Optimizing a novel green synthesis of zincite nanoparticles using knotwood biomass residue of Eucalyptus citriodora: A multi-technique characterization and antifungal analysis

This study aims to develop a sustainable, green synthesis method for zinc oxide nanoparticles (ZnO NPs) using Eucalyptus citriodora (EC) knotwood waste extract and evaluate their antifungal efficacy for potential application in wood protection. This eco-friendly approach leverages the bioactive constituents of EC knotwood, an abundant yet underutilized biomass byproduct from the wood industry, to facilitate nanoparticle formation without the use of toxic chemical reagents. Physicochemical characterization confirmed a 10.00 ± 1.2% yield of EC extract, with a high total phenolic content of 457.40 ± 3.5 mg GAE/g extract, which played a crucial role in the bioreduction and stabilization of ZnO NPs, synthesized with a 28.34 ± 1.8% yield. X-ray diffraction (XRD) analysis validated the formation of highly crystalline ZnO NPs with a hexagonal wurtzite structure and an average crystallite size of 29 nm. UV-Vis spectroscopy exhibited an absorption peak at 368 nm, resembling bulk ZnO, indicating negligible quantum confinement effects. Energy-dispersive X-ray diffraction (EDX) and Fourier Transform Infrared Spectroscopy (FTIR) confirmed elemental purity and functional group interactions, respectively. Morphological investigations using SEM and TEM revealed well-dispersed, predominantly spherical ZnO NPs ranging from 20 to 40 nm, corroborating XRD findings. The biosynthesized ZnO NPs demonstrated potent antifungal activity, significantly inhibiting mycelial growth of Laetiporus sulphureus (44 ± 2.1% – 97 ± 0.5%) and Pycnoporus sanguineus (38 ± 1.7% – 97 ± 0.5%) at concentrations of 10–50 ppm. These results highlight the potential of EC-derived ZnO NPs as a sustainable and cost-effective alternative to conventional antifungal agents, paving the way for environmentally responsible wood protection strategies.