Activity Of Noble Metal Nanoparticles Research Articles

Role of the Human Serum Albumin Protein Corona in the Antimicrobial and Photothermal Activity of Metallic Nanoparticles against Escherichia coli Bacteria.

The emergence of antibiotic-resistant bacteria has become a major public health concern, leading to growing interest in alternative antimicrobial agents. The antibacterial activity of metal nanoparticles (NPs) has been extensively studied, showing that they can effectively inhibit the growth of various bacteria, including both Gram-positive and -negative strains. The presence of a protein corona, formed by the adsorption of proteins onto the NP surface in biological fluids, can significantly affect their toxicity. Understanding the effect of the protein corona on the antimicrobial activity of metal NPs is crucial for their effective use as antimicrobial agents. In this study, the antimicrobial activity of noble metal NPs, such as platinum (Pt), silver (Ag), and gold (Au) with and without the human serum albumin (HSA) protein corona against Escherichia coli strains, was investigated. In addition, the plasmonic photothermal effect related to AuNPs, which resulted to be the most biocompatible compared to the other considered metals, was evaluated. The obtained results suggest that the HSA protein corona modulated the antimicrobial activity exerted by the metal NPs against E. coli bacteria. These findings may pave the way for the investigation and development of innovative nanoapproaches to face antibiotic resistance emergence.

Bimetallic RhIn/ZIF-8 for the catalyic chemoselective hydrogenation of nitrostyrene: Exploration of natural selectivity of hydrogen sources and enhancing intrinsic selectivity

Chemoselective hydrogenation of nitrostyrene to aminostyrene still faces the trouble of low selectivity and poor activity. The bimetallic catalysts, which adjust the activity of noble metal nanoparticles through the doping of non-noble metals, are promising for selectively catalytic transfer hydrogenation (CTH). For another aspect, the hydrogen source also plays a vital role in selective CTH. Based on this, we prepared activity-inhibited bimetallic RhIn/ZIF-8 catalyst to study the catalytic performance towards different hydrogen sources (N2H4·H2O, NaBH4, NH3·BH3 and H2) and to explore the natural selectivity of these hydrogen sources. We found that the hydrazine hydrate was the most selective H-donor for the nitro group, while the H2 had the highest natural selectivity to olefins. The H2 produced from hydrazine hydrate is responsible for the formation of completely reduced products. The potential reduction by the intermediate imine did not occur to CC double bonds, this indicates controlling the decomposition of N2H4 will enhance the selectivity of nitroarenes. Based on this, the reaction system with the catalyst bimetallic RhIn/ZIF-8 and N2H4·H2O as the hydrogen source is established, which can fully reduce many nitrostyrenes with >98% selectivity to corresponding aminostyrenes.

Copper nanoparticles obtained by laser ablation in liquids as bactericidal agent for dental applications

The dramatic increase of antibiotic-resistant bacteria is considered one of the greatest threats to human health at global scale. The antibacterial activity of noble metal nanoparticles, could be the solution against bacterial infectious diseases which currently do not respond to conventional treatments.In this work, copper nanoparticles were produced by laser ablation using two different lasers. A nanosecond laser operating at 532 nm and a picosecond laser at 1064 nm were used to ablate a copper target submerged in water and methyl alcohol. The obtained colloidal solutions consisted of copper oxide nanoparticles in suspension with diameters ranging from few nanometers to 45 nm. The nanoparticles formation process is highly influenced by laser parameters, but the solvent plays a crucial role on their characteristics. Cu oxide nanoparticles obtained in water present chain-like nanostructure, while those obtained in methyl alcohol are spherical with lower presence of oxide. All the obtained nanoparticles are crystalline and noticeably stable.Microbiology tests confirm their strong activity against Aggregatibacter actinomycetemcomitans. Cytocompatibility with human periodontal ligament stem cells is also confirmed. The biological assays evidence that ions release is not the main parameter responsible for the bactericidal activity of copper nanoparticles. Other factors such as oxidation state, size and crystallographic structure, have a greater influence on the process.

Polyethyleneimine-oleic acid micelle-stabilized gold nanoparticles for reduction of 4-nitrophenol with enhanced performance

