Green synthesis of copper oxide nanoparticles from coffee effluent for antimicrobial and photocatalytic degradation applications

Copper oxide nanoparticles (CuO-NPs) were synthesized using coffee effluent as a reducing agent through a simple, cost-effective and eco-friendly approach. The synthesized nanoparticles were characterized by UV–Vis spectroscopy, FTIR, SEM, DLS and XRD analyses. SEM revealed an average particle size of 165 nm, while DLS analysis showed a zeta potential of 32.57 mV, indicating good nanoparticle stability. XRD confirmed the crystalline nature of the CuO-NPs with a monoclinic phase. The antioxidant potential of the nanoparticles was evaluated using the DPPH assay, which demonstrated 61.79% radical scavenging activity at a concentration of 500 μg/mL. Antibacterial activity assessed by the well diffusion method against Streptococcus mutans, Bacillus subtilis and Pseudomonas putida showed the highest inhibition against S. mutans, with a 27 mm zone of inhibition at 5 mg/mL. The photocatalytic efficiency of CuO-NPs was investigated using two azo dyes, malachite green and congo red, achieving degradation efficiencies of 94% and 77%, respectively, within 210 min. These findings demonstrate the multifunctional potential of coffee effluent-mediated CuO-NPs as antioxidant, antibacterial, and photocatalytic agents, highlighting their promising applications in environmental remediation, water treatment, food packaging and biomedical fields. Further studies are needed to evaluate their cytotoxicity, biocompatibility, and in vivo performance.