Green biomimetic preparation of efficient Ag-ZnO heterojunctions with excellent photocatalytic performance under solar light irradiation: a novel biogenic-deposition-precipitation approach

Herein, we report a unique single-step biogenic deposition precipitation (BDP) approach as a straightforward route for producing efficient Schottky contact between noble metal nanoparticles and wide-band-gap semiconductors. Successful preparation of Ag-ZnO heterojunctions using fennel seed extract (FSE) has been described. The effective biomolecules available in the seeds functioned as novel biogenic materials for the precipitation of adsorbed silver ions (Ag+) on ZnO particles as metallic silver (Ag-0). The as-prepared composite materials were characterized using diffuse reflectance spectroscopy (DRS), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), energy dispersive X-ray (EDX) study, X-ray photoelectron spectroscopy (XPS), photoluminescence spectroscopy (PL) and high-resolution transmission electron microscopy (HR-TEM). The biogenically prepared Ag-ZnO nanocomposites exhibited excellent photocatalytic activity towards reduction/degradation of colored (rhodamine B (Rh-B) dye) as well as colorless (chlorpyrifos pesticide) pollutants when irradiated under solar light. Among the prepared photocatalysts, 3 wt% Ag-ZnO hybrid composite showed the best photocatalytic activity by efficiently degrading hazardous organic pollutants within a very short time. The superior photocatalytic performance of biogenically prepared Ag-ZnO heterojunctions can be ascribed to the clean production of steady and efficient Schottky contact between plasmonic AgNPs and semiconducting ZnO NPs.