Formation and characterization of surfactant stabilized silver nanoparticles: a kinetic study

Kinetic data for the silver nitrate-ascorbic acid redox system in presence of three surfactants (cationic, anionic and nonionic) are reported. Conventional spectrophotometric method was used to monitor the formation of surfactant stabilized nanosize silver particles during the reduction of silver nitrate by ascorbic acid. The size of the particles was determined with the help of transmission electron microscope. It was found that formation of stable perfect transparent silver sol and size of the particles depend upon the nature of the head group of the surfactants, i.e., cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulphate (SDS) and Triton X-100. The silver nanoparticles are spherical and of uniform particle size, and the average particle size is about 10 and 50 nm, respectively, for SDS and CTAB. For a certain reaction time, i.e., 30 min, the absorbance of reaction mixture first increased until it reached a maximum, then decreased with [ascorbic acid]. The reaction follows a fractional-order kinetics with respect to [ascorbic acid] in presence of CTAB. On the basis of various observations, the most plausible mechanism is proposed for the formation of silver nanoparticles.