Silica-supported Silver Nanoparticles Research Articles

Silica supported biosynthesized silver nanoparticles as effective adsorbent and photocatalyst for removal of methylene blue from water

The silica supported silver nanoparticles (Ag@SG) were prepared by wet impregnation of silica gel (SG) using different concentrations of biogenic silver nanoparticles (AgNPs; 0.25–5 mM) solution, prepared from Cicer arientinum pod extract. Among them, the Ag@SG composite prepared by using 1.25 mM AgNPs solution (Ag1.25@SG) was found to contain only Ag0 species as nanoparticles, whereas the samples prepared by higher concentrations contained Ag0 as well as Ag+ (silver oxide) species. All the Ag@SG composites including SG, exhibited good adsorption capacity for a cationic dye (methylene blue; MB) in water. However, Ag1.25@SG having only Ag0 species exhibited higher photocatalytic activity for degradation of MB under visible light irradiation as compared to other composites. The study reveals that the plasmonic Ag0 species supported on silica are catalytically more active than Ag+ species. Furthermore, the AgNPs (Ag0) in supported form exhibits much higher (∼5-fold) photocatalytic activity than unsupported AgNPs. The synergistic effect of adsorption property of silica surface and plasmonic photocatalytic activity of AgNPs in the synthesized composites was found to be effective for the removal of MB. In addition, the fine dispersion of AgNPs on internal surface of silica provides better activity for photocatalysis. The study shows that this material is a promising adsorbent as well as photocatalyst for the removal of dyes from water.

Photocatalytic degradation of ciprofloxacin antibiotic in water by biosynthesized silica supported silver nanoparticles

This study reports photocatalytic degradation of ciprofloxacin (CIP) in the presence of silver nanoparticles impregnated over amorphous silica extracted from rice husk through a green approach using Melia Azedarach fruit extract. Various analyses such as X-ray diffraction analysis (XRD), Fourier-transform infrared (FTIR) spectroscopy, and field emission scanning electron microscopy (FESEM) were employed to characterize the obtained nanocomposite. Afterward, the photocatalytic activity of the nanocomposite was studied in the removal of CIP from an aqueous solution under natural sunlight irradiation. Moreover, the effect of various parameters such as solution initial pH (3–11), reaction time (30–180min), and catalyst loading (0.03–0.12 g) on degradation efficiency were studied by applying a design of experiment (DOE) methodology. The results indicated the successful synthesis and deposition of Ag nanoparticles over amorphous silica. The results of degradation experiment confirmed the acceptable performance of Ag/silica nanocomposite in photo-degradation of CIP. According to the experimental design, both catalyst loading and reaction time are highly significant; whereas the initial pH is not significant compared to other factors. Moreover, the optimal conditions were determined to be initial pH = 6.7, reaction time = 180 min, and catalyst loading of 0.12 g. By applying these optimal conditions, degradation efficiency reached to 98%. Moreover, the results of kinetic study revealed that the photo-degradation of CIP in presence of Ag/silica nanocomposite obeys a first-order kinetic model. The Ag/silica nanocomposite exhibited a high level of stability as the nanocomposites could preserve their stability after three sequential degradation cycles.

Synthesis of cyclic carbonates of different epoxides using CO2 as a C1 building block over Ag/TUD-1 mesoporous silica catalyst: A solvent free approach

Utilization of abandoned CO2 that is generated from fossil fuels and industrial sources into valuable chemicals is a smart approach for a greener future. The fixation of CO2 over epoxides and the production of cyclic carbonates is one of the popular CO2 utilization techniques. Silica supported silver nanoparticles have been used before in different important reactions like nitrophenol reduction, alcohol oxidation etc., due to the high surface area, pore size of silica and high activity of the Ag0 species. In this study, Technische Universiteit Delft -1 (TUD-1) is used as silica support for stabilizing silver nanoparticles and CO2 has been converted to cyclic carbonate under solvent less condition. The Lewis acidic nature of the silver particles have aided into the solvent-less CO2 conversion, resulting into the maximum yield of 98% at 60 °C and 1 MPa pressure.

