Biomimetic Synthesis, Characterization, and Evaluation of Fluorescence Resonance Energy Transfer, Photoluminescence, and Photocatalytic Activity of Zinc Oxide Nanoparticles

Owing to the development of nanotechnology, biosynthesis of nanoparticles (NPs) is gaining considerable attention as a cost-effective and eco-friendly approach that minimizes the effects of toxic chemicals used in NP fabrication. The present work reports low-cost phytofabrication of zinc oxide (ZnO) NPs employing aqueous extracts of various parts (leaves, stems, and inflorescences) of Tephrosia purpurea (T. purpurea). The formation, structure, morphology, and other physicochemical properties of ZnO NPs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, and dynamic light scattering (DLS). UV-Vis spectral analysis revealed sharp surface plasmon resonance (SPR) at around 250-280 nm, while the XRD patterns confirmed distinctive peaks indices to the crystalline planes of hexagonal wurtzite ZnO NPs. TEM analysis confirmed the presence of spherical-shaped ZnO NPs with average particle sizes (PS) between 25-35 nm, which was in agreement with the XRD results. FTIR analysis revealed that phenolics, flavonoids, amides, alkaloids, and amines present in the plant extract are responsible for the stabilization of the ZnO NPs. Further, the hydrodynamic diameter in the range of 85-150 nm was measured using the DLS technique. The fluorescence resonance energy transfer (FRET) ability of biogenic ZnO NPs was evaluated, and the highest efficiency was found in ZnO NPs synthesized via T. purpurea inflorescences extract. Photoluminescence (PL) spectra of biogenic ZnO NPs showed three emission peaks consisting of a UV-Vis region with high-intensity compared to that of chemically synthesized ZnO NPs. The biosynthesized ZnO NPs showed photocatalytic activity under solar irradiation by enhancing the degradation rate of methylene blue (MB). Among the prepared biogenic ZnO NPs, T. purpurea leaves mediated with NPs acted as the most effective photocatalyst, with a maximum degradation efficiency of 98.86% and a half-life of 84.7 min. This is the first report related to the synthesis of multifunctional ZnO NPs using T. purpurea, with interesting characteristics for various potential applications in the future.