Noble metal nanoparticles have been drawing great attention for the treatment of water pollutants. The catalytic activity of noble metal nanoparticles is usually reduced due to their aggregation. Amphiphilic molecule micelles have potential to stabilize the noble nanoparticles against aggregation. In this study, a novel facile method was reported for preparing polyethyleneimine-oleic acid (PEI-oleic acid) micelle-stabilized gold nanoparticles (PO-AuNPsn), where the gold nanoparticles (AuNPs) were embedded in the shell area of micelles. When the molar ratio of [N] to [Au] was 50, 100, and 200, the mean diameter of AuNPs was 3.52 ± 0.42, 3.11 ± 0.28, and 2.85 ± 0.48 nm, respectively. The corresponding zeta potential of the PO-AuNPsn was determined to be 26.2, 28.9 and 35.7 mV, respectively. Furthermore, PO-AuNPsn remained stable in aqueous solution at room temperature for more than 1 month. More importantly, PO-AuNPsn had higher catalytic activity for 4-nitrophenol (4-NP) reduction in aqueous solution compared with previous reports, where PO-AuNPs200 showed a Knor value of 9367 s−1 g−1. It is believed that PO-AuNPsn showed high catalytic activity because of their small size, high stability, and the location of AuNPs in the shell area, which made it easier for AuNPs to contact with 4-NP. The method described in this report represents a new method to prepare small and stable noble metal nanoparticles for catalytic applications in the future.

Size Regulation of Platinum Nanoparticles by Using Confined Spaces for the Low-Temperature Oxidation of Ethylene.

Noble-metal nanoparticles have attracted great attention because of their excellent catalytic activity. However, the activity of noble-metal nanoparticles is severely dependent on the size of the metal nanoparticles. Therefore, regulation of the nanoparticle size is of great importance. Herein we report an efficient strategy for the first time to regulate the size of platinum (Pt) nanoparticles in a typical mesoporous silica SBA-15 by using the confined spaces. The Pt-containing precursor is introduced to the confined spaces between the template and silica walls in as-prepared SBA-15 by grinding. Subsequent calcination allows template removal and precursor conversion in one step and avoids repeated calcination in conventional modification processes. This leads to the formation of Pt nanoparticles with smaller size, making Pt metal catalysts highly active. Hence, the catalytic activity of the oxidation of trace ethylene is very superior to that of those prepared by the conventional method. For a typical material, PtAS-5, containing 5.0 wt % Pt, the complete conversion of ethylene was achieved at 40 °C, which is lower than that on the catalyst PtCS-5 prepared by the conventional method (50 °C) as well as that on a series of catalysts reported previously.

Tricobalt tetraoxide-supported palladium catalyst derived from metal organic frameworks for complete benzene oxidation

The structure and the chemical state of the metal oxide support have significant effect on the activity of noble metal nanoparticles for the catalytic oxidation of organic pollutants. In this work, we report the synthesis of porous tricobalt tetraoxide-supported palladium (Pd/Co3O4) catalysts derived from direct pyrolysis of metal-organic framework (MOF) for the complete oxidation of benzene. The porosity and nanoparticle size of the catalyst could be controlled by adjusting the calcination temperature. The X-ray photoelectron spectroscopy (XPS) analyses reveal that the surface adsorbed oxygen, which is associated with the PdO x species, is crucial for catalytic performance. H2-temperature programmed reduction (H2-TPR) results indicate that the reducibility of the catalyst has significant effect on the catalytic activity for the oxidation of benzene. In general, Pd nanoparticles supported on the porous polyhedron Co3O4 support calcined at 350 °C (Co3O4-PP-350), which possess abundant porous structures and the most active surface adsorbed oxygen, exhibit the highest activity for the complete catalytic conversion of benzene compared with those supported on the porous polyhedron Co3O4 support calcined at 250 °C (Co3O4-PP-250), 550 °C (Co3O4-PP-550), and the Co3O4 nanoparticle support calcined at 350 °C (Co3O4-NP-350).

Study on the Catalytic Activity of Noble Metal Nanoparticles on Reduced Graphene Oxide for Oxygen Evolution Reactions in Lithium-Air Batteries.

Among many challenges present in Li-air batteries, one of the main reasons of low efficiency is the high charge overpotential due to the slow oxygen evolution reaction (OER). Here, we present systematic evaluation of Pt, Pd, and Ru nanoparticles supported on rGO as OER electrocatalysts in Li-air cell cathodes with LiCF3SO3-tetra(ethylene glycol) dimethyl ether (TEGDME) salt-electrolyte system. All of the noble metals explored could lower the charge overpotentials, and among them, Ru-rGO hybrids exhibited the most stable cycling performance and the lowest charge overpotentials. Role of Ru nanoparticles in boosting oxidation kinetics of the discharge products were investigated. Apparent behavior of Ru nanoparticles was different from the conventional electrocatalysts that lower activation barrier through electron transfer, because the major contribution of Ru nanoparticles in lowering charge overpotential is to control the nature of the discharge products. Ru nanoparticles facilitated thin film-like or nanoparticulate Li2O2 formation during oxygen reduction reaction (ORR), which decomposes at lower potentials during charge, although the conventional role as electrocatalysts during OER cannot be ruled out. Pt-and Pd-rGO hybrids showed fluctuating potential profiles during the cycling. Although Pt- and Pd-rGO decomposed the electrolyte after electrochemical cycling, no electrolyte instability was observed with Ru-rGO hybrids. This study provides the possibility of screening selective electrocatalysts for Li-air cells while maintaining electrolyte stability.

