Modifying SnS(2) 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. SnS(2) 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 SnS(2) nanoparticles via an in situ method. The resulting composite samples (NC@SnS(2)) were characterized, and their photocatalytic performance was discussed. SnS(2) nanoparticles were obtained as hexagonal ones with a bandgap of 2.19 eV. The optimal doping level for NC@SnS(2) was citric acid: urea:SnS(2) = 1.2 mmol:1.8 mmol:3.0 mmol. It showed an average diameter of 40 nm and improved photocatalytic performance, compared to pure SnS(2), 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 SnS(2) with CQDs can not only improve the light-harvesting ability but also stimulate the charge separation, which therefore can enhance the photoreactivity of SnS(2) toward Cr(VI) reduction. The excellent stability of NC@SnS(2) indicates that it is promising to be practically used in industrial wastewater purification.