Biocompatible alginate silica supported silver nanoparticles composite films for wound dressing with antibiofilm activity.

Alginate films containing pyrogenic silica supported silver nanoparticles were prepared as potential wound dressings. First silica supported silver nanoparticles (CAB-O-SIL-Ag) were prepared via solid state sintering route without the use of any solvent and reducing agent. The obtained composite was characterized by X-ray powder diffraction, transmission electron microscopy and UV-vis spectroscopy which evidenced the presence of 8-20nm spherical silver nanoparticles uniformly distributed and grown on the silica surface. Then the CAB-O-SIL-Ag was used as filler to prepare alginate films by casting method and successive gelation. Films with two different silver concentrations were prepared. They showed good hydration properties and a very slow silver release. Films exhibited antimicrobial and antibiofilm activities against Staphylococcus aureus and Pseudomonas aeruginosa and showed no cytotoxicity towards human skin keratinocytes and human fibroblasts HuDe.

Lewis acidic supports promote the selective hydrogenation of carbon dioxide to methyl formate in the presence of methanol over Ag catalysts

Silica-supported silver nanoparticles exhibit outstanding efficiency in the CO2 hydrogenation to methyl formate in the presence of methanol under high pressure. Here, we show that ZrO2 and Al2O3 supports significantly increase the catalyst activity, in line with their higher Lewis acidity. The weight time yield of methyl formate over Ag/ZrO2 is up to 16.2 gMF gAg h−1 without detectable side-products, 25 times higher compared to Ag/SiO2 at the same temperature. Transient in situ and operando DRIFTS studies uncover spillover processes of formate species from Ag onto the acidic support materials and show that the surface formates can further react with adsorbed methanol at the sites near the perimeter between Ag and the support to yield methyl formate.

Decisive Role of Perimeter Sites in Silica-Supported Ag Nanoparticles in Selective Hydrogenation of CO2 to Methyl Formate in the Presence of Methanol.

Methyl formate synthesis by hydrogenation of carbon dioxide in the presence of methanol offers a promising path to valorize carbon dioxide. In this work, silica-supported silver nanoparticles are shown to be a significantly more active catalyst for the continuous methyl formate synthesis than the known gold and copper counterparts, and the origin of the unique reactivity of Ag is clarified. Transient in situ and operando vibrational spectroscopy and DFT calculations shed light on the reactive intermediates and reaction mechanisms: a key feature is the rapid formation of surface chemical species in equilibrium with adsorbed carbon dioxide. Such species is assigned to carbonic acid interacting with water/hydroxyls on silica and promoting the esterification of formic acid with adsorbed methanol at the perimeter sites of Ag on SiO2 to yield methyl formate. This study highlights the importance of employing combined methodologies to verify the location and nature of active sites and to uncover fundamental catalytic reaction steps taking place at metal-support interfaces.

Paracrystalline structure of gold, silver, palladium and platinum nanoparticles

Metallic nanoparticles are of great importance because of their unique physical, chemical, antimicrobial, diagnostic, therapeutic, biomedical, sensing, biosensing, catalytic and optical properties. Detailed knowledge of the atomic scale structure of these materials is essential for understanding their activities and for exploiting their potential. This paper reports structural studies of silica-supported silver, gold, palladium and platinum nanoparticles using X-ray diffraction and high-resolution transmission electron microscopy. Electron microscopy observation allowed the determination of nanoparticle sizes, which were estimated to be in the range of 45–470 Å, and their distribution. The obtained histograms exhibit a multimodal distribution of the investigated nanoparticle sizes. The X-ray diffraction data were analyzed using the Rietveld method in the form of Williamson–Hall plots, the PDFgui fitting procedure and model-based simulation. The Williamson–Hall plots provide evidence for the presence of strain in all investigated samples. The PDFgui fitting results indicate that the investigated nanoparticles consist of atomic clusters with different sizes and degrees of disorder as well as slightly different lattice parameters. The detailed structural characterization performed via model-based simulations proves that all samples exhibit a face-centered cubic type structure with paracrystalline distortion. The degree of disorder predicted by the paracrystalline theory is correlated with the sizes of the nanoparticles. The catalytic properties of the investigated noble metals are discussed in relation to their disordered structure.

