Copper oxide nanoparticles using Mentha spicata leaves as antibacterial, antibiofilm, free radical scavenging agent and efficient photocatalyst to degrade methylene blue dyes

Abstract

In this findings, CuO NPs were made by an easy, eco-friendly, and economical approach using the leaf extract of M. spicata . The prepared Ms-CuO NPs exhibited characteristic absorbance peak at 320 nm with a band gap of 3.87 eV. XRD revealed the presence of crystalline particle with size of 11.28 nm as determined by the Scherrer equation. FTIR revealed the role of various functional molecules in the bio-reduction of copper salts to copper ions (Cu 2+ ). The spherical shaped particles with the mean size of 36 nm were visualized through TEM microscopic image. EDX analysis also confirmed the elemental signals of Cu (91.58%) and O (8.42%) respectively. The biosynthesized Ms-CuO NPs displayed a significant inhibition of Gram-positive Streptococcus pyogenes and Staphylococcus aureus at all tested concentrations. The inhibition size against S. pyogenes and S. aureus was 27.5 ± 0.5 mm and 26.2 ± 0.2 mm at 100 µg mL −1 respectively. On the other hand, the inhibition against K. pneumoniae and E. coli was 17.4 ± 0.6 mm and 18.2 ± 0.1 mm at 100 µg mL −1 respectively. Moreover, a significant inhibition of H 2 O 2 (84%) at 100 µg mL −1 demonstrates the free radical scavenging activity of Ms-CuO NPs. Furthermore, the Ms-CuO NPs have shown excellent degradation potential for industrial dyes i.e., Methylene blue (MB) and was noticed by the gradual decrease in the absorbance (at 460 nm) within 7 h of reaction. The percentage of MB dye degraded was 34% at 1 h which was substantially increased to 98% after 7 h. This study suggests that the Ms-CuO NPs may serve as a promising bactericidal, antibiofilm and antioxidant agent. Also, Ms-CuO NPs could be effectively used in the purification of water bodies contaminated with harmful industrial dyes to reduce toxicity. • M. spicata leaf extract based CuO NPs were synthesized and characterized. • Ms-CuO NPs have shown significant antibacterial and antibiofilm effects. • Ms-CuO NPs have shown H 2 O 2 radical scavenging activity. • Ms-CuO NPs efficiently degraded the methylene blue dye.