Stabilization Of Metal Nanoparticles Research Articles

Catalytic Nanoparticles Prepared By Atomic Layer Deposition

Heterogeneous catalysts normally consist of small metal particles dispersed on a high surface area porous support. Traditional methods, such as wet-chemical processing, can produce metal particle catalysts as small as several nanometers, but these methods cannot precisely control the size of the catalytic nanoparticles and disperse them homogeneously within the porous substrates. In addition, heterogeneous catalysts cannot selectively convert specific molecules in the reactant mixture to catalyze only desired reactions. Novel approaches are required to synthesize stable metal nanoparticles catalysts with tightly controlled sizes to further advance the knowledge of their unique size-dependent catalytic behavior. Recently, atomic layer deposition (ALD) has been used to prepare highly active, highly dispersed metal nanoparticles. In this presentation, we will introduce some examples of nanostructured catalysts prepared by ALD, such as Pt nanoparticles, Ni nanoparticles, Pt-Co bimetallic nanoparticles, and CeO2 doped TiO2 nanoparticles.

BASF introduces Boroflex FCC catalyst for superior bottoms upgrading

In-situ synthesis of chemically pure noble metal (Au, Pt, Pd, Ru) nanoparticles was performed via redox reaction under ambient conditions from aqueous noble metal salt solutions on non-porous fumed silica. Nanoparticles of average sizes <5 and up to 19 nm were obtained. The nanostructured fumed silica with surface modified by triethoxysilane has been proven an effective support for noble metal nanoparticles synthesis. The silicon-hydride groups on the silica surface not only directly reduce noble metal ions from solution, but they also stabilize metal nanoparticles by bonding with the solid matrix. The nanocomposites were studied for the reduction of 2-nitrophenol showing very high activity at room temperature following the order Pd > Au > Ru > Pt.

Ru Nanoparticles Confined within a Coordination Cage

Metal nanoparticles (MNPs) are very promising for industrial catalysis. However, the synthesis of ultrafine, highly dispersed and stable MNPs with desirable structures is still challenging. In this issue of Chem, Zhou and co-workers have successfully fabricated ultrafine face-centered-cubic (fcc) Ru nanoparticles with an average size of 2.5 nm by using a negatively charged metal-organic polyhedron as the template. These MNPs exhibited high activity, selectivity, and stability for the catalytic methanolysis of ammonia borane.

Metal nanoparticles in ionic liquid‐cosolvent biphasic systems as active catalysts for acetylene hydrochlorination

Ionic liquid (IL)‐stabilized metal nanoparticles (NPs) have attracted increased attention as novel catalysts for various reactions due to their excellent stability and high activity. However, the high viscosity of ILs limits their applications. Here, for the first time, we reported an NPs@IL‐cosolvent liquid–liquid biphasic system for metal NPs catalysis. The NPs were successfully confined to IL phase, and abundant IL droplets containing NPs were generated under the reactant flow. The NPs@IL droplets served as microreactors for the catalysis; while the low viscosity organic phase enabled the rapid mass transfer of substances. The biphasic system exhibited improved performance for acetylene hydrochlorination than that of the pure IL system. An acetylene conversion of 98% and a selectivity of 99.5% were achieved along with a 90% decrease on IL usage. The tolerable gas hourly space velocity in the biphasic system for a satisfactory conversion was almost double that of the pure IL system. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2536–2544, 2018

Engineered Nanoparticles with Antimicrobial Property.

