Remarkable Improvement in Photocatalytic Performance for Tannery Wastewater Processing via SnS2 Modified with N-Doped Carbon Quantum Dots: Synthesis, Characterization, and 4-Nitrophenol-Aided Cr(VI) Photoreduction

Photocatalytic pathways are proved crucial for the sustainable production of chemicals and fuels required for a pollution-free planet. Electron-hole recombination is a critical problem that has, so far, limited the efficiency of the most promising photocatalytic materials. Here, the efficacy of the 0D N doped carbon quantum dots (N-CQDs) is demonstrated in accelerating the charge separation and transfer and thereby boosting the activity of a narrow-bandgap SnS2 photocatalytic system. N-CQDs are in situ loaded onto SnS2 nanosheets in forming N-CQDs/SnS2 composite via an electrostatic interaction under hydrothermal conditions. Cr(VI) photoreduction rate of N-CQDs/SnS2 is highly enhanced by engineering the loading contents of N-CQDs, in which the optimal N-CQDs/SnS2 with 40 mol% N-CQDs exhibits a remarkable Cr(VI) photoreduction rate of 0.148 min(-1), about 5-time and 148-time higher than that of SnS2 and N-CQDs, respectively. Examining the photoexcited charges via zeta potential, X-ray photoelectron spectroscopy (XPS), surface photovoltage, and electrochemical impedance spectra indicate that the improved Cr(VI) photodegradation rate is linked to the strong electrostatic attraction between N-CQDs and SnS2 nanosheets in composite, which favors efficient carrier utilization. To further boost the carrier utilization, 4-nitrophenol is introduced in this photocatalytic system and the efficiency of Cr(VI) photoreduction is further promoted.