Silica-supported silver nanoparticles as an efficient catalyst for aromatic C-H alkylation and fluoroalkylation.

The efficient catalysis of oxidative alkylation and fluoroalkylation of aromatic C-H bonds is of paramount importance in the pharmaceutical and agrochemical industries, and requires the development of convenient Ag0-based nano-architectures with high catalytic activity and recyclability. We prepared Ag-doped silica nanoparticles (Ag0/+@SiO2) with a specific nano-architecture, where ultra-small sized silver cores are immersed in silica spheres, 40 nm in size. The nano-architecture provides an efficient electrochemical oxidation of Ag+@SiO2 without any external oxidant. In turn, Ag+@SiO2 5 mol% results in 100% conversion of arenes into their alkylated and fluoroalkylated derivatives in a single step at room temperature under nanoheterogeneous electrochemical conditions. Negligible oxidative leaching of silver from Ag0/+@SiO2 is recorded during the catalytic coupling of arenes with acetic, difluoroacetic and trifluoroacetic acids, which enables the good recyclability of the catalytic function of the Ag0/+@SiO2 nanostructure. The catalyst can be easily separated from the reaction mixture and reused a minimum of five times upon electrochemical regeneration. The use of the developed Ag0@SiO2 nano-architecture as a heterogeneous catalyst facilitates aromatic C-H bond substitution by alkyl and fluoroalkyl groups, which are privileged structural motifs in pharmaceuticals and agrochemicals.

Room-temperature synthesis of silica supported silver nanoparticles in basic ethanol solution and their antibacterial activity

A facile and environmentally friendly route was developed to synthesize silica supported silver nanoparticles through the reduction of Ag+ ions in basic ethanol solution without adding any other reducing agents or surfactants at room temperature.

Reactions of methyl radicals with silica supported silver nanoparticles in aqueous solutions

Silica supported silver nanoparticles (Ag°–SiO2–NCs, NCs=nanocomposites) suspended in aqueous solutions are efficient catalysts for the dimerization of methyl radicals to produce ethane, while bare silica is quite inert towards the interaction with methyl radicals. In the presence of small amounts of ethanol adsorbed on the SiO2 surface, the reaction path with methyl radicals is changed and methane is formed as the major product.

Polymer microcapsules loaded with Ag nanocatalyst as active microreactors

Silica-supported silver nanoparticles (Ag/SiO2) encapsulated inside the PNIPAM-based microcapsules (MC) were proved to be an efficient and easy-to-handle catalyst. Due to the hydrophilic nature of MCs, they act as microreactors in a mixed organic–aqueous environment. It was demonstrated that the catalytic activity of encapsulated Ag/SiO2 substantially exceeds that of freely dispersed catalyst.

Submicron silica spheres decorated with silver nanoparticles as a new effective sorbent for inorganic mercury in surface waters

An analytical method using silica supported silver nanoparticles as a novel sorbent for the enrichment and determination of inorganic mercury (iHg) in surface water samples has been developed. Silver nanoparticles (AgNPs) were synthesized by a completely green procedure and were deposited onto the amine functionalized surface of silica submicrospheres (SiO2-NH2). The prepared nanocomposite material (SiO2/AgNPs) was characterized by transmission electron microscopy, UV-vis spectroscopy, X-ray diffraction and atomic force microscopy. The sorption and desorption characteristics of the nanosorbent SiO2/AgNPs toward Hg species were investigated by a batch method. An excellent separation of iHg and methylHg was achieved in 20 minutes at pH 2. The high selectivity of the SiO2/AgNPs toward iHg was explained by Hg(ii) reduction and subsequent silver-mercury amalgam formation. The analytical procedure for the enrichment and determination of inorganic mercury in surface waters was developed based on solid phase extraction and ICP-MS measurements. The total Hg content was determined after water sample mineralization. The recoveries reached for iHg in different surface waters e.g. river and Black sea water samples varied from 96-101%. The limits of quantification are 0.002 μg L(-1) and 0.004 μg L(-1) for iHg and total Hg, respectively; the relative standard deviations varied in the ranges of 5-9% and 6-11% for iHg and total Hg, respectively, for Hg content from 0.005 to 0.2 μg L(-1). The accuracy of the procedure developed for total Hg determination was confirmed by a comparative analysis of surface river (ICP-MS) and sea (CV AFS) waters.