The urge for the development and manufacture of new and effective antimicrobial agents is particularly demanding especially in the present scenario of emerging multiple drug resistant microorganisms. A promising initiative would be to converge nanotechnology to develop novel strategies for antimicrobial treatment. These distinct nano scale properties confer impressive antimicrobial capabilities to nanomaterials that could be exploited. Nanotechnology particularly modulates the physicochemical properties of organic and inorganic nanoparticles, rendering them suitable for various applications related to antimicrobial therapy compared to their bulk counterparts. However, a major issue associated with such usage of nanomaterials is the safety concern on heath care system. Hence, a thorough put knowledge on biocompatible nanostructures intended for antimicrobial therapy is needed. A systematic review of the existing scientific literature is being attempted here which includes the properties and applications of a few nano structured materials for antimicrobial therapy and also the mechanism of action of nanomaterials as antimicrobial agents. Silver (Ag), Graphene, Quantum dots (QDs), Zinc oxide (ZnO) and chitosan nanoparticles are taken as representatives of metals, semiconductors, metal oxides and organic nanoparticles that have found several applications in antimicrobial therapy are reviewed in detail. An ideal anti microbial should selectively kill or inhibit the growth of microbes but cause little or no adverse effect to the host. Each of the engineered nanomaterials reviewed here has its own advantages and disadvantages. Nanomaterials in general directly disrupt the microbial cell membrane, interact with DNA and proteins or they could indirectly initiate the production of reactive oxygen species (ROS) that damage microbial cell components and viruses. Some like silver nanoparticles have broad spectrum antibacterial activity while others like cadmium containing QDs shows both antibacterial as well as antiprotozoal activity. Nano material formulations can be used directly or as surface coatings or as effective carriers for delivering antibiotics. Polycationic nature of Chitosan NPs helps in conjugation and stabilization of metallic nanoparticles which will enhance their effective usage in antimicrobial therapy.

Nanoparticles Formed onto/into Halloysite Clay Tubules: Architectural Synthesis and Applications.

Nanoparticles, being objects with high surface area are prone to agglomeration. Immobilization onto solid supports is a promising method to increase their stability and it allows for scalable industrial applications, such as metal nanoparticles adsorbed to mesoporous ceramic carriers. Tubular nanoclay - halloysite - can be an efficient solid support, enabling the fast and practical architectural (inside / outside) synthesis of stable metal nanoparticles. The obtained halloysite-nanoparticle composites can be employed as advanced catalysts, ion-conducting membrane modifiers, inorganic pigments, and optical markers for biomedical studies. Here, we discuss the possibilities to synthesize halloysite decorated with metal, metal chalcogenide, and carbon nanoparticles, and to use these materials in various fields, especially in catalysis and petroleum refinery.

Yeast cells carrying metal nanoparticles

Yeast cells can be used as carriers for hosting metal nanoparticles via in situ metal ion reduction methods. We synthesized Ag and Pd nanoparticles (NPs) located in different positions of yeast cells, either in yeast cell envelope or inside yeast cells. Ag NPs were able to grow at the cell wall and inside the cells depending on the preparation methods. Glucans at the cell wall functioned as reductive reagents in Tollens's reaction and Ag NPs with average size of about 9 nm (measured with Scherrer equation) were formed covering yeast cells. By UV illumination on yeast cells with AgNO3 solution imported in cytoplasm in advance, Ag nanoparticles with size of about 4 nm were produced inside yeast cells. UV illumination in the presence of Ag ions could carbonize the yeast cells as indicated by Raman spectroscopic analysis, which may be conducive to establishing new sterilization mechanism. Yeast cells carrying palladium nanoparticles were also synthesized by hydrazine hydrate reduction inside cells. It was found that Pd nanoparticles with size of about 11 nm were almost evenly distributed in every parts of yeast cells, in the envelope and inside cells. Ag NPs and Pd NPs on yeast cells were observed with optical microscopy, scanning electronic microscopy (SEM), and transmission electron microscopy (TEM). Crystal structures of Ag NPs and Pd NPs were confirmed by X-ray powder diffraction (XRD). The sizes of the NPs were calculated based on XRD results and Scherrer equation. The size distribution of NPs was obtained by counting the sizes of NPs on TEM images. Those results showed that easily affordable yeast cells are good bio-carriers for synthesis and stabilization of metal nanoparticles in aqueous environments, and no other chemical stabilizers were needed. The yeast carrying metal nanoparticles structures may find applications in medical or environmental treatment fields.

Sonication-enabled rapid production of stable liquid metal nanoparticles grafted with poly(1-octadecene-alt-maleic anhydride) in aqueous solutions.

