Dendrimer-encapsulated nanoparticle precursors to supported platinum catalysts

In this contribution, we report the successful preparation of supported metal catalysts using dendrimer-encapsulated Pt nanoparticles as metal precursors. Polyamidoamine (PAMAM) dendrimers were first used to template and stabilize Pt nanoparticles prepared in solution. These dendrimer-encapsulated nanoparticles were then deposited onto a commercial high surface area silica support and thermally activated to remove the organic dendrimer. The resulting materials are active oxidation and hydrogenation catalysts. The effects of catalyst preparation and activation on activity for toluene hydrogenation and CO oxidation catalysis are discussed.     

New findings on CO electrooxidation at platinum nanoparticle surfaces

Different unsupported platinum nanoparticles are synthesized via water-in-oil microemulsion and colloidal methods (PAA). TEM, adatom adsorption and cyclic voltammetry measurements give very coherent results concerning the surface structure of the crystallites. The combination of these results with CO stripping experiments leads us to assign the oxidation peak multiplicity to surface structure rather than to pure size effect.     

Molecular sieving platinum nanoparticle catalysts kinetically frozen in nanoporous carbon

Highly active shape selective catalysts with excellent thermal stability are synthesized by entrapping well dispersed platinum nanoparticles in a polyfurfuryl alcohol derived nanoporous carbon matrix; these nanocomposites are excellent candidates for new catalytic applications including fuel cells, pharmaceutical synthesis and biomass conversion.     

Shape‐directed platinum nanoparticle synthesis: nanoscale design of novel catalysts

Platinum‐based catalytic materials have received significant attention, particularly in the shape and size control of faceted materials for catalysis. More recently, there has been a rapid increase in the number of reports of successful preparations in this field; however, a fundamental understanding of controlled growth towards catalytic material design is essential for future implementation and broad application. In this review, we provide an overview of the recent findings reported since 2009, focusing on methods for shape control as well as the effects of exposed surface facets on select catalytic reactions. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of gold nanoparticle catalysts based on a new water-soluble ionic polymer

A new water-soluble methyl-imidazolium-based ionic polymer was synthesized by ring-opening metathesis polymerization that was subsequently used to prepare aqueous gold nanoparticle solutions which were characterized by UV-vis spectroscopy and transmission electron microscopy (TEM). The aqueous gold nanoparticle solutions were employed as catalysts in the reduction of p-nitrophenol and in the hydrogenation of cinnamaldehyde and were found to exhibit excellent activity under mild conditions.     

Silica nanoparticle formation in the TPAOH-TEOS-H2O system: a population balance model

A model describing the kinetics of silica nanoparticle formation in the TPAOH-TEOS-H(2)O system is presented. These nanoparticles are an important intermediate in the clear-solution synthesis of silicalite-1, so understanding the mechanisms by which they are formed and stabilized is a key step in determining the crystallization behavior of pure-silica zeolites. The model presented here is based on the mass-conserving form of the Becker-D?ring population balance equations, describing growth and fragmentation by addition or removal of monomeric units, and modified to account for rapid equilibration of small silicate species and electrostatic and/or template stabilization of nanoparticles. The model predictions compare favorably with the experimental results. It is found that nanoparticle evolution exhibits distinct time regimes consisting of TEOS hydrolysis, condensation, nanoparticle formation, Ostwald ripening, and a self-sharpening mechanism in particle size distribution toward equilibrium due to stabilization during which no apparent changes in average particle size and pH are observed. Finally, the model provides an alternative, to a recent hypothesis, kinetics point of view to explain the enhanced stability of nanoparticles over extended periods of time.     

Self-organization of surfactant-metal-ion complex nanofibers on graphite surfaces and their application to fibrously concentrated platinum nanoparticle formation

We report the fabrication of self-organized surfactant nanofibers containing platinum ions on a highly oriented pyrolytic graphite (HOPG) surface from mixed solutions of hexadecyltrimethylammonium hydroxide (C16TAOH) and hydrogen hexachloroplatinate (IV) (H2PtCl6). The fibrous surfactant self-assembly was stable in air, even after being soaked in water, in contrast to surfactant hemicylindrical micelles, which are stable only at graphite/solution interfaces. The results show that the graphite surface served as an essential template for the specific formation of fibrous surfactant self-assemblies. In addition, when surfactant nanofibers containing metal ions were treated with hydrazine, platinum nanoparticles concentrated in the nanofibers formed on the HOPG surface. We also prepared surfactant nanofibers containing gold ions on HOPG surfaces and formed gold nanoparticles in the nanofibers.     

