Mild fabrication of silica-silver nanocomposites as active platforms for environmental remediation† A. Mignani, * a S. Fazzini, b B. Ballarin, * b E. Boanini, c M. C. Cassani, b C. Maccato, d D. Barreca e and D. Nanni b Herein we report a new, simple, low cost and one step way to obtain silica-supported silver nanoparticles (AgNPs) on commercial polyethyleneimine-functionalized silica beads (SiO 2 -PEI) under mild experimental conditions. The novel AgNPs/(SiO 2 -PEI) material has been thoroughly analyzed using FE-SEM, BET, XRD, XPS and XE-AES analysis. The reduction of Methylene Blue (MB) to Leuco Methylene Blue (LMB) in the presence of NaBH 4 was chosen for testing the catalytic properties of AgNPs/(SiO 2 -PEI) towards dyes decoloration. Moreover, the prepared supported nanocatalyst was also found to exhibit excellent catalytic activity towards decoloration of some azo dyes such as E110 and E122. 1. Introduction Dyes and pigments that contain heterocyclic aromatic compounds are normally present in the waste waters of textiles, paper, cosmetics and leather industries. They are very dangerous to the environment and human health 1 and, for example, prolonged exposure to them causes irritation of the respiratory system and the gastro-intestinal track. Moreover, most of these dyes (in particular azo dyes) are highly recalcitrant to conventional waste water biological treatment 2 and pretreatment processes are required to decolorize them effi- ciently. Many methods are available for this purpose, such as oxidation (with ozone, H 2 O 2 or chlorine dioxide), Fenton, photo Fenton, or electrochemical advanced Fenton oxidation, but they are expensive, require harsh working pH ranges or can generate a large volume of ferrous slurry. 3 Photocatalytic materials such as TiO 2 have been even largely employed to achieve the thor- ough degradation of azo dyes, but normally they are active only in the UV range because of their wide band gap. 4 Thus the development of simple and low cost materials/methods for efficient dye degradation has gained enormous signicance. In this context extensive research has been carried out to explore the use of noble metal nanoparticles (NPs i.e. Au or Ag) for catalytic reduction of dyes, due to their enhanced catalytic activity. 5 Additionally, due to the interest and progress in heterogeneous catalysis, signicant attention has been focused on the possibility of stabilizing the NPs onto solid supports such as silica, indium tin oxide, alumina, graphene oxide, etc. 5 with the purpose of removing and recycling them, aer the decolor- ation treatment, in a simple way. Recently, detailed investiga- tions into the syntheses of silver nanoparticles (AgNPs), with tunable size and shape, have drawn much attention. 6–8 On the basis of our previous results, 9 in this paper we propose an innovative, simple and low cost procedure for preparing silica-supported AgNPs by using AgNO 3 and commercial polyethyleneimine functionalized silica beads (SiO 2 -PEI), under mild conditions. Polyethyleneimine (PEI) is an interesting material for reducing and stabilizing metal NPs; it is a cationic polymer with a high charge density. PEI fragments containing amino groups can easily chelate with metal ions, and they can also act as both reducing agents and stabilizers in preparation of metal NPs. Indeed, rapid formation of silver nanoparticles occurred within few minutes by heating the solution, indicating that the heat treatment promotes the direct redox reaction between PEI and AgNO 3 , without the additional step of introducing other reducing and/or protective agents. 10 Silica beads provide high surface area, give excellent mechanical strength and offer thermal stability. We have investigated the effect of the silver nitrate precursors concentrations and of the reaction times with the aim to optimize the synthesis of AgNPs/(SiO 2 -PEI) catalyst. All the samples have been characterized by X-ray Fluorescence a Center for Industrial Research – Advanced Applications in Mechanical Engineering and Materials Technology (CIRI-MAM), University of Bologna, Viale del Risorgimento, 2 I-40136 Bologna, Italy. E-mail: a.mignani@unibo.it; Fax: +39 0512093690; Tel: +39 0512093704 b Department of Industrial Chemistry “Toso Montanari”, University of Bologna and INSTM, Viale del Risorgiento, 4 I-40136 Bologna, Italy. E-mail: barbara.ballarin@ unibo.it c Department of Chemistry “Giacomo Ciamician”, University of Bologna, Via Selmi, 2 I- 40126 Bologna, Italy d Department of Chemical Sciences, University of Padova and INSTM, Via Marzolo 1, I- 35131 Padova, Italy e CNR-IENI and INSTM, c/o Department of Chemical Sciences, University of Padova, Via Marzolo 1, I-35131 Padova, Italy † Electronic supplementary information (ESI) available: Additional XRD, FE-SEM, XPS, XE-AES characterizations for the AgNPs/(SiO 2 -PEI-2) samples, UV-Vis spectra for the catalytic reduction of SY and AZ and a comparison of catalytic data. See DOI: 10.1039/c4ra14069a Cite this: RSC Adv. , 2015, 5, 9600 Received 7th November 2014 Accepted 5th January 2015 DOI: 10.1039/c4ra14069a www.rsc.org/advances 9600 | RSC Adv. , 2015, 5, 9600–9606 This journal is © The Royal Society of Chemistry 2015 RSC Advances PAPER Published on 06 January 2015. Downloaded by University College London on 15/01/2015 13:01:18. View Article Online View Journal | View Issue