Facile Synthesis of Hybrid Copper and Zinc Nanocarriers Based on Biorefinery Waste for the Control of Phytopathogenic Fungi

The extensive use of copper- and zinc-based fungicides has supported global food production but has concomitantly caused soil metal accumulation and ecotoxicity, thereby emphasizing the need for sustainable crop protection systems. Hereby, humic-like substances (HLS) derived from biorefinery lignin-rich waste were used to first chelate copper or zinc ions and then cross-link chitosan chains in order to synthesize green nanocarriers (NCs) for the control of the growth of fungal pathogens. Spectroscopic analyses (infrared, nuclear magnetic resonance, fluorescence) were used to reveal the chemical composition of HLS and their metal ion complexation through their electron-donating groups, while dynamic light scattering indicated tunable NC size and zeta potential, as a clear dose dependency was noticed for both parameters. The resulting nanocarriers showed significant antifungal activity against all the fungal strains studied, with those entrapping Cu2+ having the highest efficacy, followed by the Zn2+-loaded NCs. A lower bioactivity, but with the same trend, was observed for the prepared HLS-chelates. Our findings establish HLS–chitosan nanocarriers as biodegradable, circular-economy platforms coupling structural functionality with reduced environmental impact, offering a viable alternative to conventional metal-based fungicides.