Synthesis and application of ZnO/chitosan oligosaccharide/humic acid derived from natural peat

Abstract

This study reports the synthesis of a ZnO/chitosan oligosaccharide/humic acid-rich fraction (ZnO/COS/HA) bioformulation based on zinc oxide particles consisted of nanosized crystallites (11.4–23.7 nm) assembled into larger submicron rod-like particles stabilized by chitosan oligosaccharides and humic acid derived from natural peat. The material was characterized using x-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier-transform infrared spectroscopy, and energy-dispersive x-ray analysis, confirming the formation of an organic–inorganic hybrid system. The ZnO/COS/HA bioformulation exhibited measurable antibacterial activity against five bacterial strains, including S. aureus, Bacillus subtilis, E. coli, P. aeruginosa, and Enterobacter, with minimum inhibitory concentration values ranging from 75–100 mg l−1. The material also enhanced seed germination and early root development of chestnut (Castanea mollissima), with the most favorable performance observed at 1000 ppm. Higher concentrations resulted in reduced germination and root growth, suggesting concentration-dependent phytotoxic effects. In a field trial conducted from January–April 2025, foliar application of ZnO/COS/HA improved several growth and yield-related parameters of peanut (Arachis hypogaea) compared with the untreated control, resulting in an increase in yield of approximately 14.9%. Although the mechanisms underlying the antibacterial and plant-growth-promoting effects were not directly investigated, the results demonstrate the multifunctional characteristics of the ZnO/COS/HA bioformulation and suggest its potential utility as a combined antibacterial and plant-growth-promoting material.