Green synthesis of noble metal and bimetal nanosols and their applications as catalysts M. Blosi*, S. Ortelli*, S. Albonetti**, A. L. Costa*, L. Ortolani***, M. Dondi* * - ISTEC-CNR, Institute of Science and Technology for Ceramics, National Research Council, Via Granarolo 64, 48018, Faenza (Italy) **- Department of Industrial Chemistry “Toso Montanari”, INSTM, Research Unit of Bologna *** - IMM-CNR Bologna - Via Gobetti 101, 40129 Bologna (Italy) ABSTRACT Bimetallic nanoparticles with various noble metals (AuCu, AuAg, PdCu, PdAu) as well as the respective monometallic nanoparticles protected by PVP shell were synthesized following the developed strategy. A deep characterization was performed on prepared sols using HR- TEM, XEDS, UV-vis, ICP-OES and XRD. Microwave heating has been shown to provide more homogeneous particle nucleation and shorter synthesis time than traditional heating. This synthesis route showed several advantages with respect to other methods, in fact it is simple, eco-friendly, carried out at low temperature and easy transferable on large scale production. Particle size- control, total reaction yield, high solid loading and long time stability of colloids, were achieved thanks to an accurate reaction optimization. Prepared nanoparticles acted as effective catalysts in the reduction of 4-nitrophenol with NaBH 4 , a typical probe reaction. Keywords: colloidal nanosols, green synthesis, microwave, noble metals, bimetals 1 INTRODUCTION Recently a great interest has been addressed toward the synthesis of noble metal nanoparticles in order to explore their special features, due to their typical chemico-physical properties. Integration of green chemistry principles into nanotechnology and nanoscience have attracted much attention over the past decade aiming at the design of more sustainable processes synthesis. Most of the synthetic routes reported in the literature are based on organic solvents thus implying a complex environmental path to the industrial production. So far, some expensive and toxic chelating agents (thiols, oleic acid, hexadecylamine, trioctylphosphine oxide) together with hazardous reducing agents are employed (hydrazine, sodium borohydride, dimethyl formamide) making these processes less promising for a subsequent industrial scale up. In this work, we report an environmentally benign approach to the production of stable metal nanosols. Water has been chosen as environmentally benign solvent, glucose serve as a mild, renewable and non-toxic reducing agent and microwave irradiation was used as heating method. The so-obtained sols were characterized and used in a catalytic probe reaction, showing interesting catalytic properties. Moreover the versatility of these products makes them useful for different applications. In fact AuAg sols were tested as ceramic inks for ink jet printing technology [2], supported catalysts for different reactions of interest were prepared by immobilization of these preformed colloids [3], while Ag-antibacterical characterization are now ongoing. 2 EXPERIMENTAL PROCEDURE 2.1 Synthesis of nanosols All the chemical reagents used in this experiment were analytical grade (Sigma Aldrich). Metallic nanoparticles were prepared following a patented procedure [4], which provides stable nanosols. Monometallic colloids - PVP (from 0.35 to 5.66 g), glucose (from 0.20 to 7.2 g) a and NaOH solution were mixed in a round bottom flask containing water and the solution was microwave heated at ambient pressure to a temperature ranging from 70 to 90 °C. At this temperature the precursor salts (HAuCl 4 , AgNO 3 , CuSO 4 , PdCl 2 ) were added to the flask and stirred for a time ranging from 2.5 to 40 min. After reaction, a stable suspension of metal nanoparticles with a solid loading ranging from 0.1 to 4 %wt was obtained. In order to optimize the system for each metal the following synthesis parameters were evaluated: synthesis temperature, synthesis time, glucose/metal and NaOH/metal molar ratios. NSTI-Nanotech 2013, www.nsti.org, ISBN 978-1-4822-0581-7 Vol. 1, 2013 327