Gallium-based liquid metals are attractive due to their unique combination of metallic and fluidic properties. Liquid metal nanoparticles (LM NPs), produced readily using sonication, find use in soft electronics, drug delivery, and other applications. However, LM NPs in aqueous solutions tend to oxidize and precipitate over time, which hinders their utility in systems that require long-term stability. Here, we introduce a facile route to rapidly produce an aqueous suspension of stable LM NPs within five minutes. We accomplish this by dissolving poly(1-octadecene-alt-maleic anhydride) (POMA) in toluene and mixing with deionized water in the presence of a liquid metal (LM). Sonicating the mixture results in the formation of toluene-POMA emulsions that embed the LM NPs; as the toluene evaporates, POMA coats the particles. Due to the POMA hydrophobic coating, the LM NPs remain stable in biological buffers for at least 60 days without noticeable oxidation, as confirmed by dynamic light scattering and transmission electron microscopy. Further stabilization is achieved by tuning the LM composition. This paper elucidates the stabilization mechanisms. The stable LM NPs possess the potential to advance the use of LM in biomedical applications.

Carbon Precursor Structures and Graphene on Palladium Nanoparticles

Due to their stable catalytic properties graphene-encapsulated metal nanoparticles (NPs) have come into the focus of heterogeneous catalysis. Research on graphene’s atomic structure is a prerequisite for understanding and controlling catalytic processes; however, it is still at its very beginning considering metal NPs. This atomic-scale scanning tunnelling microscopy study documents preliminary growth stages and the structural properties of graphene on highly oriented pyrolytic graphite (HOPG) supported palladium NPs. It is shown that an annealing of the NPs at ∼650 °C in a few tens of Langmuir of ethylene (ethene) leads first to a carbon precursor structure covering the NP’s (111) facets. At higher ethylene exposures, the precursor structure turns into single-layer graphene encapsulating the NPs. Graphene-encapsulated palladium NPs with a size larger than ∼30 nm exhibit mostly one single and an almost defect-free graphene sheet on a facet. In most of the cases, such a perfect growth does not take place o...

Hydrogenation of CO2 over Co supported on carbon nanotube, carbon nanotube-Nb2O5, carbon nanofiber, low-layered graphite fragments and Nb2O5

CO2 hydrogenation was studied with catalysts containing 1.5–35 wt% Co supported on carbon nanotubes, nanofibers, low-layered graphite fragments and composites of carbon nanotube-Nb2O5. All catalytic processes with Co/supported catalysts were investigated using XRF, DSC, TGA, H2-TPR, TEM, SEM and XPS. Based on obtained results, it is indicated that the products from CO2 hydrogenation were CH4 and/or CO under reaction conditions pressure of 1.5 MPa and temperature of 200–500 °C, as well as the size of the particles of Co and their phase state directly affected on the catalysts activity. 3 wt% Co catalyst supported on carbon nanotubes has shown catalytic inactivity due to amorphous state of metal. It is possible to activate them during Co crystallization after thermal treatment. It is shown, that the size of Co particles supported on carbon nanotubes is 4–6 nm. The methods of fictionalization the surface of carbon nanomaterials ensuring an additional stability of metal nanoparticles is recommended.

Preparation, Characterization and Application of Polysaccharide-Based Metallic Nanoparticles: A Review.

Polysaccharides are natural biopolymers that have been recognized to be the most promising hosts for the synthesis of metallic nanoparticles (MNPs) because of their outstanding biocompatible and biodegradable properties. Polysaccharides are diverse in size and molecular chains, making them suitable for the reduction and stabilization of MNPs. Considerable research has been directed toward investigating polysaccharide-based metallic nanoparticles (PMNPs) through host–guest strategy. In this review, approaches of preparation, including top-down and bottom-up approaches, are presented and compared. Different characterization techniques such as scanning electron microscopy, transmission electron microscopy, dynamic light scattering, UV-visible spectroscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and small-angle X-ray scattering are discussed in detail. Besides, the applications of PMNPs in the field of wound healing, targeted delivery, biosensing, catalysis and agents with antimicrobial, antiviral and anticancer capabilities are specifically highlighted. The controversial toxicological effects of PMNPs are also discussed. This review can provide significant insights into the utilization of polysaccharides as the hosts to synthesize MPNs and facilitate their further development in synthesis approaches, characterization techniques as well as potential applications.

Dioxygen in Polyoxometalate Mediated Reactions.

