Reduction of Copper (II) To Copper and Copper (I) Oxide Nanoparticles for Antimicrobial Application Using Calamansi (Citrus Microcarpa) Peel Extract

Calamansi (Citrus microcarpa) is a common citrus fruit in the Philippines that is widely used for food and medicine industries, but its peels are considered as wastes. This study aims to reduce copper (II) ions to copper and copper (I) oxide nanoparticles using calamansi peel extract (CPE). Copper sulfate solution containing 1000 ppm copper was mixed with calamansi peel extract at varying CPE to copper solution volume ratio (1:4, 1:2, 3:4). The reduction process involved adjusting the initial pH to 8 and having constant agitation rate of 185 rpm for 4 hours at varying temperatures (40^oC, 60 ^oC, 80 ^oC). The amount of copper reduced was calculated using the initial and final copper concentration in the solution. The produced solids were subjected to X-Ray Diffraction (XRD) and Scanning Electron Microscope with Energy Dispersive X-Ray Spectroscopy (SEM-EDX) to determine the composition and morphology of the solids. It was determined that % Cu reduction increases with temperature and volume ratio. The highest copper reduction of 67% is attained at 80^oC and 3:4 volume ratio. Solids produced were determined to be Cu and Cu₂O and observed to be spherical with diameter of 42 – 180 nm indicating that the particles are Cu and Cu₂O nanoparticles. The Cu/Cu2O nanoparticles exhibited a zone of inhibition of 11 mm against E.coli. Based on the results, calamansi peel extract can be an eco-friendly and cost-effective alternative in the reduction of copper (II) ions to antimicrobial Cu/Cu₂O nanoparticles.