Straightforward Synthesis of Gold Nanoparticles Supported on Commercial Silica-Polyethyleneimine Beads

Abstract

Stable silica-supported gold nanoparticles (Au NPs ) suitable for catalysis applications were conveniently obtained in a straightforward, one-step synthesis by simply adding an aqueous solution of HAuCl 4 to commercial polyethyleneiminefunctionalized silica beads (SiO 2 -PEI) as the only reactant without any external reducing agent and/or conventional stabilizing moieties. Six different types of Au NPs /(SiO 2 -PEI) beads termed Au x−y h, where x is the initial HAuCl 4 concentration (1, 5, or 10 mM) and y is the reaction time (1 or 24 h), were prepared and characterized by UV−vis diffuse reflectance spectroscopy, X-ray fluorescence, FE-SEM microscopy, and X-ray absorption spectroscopy. The SEM micrographs of Au x−y h samples showed that the particle size distribution decreases with the increase of the starting gold concentration, i.e., 70−100 nm for Au 1−x h, 40−70 nm for Au 5−x h, and Au 10−x h, whereas on passing from 1 to 24 h the aggregation phenomena overcome the nucleation ones, promoting the formation of bigger aggregates at the expense of small Au NPs . The XAS analysis as a combination of XANES and EXAFS studies provided detailed structural information regarding the coordination geometry and oxidation state of the gold atoms present on the beads. Moreover, the catalytic activity of the modified silica beads in the reduction of 4-nitrophenol to 4aminophenol by NaBH 4 was investigated and in one case the XAS analysis was repeated after recovery of the catalyst, demonstrating further reduction of the Au site to Au(0).

Supported Gold Nanoparticles for Alcohols Oxidation in Continuous-Flow Heterogeneous Systems

“…[28][29][30] In our previous works we have presented the preparation, without any need of additional reducing and/or stabilizing agents, of a variety of stable silica-supported Au NPs by using different functionalized-silica supports and a chloroauric acid (HAuCl 4 ) aqueous solution as the only reactants. [31][32][33][34] We started using commercial polyethyleneimine-functionalized silica beads 30 and we went on preparing silica nanoparticles with alkynyl carbamate moieties synthetized by cocondensation of the di-functional organosilane [3-(2-propynylcarbamate)propyl]triethoxysilane (PPTEOS) with tetraethoxysilane (TEOS) in alkaline medium. By this method, spherical and monodispersed functionalized silica nanoparticles with a porous structure and an average size distribution of 45 nm could be obtained.…”

“…The synergistic effect of the carbamate and alkynyl 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 4 functionalities present on the silica surface was exploited for the smooth reduction of HAuCl 4 and successive stabilization of the resulting silica-supported Au NPs . 31,32 PPTEOS, through its derivatization by radical thiol-yne chemistry, was subsequentely used to fabricate a novel aminosulfide branched silica support suitable for the preparation of analogous Au NPs -based catalytic systems. 34 In the present work we have anchored Au NPs on some alkyne-modified support materials having the right features for the application as catalysts in continuous-flow packed bed reactors.…”

Catalytic Materials Based on Surface Coating with Poly(ethyleneimine)‐Stabilized Gold Nanoparticles

“…Our first candidate was silica, which has been previously used to prepare supported metal catalysts . As the impregnation of SiO 2 with a gold precursor yields relative large NPs, different approaches have been successfully assayed to prepare catalytic composites . In addition, commercial silica‐PEI beads have been previously used to synthesize supported AuNPs, and the interaction between PAMAM and SiO 2 has been already exploited to prepare silica‐supported gold nanocomposites .…”

“…Having assessed the catalytic properties, we focused on exploring whether the affinity of PEI for different materials was retained by MW‐PEI@AuNPs and whether they can coat surfaces without any additional synthetic step. Our first candidate was silica, which has been previously used to prepare supported metal catalysts . As the impregnation of SiO 2 with a gold precursor yields relative large NPs, different approaches have been successfully assayed to prepare catalytic composites .…”

“…To rule out a desorption event, the performance of 0.5 g of silica coated with MW‐PEI@AuNPs was evaluated along 5 cycles of the catalytic reduction of 4‐NP. In full agreement with the results reported for AuNPs supported on commercial silica‐PEI beads, the catalytic efficiency diminished as the material was reutilized, and k app was 0.55 and 0.16 for cycle 1 and 5, respectively (Figure S7). However, ICP–OES analyses revealed that the content of gold was 12.1 μg g −1 for the silica coated with MW‐PEI@AuNPs with no significant change after cycle 5.…”