Applied Surface Science 280 (2013) 610–618 Contents lists available at SciVerse ScienceDirect Applied Surface Science jou rn al h omepa g e: www.elsevier.com/locate/apsusc Novel microwave-synthesis of Cu nanoparticles in the absence of any stabilizing agent and their antibacterial and antistatic applications Anna Maria Raspolli Galletti a,∗ , Claudia Antonetti a , Mirko Marracci b , Fabio Piccinelli c , Bernardo Tellini b a Dipartimento di Chimica e Chimica Industriale, Università di Pisa, Via Risorgimento 35, 56126 Pisa, Italy b Dipartimento di Ingegneria dell’Energia, dei Sistemi, del Territorio e delle, Costruzioni, Università di Pisa, via Diotisalvi 2, 56125 Pisa, Italy c Laboratorio di Chimica dello Stato Solido, DB, Università di Verona, and INSTM, UdR Verona, Strada le Grazie 15, 37134 Verona, Italy a r t i c l e i n f o Article history: Received 12 March 2013 Received in revised form 6 May 2013 Accepted 10 May 2013 Available online 20 May 2013 Keywords: Copper Nanoparticles Microwave Antibacterial activity Antistatic behavior a b s t r a c t For the first time, copper nanoparticles were synthesized under microwave (MW) irradiation in the absence of any stabilizing agent. A 2-step synthetic approach was adopted working in basic ethanol solution and then ascorbic acid was added as a reducing reagent in the second step. The obtained cop- per nanoparticles were characterized by UV–vis spectroscopy, XRPD and TEM analysis. UV–vis spectra show an absorption peak at about 580–590 nm, typical of the plasma resonance of copper nanoparticles and XRPD analysis reveals that the complete reduction to metallic copper was reached at the end of the second step. Average sizes in the range 7–15 nm were ascertained through TEM microscopy. These copper nanoparticles are suitable for antibacterial and antistatic applications. The bactericidal effect was investigated in relation to the diameter of inhibition zone in disk diffusion tests on calf crust leather sample and an interesting antibacterial activity was verified against both Gram positive and Gram neg- ative bacteria (Staphylococcus aureus, Escherichia coli, Bacillus subtilis and Candida albicans). Moreover, this treated leather showed encouraging antistatic behavior: in particular, equivalent circuital parame- ters were estimated via an impedance spectroscopy technique to have a first evaluation of the charge dissipation activity by volume conduction. © 2013 Elsevier B.V. All rights reserved. 1. Introduction In the recent years, great interest has been devoted to the synthesis of metal nanoparticles (NPs) in order to explore their special properties and applications. Differently from expensive noble metals, copper nanoparticles represent an ideal compro- mise between their interesting properties and cost, thus becoming industrially important materials. In fact, they are widely stud- ied for applications in different fields, such as magnetic storage media, electronics, solar energy transformations, catalysis and, in addition, they have shown promising antimicrobial effects [1–10]. During the past few years, different methods have been developed for the preparation of copper nanoparticles, such as hydrothermal and solvothermal methods, chemical reduction, electrolytic syn- thesis, sonochemical methods, sol–gel preparations, vacuum vapor ∗ Corresponding author. Tel.: +39 050 2219290; fax: +39 050 2219260. E-mail addresses: roxy@dcci.unipi.it (A.M. Raspolli Galletti), claudia.antonetti@ns.dcci.unipi.it (C. Antonetti), mirko.marracci@ing.unipi.it (M. Marracci), fabio.piccinelli@univr.it (F. Piccinelli), bernardo.tellini@ing.unipi.it (B. Tellini). deposition and so forth [1,7,8,10–38]. However, most of these methods for the synthesis of Cu NPs are complicated, require specific and expensive equipments, involve no environmental sustainable reagents and produce only small amounts of nanomate- rials. One of the most recent interesting attempts for the synthesis of stable dispersions of nanosized copper particles is reported in the paper of Wu et al. where copper NPs were synthesized with an average size lower than 2 nm working in aqueous medium in the presence of ascorbic acid as a reducing and stabilizing agent [39]. In this procedure a relatively high ascorbic acid/Cu molar ratio (from 2 to 5 mol/mol) and traditional heating were employed. In particular, when the authors studied this reaction using aqueous solutions of 0.2 M CuCl 2 ·2H 2 O and 1.0 M ascorbic acid, the characteristic surface plasmon peak of copper nanoparticles could be observed after 2 h of reaction time and their synthesis was completed only after 14 h, a considerable long reaction time. On the other hand, microwave irradiation has been largely employed for the sustainable prepara- tion of nanoparticles of different metals, offering more promising results compared with the thermal heating. The main advantages of microwave-assisted reactions can be summarized in the increase of the rate of the reaction by one to two orders of magnitude, in the rapid initial heating which can lead to save energy and often 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.05.035