Boosting the photodegradation of rhodamine B with the CuWO4/g-C3N4 heterojunction by introducing biomass derived N-CQDs as an electron mediator: mechanism and DFT calculations

A Z-scheme heterojunction CuWO4/N-CQD/g-C3N4 (CWO/N-CQD/CN) was constructed using Euphorbia neriifolia leaf derived N-CQDs (nitrogen-doped carbon quantum dots) as an electron mediator. Among the nanocomposites prepared with different ratios of CWO and N-CQD/CN, the 0.2-CWO/N-CQD/CN nanocomposite exhibits excellent photocatalytic degradation efficiency for rhodamine B (RhB) up to 97.8% under visible light irradiation as compared to the binary CWO/CN and N-CQD/CN composites. The reduced photoluminescence intensity and higher lifetime reveal the formation of a heterojunction between the nanoparticles, thereby lowering the recombination of electron–hole pairs. Reactive oxygen species scavenging assays have established that hydroxyl radicals (˙OH), holes (h+) and singlet oxygen (1O2) are the primary reactive species in RhB dye degradation. A Z-scheme photocatalytic mechanism was suggested based on the DFT calculations and band structure of CWO/N-CQD/CN. The effect of various parameters like pH, catalyst amount, H2O2 concentration, and dye content was also examined in RhB degradation. Moreover, the Z-scheme photocatalyst possesses good recyclability up to the fourth cycle. Using the LC-MS approach, the degradation of RhB into smaller organic moieties was also observed. Hence, this study provides a unique perspective on developing an effective Z-scheme photocatalyst that has practical utility in environmental remediation.