Synthesis of silver nanoparticles using Alchemilla vulgaris and Helichrysum arenarium for methylene blue and 4-nitrophenol degradation and antibacterial applications

This study aimed to evaluate the concept of green synthesis of metallic nanoparticles (silver nanoparticles, AgNPs) by plant extracts without using any toxic or hazardous materials. Alchemilla vulgaris (AV) and Helichrysum arenarium (HA) are used as capping and reducing agents to synthesize AgNPs (as coded AV-AgNPs and HA-AgNPs). Both synthesized AgNPs were characterized by UV-visible spectrophotometry, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and transmission electron microscope (TEM). The results of characterization exhibited that AgNPs were successfully synthesized. They are highly well-dispersed, mostly spherical shape with an average size 15-20 nm. Catalytic reduction of methylene blue (MB) and 4-nitrophenol (4-NP) was assessed using synthesized AgNPs as nano-catalysts in the presence of NaBH4. The catalytic activity of the synthesized AgNPs revealed significant results in terms of degradation of MB and 4-NP to 4-AP (4-aminophenol). The reduction reactions of MB and 4-NP happen within 6-7 min using synthesized AV-AgNPs and HA-AgNPs in the presence of NaBH4. According to the reusability analysis, synthesized AgNPs demonstrated excellent degradation performances by the more than 94% removal efficiency maintained after five reuse cycles. In addition, antibacterial activities of AgNPs were investigated against Escherichia coli (E. coli; Gram-negative bacteria) and Staphylococcus aureus (S. aureus; Gram-positive bacteria) by using quantitative well-diffusion method and the inhibition zones were determined using Mueller-Hinton agar (MHA) media. AV-AgNPs and HA-AgNPs showed strong antibacterial activities against E. coli with in inhibition zone diameters 25.5 and 25 mm, respectively. AV-AgNPs and HA-AgNPs were also extremely effective on S. aureus with high inhibition zone values of 22 and 24 mm, respectively. Finally, the fabricated silver nanoparticles could be excellent candidates for the separation of hazardous materials.