Microwave assisted green synthesis of copper nanoparticles for enhanced photocatalytic, photothermal, and antibacterial applications

In this work, copper nanoparticles (Cu NPs) are synthesized via a rapid and eco-friendly microwave assisted green synthesis using Psidium guajava leaf extract as a reducing and stabilizing agent. The effect of leaf extract concentration varying from 0.5 mL to 2 mL on Cu NPs formation was systematically investigated. The presence of a surface plasmon resonance peak in UV-Vis absorbance spectra in range of 570 −585 nm confirms the formation of Cu NPs. Photoluminescence (PL) spectra exhibit an emission in the ∼590–605 nm range, with intensity variations attributed to plasmonic interactions and surface effects. Fourier transform infrared spectroscopy (FTIR) analysis confirmed phytochemical-assisted reduction and stabilization, while dynamic light scattering (DLS) analysis revealed the aggregation behaviour of Cu NPs when the volume of leaf extract exceeded 1.5 mL. High resolution transmission electron microscope (HRTEM) analysis reveals the formation of spherical Cu NPs with an average particle size of ∼86 nm, and selected area electron diffraction (SAED) pattern confirms the FCC crystalline structure. The Cu NPs synthesized with 1.5 mL extract (Cu-C) have demonstrated excellent photocatalytic activity with ∼99% degradation of Rose Bengal within 5 min, while methylene blue and acridine red degraded within 1 min and 3 min, respectively. The Cu-C NPs also showed ∼84% degradation efficiency for a mixed dye system in 4 min, indicating their practical applicability. Moreover, Cu NPs exhibited measurable photothermal conversion under solar irradiation, showing a temperature increase of ∼4 °C in 900 s and heat gain of ∼335 J due to plasmonic energy conversion. The antimicrobial activity of Cu NPs was evaluated, and the zone of inhibition for the bacteria Escherichia coli (∼28 mm), Salmonella (∼25 mm), Staphylococcus aureus (∼30 mm), and Bacillus subtilis (∼27 mm) was obtained. Gram-positive and Gram-negative bacteria confirmed strong inhibition via reactive oxygen species generation and membrane disruption. Thus, Cu NPs are promising candidates for multifunctional applications.