Zoya Zaheer

Silver nanoparticles to self-assembled films: Green synthesis and characterization

In the present paper silver nanoparticle was synthesized by chemical reduction of silver nitrate by oxalic acid in aqueous solution. The nanoparticle film (self-assembled; mirror like illumination) on the wall of the clean glass surface was also observed after some days. The synthesized silver particles show an intense surface resonance plasmon band in the visible region at 425 nm. Transmission electron microscopy, selected areas electron diffraction, and UV-visible spectroscopy have been employed to characterize Ag-nanoparticles. The nanoparticle films were also observed using conventional visual and scanning electron microscope (spherical particles and size ranging from 23 to 245 nm). The transmission electron micrograph revealed that the average size of silver nanoparticle were ≤10 nm and 21-60 nm, respectively.

Bio-conjugated silver nanoparticles: From Ocimum sanctum and role of cetyltrimethyl ammonium bromide

In this paper we have reported the spectrophotometeric and transmission electron microscopic (TEM) data to the shape-directing role of cetyltrimethylammonium bromide (CTAB) on the green extra-cellular synthesis of bio-conjugated Ag-nanoparticles using Ocimum sanctum leaves extract. TEM images revealed that the nanoparticles are mostly spherical (average particle size ranged from 18 to 35nm) with some truncated triangular nanoplates, aggregated in a beautiful manner to yield locket-like silver and capped by a thin layer of biomolecules of O. sanctum, whereas nanoparticles are highly poly-dispersed in presence of CTAB. The shape and position of wavelength maxima strongly depends on the reaction time, [leaves extract] and [CTAB]. The visual observations also suggest that the prefect transparent silver sol becomes turbid in presence of CTAB after some time.

Silver nanoparticles formation using tyrosine in presence cetyltrimethylammonium bromide.

Upon addition of silver nitrate (precursor) to a solution of tyrosine (reductant) and cetlytrimethylammonium bromide (stabilizer), a transient species appears as the reaction time increases, which is stable for several months. The formation of silver nanoparticle was observed visually by color change (pale yellow to brownish yellow). In order to confirm the nature of the transient species, spectroscopic, kinetic, coagulation, transmission and scanning electron microscopic experiments were carried out. The reaction follows first-order kinetics with respect to [tyrosine] and [Ag(+)] under our experimental conditions. The phenolic -OH group of tyrosine is responsible for the reduction of Ag(+) ions. On the basis of various observations, the most plausible mechanism is proposed and discussed.

Sub-and post-micellar catalytic and inhibitory effects of cetlytrimethylammonium bromide in the permanganate oxidation of phenylalanine

The kinetics of phenylalanine (phe) oxidation by permanganate has been investigated in absence and presence of cetyltrimethylammonium bromide (CTAB) using conventional spectrophotometric technique. The rate shows first- and fractional-order dependence on [MnO(4)(-)] and [phe] in presence of CTAB. At lower values of [CTAB] (< or =10.0x10(-4)moldm(-3)), the catalytic ability of CTAB aggregates are strong. In contrast, at higher values of [CTAB] (> or =10.0x10(-4)moldm(-3)), the inhibitory effect was observed in absence of H(2)SO(4). We find that anions (Br(-), Cl(-) and NO(3)(-)) in the form of sodium salts are strong inhibitors for the CTAB catalyzed oxidation. Kinetic and spectrophotometric evidences for the formation of an intermediate complex and an ion-pair complex between phe and MnO(4)(-), CTAB and MnO(4)(-), respectively, are presented. A mechanism consistent with kinetic results has been discussed. Complex formation constant (K(c)) and micellar binding constant (K(s)) were calculated at 30 degrees C and found to be K(c)=319mol(-1)dm(-3) and K(s)=1127mol(-1)dm(-3), respectively.

A Kinetic and Mechanistic Study of the Reaction Between and Methionine: Evidence for the Formation of Water Soluble Colloidal MnO2

The kinetic results of the oxidation of methionine by in aqueous medium are presented. Upon mixing aqueous solutions of permanganate and methionine, a readily distinguishable brown colour appears. Under pseudo-first order conditions ([methionine] > [ ]), the formation and decomposition of brown colour was very fast. Experiments have been made to confirm the nature of brown colour formed during the reduction of by methionine. The kinetics of both the stages (formation and decomposition of colloidal MnO2) was investigated spectrophotometrically. Second- and pseudo-first-order conditions were used to determine the reaction rate for the formation and decomposition of colloidal MnO2, respectively. The changes observed in the direction of the rate constant –[H+] profile correspond to the hydrolysis of the colloidal MnO2. The addition of sodium fluoride has composite effect (catalytic and inhibition). The proposed mechanism and the derived rate law are consistent with the observed kinetics.

Preparation, characterisation and kinetics of corn-shaped Ag nanoparticles

Conventional UV-vis spectroscopic and transmission electron microscopy methods were used to monitor the kinetics, formation and characterisation of silver nanoparticles in the methionine-promoted reduction of silver(I). The silver nanoparticles (purple colour; λ max = 550 nm) are corn-shaped and aggregated, and the average particle size is about 23 nm. The kinetics of silver nanoparticles formation has been studied as a function of [Ag(I)], [methionine] and [CTAB]. We see that [Ag(I)] has no effect on the rate of silver nanoparticles formation. At higher [CTAB] ≥ 40.0 × 10−4 mol dm−3, silver nanoparticles were not observed. Methionine is responsible for interparticle interaction, increase in aggregate size and cross-linking between the particles, and it acts as complexing, reducing, adsorbing and capping agents. A mechanism consistent with the observed kinetics has been proposed and discussed.

Formation, characterisation and redox behaviour of water-soluble colloidal manganese dioxide

The water-soluble colloidal MnO2 solutions were prepared by the reduction of permanganate by two sulphur-containing reductants (methionine and thiourea) in aqueous neutral media. The nature of the oxidising species present in solution was characterised by coagulation, spectrophotometric and transmission electron microscopic measurements. Upon mixing aqueous solutions of methionine and , a readily distinguishable yellow colour (spherical-shaped; size ca. 4 nm) appears immediately at 25°C. The oxidation rates of ethylenediaminetetraacetic acid (EDTA) with colloidal MnO2 were determined as a function of EDTA (2.0  ×  10−4 to 10.0  ×  10−4 mol dm−3) and Mn(II) at constant temperature (25°C). The rate constants were calculated by using the second-order kinetic conditions. The effects of added salts, such manganese(II) chloride, sodium fluoride, silver nitrate and sodium perchlorate have been investigated. Order of mixing of Mn(II) has a composite effect on both the redox reactions, i.e. a coloured intermediate (λmax  =  500 nm) was formed within the time of mixing of Mn(II), EDTA and colloidal MnO2 which is composed of the EDTA and Mn(III). Mechanisms consistent with the observed kinetic data have been proposed and discussed.