Effect of Cu²⁺ content on the size of copper-based nanoparticles deposited on coffee husk synthesized via green chemistry and its nematicidal activity against <i>Meloidogyne incognita</i> on coffee plants

Abstract A green chemistry approach utilizing coffee husk (CH) biomass waste as both a reducing agent and a carrier for the synthesis of Cu-based nanoparticles (NPs) was implemented. The reducing agents in CH, including reducing sugar and total polyphenol have been quantified. The average size of Cu-based NPs deposited to CH was determined by scanning electron microscopy from 40.4 nm to 62.6 nm and showed a dependence on the CuSO 4 precursor content from 2% to 5%, respectively. The prepared Cu-based/CH nanocomposites were characterized by x-ray diffraction, Fourier transform infrared, and energy dispersive x-ray. The reduction efficiency of Cu 2+ to Cu° and Cu 2 O by reducing agent in CH reached 97.27%–98.56% after 30 min of reaction at 105 °C. The synthesized Cu-based NPs demonstrated the ability to degrade the plant toxin caffeine in CH with an efficiency of 95.46%–96.09%. The Cu-based/CH nanocomposite containing ∼3% Cu showed in vitro nematicidal activity against root-knot Meloidogyne incognita with mortality reaching 85.46%–100% at 20–35 mg l −1 Cu. In the nematode infection experiment on coffee pots, the Cu-based/CH nanocomposite achieved 100% nematode control at 35 mg l Cu. These findings indicated that the Cu-based/CH nanocomposite has the potential to be used as an organic-micronutrient fertilizer and a nematicide for plants in agriculture.