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Colloids and Surfaces B Biointerfaces 06/2013; 102(0927 - 7765):578– 584. · 3.46 Impact Factor
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Materials Research Bulletin 01/2013; 48(0025):1137–1142.. · 2.11 Impact Factor
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ABSTRACT: The sculpturing effects of cetyltrimethylammonium bromide and poly(vinyl)alcohol on the shape transformation of silver nano-particles are presented. It is a simple process of recent interest for obtaining silver nano-rods, spherical and hexagonal nano-plates in the thiosulphate reduction of Ag + ions with or without stabilizers. Formations of silver nanoparticles were observed visually by color change of the reaction mixture from colorless to dark yellow. Interestingly, the reaction mixture remained colorless and no absorption peak due to the Ag-nanoparticles was observed at higher [S 2 O 3 2-] (≥ 20.0 × 10 -4 mol dm -3). UV-vis spectroscopy and transmission electron microscopy (TEM) were used to monitor the growth and morphology of Ag-nanoparticles, which reveal to the nano nature of the particles. These studies infer that the particles are mostly spherical in shape and have an average size of 16 nm in absence of CTAB. Selected area electron diffraction (SAED) results indicate that the Ag-nanoparticles grow along the [111] direction.
International journal of electrochemical science 01/2013; 8:204-218. · 3.73 Impact Factor
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ABSTRACT: Upon addition of tetrachloroauric(III) (HAuCl(4)) to a solution of cetyltrimethylammonium bromide (CTAB), a perfect transparent yellow colored and yellowish-precipitate appears within the time of mixing, indicating the formation of a complex between HAuCl(4) and CTAB. Morphology of gold nanoparticles in situ via chemical reduction of title reaction has been determined by using conventional techniques. The position and shape of the surface plasmon resonance (SRP) band strongly depends on the [ascorbic acid], [HAuCl(4)], [CTAB] and mixing ratio of the reactants. Sub-, post- and dilution-micellar effects are accountable to the aggregation and/or adsorption of gold nanoparticles onto the surface of CTAB. The morphology of particles was altered by changing the [reactants] as well as [CTAB]. A mechanism of nanoparticle formation has been proposed comprising different steps of particle growth.
Colloids and surfaces. B, Biointerfaces 12/2012; 104C:11-17. · 2.60 Impact Factor
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Arabian Journal of Chemistry 10/2012; 5(4):453-459. · 1.37 Impact Factor
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ABSTRACT: Silver nanoparticles were prepared by a simple chemical reduction method using ascorbic acid and starch as reducing and stabilizing agents, respectively. The effect of starch, silver ions and ascorbic acid was studied on the morphology of the silver nano-particles using UV-visible spectrophotometry. The initial reaction time min and amount of starch were important parameters for the growth of Ag-nanoparticles. The morphology was evaluated from transmission electron microscopy (TEM). The truncated triangle nano-plates (from 17 to 30nm), polyhedron, spherical with some irregular shaped Ag-nanoparticles were formed in presence of starch. Particles are aggregated in an irregular manner, leads to the formation of butterfly-like structures of silver. Starch acts as a stabilizing, shape-directing and capping agent during the growth processes. Silver nanoparticles adsorbed electrostatically on the outer OH groups of amylose left-handed helical conformation in solution.
Colloids and surfaces. B, Biointerfaces 09/2012; 102C:578-584. · 2.60 Impact Factor
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ABSTRACT: The influence of surfactants (anionic and cationic) on the reactivity of the redox couple cerium(IV) and D-glucose was examined spectrophotometerically. Various kinetic parameters have been determined in the absence and presence of surfactants. The kinetics were followed by monitoring the disappearance of the absorbance of cerium(IV) at 385nm. The reaction obeyed first-order kinetics with respect to [D-glucose] in both media. No effect of anionic micelles of sodium dodecyl sulfate (SDS) was observed due to electrostatic repulsion between the negative head group of SDS and reactive species of cerium(IV) (Ce(SO4)
3
2−
). A twofold increase in the oxidation rate was observed in the presence of cationic micelles of cetyltrimethylammonium bromide (CTAB). The observed catalytic role has been analyzed in terms of the Menger–Portnoy model. The effects of various inorganic salts (Na2SO4, NaNO3 and NaCl) were also studied in micellar media.
Colloid and Polymer Science 04/2012; 284(1):10-18. · 2.33 Impact Factor
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ABSTRACT: Stable silver nanoparticles were synthesized by the reduction of silver ions with a Paan (Piper betel) leaf petiole extract in absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium dodecyl sulphate (SDS). The reaction process was simple and convenient to handle, and was monitored using ultraviolet-visible spectroscopy. Absorbance of Ag-nanoparticles increases with the concentrations of Paan leaf extract, acts as reducing, stabilizing and capping agents. The polyphenolic groups of petiole extract are responsible to the rapid reduction of Ag(+) ions into metallic Ag(0). The results indicated that the shape of the spectra, number of peaks and its position strongly depend on the concentration of CTAB, which played a shape-controlling role during the formation of silver nanoparticles in the solutions, whereas SDS has no significant effect. The morphology (spherical, truncated triangular polyhedral plate and some irregular nanoparticles) and crystalline phase of the particles were determined from transmission electron microscopy (TEM) and selected area electron diffraction (SAED).
