Preparation of silver nanoparticles using tryptophan and its formation mechanism.

A non-toxic route was used for the preparation of silver nanoparticles using tryptophan (Trp) as reducing/stabilizing agent in the presence of cetyltrimethyl ammonium bromide (CTAB). Role of water soluble neutral polymer poly(vinylpyrrolidone) (PVP) has been studied on the growth of yellow colour silver nanoparticle formation. The synthesized nanostructures were characterized by UV-Visible absorption spectroscopy, transmission electron microscopy (TEM) by observing the size and distribution of silver nanoparticles. As the reaction proceeded, particles grew up to about 10 and 20 nm in the presence and absence of PVP, respectively, as determined by TEM. The formed nanoparticles showed the highest absorption plasmon band at 425 nm. Rate of silver sol formation increases with the [Trp], [CTAB] and [PVP], reaching a limiting value and then decreases with the increase in concentrations of these reagents. It was observed that nanoparticles are spherical, aggregated and poly dispersed in the absence and presence of PVP, respectively. On the basis of kinetic data, a suitable mechanism is proposed and discussed for the silver sol formation.

A kinetic study of silver nanoparticles formation from paracetamol and silver(I) in aqueous and micellar media.

UV-vis spectrophotometeric, transmission electron microscopy (TEM) and viscometric techniques were used for the formation, characterization and kinetics of silver sol formation using silver nitrate as source of silver, paracetamol as reducing agent and cetyltrimethylammonium bromide (CTAB) as the stabilizer in absence and presence of poly(vinyl alcohol) (PVA). The sigmoidal curve of absorbance versus the reaction time suggests an autocatalytic reaction path. Transmission electron microscopy (TEM) results show that the silver nanoparticles are all spherical, highly dispersed and aggregated in aqueous solution. In the formation of silver nanoparticles, alkaline solution is required. The presence of PVA inhibits the rate of silver nanoparticles formation. Effects of [Ag(+)], [paracetamol], [CTAB], [NaOH] and [PVA] on the silver sol formation rate were analyzed.

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.