Incorporation of Cu, Fe, Ag, and Au nanoparticles in mercapto-silica (MOS) and their CO 2 adsorption capacities Nezar H. Khdary a, *, Mohamed A. Ghanem b , Mohamed G. Merajuddine a , Fahad M. Bin Manie a a King Abdulaziz City for Science and Technology (KACST), P.O. Box 6086, Riyadh 11442, Saudi Arabia b Chemistry Department, Science College, King Saud University, P.O. Box 2455, Riyadh 11451, Saudi Arabia 1. Introduction Metal nanoparticles (MNPs) are clusters containing tens to thousands of metal atoms, and their sizes vary between one to tens of nanometers [1]. Unlike bulk metal, metal nanoparticles are very attractive catalysts because they have a large surface area and a small size, which results in higher catalytic efficiency [2–5]. A great deal of research has focused on the metal nanoparticles loaded on different supports as heterogeneous catalysts for many organic and inorganic reactions [6–8]. MNPs exhibit unusual optical, magnetic, electronic [9], and catalytic activity, and are widely used for highly selective and efficient heterogeneous catalysis in many important industrial processes [10–12], particularly in selective oxidation reactions [13,14]. The incorporation of metal nanoparticles into the support matrix of particular silica has been widely investigated due to their potential application in heterogeneous catalysts. This is because they are very stable, resistant to chemical changes, and can be used in harsh conditions. This was carried out using a variety of methods, including wet impregnation, ion exchange, and chemical surface modification [2–4,15–21]. Further synthesis of metal nanoparticles was performed by coupling metal precursors and surface functional groups, followed by the chemical reduction of metal ions into metal nanoparticles bonded to the silica surface. Copper and silver are relatively economical metals and have been widely used in the field of catalysis, such as in methanol synthesis [22,23], ester hydrogenolysis [24] hydrogenation, dehydrogena- tion of alcohols [25–27], reduction of NO x [28,29], and oxidation of CO [30]. Silver nanoparticles have recently been incorporated into the pore channels of grafted mesoporous silica SBA-15, and were shown to have excellent electrocatalytic activity toward the reduction of hydrogen peroxide [31]. Very recently, highly dispersed silica-supported copper nanomaterials with enhanced catalytic activity for butanal hydrogenation were prepared by copper nitrate impregnation drying, calcinations, and reduction [32,33]. Nanocomposites are hybrid materials in which at least one of the components has dimensions in the nanometer range [34]. They can form by incorporating metal nanoparticles or ions and organic functional groups into a substrate, such as a silica [15,35]. The incorporation can be performed physically using adsorption and impregnation or by the chemical modification of porous silica surfaces. Nanocomposites can be tailored to have tremendous surface areas, high porosity, and a variety of chemical and structural functionalities for demanding applications, particularly catalysts and toxic gas sequestrations. A novel nanocomposite was recently prepared by impregnating a mesoporous silica with Cu 2+ ions followed by functionalization Journal of CO 2 Utilization 5 (2014) 17–23 A R T I C L E I N F O Article history: Received 26 April 2013 Received in revised form 22 October 2013 Accepted 22 November 2013 Available online Keywords: CO 2 sequestration Metal nanoparticles Metal-organic-silica (MOS) A B S T R A C T Metal-organic-silica (MOS) nanocomposites of metal nanoparticles of copper, iron, silver, and gold are incorporated into mercaptopropyl-modified silica by surface chemical modification methods. A silica surface modified with mercaptopropyl functional groups (MP-S) was treated with a concentrated solution of metal salts to form metal complex-mercaptopropyl-silica composites (Cu 2+ -MP-S, Fe 3+ -MP-S, Ag 1+ -MP-S, Au 3+ -MP-S). The metal nanoparticle silica nanocomposites (Cu-MP-S, Fe-MP-S, Ag-MP-S, and Au-MP-S) were obtained by the chemical reduction of immobilized metal ions using sodium borohydride. The nanocomposites’ physicochemical properties were investigated by CHN elemental analysis, FTIR, TGA, EDAX, and transmission electron microscopy. Cu, Fe, Ag, and Au nanoparticles showed a uniform dispersion through the silica support with diameters ranging from 3 nm to 200 nm. The CO 2 adsorption capacities for metal ions and nanoparticle nanocomposites have considerably increased by 20% and 100%, respectively. Cu-MP-S shows the maximum capacity of 0.52 mmol/g as measured by TGA analysis. In addition, the preparation procedure is favorable for the synthesis of a variety of metal-silica composites for their potential application in greenhouse gas sequestration. ß 2013 Elsevier Ltd. All rights reserved. * Corresponding author. Tel.: +966 555515619. E-mail address: nkhdary@kacst.edu.sa (N.H. Khdary). Contents lists available at ScienceDirect Journal of CO 2 Utilization jo ur n al ho m ep ag e: www .els evier .c om /lo cat e/jc o u 2212-9820/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jcou.2013.11.003