Block copolymer-mediated synthesis of silver nanoparticles from silver ions in aqueous media

We report here on the silver (Ag) nanoparticle synthesis in aqueous solutions of poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) block copolymers in the absence of any additional agents. In particular, we examined the effect of reaction temperature, molecular weight of PEO-PPO block copolymer and PEO-PPO block copolymer concentration on the reduction of silver ions (Ag⁺) and the resulting formation of Ag nanoparticles in aqueous PEO-PPO block copolymer solutions. We found that Ag nanoparticles were formed from aqueous silver nitrate (AgNO₃) solutions containing PEO-PPO block copolymer above 100°C. This is most likely due to the dehydration of Ag⁺ caused by thermal motion of water molecules in higher-temperature aqueous solution at high vapor pressure. We also found that the formation of Ag nanoparticles in aqueous PEO-PPO block copolymer solutions was enhanced with larger molecular weight of PEO-PPO block copolymer and with increase in the concentration of PEO-PPO block copolymer in aqueous solutions.