Green synthesis of copper-based nanoparticles using coffee husk and investigation of its antifungal activity and phytotoxicity <i>in vitro</i>

Coffee husks (CH) are waste with abundant reserves in Vietnam. This type of waste is mainly composed of cellulose, hemicellulose, minerals, and some reducing active ingredients such as polyphenols, reducing sugars, and lignin, so it is suitable for use as raw material for producing organic fertilizer for reuse in agriculture. In this study, we present a new method to quickly treat CH by directly using it as a reducing and stabilizing agent to green synthesize the Cu/Cu2O/CH nanocomposite with Cu content of 3% (w/w). The size of the obtained Cu/Cu2O nanoparticles (NPs) determined from scanning electron microscope (SEM) images was 54.6 ± 28.2 nm. The characteristic properties of the materials are determined by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), energy dispersive X-ray (EDX), and elemental mapping. In the in vitro experiment, the Cu/Cu2O/CH nanocomposite achieved 93.52% effectiveness against Phytophthora capsici at a concentration of 55 mg/L Cu, and the inhibitory concentration 50% (IC50) value was determined to be 19.67 mg/kg. Furthermore, the obtained the Cu/Cu2O/CH nanocomposite with a content of ∼3% Cu (w/w) can degrade caffeine, a toxic substance to plants in CH by ∼95%. The Cu/Cu2O/CH nanocomposite can be potentially used as a disease control agent and micronutrient fertilizer for plants.