In this review article, we consider the use of molecular oxygen in reactions mediated by polyoxometalates. Polyoxometalates are anionic metal oxide clusters of a variety of structures that are soluble in liquid phases and therefore amenable to homogeneous catalytic transformations. Often, they are active for electron transfer oxidations of a myriad of substrates and upon reduction can be reoxidized by molecular oxygen. For example, the phosphovanadomolybdate, H5PV2Mo10O40, can oxidize Pd(0) thereby enabling aerobic reactions catalyzed by Pd and H5PV2Mo10O40. In a similar vein, polyoxometalates can stabilize metal nanoparticles, leading to additional transformations. Furthermore, electron transfer oxidation of other substrates such as halides and sulfur-containing compounds is possible. More uniquely, H5PV2Mo10O40 and its analogues can mediate electron transfer-oxygen transfer reactions where oxygen atoms are transferred from the polyoxometalate to the substrate. This unique property has enabled correspondingly unique transformations involving carbon-carbon, carbon-hydrogen, and carbon-metal bond activation. The pathway for the reoxidation of vanadomolybdates with O2 appears to be an inner-sphere reaction, but the oxidation of one-electron reduced polyoxotungstates has been shown through intensive research to be an outer-sphere reaction. Beyond electron transfer and electron transfer-oxygen transfer aerobic transformations, there a few examples of apparent dioxygenase activity where both oxygen atoms are donated to a substrate.

Synthesis and stabilization of small Pt nanoparticles on TiO2 partially masked by SiO2

Controlling metal nanoparticle size and preserving metal dispersion at elevated temperature remain key challenges in designing new supported metal catalysts. Many methods have been proposed to stabilize metal nanoparticles for catalysis, but the use of specialized equipment or metal precursors can limit the application of these methods for scalable production. Here, we demonstrate a synthesis strategy to improve the dispersion and thermal stability of Pt nanoparticles on an oxide support. A thin SiO2 coat (<2 nm) was deposited on TiO2 through repeated condensation cycles of tetraethyl orthosilicate (TEOS) with or without an organic template on the surface. H2PtCl6 was deposited using wetness impregnation, and the samples were dried, calcined, and reduced. The as-synthesized Pt nanoparticles are 1–2 nm by TEM and maintain dispersion >45% by CO chemisorption even after prolonged heating at 500 °C, whereas Pt nanoparticles on unmodified TiO2 are less dispersed (∼33%) and their dispersion falls further upon prolonged heating. Ethylene hydrogenation demonstrates that the Pt nanoparticles on modified TiO2 preserve the catalytic activities of Pt on unmodified TiO2. The use of wet chemistry-based oxide modification and wetness impregnation makes this strategy a scalable and generalizable synthesis method to prepare other supported metal nanoparticles for catalysis applications.

Mesoporous metal - silica materials: Synthesis, catalytic and thermal properties

Here, we report a simple and scalable synthesis strategy of metal (Ni or Cu) nanoparticles uniformly distributed inside a mesoporous silica matrix. This method involves incorporation of metal nitrates and citric acid in a stable silica gel through controlled hydrolysis of tetraethyl orthosilicate. Combustion of dried gels with ammonium nitrate in an inert gas atmosphere enables preparation of highly porous Ni/SiO2 and Cu/SiO2 nanomaterials with tunable metal content (∼5–30 wt.%). This approach also allows for independent tuning of the metal nanoparticle size (from 2 to 50 nm) and textural parameters, such as surface area (50–600 m2/g), average pore size (3–8 nm), and pore volume (0.05–0.6 cm3/g) of the materials during the one-step combustion. This new approach also enables uniform incorporation of metal nanoparticles within a porous silica matrix. This feature allows for synthesis of encapsulated stable ultra-small metallic nanoparticles with unusual properties. We tested Ni/SiO2 nanoscale materials with different textural parameters as catalysts in the ethanol decomposition reaction. The catalysts exhibited high activity toward hydrogen generation for ∼100 h. The relevant links between the textural parameters and stability of the catalysts are revealed. Characterization of the spent catalysts showed no structural changes, indicating superior stability over long periods of time. We also used spark plasma sintering (SPS) of Ni/SiO2 and Cu/SiO2 nanoscale materials to fabricate porous (70–80%) compact samples. These materials exhibited significantly low thermal diffusivity, which makes them attractive for thermal management applications. We also showed that the simple preparation method allows for production of large batches of final product, such as 10–50 g, in laboratory conditions.

