Enhanced visible light photocatalytic inactivation of Escherichia coli using silver nanoparticles as photocatalyst

• Green synthesis of AgNPs using Cirsium arvense plant extract.
• The AgNPs were well dispersed, spherical shape and small sized (< 15 nm).
• We determined the effect of extract concentration and pH on the formation of AgNPs.
• The AgNPs were screened for photo inactivation of E. coli.
• Effect of irradiation time, size and shape of AgNPs on the inhibition of E. coli.

The silver nanoparticles (AgNPs) were green synthesized using Cirsium arvense plant extract as a reducing and stabilizing agent, with superior photo inactivation activity against Escherichia coli (E. coli). The synthesized AgNPs had crystalline structure and were characterized by UV–vis spectroscopy, XRD, HRTEM, SEM, EDX and FT-IR. The formation of nanoparticles was observed at different pH and different plant extract concentrations and it was found that at higher pH (pH > 6) and at lower concentration (10 mL), the reducing and stabilizing efficiency of plant extract was increased. The synthesized AgNPs had small size (< 15 nm) and spherical shape. The AgNPs were evaluated for antibacterial activity against E. coli. Before transferring it to antibacterial activity, it was placed under visible light for 120 min. The same experiment was performed in dark as a control medium. The photo irradiated AgNPs were observed to be more effective against E. coli. The results showed, that the diameter of zone of inhibition of visible light irradiated AgNPs against E. coli was 23 (± 0.5) mm and in dark was 11 (± 0.4) mm.