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

www.nature.com/scientificreports OPEN Valorization of domestic wastes into Cu-MOF-derived CuO@ZnO nanocomposites for sustainable photocatalytic degradation of methylene blue and rhodamine B dyes M. S. Samy1, H. M. Abou El Nadar1, E. A. Gomaa1, Amr Awad Ibrahim1,2 & Mina Shawky Adly1,2 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. CuO0.25@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 CuO0.25@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. Keywords Photocatalytic degradation, Metal–organic frameworks, Waste PET, Mott-Schottky Water supplies must remain intact for humans to survive and for Earth’s ecosystems to thrive. In recent decades, industrial growth and evolving human lifestyles have led to various health issues caused by water and air pollution1,2. The wide use of dyes in the printing, leather, and textile industries has raised significant environmental and health concerns3,4. It is estimated that about 20% of textile dyes are released as wastewater, dyeing and textile effluents account for 17–20% of global water pollution5. These dyes are non-biodegradable and carcinogenic, posing serious health risks to humans and aquatic ecosystems6. In particular, rhodamine B (RhB) dye, a water-soluble cationic xanthene dye, can irritate the skin, eyes, and respiratory tract and exhibit carcinogenic and neurotoxic effects7. According to recent survey results, about 65% of the world’s population will be adversely affected by freshwater scarcity by 20508,9. These dye effluents are degraded naturally by sunlight, but the process is slow10. The traditional methods for reducing dye contamination, such as ozonation, chlorination, and membrane filtration, are ineffective due to their high operating costs, prolonged treatment times, and secondary sludge formation11,12. Nowadays, chemical methods, including advanced oxidation processes (AOPs) such as photocatalysis, are more effective. It is highly efficient, low-cost, and environmentally 1Department of Chemistry, Faculty of Science, Mansoura University, Al-Mansoura 35516, Egypt. & Desalination Center, Faculty of Science, Mansoura University, Mansoura, Egypt. email: 2Energy Scientific Reports | (2026) 16:15042 | https://doi.org/10.1038/s41598-026-51864-6 1 friendly, with high reaction rates that are not time-consuming, and it does not produce secondary pollution13. That is dependent on the presence of a semiconductor material, which produces electron–hole pairs (e− /h+ ), that react with water and dissolved oxygen to produce(reactive ) oxygen species (ROS). These species include hydroxyl radicals (HO•) and superoxide radical anions O•− to oxidize and degrade organic and inorganic 2 pollutants in water without toxic byproducts, thereby ensuring their success14–20. Additionally, adding activators such as sodium borohydride (NaBH4) and peroxymonosulfate (PMS) can improve the breakdown of organic • 21,22. Photocatalysis has become contaminants by the formation of SO− 4 and HO radicals that target pollutants a highly promising and adaptable technique that has attracted considerable attention across a variety of fields, including wastewater treatment, owing to its efficiency and sustainability. It has shown remarkable potential for applications like hydrogen production, CO2 reduction, and microbial disinfection23,24. Furthermore, the photoFenton process is important for pollutant removal, as it generates reactive hydroxyl radicals via ferrous ions and H2O2 under visible light, thereby facilitating pollutant degradation25,26. Semiconductor nanostructures based on metal oxides, including ZnO, CuO, Cu2O, TiO2, BiVO4, WO3, and NiO, have superior photocatalytic degradation capabilities and improve incident photon absorption27–32. ZnO and TiO2 nanoparticles have similar valence and conduction bands, as well as similar electron affinities and energy levels33,34. Because ZnO absorbs a larger fraction of the solar spectrum than TiO2, it has become increasingly popular recently due to its simple fabrication, affordability, environmental sustainability, and improved photocatalytic activity30,35. However, ZnO has many disadvantages, including a wide band gap of approximately 3.2 eV that impedes electron and hole transport to the surface for reaction and increases the recombination rate. It also absorbs in the UV region (λ = 380 nm) with only 5% absorption in the visible spectrum36–39. Enhancing photocatalytic efficiency largely depends on suppressing the recombination of electron–hole pairs. Therefore, understanding and regulating the recombination mechanism is essential for improving photocatalyst performance. Various strategies have been adopted to inhibit charge recombination, including doping ZnO with non-metals, transition metals, and constructing semiconductor heterojunctions40,41. Heterojunction formation using low-bandgap CuO semiconductors (1.2–2.1 eV) is an effective method to overcome ZnO’s low photodegradation efficiency by extending its absorption into the visible. It also enhances charge separation of photogenerated electron–hole pairs, reduces charge-carrier recombination, and increases surface area via additional pore sites, thereby maximizing photodegradation activity42–44. Moreover, CuO@ ZnO nanocomposites have already been proposed for various applications, including photocatalytic activity, magnetic properties, conductivity studies, and gas sensing45,46. Metal oxides with well-controlled morphologies can be synthesized via direct air annealing of MOFs, yielding materials with higher surface areas and optimal pore structures47. Doustkhah et al. demonstrated t (...truncated)