Colloidal Stability of Metal Nanoparticles in Engine Oil under Thermal and Mechanical Load

AbstractExtended colloidal stability and high dispersion degree of nanolubricants are required to avoid nanoparticle deposition in combustion engines and to reduce friction and wear. The simple and rapid one‐step technique of pulsed laser ablation in liquids is employed to synthesize precursor‐free and highly dispersed gold nanoparticles in lubricants while the colloidal stability is measured by optical spectroscopy and transmission electron microscopy. A remarkable colloidal stability is determined under engine‐like and ambient conditions for nine months in terms of constant primary particle size. In contrast to additive‐free oils, almost no agglomeration is observed, which might be attributed to the attachment of engine oil additives or pyrolyzed/oxidized molecules to the nanoparticles preventing attractive nanoparticle interactions.

Enhancement of catalytic activity of a programmed gold nanoparticle superstructure modulated by supramolecular protein assembly

Improving the efficiency of the oxygen reduction reaction (ORR) for use in commercial fuel cells has been the subject of diverse synthetic research activities. However, due to their inferior catalytic performance and dispensability, there are still limitations to achieving breakthroughs regarding ORR catalytic activity using carbon nanomaterials, despite their high electron-transfer and mass-transport properties. In this study, we mimicked nature by using a biomineralization approach for controlling the growth of inorganic materials and demonstrated improved ORR values. The designed peptide, Hexcoil-Ala, is able to supramolecular assembly on single-walled carbon nanotubes (SWNTs), leading to SWNTs that are well dispersed in aqueous solution. In order to direct gold nanoparticle (AuNP) nucleation sites, we substitute two residues in Hexcoil-Ala with cysteine to provide the mutated peptide, HexCoil-Ala-2Cys. This peptide affords a sophisticated, size-controlled, and well-dispersed arrangement of AuNPs. High-resolution transmission electron microscopy studies confirmed the homogeneously well-aligned distribution of nanosized AuNPs on the HexCoil-Ala-2Cys structure, along the direction of SWNT axis. The (AuNPs/P-SWNT) composite in water provides dispersed and stable metallic nanoparticles of electrostatically modified Au through synergistic effects involving the peptide. Consequently, this catalyst exhibits improved ORR performance compared to bulk gold and even, in case of number of electrons (n) transferred, higher than the number of Pt/C. X-ray photoelectron and Raman spectroscopies reveal the details of the electronic interactions among the components of the AuNP/P-SWNT composite, and how they facilitate the four-electron reaction pathway. This study provides valuable information for the optimization of catalyst synthesis and precise particle-size control, leading to stable, water-dispersive composites, with improved electronic properties for enhanced ORR performance in fuel cells.

Thermally Stable Metallic Nanoparticles Prepared via Core-Cross-linked Block Copolymer Micellar Nanoreactors.

Thermally stable metallic nanoparticles (MNPs) are highly desirable for the melt processing of polymer nanocomposites. However, due to the high surface energy penalty and decreased melting temperature, MNPs are easy to agglomerate and lose their unique properties if there is no protection or confinement layer. In this work, we report a facile and efficient way to synthesize thermally stable MNPs using core-cross-linked polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) reverse micelles as nanoreactors. From infrared results, gold, silver, and palladium ions exhibited distinctive coordination to the 4VP groups with varying chelation strengths. Compared to the non-cross-linked micelles, 1,4-dibromobutane (DBB)-cross-linking of the P4VP cores provided several advantages. First, it prevented severe swelling of the P4VP cores caused by the reducing agents and subsequent merger of swollen micelles. Second, the quaternized P4VP with hydrophilicity enhanced the uptake speed of precursor metal ions into the cores. Third, the cross-linked cores greatly stabilized the MNPs against the high-temperature environment (e.g., 110 °C for 40 h in toluene). In addition, the solubility of the reducing agents also played an important role. Anhydrous hydrazine could swell the P4VP cores and concentric core-shell particle morphology was obtained. On the contrary, triethylsilane could not swell the P4VP cores and thus eccentric core-shell particle morphology was observed. Only the concentric core-shell MNPs exhibited good thermal stability, whereas the eccentric core-shell MNPs did not. This work suggested that these thermally stable MNPs could be good candidates for the melt processing of functional polymer nanocomposites.