Colloids and surfaces. B, Biointerfaces 04/2012; 98:85-90. · 2.60 Impact Factor
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ABSTRACT: Aqueous solution of water soluble colloidal MnO2 was prepared by Perez-Benito method. Kinetics of l-methionine oxidation by colloidal MnO2 in perchloric acid (0.93 × 10−4 to 3.72 × 10−4mol dm−3) has been studied spectrophotometrically. The reaction follows first-order kinetics with respect to [H+]. The first-order kinetics with respect to l-methionine at low concentration shifts to zero order at higher concentration. The effects of [Mn(II)] and [F−] on the reaction rate were also determined. Manganese (II) has sigmoidal effect on the rate reaction and act as auto catalyst.
The exact dependence on [Mn(II)] cannot be explained due to its oxidation by colloidal MnO2. Methionine sulfoxide was formed as the oxidation product of l-methionine. Ammonia and carbon dioxide have not been identified as the reaction products. The mechanism with the observed
kinetics has been proposed and discussed.
Colloid and Polymer Science 04/2012; 285(10):1169-1173. · 2.33 Impact Factor
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ABSTRACT: Spectrophotometric kinetic technique has been used to investigate the effect of cetyltrimethylammonium bromide (CTAB) and
sodium dodecyl sulfate (SDS) surfactants on the redox reaction of cerium(IV)+l-sorbose in aqueous sulfuric acid media. The anionic SDS has no effect, whereas the reaction rate increases in the presence
of cationic CTAB, which is due to favorable conditions provide by the cationic micelles. The reaction rate decreases with
[H2SO4], and no acid-dependent path has been observed. At constant [H2SO4], the rate of the reaction is dependent on the first powers of the l-sorbose and cerium(IV) concentrations. The CTAB-assisted reaction is retarded by addition of electrolytes (Na2SO4, NaNO3, and NaCl), which is attributed to the competition between electrolyte anions and cerium(IV)-sulfato species. Bromide ion
(of CTAB or externally added in the form of NaBr) is not oxidized by the cerium(IV) (as a main or side reaction).
Colloid and Polymer Science 04/2012; 285(7):745-752. · 2.33 Impact Factor
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ABSTRACT: The shape-directing role of cetyltrimethylammonium bromide, CTAB, is reported to the green synthesis of Ag-nanoparticles for the first time using Neem (Azadirachta indica) leaf extract. UV-vis spectroscopy, transmission electron microscopy (TEM), and selected area electron diffraction (SAED) patterns were used to monitor the growth kinetics, morphology and crystalline nature of Ag-nanoparticles, respectively. It was observed that the growths of Ag-nanoparticles are stopped within 40 min of reaction time. The Ag-nanoparticles are polydispersed spherical and exhibiting an interesting triangle, flat, plate-like hexagonal and some irregular morphology in presence of different [CTAB]. Hexagonal particles aggregated in a systematic manor, leads to produce a fine tiles-like arrangement of Ag-nanoparticles with dimensions between 10 and 37 nm. The nature of reaction-time curves to the reduction of Ag(+) ions by Neem leaf extract are much different than those observed by us in our earlier studies using different bio-reductants.
Colloids and surfaces. B, Biointerfaces 03/2012; 95:229-34. · 2.60 Impact Factor
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ABSTRACT: We report a simple chemical reduction method for the synthesis of different colored silver nanoparticles, AgNP, using tyrosine as a reducing agent. Effects of cetyltrimethylammonium bromide, CTAB, and tyrosine concentrations are analyzed by UV-visible measurements and scanning electron microscopy (SEM) to evaluate the mode of AgNP aggregation. The position and shape of the surface resonance plasmon absorption bands strongly depend on the reaction conditions, i.e., [CTAB], [tyrosine], and reaction time. Sub-, post-, and dilution-micellar effects are accountable for the fast and slow nucleation and growth processes. Spectrophotometric measurement also shows that the average size and the polydispersity of AgNP increase with [CTAB] in the solution. CTAB acted as a shape-directing agent.
Journal of Colloid and Interface Science 10/2011; 367(1):101-8. · 3.07 Impact Factor
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Colloids and Surfaces A: Physicochem. Eng. Aspects. 10/2011; 390(1-3):120-125.
