Labeo Rohita fish bone derived ZnO/CaO composite material for efficient photocatalytic degradation of methylene blue under the irradiation of natural sunlight

Developing new functional composite materials for efficient wastewater treatment can significantly enhance the treatment process. In this study, a ZnO/CaO composite was synthesized using fish bones of Labeo rohita, (commonly referred to as LR) via a modified hydrothermal method. The composite was characterized using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), powder X-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, and UV–visible spectrometry. SEM analysis revealed a surface-etched morphology with densely packed nanorod-like structures, while EDS confirmed the presence of Zn, O, and Ca. XRD identified the monoclinic phase of CaO and the hexagonal phase of ZnO, confirming the successful synthesis of ZnO/CaO. FTIR analysis supported the XRD results. The optical band gap of the composite was measured at 2.76 eV. The photocatalytic activity of ZnO/CaO was assessed during the degradation of methylene blue (MB) under natural sunlight. MB degradation was influenced by dye concentration, catalyst dose, pH, and cycling stability. The photocatalytic evaluation parameters such as a catalyst dose of 15 mg, a low dye concentration of 5 ppm, and a pH of 12, achieved degradation efficiencies of nearly 100 %, respectively. The composite exhibited excellent cycling stability over five recycling tests. These findings underscore the potential of ZnO/CaO as a low-cost, ecofriendly, and scalable photocatalyst for wastewater treatment. The proposed strategy of photocatalyst design is low-cost, facile, and ecofriendly, making it suitable for large-scale production.