Facile synthesis of chitosan/CuO nanocomposites for potential use as biocontrol agents

Chitosan/CuO nanocomposites (Chi/CuO) were prepared by facile and eco-friendly technique. The 2%w/v chitosan solution was mixed with 0.5 %w/w sodium tripolyphosphate (STPP), resulting in the formation of ionically crosslinked chitosan. The crosslinked chitosan was soaked in an aqueous solution containing 0.001, 0.01 or 0.1 mol/L CuSO₄·5H₂O for 24 hrs, in which the Cu²⁺ ions were absorbed into the chitosan network, forming as the chitosan/Cu²⁺ precursors. The chitosan/Cu²⁺ precursors were hydrothermally reacted in two different basic media, i.e. NaOH and NH₄OH, at 100^°C for 24 hrs, resulting in the nano-sized CuO crystals hydrothermally grew and embedded in the crosslinked chitosan matrix. The CuO grown in the NaOH possessed larger crystallite size and higher crystallinity than that in the NH₄OH. In addition, the CuO crystallite size in the nanocomposites increased with the increase of initial concentration of Cu²⁺ starting agent due to the increase of Cu²⁺ quantity in the chitosan/Cu²⁺ precursors. The chitosan/CuO nanocomposites prepared by using 0.01 and 0.1 mol/L Cu2+ could exhibit the antibacterial activities after intimate contact with Staphylococcus aureus and Escherichia coli under JIS L 1902:1998 (Qualitative) test method, indicating their potential use as biocontrol agents.