Effect of pyrene on formation of natural silver nanoparticles via reduction of silver ions by humic acid under UV irradiation.

This work reported the role of pyrene in formation of naturally occurring silver nanoparticles (AgNPs) via the reduction of silver ions by humic acid under the UV irradiation in the aquatic environment. An increase in temperature (25-90 °C), pH (5-9) or concentration of humic acid (2.5-15 mg/L) led to an enhanced formation of AgNPs. The TEM images indicated the formed AgNPs were spherical with an average particle size of ∼20 nm. Pyrene showed a limited capacity for the photoreduction of silver ions, and when both pyrene and humic acid were present, pyrene would compete with humic acid for the reduction of silver ions. However, the presence of pyrene would enhance the stability and suppress the antibacterial activity of natural AgNPs. The UV-vis spectra of AgNPs suspensions generated with pyrene did not change within 45 days. The inhibition rates against Escherichia coli of AgNPs generated with pyrene were 8-32% lower than those of AgNPs generated without pyrene. This study provides environmental implications on the fate and ecotoxicity of natural AgNPs with interaction of polycyclic aromatic hydrocarbons.