A Study on the Catalytic Activity of Noble Metal Nanoparticles on Reduced Graphene Oxide for Oxygen Evolution Reactions in Lithium-Air Batteries

Among many challenges present in Li-air batteries, one of the main reasons of low efficiency is the high charge overpotential due to the slow oxygen evolution reaction (OER). Here we present systematic evaluation of Pt, Pd, and Ru nanoparticles supported on rGO as OER electrocatalysts in Li-air cell cathodes with LiCF3SO3-TEGDME salt-electrolyte system. All of the noble metals explored could lower the charge overpotentials, and among them, Ru-rGO hybrids exhibited the most stable cycling performance and the lowest charge overpotentials. Role of Ru nanoparticles in boosting oxidation kinetics of the discharge products were investigated. Apparent behavior of Ru nanoparticles was different from the conventional electrocatalysts that lower activation barrier through electron transfer, since the major contribution of Ru nanoparticles in lowering charge overpotential is to control the nature of the discharge products. Ru nanoparticles facilitated thin film-like or nanoparticulate Li2O2 formation during oxygen reduction reaction (ORR), which decomposes at lower potentials during charge, although the conventional role as electrocatalysts during OER cannot be ruled out. Pt-and Pd-rGO hybrids showed fluctuating potential profiles during the cycling. While Pt- and Pd-rGO decomposed the electrolyte after electrochemical cycling, no electrolyte instability was observed with Ru-rGO hybrids. This study provides the possibility of screening selective electrocatalysts for Li-air cells while maintaining electrolyte stability.

Catalytic activity of noble metal nanoparticles toward hydrodechlorination: influence of catalyst electronic structure and nature of adsorption

In this study, stabilized Pd, Pt and Au nanoparticles were successfully prepared in aqueous phase using sodium carboxymethyl cellulose (CMC) as a capping agent. These metal nanoparticles were then tested for catalytic hydrodechlorination toward two classes of organochlorinated compounds (vinyl polychlorides including trichloroethylene (TCE), tetrachloroethylene (PCE), and alkyl polychlorides including 1,1,1-trichloroethane (1,1,1-TCA), and 1,1,1,2-tetrachloroethane (1,1,1,2- TeCA)) to determine the rate-limiting steps and to explore the reaction mechanisms. The surface area normalized reaction rate constant, k SA, showed a systematic dependence on the electronic structure (the density of states at the Fermi level) of the metals, suggesting that adsorption of organochlorinated reactants on the metal catalyst surfaces is the rate-limiting step for catalytic hydrodechlorination. Hydrodechlorination rates of 1,1,1-TCA and 1,1,1,2-TeCA agreed with the bond strength of the first (weakest) dissociated C-Cl bond, suggesting that C-Cl bond cleavage, which is the first step for dissociative adsorption of the alkyl polychlorides, controlled the catalytic hydrodechlorination rate. However, hydrodechlorination rates of TCE and PCE correlated with the adsorption energies of their molecular (non-dissociative) adsorption on the noble metals rather than with the first C-Cl bond strength, suggesting that molecular adsorption governs the reaction rate for hydrodechlorination of the vinyl polychlorides.

Enhancement of Activity of Noble Metal Nanoparticles in Oxidative Electrocatalysis through Modification with Mixed-Metal Oxo-Species

Platinum has been recognized as the most active catalytic metal towards oxidation of ethanol at low and moderate temperatures. But Pt anodes are readily poisoned by the strongly adsorbed intermediates, namely by CO-type species, requiring fairly high overpotentials for their removal. To enhance activity of Pt catalysts towards methanol and ethanol oxidation, additional metals including ruthenium, tin, molybdenum, tungsten or rhodium are usually introduced as the alloying component. More recently it has been demonstrated that catalytic activity of platinum-based nanoparticles towards electrooxidation of ethanol has been significantly enhanced through interfacial modification with ultra-thin monolayer-type films of metal oxo species of tungsten, titanium or zirconium. Also gold in combination with platinum has been demonstrated to produce novel high performance bimetallic catalysts.We pursue a concept of utilization of hybrid mixed metal (tungsten(VI)/zirconium(IV), tungsten(VI)/titanium(IV), tungsten(VI)/cerium(IV)) oxides as matrices for supporting and activating noble metal nanoparticles (e.g. Pt, Pt-Ru, Pd, Ru or Rh) during electrooxidation of methanol, ethanol, dimethyl ether and formic acid. Remarkable increases of electrocatalytic currents measured under voltammetric and chronoamperometric conditions have been observed. The most likely explanation takes into account possibility of specific interactions of noble metals with transition metal oxide species as well as existence of active hydroxyl groups in the vicinity of catalytic noble metal sites.The concept of utilization of mixed metal oxide supports to active noble metal catalytic sites will be extended to oxidation of such inert reactants as arsenate(III) and nitrate(III) that of importance to analytical chemistry, namely to electroanalytical determinations of toxic oxoanions. Mechanistic considerations will be provided, and comparison will be made to the behavior of small organic molecules mentioned above.

