Modifying SnS₂ With Carbon Quantum Dots to Improve Photocatalytic Performance for Cr(VI) Reduction

The photoreduction for hazardous Cr(VI) in industrial wastewater has been considered a "green" approach with low-cost and easy-to-go operation. SnS₂ is a promising narrow bandgap photocatalyst, but its low charge carrier separation efficiency should be solved first. In this work, N-doped carbon quantum dots (CQDs) were prepared and loaded onto SnS₂ nanoparticles via an in situ method. The resulting composite samples (NC@SnS₂) were characterized, and their photocatalytic performance was discussed. SnS₂ nanoparticles were obtained as hexagonal ones with a bandgap of 2.19 eV. The optimal doping level for NC@SnS₂ was citric acid: urea:SnS₂ = 1.2 mmol:1.8 mmol:3.0 mmol. It showed an average diameter of 40 nm and improved photocatalytic performance, compared to pure SnS₂, following a pseudo-first-order reaction with a kinetic rate constant of 0.1144 min^-1. Over 97% of Cr(VI) was photo-reduced after 30 min. It was confirmed that modification of SnS₂ with CQDs can not only improve the light-harvesting ability but also stimulate the charge separation, which therefore can enhance the photoreactivity of SnS₂ toward Cr(VI) reduction. The excellent stability of NC@SnS₂ indicates that it is promising to be practically used in industrial wastewater purification.