Photocatalytic and anticancer potentials of green-synthesized neodymium-doped zinc oxide nanoparticles

Zinc oxide nanoparticles (ZnO NPs) doped with rare-earth elements such as neodymium (Nd) demonstrate improved optical, catalytic, and biomedical functionalities, making them promising for multifunctional applications. However, investigations into these properties in green-synthesized Nd-doped ZnO NPs are still limited. Thus, this study aimed to synthesize, characterize, and evaluate the environmental and biomedical potentials of pure and Nd-doped ZnO NPs using Psidium guajava (P. guajava) leaf extract (PGLE). Pure and Nd-doped ZnO nanoparticles were synthesized using PGLE. Their structural, morphological, and optical properties were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, photoluminescence (PL), and X-ray photoelectron spectroscopy (XPS). Photocatalytic performance was assessed through methylene blue degradation under sunlight, while cytotoxicity and apoptosis were evaluated in MCF-7 human breast cancer cells using acridine orange/ethidium bromide (AO/EB) staining. XRD and HRTEM analyses confirmed the hexagonal wurtzite structure of ZnO and revealed a notable reduction in particle size with Nd doping. Raman spectra and PL results indicated that Nd incorporation enhanced defect states and influenced luminescence properties. XPS verified successful Nd substitution, introducing lattice strain and defect sites. Photocatalytic studies showed ~ 99% methylene blue degradation within 150 min, with strong reusability. Cytotoxic assays revealed lower cell viability for Nd-ZnO (22%) compared to pure ZnO (24%), with AO/EB staining confirming apoptosis as the primary mode of cell death. Nd doping into ZnO lattices enhances reactive oxygen species (ROS) generation, improving photocatalytic efficiency and anticancer activity. The green synthesis using P. guajava leaf extract demonstrates a sustainable route for developing multifunctional Nd-ZnO-based nanomaterials for environmental and biomedical applications.