The role of poly(ethylene glycol) in the formation of silver nanoparticles

Silver nanoparticles were prepared under mild conditions by exploiting poly(ethylene glycol) (PEG) in the absence of other chemicals. The chain length of PEG was discovered to play the key role in the formation of silver nanoparticles. Ethylene glycol, which was used as a reducing agent for the preparation of metal particles at high temperatures (>170 °C), was inactive for the reducing of Ag+ at 80 °C. Surprisingly, Ag+ can be smoothly reduced to silver nanoparticles at the same condition in PEG 2000. Further studies demonstrated that the reducing rate of Ag+ to nano-Ag was remarkably enhanced with the increase of polymer chain length of PEG. The particle size depended upon the reaction temperature and concentration of the precursor and an increase in temperature effected a shift of particle size range from ca. 10 to 80 nm. In addition, a noticeable change of sphere to polyprism nanosilver was observed when the reaction temperature was elevated to 120 °C.