Temperature dependent sono-photocatalysis via optimized N,S-codoped carbon quantum dots@MOF: MIL-88B composite for Cr(VI) reduction and dye degradation

Abstract

Fast industrialization influences numerous sectors, including freshwater resources contaminated with toxic substances, which is responsible for the sharp increase in pollution. Metal-organic frameworks (MIL-88B) and the sono-photocatalysis method can remove these organic and inorganic pollutants. However, their fast recombination limits the photo & sono-photocatalytic performance. Therefore, Nitrogen and Sulfur co-doped carbon quantum dots (N,S-CQDs-doped) MIL-88B were designed here, to enhance the charge separation and associated catalysis, The crystal structure of N,S-CQDs was controlled by adjusting the synthesis temperature and compatibility of different degree of crystallinity was analyzed for composite formation with MIL-88B. N,S-CQDs synthesized at 140 °C showed better performance in composite, which was 82 % and 92 % higher than undoped MIL-88B for photo & sono-photocatalysis, respectively. However, in basic circumstances, the optimum N,S-CQDs@MIL-88B concentration showed 96 % degradation due to the significant impact of –OH groups in photocatalysis. Furthermore, the optimum N,S-CQDs@MIL-88B concentration was observed for 0.08 w/w%, resulting in 71 % and 87 % photo & Sono photocatalytic activity (PCA, SPCA) in 120 min. N,S-CQDs@MIL-88B also offers a 99 % Cr(VI) transition to Cr(III), demonstrating how it applies to organic and inorganic substances. The better performance composite is due to better light absorbance and charge separation, as confirmed by optical properties.