Catalytic Performance of Silica-Supported Silver Nanoparticles for Liquid-Phase Oxidation of Ethylbenzene

In this study silver nanoparticles were prepared by chemical reduction method using silver nitrate as metal precursor, starch as protecting agent, and sodium borohydride (NaBH4) as a reducing agent. Formation of silver nanoparticles was monitored using UV–vis absorption spectroscopy and dynamic light scattering (DLS). They were supported on silica by dispersing silica powder in the suspension of destabilized silver nanoparticles. Samples containing different proportions of silver were thus prepared. This method is at variance from the conventionally employed method, i.e., impregnation of silver salt from its solution on support. Ag/SiO2 samples were characterized by UV–vis absorption spectroscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), inductive coupled plasma optical emission spectroscopy (ICP-OES), and N2 adsorption–desorption. Superior catalytic performance of the catalyst prepared by the present method could be observed in a test reaction of ethylbenzene oxidation affording high selectivity to acetophenone as compared to the catalyst prepared by the conventional reported methods. The 5 wt % Ag/SiO2 catalyst was found not much susceptible to sintering as could be inferred from the comparable performance of the regenerated and fresh catalysts.

ChemInform Abstract: Silver Nanoparticle‐Catalyzed Diels—Alder Cycloadditions of 2′‐Hydroxychalcones.

Metal nanoparticles are currently being employed as catalysts for a number of classical chemical transformations. In contrast, identification of novel reactions of nanoparticles, especially toward the synthesis of complex natural products and derivatives, is highly underdeveloped and represents a bourgeoning area in chemical synthesis. Herein, we report silica-supported silver nanoparticles as solid, recyclable catalysts for Diels-Alder cycloadditions of 2'-hydroxychalcones and dienes in high yield and turnover number. The use of silver nanoparticle catalysts is further demonstrated by the total synthesis of the cytotoxic natural product panduratin A employing a highly electron-rich dienophile and Lewis acid sensitive diene.

Silver Nanoparticle-Catalyzed Diels−Alder Cycloadditions of 2′-Hydroxychalcones

Metal nanoparticles are currently being employed as catalysts for a number of classical chemical transformations. In contrast, identification of novel reactions of nanoparticles, especially toward the synthesis of complex natural products and derivatives, is highly underdeveloped and represents a bourgeoning area in chemical synthesis. Herein, we report silica-supported silver nanoparticles as solid, recyclable catalysts for Diels-Alder cycloadditions of 2'-hydroxychalcones and dienes in high yield and turnover number. The use of silver nanoparticle catalysts is further demonstrated by the total synthesis of the cytotoxic natural product panduratin A employing a highly electron-rich dienophile and Lewis acid sensitive diene.

Inside Cover: Silica-Supported Silver Nanoparticles with Surface Oxygen Species as a Reusable Catalyst for Alkylation of Arenes (ChemCatChem 1/2010)

Inside Cover: Silica-Supported Silver Nanoparticles with Surface Oxygen Species as a Reusable Catalyst for Alkylation of Arenes (ChemCatChem 1/2010)

Silica-Supported Silver Nanoparticles with Surface Oxygen Species as a Reusable Catalyst for Alkylation of Arenes

