Various light sources-assisted photodegradation of Rhodamine B using magnetically separable and reusable...

Persistent organic dyes such as Rhodamine B (RhB) pose a serious threat to water quality due to their toxicity at trace concentrations and resistance to biodegradation. In this study, magnetic MnFe₂O₄/Cdots (MFC) nanocomposites were synthesized via a green coprecipitation method using Moringa oleifera leaf extract and watermelon peel waste as sustainable precursors. The nanocomposites were prepared by sonication with Cdot concentrations of 10, 15, 20, 25, and 30 mL, referred to as MFC1-MFC5. X-ray diffraction confirmed a single-phase cubic spinel structure, while morphological analysis revealed nearly spherical, semi-uniform particles with slight aggregation and sizes of 12-14.1 nm, strongly attached to Cdots. Increasing Cdot concentration induced a redshift in absorption and band gap narrowing. The nanocomposites exhibited saturation magnetization values of 14-18.9 emu/g, indicating good magnetic properties. Photocatalytic performance improved with increasing Cdots concentration, resulting in enhanced RhB degradation efficiency. Under ultraviolet irradiation for 90 min, MFC4 achieved the highest degradation efficiency of 98.56%, while degradation efficiencies of 76.8% under visible light and 85.7% under sunlight were obtained. Furthermore, the magnetic nanocomposites were easily recovered using an external magnetic field and maintained high degradation efficiency over multiple cycles, highlighting their potential as eco-friendly, magnetically separable, and reusable photocatalysts for wastewater treatment.