Metal Nanoparticles in Ionic Liquids.

During the last years ionic liquids (ILs) were increasingly used and investigated as reaction media, hydrogen sources, catalysts, templating agents and stabilizers for the synthesis of (monometallic and bimetallic) metal nanoparticles (M-NPs). Especially ILs with 1,3-dialkyl-imidazolium cations featured prominently in the formation and stabilization of M-NPs. This chapter summarizes studies which focused on the interdependencies of the IL with the metal nanoparticle and tried to elucidate, for example, influences of the IL-cation, -anion and alkyl chain length. Qualitatively, the size of M-NPs was found to increase with the size of the IL-anion. The influence of the size of imidazolium-cation is less clear. The M-NP size was both found to increase and to decrease with increasing chain lengths of the 1,3-dialkyl-imidazolium cation. It is evident from such reports on cation and anion effects of ILs that the interaction between an IL and a (growing) metal nanoparticle is far from understood. Factors like IL-viscosity, hydrogen-bonding capability and the relative ratio of polar and non-polar domains of ILs may also influence the stability of nanoparticles in ionic liquids and an improved understanding of the IL-nanoparticle interaction would be needed for a more rational design of nanomaterials in ILs. Furthermore, thiol-, ether-, carboxylic acid-, amino- and hydroxyl-functionalized ILs add to the complexity by acting also as coordinating capping ligands. In addition imidazolium cations are precursors to N-heterocyclic carbenes, NHCs which form from imidazolium-based ionic liquids by in situ deprotonation at the acidic C2-H ring position as intermediate species during the nanoparticle seeding and growth process or as surface coordinating ligand for the stabilization of the metal nanoparticle.

Actinomycetes-mediated biogenic synthesis of metal and metal oxide nanoparticles: progress and challenges.

Actinomycetes-mediated biogenic synthesis of metal nanoparticles and their antimicrobial activities are well documented. Actinomycetes facilitate both intracellular and extracellular metal nanoparticles synthesis and are efficient candidates for the production of polydispersed, stable and ultra-small size metal nanoparticles. Secondary metabolites and new chemical entities derived from Actinomycetes have not been extensively studied for the synthesis of metal/metal oxide nanoparticles. The present review focuses on biogenic synthesis of metal nanoparticles from Actinomycetes and the scope for exploring Actinomycetes-derived compounds (enzymes, organics acids and bioactive compounds) as metal and metal oxide reducing agents for the synthesis of desired nanoparticles. This review also focuses on challenges faced in the applications of nanoparticles and the methods to synthesize biogenic metal nanoparticles with desired physiochemical properties such as ultra-small size, large surface to mass ratio, high reactivity etc. Methods to evade their toxicity and unique interactions with biological systems to improve their chance as an alternative therapeutic agent in medical and pharmaceutical industry are also discussed.

Colorimetric detection of manganese(II) ions using alginate-stabilized silver nanoparticles

Marine algal polysaccharides have been recognized as the most effective and promising substrates for reduction and stabilization of metal nanoparticles. Ecofriendly synthesis of highly stable silver nanoparticles using alginate, an algal polysaccharide, is described herein. These alginate-stabilized silver nanoparticles (Alg-AgNPs) act as a label-free colorimetric sensor for quantification of manganese(II) metal ions (Mn2+) with excellent selectivity and sensitivity and detection in aqueous solution in the range of 1–10 µM. On addition of Mn2+ ions, the binding forces between Alg-AgNPs and Mn2+ ions bring the silver nanoparticles closer, decreasing the interparticle distance and causing slight agglomeration, with a color change from pale yellow to brownish yellow. Transmission electron microscopy images of Alg-AgNPs in presence of Mn2+ ions showed aggregation of AgNPs. Photon correlation spectroscopy showed decreases in the surface charge of Alg-AgNPs in presence of Mn2+ ions, thus predicting cross-linking aggregation. The ratio of absorbance at 500 nm to 400 nm (A 500/A 400) versus the Mn2+ ion concentration was linear with calibration curve of A 500/A 400 = 0.1611 + 0.0201 × C Mn. Such selective and sensitive detection of Mn2+ ions over other analytes appears suitable for application in point-of-use analysis of aqueous environmental samples.