Size-dependent antioxidative activity of platinum nanoparticles

Background So far, most of studies on nanometer-sized metal particles have focused on biological safety and potential hazards. However, anti-oxidative activity of noble metal nanoparticles (NPs) attracts much attention, recently. Platinum nanoparticles (Pt NPs) are one of the most important noble metals in nanotechnology because Pt NPs have negative surface potential from negative charges and are stably suspended from an electric repulsion between the same charged particles [1]. We previously reported that Pt NPs of 2-3 nm sizes scavenged reactive oxygen species (ROS) such as superoxide anion radical, hydrogen peroxide and hydroxyl radical in vitro [2]. Here, we report the cytotoxicity and size-dependent antioxidative activity of Pt NPs on rat skeletal muscle cell line, L6.

Antibacterial properties of green-synthesized noble metal nanoparticles

We report on the antibacterial activity of noble metal nanoparticles prepared by direct sputtering into liquid medium (propane-1,2,3-triol). Silver and gold spherical nanoparticles with diameter of 4–6nm (AgNP4–6, AuNP4–6) and gold spherical nanoparticles with diameter of 9–12nm (AuNP8–12) were investigated. The possibility of managing nanoparticle diameter via controlling temperature of capturing media is also demonstrated. Nanoparticle size and shape were studied by transmission electron microscopy. Optical response of nanoparticle solutions was determined by UV–vis absorption spectroscopy. Antibacterial properties were tested against two common pollutants (Escherichia coli DBM 3138, a Gram-negative bacteria and Staphylococcus epidermidis DBM 3179, a Gram-positive bacteria). The cells (concentration of 11,000 cellsml−1) were incubated together with nanoparticles (concentration 0.8mgml−1). In the presence of silver nanoparticles the growth of E. coli and S. epidermidis was completely inhibited after 24h. Any growth inhibition of E. coli was observed neither in the presence of smaller nor bigger gold nanoparticles during the whole experiment. Surprisingly, AuNP4–6, but not AuNP8–12 were able to inhibit the growth of S. epidermidis.

Electrocatalytic oxidation of small organic molecules in acid medium: Enhancement of activity of noble metal nanoparticles and their alloys by supporting or modifying them with metal oxides

Different approaches to enhancement of electrocatalytic activity of noble metal nanoparticles during oxidation of small organic molecules (namely potential fuels for low-temperature fuel cells such as methanol, ethanol and formic acid) are described. A physical approach to the increase of activity of catalytic nanoparticles (e.g. platinum or palladium) involves nanostructuring to obtain highly dispersed systems of high surface area. Recently, the feasibility of enhancing activity of noble metal systems through the formation of bimetallic (e.g. PtRu, PtSn, and PdAu) or even more complex (e.g. PtRuW, PtRuSn) alloys has been demonstrated. In addition to possible changes in the electronic properties of alloys, specific interactions between metals as well as chemical reactivity of the added components have been postulated. We address and emphasize here the possibility of utilization of noble metal and alloyed nanoparticles supported on robust but reactive high surface area metal oxides (e.g. WO3, MoO3, TiO2, ZrO2, V2O5, and CeO2) in oxidative electrocatalysis. This paper concerns the way in which certain inorganic oxides and oxo species can act effectively as supports for noble metal nanoparticles or their alloys during electrocatalytic oxidation of hydrogen and representative organic fuels. Among important issues are possible changes in the morphology and dispersion, as well as specific interactions leading to the improved chemisorptive and catalytic properties in addition to the feasibility of long time operation of the discussed systems.

Synthesis of Noble Metal Nanoparticles Embedded in the Shell Layer of Core−Shell Poly(styrene-co-4-vinylpyridine) Micospheres and Their Application in Catalysis

The noble metal nanoparticles of Pd, Au, and Ag embedded in the shell layer of core−shell poly(styrene-co-4-vinylpyridine) micospheres were synthesized, and the catalytic activity of the shell-embedded Pd nanoparticles was investigated. To increase the accessible active site and therefore increase the catalytic activity of noble metal nanoparticles, the in situ synthesized noble metal nanoparticles are selectively immobilized in the outer shell layer of the core−shell poly(styrene-co-4-vinylpyridine) microspheres, which are synthesized by one-stage soap-free emulsion polymerization in water and contain a core of polystyrene and a coordinative shell of poly(4-vinylpyridine). It is found the Pd nanoparticles embedded in the shell layer of the core−shell micospheres are an efficient and easily reusable catalyst for Suzuki reactions performed in water.