FULL PAPER DOI:10.1002/ejic.201301193 A Facile Synthesis of Multifunctional Iron Oxide@Ag Core–Shell Nanoparticles and Their Catalytic Applications Geetu Sharma [a] and Pethaiyan Jeevanandam* [a] Keywords: Nanoparticles / Silver / Iron oxide / Magnetic properties / Supported catalysts A facile approach for the synthesis of iron oxide@Ag core– shell nanoparticles in which iron oxide microspheres serve as the core and the shell consists of silver nanoparticles has been reported. Thermal decomposition of silver acetate at 200 °C in the presence of iron oxide microspheres in diphenyl ether leads to the formation of iron oxide@Ag core–shell nanoparticles. The core–shell nanoparticles were charac- terized using powder X-ray diffraction, diffuse reflectance Introduction Core–shell nanoparticles have attracted immense interest in recent times since they exhibit multiple functions that are difficult to achieve using individual components. Magnetic metal oxide–metallic core–shell nanoparticles are an impor- tant class of functional nanomaterials owing to their wide- spread applications in catalysis, [1] sensors, [2] environmental remediation, [3] imaging, and drug delivery. [4] Magnetic metal oxide@metal core–shell nanoparticles exhibit inter- esting magnetic properties, and the shell imparts interesting optical properties owing to localized surface plasmon reso- nance. [5] Among various noble-metal nanoparticles that have been used as the shell, Ag nanoparticles have been extensively investigated because they are relatively less ex- pensive, nontoxic, and possess unique optical, catalytic, electrical, and antibacterial properties. [6,7] The synthetic methods for the preparation of magnetic core–silver shell nanoparticles include chemical reduction, [8] the seed-medi- ated method, [9] polyol reduction, [10] transmetalation, [11] and electroless plating. [12] Different multifunctional core–shell nanoparticles based on silver such as Co@Ag, [8] Fe@Ag, [9] FePt@Ag, [10] Fe 70 Co 30 @Ag, [11] α-Fe 2 O 3 @Ag, [12] Fe 3 O 4 @SiO 2 @Ag, [13] and FeOOH@Ag [14] have been suc- cessfully synthesized. Among the silver-based core–shell nanoparticles, the iron oxide@Ag system has been extensively investigated. [1,3,15,16] Iron oxide nanoparticles exhibit superparamagnetic behav- ior, which is desirable in applications such as bioseparation, [a] Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India E-mail: jeevafcy@iitr.ernet.in http://www.iitr.ac.in/departments/CY/pages/ People+Faculty+jeevafcy.html Eur. J. Inorg. Chem. 2013, 6126–6136 © 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 6126 spectroscopy, field emission scanning electron microscopy coupled with energy-dispersive X-ray analysis, transmission electron microscopy, and magnetic measurements. The cata- lytic activity of iron oxide@Ag core–shell nanoparticles has been demonstrated by using two reactions, namely, re- duction of 4-nitrophenol and reduction of methylene blue in aqueous solution. catalysis, and magnetic resonance imaging. [17–19] Silver nanoparticles not only improve the stability and dispersion of iron oxide but also modify its surface for further applica- tions. [5] For example, Du et al. have reported thiol-modified Fe 3 O 4 @Ag core–shell nanoparticles, which serve as a sur- face-enhanced Raman scattering (SERS) probe for the de- tection of polyaromatic hydrocarbons. [20] Hu et al. have re- ported the synthesis of silver-coated Fe 3 O 4 @SiO 2 micro- spheres and have used them as a SERS substrate for the detection of melamine. [13] Liu et al. have developed Fe 3 O 4 @Ag hybrid submicrospheres as an electrochemical sensor for the detection of H 2 O 2 . [21] Chen et al. have de- signed Fe 3 O 4 @C@Ag core–shell nanoparticles for near-in- frared (NIR)-light-responsive targeted delivery of doxorub- icin. The NIR-modulated delivery of the drug reduces the damage of normal cells, thereby improving its efficiency. [4] Durmus et al. have reported silver-conjugated superpara- magnetic iron oxide nanoparticles to produce antibiotic-re- sistant films, [22] and Sun et al. have reported enhanced elec- trical conductivity for iron oxide decorated with silver nanoparticles. [23] Various authors have used silver-coated iron oxide nanoparticles for the catalytic reduction of p- nitrophenol (4-nitrophenol) to p-aminophenol (4-amino- phenol) using sodium borohydride. [1,24,25] The nanoparticles show good performance in catalytic reduction and can be separated by an external magnet for easy recycling. The synthetic methods used for the preparation of iron oxide@Ag core–shell nanoparticles include impregnation, [2] surface functionalization followed by deposition, [21] solvo- thermal reduction, [26] and chemical reduction. [13,23] In the present study, a thermal decomposition approach for the synthesis of iron oxide@Ag core–shell nanoparticles has been reported. The previously reported methods for the preparation of iron oxide@Ag core–shell nanoparticles