Carbon Dot–SnS2 Heterojunction Photocatalyst for Photoreduction of Cr(VI) under Visible Light: A Combined Experimental and First-Principles DFT Study

The use of solar energy to convert highly toxic Cr(VI) into hypotoxic Cr(III) is an attractive strategy to address heavy metal pollution. In this work, a facile method for the preparation of carbon nanodot–SnS2 nanocomposites (SnSCD) is reported. In this system, CDs serve as excellent photosensitizers in combination with SnS2. The photogenerated electrons produced by the conduction band of SnS2 could be easily injected into the CDs, which suppress the charge recombination, and thus show improved photocatalytic activity. Meanwhile, the SnSCD-5 sample with a CD content of 5 wt % showed the highest catalytic activity in the photocatalytic removal of Cr(VI) under visible light. The total Cr(VI) removal rate and the reaction kinetic coefficient of the SnSCD-5 photocatalyst were found to be 77.34% and 6.95 min–1, respectively. These values were 4.15 and 6.56 times higher than pure SnS2, respectively. Furthermore, the high stability and durability of SnSCD-5 were demonstrated by three cycling experiments. The first-principles density functional theory calculations were performed to study the energy band and electron–hole density distribution of SnS2 and SnSCD photocatalysts. The calculation results were consistent with our experimental results, it further confirms that CDs play a vital role in this system. In general, this study highlights the highly efficient charge transfer and separation and the potential application of the SnSCD photocatalyst in the removal of Cr(VI).