Ultrasonic-assisted green synthesis of silver nanoparticles using Mentha aquatica leaf extract for enhanced antibacterial properties and catalytic activity

In the current paper, ultra-small Ag nanoparticles (AgNPs) were synthesized by green and straightforward biogenic technique using Mentha aquatica leaf (MAL) extract as reducing and capping agent. The phytochemicals present in the extract could reduce the Ag⁺ ions to Ag⁰ and form nanoparticles. Several analytical techniques including UV–VIS spectroscopy, Transmission microscopy (TEM) coupled to energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Fourier transforms infrared spectroscopy (FTIR) were performed to the characterization of biosynthesized AgNPs. The effective parameters on synthesis were fully optimized to achieve small nanoparticles. The results showed that applying the ultrasound during the synthesis could result in smaller AgNPs (8 nm) with enhanced antibacterial activity by lowering the minimum inhibitory concentration (MIC). In particular, the MIC values for ultrasound-assisted synthesized AgNPs against P. aeruginosa, E. coli, B. cereus, and S. aureus were 2.2, 58, 20 and 198 μg/mL. In addition, the as-synthesized ultrasound-assisted AgNPs showed considerable catalytic activity for reduction of different types of dyes as environmental pollutants. The effective parameters on the catalytic reduction of methylene blue were fully optimized, where 807.69 s⁻¹ g⁻¹ was found as normalized first-order kinetic constant for catalytic degradation of methylene blue under optimized conditions. This study provides an insight into the controlled green synthesis AgNPs and how to manipulate their activities for different applications.