F.M. Al-Nowaiser

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.

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.

Effect of Poly(Vinyl Alcohol) on the Size, Shape, and Rate of Silver Nanoparticles Formation

The kinetics of cetyltrimethylammonium bromide (CTAB) stabilized silver nanoparticles have been studied spectrophotometrically at 425 nm (λmax of silver sol) in the absence and presence of water soluble polymer (poly(vinyl alcohol); PVA). Transmission electron microscopy (TEM), ultraviolet-visible spectroscopy, and viscosity measurements were used to determine the size, shape, and the size distribution of the silver nanoparticles. The reaction follows the same behavior with respect to [CTAB], [tri-sodium citrate], and [Ag+] in both the media indicating the silver nonoparticles were formed through the same reaction path. The sigmoid nature of the kinetic curves suggests an autocatalytic path in the growth of nanoparticles. The reaction rate is increased by increasing [CTAB]. The presence of PVA inhibits nucleation and retards the rate of particle growth, absorbance and size of the particles. Polymer-surfactant interactions were analyzed based on the viscosity of the reaction mixture.

Formation and Decomposition of Water Soluble Colloidal Manganese Dioxide During the Reduction of by Cysteine. A Kinetic Study

Upon addition of cysteine to a solution of , a transient species appears within the time of mixing, which is stable for several months. In order to conform the nature of the transient species, spectroscopic, kinetic and coagulation experiments were carried out. For the formation of water-soluble colloidal MnO2, the stiochiometry was found to be 1:1 (cysteine: ). On adding of HClO4, there is a decrease in the absorbance of colloidal MnO2. At higher [cysteine] (≥2.0 × 10−4 mol dm−3), as the reaction became so fast, the formation and decomposition of colloidal MnO2 are not observed. Thus in presence of [HClO4] and excess of [cysteine], the intermediate colloidal MnO2 is unstable. Kinetic studies of the decomposition of water soluble colloidal MnO2 have been investigated by visible spectrophotometry at 25°C. The observed kinetics was explained by assuming fast adsorption of cysteine on the surfaces of colloidal MnO2. The adsorption formation constants between MnO2-cysteine and MnO2-F− have been determined (Kad = 8.5 × 103 dm3 mol−1 and Kf = 4.9 × 104 dm3 mol−1 for cysteine and F−, respectively). The deposition of solid MnO2 was observed in presence of externally added Mn(II) and Ag+ ions. On the basis of the various observations, a most plausible mechanism has been envisaged for the decomposition of water soluble colloidal MnO2.

Physico chemical studies for the formation of nanosize silver particles

Transmission electron microscopic and kinetic data for the formation of surfactant stabilised growing microelectrode nanosize silver particles during the reduction of silver nitrate by ascorbic acid in the presence of ionic and non-ionic surfactants are reported for the first time. Upon mixing ascorbic acid to a solution of silver nitrate and cationic and/or anionic surfactants (cetyltrimethylammonium bromide and sodium dodecylsulphate), a readily distinguishable yellow colour appears, which is stable for several weeks. The plots of maximum wavelength absorbance versus time clearly indicate that the silver particles formation has an induction period followed by auto acceleration (sigmoid behaviour). The extent of induction period depends on the experimental conditions. The reaction follows zero-order kinetics with respect to (ascorbic acid) for nanosize silver particles formation.