Fabrication of visible light responsive nitrogen-doped carbon quantum dots/MIL-101(Cr) composites for enhanced photodegradation of Rhodamine B

Abstract

In this study, an environmentally friendly hydrothermal process was successfully utilized for the fabrication of MIL-101(Cr) (MIL-Cr) and nitrogen-doped carbon quantum dots (N-CQDs) without employing toxic and hazardous hydrofluoric acid and organic solvents. Then, a simple solvent-deposition technique was used to prepare MIL-Cr/N-CQDs(x) composites without requiring specialized equipment. To assess the photocatalytic capabilities of the synthesized materials, Rhodamine B (RhB) was chosen as one of the wastewater toxic organic dye pollutants for photo-degradation experiments. The optimum amount of N-CQDs in composite structure was determined by mixing different volumes of N-CQDs with MIL-Cr, in which MIL-Cr/N-CQDs(2) composite exhibited the highest photocatalytic performance (95%) under visible light illumination. Also, all composites showed better photocatalytic activity in comparison with pristine MOF and N-CQDs individually because N-CQDs can operate as electron acceptors when coupled with MOF, which can prevent the fast electron-hole recombination and increase the visible light absorption. Based on the results of the kinetic investigation, the MIL-Cr/N-CQDs(2) depicted the highest kinetic rate, which is 2.63 and 9.5 times larger than pristine MIL-Cr and N-CQDs under the same experimental conditions. Furthermore, a photocatalytic mechanism was postulated through reactive species scavenging experiments, and it was found that •OH and photo-generated h+ were crucial to the degradation process.