Effective platinum catalysts for low-temperature oxidation of CO

A number of platinum-based catalysts bonded on carbon fiber karbopon were prepared using alcohol solutions of H₂PtCl₆. The catalytic activity of the samples was determined in the low-temperature oxidation of carbon monoxide by oxygen. The effect of the solvent nature of the precursor on the activity of the catalysts was determined. The best results were obtained in the presence of 1.5% Pt/karbopon catalyst prepared using isobutyl alcohol; 100% CO conversion was achieved in respiratory treatment (12000 h^?1, room temperature).     

A general synthetic strategy for oxide-supported metal nanoparticle catalysts

Despite recent exciting progress in catalysis by supported gold nanoparticles, there remains the formidable challenge of preparing supported gold catalysts that collectively incorporate precise control over factors such as size and size-distribution of the gold nanoparticles, homogeneous dispersion of the particles on the support, and the ability to utilize a wide range of supports that profoundly affect catalytic performance. Here, we describe a synthetic methodology that achieves these goals. In this strategy, weak interface interactions evenly deposit presynthesized organic-capped metal nanoparticles on oxide supports. The homogeneous dispersion of nanoparticles on oxides is then locked in place, without aggregation, through careful calcination. The approach takes advantage of recent advances in the synthesis of metal and oxide nanomaterials and helps to bring together these two classes of materials for catalysis applications. An important feature is that the strategy allows metal nanoparticles to be well dispersed on a variety of oxides with few restrictions on their physical and chemical properties. Following this synthetic procedure, we have successfully developed efficient gold catalysts for green chemistry processes, such as the production of ethyl acetate from the selective oxidation of ethanol by oxygen at 100 degrees C.     

Amperometric glucose biosensor based on platinum nanoparticle encapsulated with a clay

Electrically conductive hollow nanospheres with an average diameter between 100 and 200 nm were prepared via a one-step polymerization of aniline in the presence of lignosulfonate (LS) by using ammonium persulfate (APS) as the oxidant. The LS concentration and molar ratio between APS and aniline, the temperature and time for polymerization were adjusted to optimize morphology, structure and electrochemical properties. Uniform hollow nanospheres are best obtained at a concentration of 18 wt% of LS, at a polymerization temperature at 25 °C, at an APS/aniline molar ratio of 1:1, and at a polymerization time of 1 to 12 h. This kind of preparation of nanospheres represents a simple and general route to polymer hollow nanospheres of controllable size, high stability, and optimizable electroconductivity.     

Evidence for patchy lipid layers on gold nanoparticle surfaces

Gold nanoparticles bearing multiple surface ligands are becoming favored candidates as multifunctional targeting, imaging, and therapeutic vehicles for biomedicine. The question of spatial location of different ligands on nanoparticle surfaces, especially with those of diameters less than 100 nm, is an important one that is difficult to quantitatively address. Here we functionalize the surface of 20, 50, and 90 nm gold nanoparticles with two different lipids, both single and mixed, using two different surface chemical procedures. Mass spectrometry supports the presence of both lipids in the mixed-lipid systems on nanoparticles, while electron microscopy evidence shows domain sizes for one lipid apparently a quarter to a half the projected diameter for 50 and 90 nm particles; but for 20 nm particles, there is no evidence for the existence of patches of the two lipids. Larger gold nanoparticles (90 nm) can be decorated with an array of 12 nm gold nanoparticles by use of a third lipid and antibody-antigen connectors; the display of the 12 nm particles about the 90 nm particles can be controlled to some extent by the initial surface chemistry and is quantified via a new angle analysis procedure.     

Structure and reactivity of Ru nanoparticles supported on modified graphite surfaces: a study of the model catalysts for ammonia synthesis

Supported ruthenium metal catalysts have higher activity than traditional iron-based catalysts used industrially for ammonia synthesis. A study of a model Ru/C catalyst was carried out to advance the understanding of structure and reactivity correlations in this structure-sensitive reaction where dinitrogen dissociation is the rate-limiting step. Ru particles were grown by chemical vapor deposition (CVD) via a Ru(3)(CO)(12) precursor on a highly oriented pyrolytic graphite (HOPG) surface modified with one-atomic-layer-deep holes mimicking activated carbon support. Scanning tunneling microscopy (STM) has been used to investigate the growth, structure, and morphology of the Ru particles. Thermal desorption of dissociatively adsorbed nitrogen has been used to evaluate the reactivity of the Ru/HOPG model catalysts. Two different Ru particle structures with different reactivities to N(2) dissociation have been identified. The initial sticking coefficient for N(2) dissociative adsorption on the Ru/HOPG model catalysts is approximately 10(-6), 4 orders larger compared to that of Ru single-crystal surfaces.     

