Green synthesis of catalytic and ferromagnetic gold nanoparticles Sudip Mohapatra, Ramachandran Krishna Kumar, Tapas Kumar Maji ⇑ Molecular Materials Laboratory, Chemistry and Physics of Materials Unit, Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bangalore 560 064, India article info Article history: Received 14 February 2011 In final form 1 April 2011 Available online 5 April 2011 abstract A facile and green method has been developed to synthesize gold nanoparticles using a novel reducing agent 2,3-dihydroxyfumaric acid (DHFA). PVP stabilized gold nanoparticles show excellent catalytic activity for controlled and complete aerial oxidation of hydroxybenzylalcohols to hydroxybenzaldehydes. Uncapped gold nanoparticles are ferromagnetic in nature at room temperature. Ó 2011 Elsevier B.V. All rights reserved. 1. Introduction Coinage metal nanoparticles play tremendously important role in modern science and technology. Among them colloidal gold rep- resents the best known type of nanoparticle with fascinating quan- tum size related properties, catalytic, optical, electronic properties, and biological applications [1–8]. Among the various properties, catalytic activity of gold nanostructure is most important and it is not well explored [6]. Despite a large number of methods re- ported it is still desirous to develop a simple and effective method for the synthesis of gold nanoparticles in aqueous medium and bio- compatible condition because this would contribute towards the development of biological applications [9–15]. Gold nanoparticle normally prepared by bottom up approach of reducing Au(III) salt by sodium citrate or sodium borohydride [10,11]. Recently, we have reported a novel synthetic method for fabrication of func- tional Cu(I) and porous Cu(I)/Cu(II) mixed-valent metal–organic frameworks (MOFs) and silver nanostructure using 2,3-dihydroxy- fumaric acid (DHFA) as a reducing agent in aqueous medium under aerobic condition [16,17]. As we have referred, synthesis of nano- particles by using this reagent does not require any instrumental perplexity, toxic chemicals and additional capping agents, there- fore, this environmentally benign method demands its high impact in the literature of nanoparticle synthesis. In this contribution we are introducing a novel reducing agent, DHFA into the nanoworld of gold. We present the catalytic activity of PVP stabilized gold nanoparticles for the controlled and complete aerial oxidation of hydroxybenzylalcohol to aldehyde, which is a challenging task in the synthetic organic chemistry. We also report interesting ferro- magnetic property of uncapped gold nanoparticle which supports recent theoretical findings [19–27]. 2. Experimental 2.1. Materials HAuCl 4 , 2,3-dihydroxyfumaric acid, o-, m-, and p-hydroxyben- zyl alcohols were obtained from Sigma–Aldrich Chemical Inc. and used without further purifications. Other reagents and solvents used were of AR grade. 2.2. Synthesis of gold nanoparticle without capping agent In a 30 mL vial 0.010 g DHFA was dissolved in 15 ml water (pH 4.5) and 1000 lL HAuCl 4 solution was added slowly under constant stirring and instantaneously a deep red color solution appeared indicating the formation of carboxylic group stabilized gold nanoparticles. The solution was employed for UV–Visible study and TEM analysis. For the magnetic measurement as synthesized gold nanoparticles was washed with water and ethanol for several times. 2.3. Synthesis of PVP stabilized gold nanoparticle for catalysis In 25 mL water 0.008 g PVP and 0.010 g of DHFA were dissolved and 1 mL of HAuCl 4 solution was added slowly to it and kept reac- tion mixture for 30 min under constant stirring. A red color solu- tion appeared indicating the formation of PVP stabilized gold nanoparticle which is characterized by TEM analysis. To the above gold nanoparticle solution 1.5 mmol (0.207 g) K 2 CO 3 and 0.5 mmol (0.062 g) hydroxybenzylalcohols were added and the catalytic activity studies were carried out at 300 and 333 K. The particle obtained at 333 K were further characterized by TEM analysis. 2.4. Details of the instruments For TEM analysis, dispersed gold nanoparticles in aqueous med- ium were put on a carbon-coated copper grid. TEM images were 0009-2614/$ - see front matter Ó 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.cplett.2011.04.006 ⇑ Corresponding author. Fax: +91 80 2208 2766. E-mail address: tmaji@jncasr.ac.in (T.K. Maji). Chemical Physics Letters 508 (2011) 76–79 Contents lists available at ScienceDirect Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett