Effect of SDS concentration on colloidal suspensions of Ag and Au nanoparticlesSpectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

About

Authors
Ridhima Chadha, Rajeshwar Sharma, Nandita Maiti, Anand Ballal, Sudhir Kapoor
Year
2015
DOI
10.1016/j.saa.2015.06.005
Subject
Instrumentation / Analytical Chemistry / Spectroscopy / Atomic and Molecular Physics, and Optics

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Introduction

Nanoparticles are gradually being used in numerous applications in biology and photo catalytic reactions [1]. In literature, several synthesis methods have been reported for the production of metal nanoparticles. These methods are classified as top–down and bottom–up approaches. In top–down approach the prod of the nanoparticles is carried out through breakage of bulk by grinding [2] laser ablation [3–6], electron beam irradiat and thermal decomposition of bulk, followed by vapor condensation [8]. In the bottom–up approach the chemical reduction of metal ions in aqueous and non-aqueous media is carried out.

Reduction can be achieved using various reducing agents in bulk solutions and in reverse micelles. The most common reducing agents are citrate [9–13] and sodium borohydride [14]. Recently,⇑ Corresponding author. Tel.: +91 22 25590298; fax: +91 22 25505151.

E-mail address: sudhirk@barc.gov.in (S. Kapoor).

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 150 (2015) 664–670

Contents lists availab

Spectrochimica Acta P

S w.http://dx.doi.org/10.1016/j.saa.2015.06.005 1386-1425/ 2015 Elsevier B.V. All rights reserved.uction metal ion [7]Available online 11 June 2015

Keywords:

Metal nanoparticles

TEM

UV–visible spectroscopy

Radiolysis

Catalysis existence of two competing SDS-induced processes: stabilization of the Ag nanoparticles due to adsorption and aggregation of the Ag nanoparticles due to increase in ionic strength. However, SDS induced aggregation of Au nanoparticles is negligible because of less surface passivity as evident from eaq reaction with AuCl4. Nevertheless, the average size of the Ag and Au nanoparticles remains almost similar at all SDS concentrations. UV–Vis spectrophotometry and transmission electron microscopy are used to characterize the nanoparticles. Moreover, it is shown that these SDS-capped Ag, Au and Au/Ag bimetallic nanoparticles could function as catalysts for the reduction of o-nitro aniline in the presence of NaBH4.  2015 Elsevier B.V. All rights reserved.a r t i c l e i n f o

Article history:

Received 2 June 2014

Received in revised form 22 August 2014

Accepted 1 June 2015a b s t r a c t

We present a kinetic study of the effects of sodium dodecyl sulfate (SDS) concentration on reduction and aggregation of Ag+ and Au3+ ions in aqueous solutions. There are distinct differences between the surface plasmon absorption bands of Ag nanoparticles at different concentrations of SDS. The results reveal thein the presence of SDS.  Catalytic activity of the formednanoparticles

Ridhima Chadha a, Rajeshwa aRadiation & Photochemistry Division, Bhabha bMolecular Biology Division, Bhabha Atomic Re h i g h l i g h t s  Complexation of SDS towards Ag+ and

Au3+ ions.  Synthesis of small Ag and Au nanoparticles using radiolytic methodrma a, Nandita Maiti a, Anand Ballal b, Sudhir Kapoor a,⇑ esearch Centre, Trombay, Mumbai 400 085, India entre, Trombay, Mumbai 400 085, India g r a p h i c a l a b s t r a c t

TEM image of SDS capped gold nanoparticles.Effect of SDS concentration on colloidal suspensions of Ag and AuBiomolecular journal homepage: wwle at ScienceDirect art A: Molecular and pectroscopy elsevier .com/locate /saa heating [16,17]. Generally, high molecular weight polymers bilizers for stabilization of metal nanoparticles [1]. Depending on lar athe capability of the stabilizer to get adsorb on different crystalline phases of metals different shape of the particles can be formed [1].

Recently, it has been shown that it is possible to get either core– shell or alloy type particles depending on the use of stabilizer. It is suggested that the use of hexadecyltrimethylammonium chloride (CTAC) produces Au(core)–Ag(shell) nanoparticles, as expected on the basis of the redox properties of the two metals.

However, when sodium dodecyl sulfate (SDS) was used as surfactant it was observed that it promotes the formation of Au–Ag alloy nanoparticles. This effect was attributed to silver’s Coulombic advantage that compensates for the fact that Au is a ‘‘more noble’’ metal [20]. It is also reported that Ag nanoparticles can take different shape in high SDS concentration [21]. Laser ablation studies have shown that there is no significant effect of SDS concentration on Au nanoparticles [5]. This work is motivated by these studies to explore the binding capability of SDS with Ag and Au clusters. In radiation and photochemical induced reduction methods the reducing agent is not added from outside. Hence, the dependence of the stability of the particles on the molar ratio of reducing agent/Ag-salt can be eliminated. In addition, there is no change in the environment conditions such as temperature. Thus, the external effects on the formation and stability of the particles are minimal. This can be useful in studying the dependence of the stability of the particles on the stabilizer concentration. In this contribution, Ag and Au nanoparticles were produced by ionizing radiation in aqueous solution, both in monometallic state and when present together. The influence of experimental parameters, such as surfactant concentration on the stabilization of the nanoparticles was also investigated via UV–Vis spectroscopy, transmission electron microscopy and measurement of Zeta (f) potential.

Experimental

Reagents

Chloroauric acid hydrate, HAuCl43H2O, silver per chlorate,

AgClO4, o-nitro aniline, sodium borohydride and sodium dodecyl sulfate, SDS, obtained from Sigma–Aldrich, were used as received.

Tert-butanol was obtained from Sisco and used as received. All other chemicals used in this study were analytical grade reagents.

All aqueous solutions were prepared with Millipore purified water having a resistivity of 18.0 MX/cm.

Characterization[1,18,19] are used as stabilizer to stabilize the particles in nanometer regime.

The preparation and optical properties of coinage nanoparticles such as Au and Ag have been extensively studied [1,18,19].