generation, self-doped SnS could potentially serve as an efficient photocatalyst of wastewater. Here, Sn2+ self-doping results in insertion of an energy level slightly below the conduction band of SnS, thereby decreasing the photoexcitation energy. Furthermore, dopant sites can act as charge trapping sites, which can consequently minimize problematic charge recombination. Synthesized materials were characterized by various spectroscopic, microscopic, and surface characterization techniques, all of which confirmed the formation of self-doped SnS. The Sn2+ self-doped SnS photocatalyst successfully reduced carcinogenic Cr(VI) to the water-insoluble Cr(III) form under visible light illumination. The best photocatalytic efficiency was obtained from an optimal balance between increased numbers of trapping sites leading to longer charge carrier lifetime, and decreased distance between trapping sites, favoring charge recombination. We anticipate that similar methodologies can be applied to other non-stoichiometric semiconducting photocatalysts with tunable electronic properties and enhanced photocatalytic efficiency.