A series of silica-supported silver catalysts with various Ag loading (3–30 wt %) and different treatment (oxidation and subsequent reduction by H2) were prepared, and their local structures were characterized by extended X-ray absorption fine structure (EXAFS) analysis. In oxidized catalysts, silver were mainly present as small nanoparticles with surface oxygen atoms, and the number of surface oxygen atoms decreased with increased silver loading. The H2 reduction of these samples resulted in a removal of the surface oxygen atoms. The structure–activity relationship was studied for the alkylation of anisole with benzyl alcohol and styrene. AgI oxide, AgI ion, bulk silver metal, and silica-supported silver nanoparticles were non-active species. In contrast, silica-supported silver nanoparticles with the surface oxygen atoms acted as an effective heterogeneous catalyst for the alkylation of arenes with alcohols and styrenes. Kinetic studies in alkylation of anisole with alcohols showed that the cleavage of the α-CH bond of alcohol was the rate-limiting step. It is proposed that the surface oxygen adjacent to the silver surface atoms plays an important role in the dissociation of the α-CH bond.

Silica supported silver nanoparticles from a silver(I) carboxylate: Highly active catalyst for regioselective hydrogenation

Abstract The selective hydrogenation of the α,β-unsaturated aldehyde citral (3,7-dimethyl-2,6-octadienal) was investigated with nano-sized silver particles on silica (Ag/SiO 2 ). The catalysts were synthesized from the precursors silver nitrate and silver 2-[2-(2-methoxyethoxy)ethoxy]acetate [AgO 2 C(CH 2 OCH 2 ) 3 H], respectively, and a mean particle diameter in the range of 4–8 nm could be detected via TEM. The results show that these catalysts are selective for C O hydrogenation of citral ( S UOL = 71–77% at X = 50%) even at high conversion levels. In addition, the silver carboxylate [AgO 2 C(CH 2 OCH 2 ) 3 H], soluble in water as well as in polar organic solvents, offers a straightforward preparation route for nano-sized silver particles generation.

Effect of Silica-Supported Silver Nanoparticles on the Dihydrogen Yields from Irradiated Aqueous Solutions

Metal nanoparticles (NPs) are used to catalyze the formation of molecular multielectron transfer products, for example, H2, from single-electron reductants, such as radicals. Noble metals, like silver and gold, were very instrumental in unraveling the mechanism of this interfacial process. In this study, we explore the effect of the support, silica nanoparticles, on the catalytic production of H2 on silver from radiolytically produced •C(CH3)2OH radicals and water. We obtain very high concentrations of stable silica-supported silver nanoparticles that remain suspended in solution for long periods of time. The presence of metallic silver particles on the silica surface further induces a very effective deposition of silver particles on the same silica particle leading to cooperative deposition of the silver. The silica support changes appreciably the reactivity of the silver NPs, reducing the yield of the molecular hydrogen produced at the high concentrations of the supported NPs to that of the primary molecular hydrogen G(H2) = 0.45 molecules/100 eV from water radiolysis indicating that H2 production at the surface of the silver is inhibited. A possible explanation is that the catalyst (Ag on SiO2) catalyzes the disproportionation of the reducing radicals or the reduction of acetone at the expense of the H2 evolution catalysis.

Silica-supported silver nanoparticles: Tailoring of structure-property relationships

Silica-supported silver nanoparticles were obtained by rf sputtering from Ar plasmas under soft synthesis conditions, with particular attention to the combined influence of rf power and total pressure on the system composition, nanostructure, morphology, and optical properties. In order to attain a thorough insight into the nucleation and growth phenomena of Ag nanoparticles on the silica substrate, several in situ and ex situ characterization techniques were used. In particular, a laser reflection interferometry system was employed for a real-time monitoring of the deposition process, providing useful and complementary information with respect to the other ex situ techniques (x-ray photoelectron spectroscopy and x-ray excited Auger electron spectroscopy, glancing incidence x-ray diffraction, atomic force microscopy, optical-absorption spectroscopy, and transmission electron microscopy). The above investigations evidenced the formation of silver-based nanosystems (average crystallite size ⩽10nm), whose features (metal content, Ag particle size and shape, structure and optical properties) could be carefully tailored by moderate and controlled variations of the synthesis parameters.