Recent advances in neem-mediated green synthesis of Ag-doped ZnO nanostructures: fundamentals, characterization, visible-light photocatalysis, and optoelectronic applications

Abstract

Zinc oxide (ZnO) is among the most heavily studied wide-band-gap semiconductors, but its practical use in visible-light Photocatalysis and optoelectronic devices is limited by a band gap confined to the near-ultraviolet and by fast electron-hole recombination. Doping with silver addresses both limitations, and synthesizing the resulting Ag-doped ZnO (Ag-ZnO) nanostructures through plant-mediated green routes avoids the toxic reagents associated with conventional chemical synthesis. This review consolidates in a single treatment, the synthesis mechanism, characterization evidence, and application performance reported for neem ( Azadirachta indica )-mediated Ag-ZnO. Following a PRISMA-informed literature search, the review sets out the structural and electronic basis for Ag doping in ZnO, the phytochemical mechanism by which neem extract reduces and caps the resulting nanostructures, and the structural, morphological, and spectroscopic evidence (XRD, electron microscopy, FTIR, UV-visible, photoluminescence, XPS, BET) used to confirm successful synthesis. It then reviews the two principal application domains reported for this material: visible-light photocatalytic degradation of dyes, antibiotics, and pesticide/phenolic pollutants, and optoelectronic performance in UV photodetectors, dye-sensitized solar cells, and light-emitting diodes, in each case tracing performance back to the shared surface-Plasmon-resonance and Schottky-junction mechanisms silver doping introduces. The review closes with a critical assessment of the reproducibility, scalability, toxicological, and characterization-reporting gaps that currently limit translation of this material beyond the laboratory, and outlines the specific steps needed to close them.