A Mechanistic View of the Light-Induced Synthesis of Silver Nanoparticles Using Extracellular Polymeric Substances of Chlamydomonas reinhardtii

In the current study, extracellular polymeric substances (EPS) of and photon energy biosynthetically converted Ag to silver nanoparticles (AgNPs). The reaction mechanism began with the non-photon-dependent adsorption of Ag to EPS biomolecules. An electron from the EPS biomolecules was then donated to reduce Ag to Ag , while a simultaneous release of H acidified the reaction mixture. The acidification of the media and production rate of AgNPs increased with increasing light intensity, indicating the light-dependent nature of the AgNP synthesis process. In addition, the extent of Ag disappearance from the aqueous phase and the AgNP production rate were both dependent on the quantity of EPS in the reaction mixture, indicating Ag adsorption to EPS as an important step in AgNP production. Following the reaction, stabilization of the NPs took place as a function of EPS concentration. The shifts in the intensities and positions of the functional groups, detected by Fourier-transform infrared spectroscopy (FTIR), indicated the potential functional groups in the EPS that reduced Ag , capped Ag , and produced stable AgNPs. Based on these findings, a hypothetic three-step, EPS-mediated biosynthesis mechanism, which includes a light-independent adsorption of Ag , a light-dependent reduction of Ag to Ag , and an EPS concentration-dependent stabilization of Ag to AgNPs, has been proposed.