Valorization of domestic wastes into Cu-MOF-derived CuO@ZnO nanocomposites for sustainable photocatalytic degradation of methylene blue and rhodamine B dyes

Abstract

Abstract The conversion of waste materials into value-added functional photocatalysts represents a sustainable strategy for environmental restoration. Metal–organic frameworks (Cu-BDC) synthesized from waste-derived precursors were utilized as templates to construct CuO@ZnO n–n heterojunction photocatalysts. XRD analysis confirmed the growth of wurtzite ZnO and monoclinic CuO phases, as evidenced by selected-area electron diffraction (SAED) patterns showing well-defined diffraction rings, indicating crystallinity. HRTEM revealed lattice spacings of 0.262 nm and 0.232 nm corresponding to ZnO (002) and CuO (111), respectively. DRS-Tauc analysis demonstrated enhanced visible-light absorption and a narrowing of the bandgap from 3.1 to 2.89 eV upon CuO incorporation. CuO 0.25 @ZnO achieved the highest photocatalytic performance, with 99.0% and 97.7% degradation of methylene blue (MB) and rhodamine B (RhB), respectively. The degradation kinetics followed pseudo-first-order kinetics, with rate constants of 0.025 and 0.024 min −1 for MB and RhB, respectively, which were higher than those for pure ZnO. Photoelectrochemical measurements and photoluminescence (PL) spectra revealed high charge separation and reduced recombination of CuO 0.25 @ZnO. Scavenger experiments and terephthalic acid fluorescence analysis confirmed the generation of reactive species, supporting a Z-scheme charge-transfer mechanism. Ultimately, we anticipate that this novel photocatalyst will have meaningful applications in the energy sector and environmental remediation.