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ABSTRACT: This paper describes a simple preparation of single-crystalline Ag-nanoparticles including plates, and wires in water by truncated triangular particles for the first time during the reduction of [Ag(NH₃)₂]⁺ complex with glucose at room temperature. Silver particles were characterized by means of the conventional transmission electron microscopy (TEM) and UV-VIS spectroscopy. Cetyltrimethylammonium bromide, CTAB, plays a number of roles during the redox process by solubilizing the reactants, controlling the nucleation and/or growth of nanoparticles, stabilizing the thus-prepared Ag-nanoparticles and minimizing the formation of Ag₂O, AgCl, and AgBr precipitates. It was found that the rate constant and absorbance of silver nanoparticles were sigmoidal to the concentration of silver nitrate.
Colloids and surfaces. B, Biointerfaces 08/2011; 86(1):87-92. · 2.60 Impact Factor
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ABSTRACT: Upon the addition of permanganate to a solution of thioacetamide, yellow-brown colour species appeared within the time of mixing, which was unstable in excess [thioacetamide]. At higher [thioacetamide] (≥2.0 × 10−4 M dm−3), the formation and decomposition of yellow–brown colour were not observed. Experiments have been done to confirm the nature of that colour. Mn(IV) (water-soluble colloidal MnO2) and Mn(III) were formed as intermediates. Conventional transmission electron microscopic (TEM) and spectrophotometric techniques were used to determine the size of colloidal MnO2 and oxidation rate of thioacetamide by MnO2, respectively. MnO2 nanoparticles are spherical and are of uniform particle size, and the average particle size is ca. 25 nm. The influence of different parameters was measured, i.e. [reactants], [HClO4] and temperature. A comparison was made of the oxidation rates of different organic reductants (acetamide and thiourea) by permanganate. The order of the effectiveness was as follows: thioacetamide thiourea acetamide. The presence of electron-donating -group and sulphur atom is responsible for the higher reactivity of thioacetamide which easily transfers the proton to . The mechanism of the observed kinetics has been proposed and discussed.
Journal of Experimental Nanoscience 04/2011; 6(2):149-158. · 1.01 Impact Factor
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ABSTRACT: In this paper we report the effect of aniline concentrations on the growth and size of silver nanocrystals using aniline and silver nitrate as reductant and oxidant, respectively. UV-Vis spectroscopy, transmission electron microscopy (TEM) and selected areas electron diffraction (SAED) have been employed to characterize silver nanoparticles. The TEM images show that silver nanocrystals are roughly spherical and of uniform particle size, and the average particle size is ca. 25 nm. A broad surface plasmon resonance band appears at 400 nm. The rings patterns are in good agreement with the standard values of the face-centered-cubic form of silver nanocrystals. This is attributed to the adsorption of aniline and /or interparticle interaction onto the surface of Ag-nanocrystals through electrostatic interactions between the lone-pairs electrons of –NH 2 and positive surface of Ag-nanoparticles. Copyright © 2011 VBRI press. Athar Adil Hashmi is working as Associate Professor in the Department of Chemistry, Jamia Millia Islamia, New Delhi, India. His work area includes organometallic chemistry, metal containing polymers and bio-inorganic chemistry. Zaheer Khan is the Professor in the Department of Chemistry, Jamia Millia Islamia, New Delhi, India. His current research interests include the synthesis, kinetics and mechanism of the advanced nano materials of silver and manganese by green routs.
ADVANCED MATERIALS Letters. 03/2011; 2(3-10.5185/amlett.2011.1206):188-194.
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Science of Advanced Materials 01/2011; 3(6):912-918. · 3.31 Impact Factor
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ABSTRACT: Colloidal silver nanoparticles were prepared by reducing silver nitrate with oxalic acid in presence of cetyltrimethylammo-nium bromide (CTAB). The synthesized silver particles show an intense surface plasmon band in the visible region. The work reported in this paper describes the effect of concentration of various additives (NaCl, NaBr, NaNO 3 , Na 2 SO 4 and NaH 2 PO 4) and ammonia on the growth and stability of Ag-nanoparticles. In all the cases the rate decreases as the [electro-lytes] or [ammonia] increases. The nature, polarizability and coordinating ability of the anions play vital roles for nucleus formation and the growth process, which subsequently form different size particles. Transmission electron microscopy, se-lected areas electron diffraction, and UV-visible spectroscopy have been employed to characterize Ag-nanoparticles. The effect of the following variables on the particle size and size distribution was investigated: the [oxalic acid], [CTAB] and [Ag + ]. The nanoparticles are stable in NaNO 3 and NaH 2 PO 4 solutions; but NaCl, NaBr and Na 2 SO 4 causes their aggrega-tion.
Journal of Biomaterials and Nanobiotechnology 01/2011; 2:390-399.
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ABSTRACT: 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.
Colloids and surfaces. B, Biointerfaces 12/2010; 81(2):587-92. · 2.60 Impact Factor
