A green chemical approach for synthesis of shape anisotropic gold nanoparticles

A complete green chemical reaction between aurochloric acid and tea polyphenols resulted in the reduction of Au3? ? Au0 . The reaction was carried out in a Teflon-coated bomb digestion vessel at 200 C. It was observed that with increasing the reaction time from 1 to 5 h, the shape of the nanoparticles changed from sphericalto rod-like structures. The reaction was followed with the help of UV–vis spectrometer, which showed a single absorption peak at 548 nm for 1-h reaction product and two peaks for a 5-h reaction product at 533 and 745 nm corresponding to the transverse and longitudinal surface plasmon resonance bands. Microstructures obtained from transmission electron microscope revealed that the samples obtained after 1-h reaction are predominantly spherical in shape with an average size of 15 nm. Whereas samples obtained after 5 h of reaction exhibited rod-like structures with an average size of 45 nm.