pH-Sensitive gold nanoparticle catalysts for the aerobic oxidation of alcohols

Gold nanoparticles (NPs) stabilized by carboxylate modified polyvinylpyrrolidone have been prepared and fully characterized. The gold NPs efficiently catalyze the aerobic oxidation of benzyl alcohol in water at ambient temperature and are easily separated from the reaction mixture by lowering the pH of the solution, causing the NPs to precipitate. The mechanism of the precipitation process has been studied. Due to the efficiency of this process, the NPs may be reused as catalysts by readjusting their pH.     

Styrene synthesis over iron oxide catalysts: from single crystal model system to real catalysts

Surface science methods originating from analysis of noble metal catalysts are increasingly applied to metal oxides. These methods provide direct access to fundamental structural properties and phase equilibria governing the catalytic properties of metal oxide surfaces. However, no systematic way existed so far for transferring this knowledge to technical catalysts. The aim of this paper is to combine surface science with chemical engineering methods to bridge this gap. Styrene synthesis over pure and K-doped iron oxides is used as an example to develop and to explain the methodology. Single crystal films (SCF), grown epitaxially on a Pt-carrier are considered as ideal model surfaces. Comprehensive UHV analyses yield the structural properties of SCF as well as their interaction with relevant components of the reaction mixture. Their results are combined with conversion experiments to derive a mechanistic catalyst model along with quantitative information on the reaction rates. The activity of SCF as well as their phase transitions under reactive conditions can be described with a continuum model depending on the macroscopic properties of the system. This model forms the crucial link towards technical catalysts. It is shown that the behaviour of a powder catalyst can be described as a superposition of the above kinetic model and an appropriate porous model. In this paper we review the developed methodology and conclude with the evaluation of the concept.     

Combinatorial chemistry: a tool for the discovery of new catalysts

The discovery of new reactions and catalysts has always presented an intriguing challenge to scientists. With the rise of combinatorial chemistry, a new method has emerged that holds considerable promise to facilitate the task since it allows for the simultaneous generation and testing of a large number of compounds. The crucial difficulty lies in establishing general technologies for rapid and reliable screening of libraries to determine the catalytic activity of their members. Several recent publications have addressed this question by using infrared thermography, colorimetric assays and fluorescence spectroscopy. These techniques have not only been applied successfully to the high-throughput screening of parallel compound arrays but also to the screening of one-bead-one-compound libraries. This demonstrates that combinatorial chemistry possesses indeed the potential to establish itself as a powerful tool for the discovery of new catalysts. This review describes the methodologies used so far for the detection of catalytic events and will place particular emphasis on the on-bead screening of one-bead-one-compound libraries.     

温控聚乙二醇两相体系中纳米钯催化肉桂醛选择性加氢反应

将具有“高温混溶、室温分相”功能的聚乙二醇4000(PEG₄₀₀₀)与甲苯-正庚烷组成的两相体系用于纳米钯催化的肉桂醛选择性加氢反应中.在优化的反应条件下,肉桂醛转化率和氢化肉桂醛选择性分别为99%和98%.钯纳米催化剂经简单分相即可与产物分离,且循环使用8次,其活性和选择性基本保持不变.     

Phase transitions in DNA-linked nanoparticle assemblies: a decorated-lattice model

We use decorated-lattice models to explore the phase behavior of two types of DNA-linked colloidal mixtures: systems with identical nanoparticles functionalized with two different DNA strands (mixture Aab) and mixtures involving two types of particles each one functionalized with a different DNA strand (mixture Aa-Ab). The model allows us to derive the properties of the mixtures from the well-known behavior of underlying spin-n Ising models with temperature and activity dependent effective interactions. The predicted evolution of the dissolution profiles for the colloidal assemblies as a function of temperature and number of single DNA strands on a nanoparticle M is in qualitative agreement with that observed in real systems. According to our model, the temperature at which the assemblies dissolve can be expected to increase with increasing M only for concentrations of colloids below a certain threshold. For more concentrated solutions, the dissolution temperature is a decreasing function of M. Linker-mediated interactions between Aa and Ab particles in the Aa-Ab mixture render the phase separation involving disordered aggregates metastable with respect to a phase transition between a solvent-rich and an ordered phase. The stability of the DNA-linked assembly is enhanced by the ordering of the colloidal network and the ordered aggregates dissolve at higher temperatures. Our results may explain the contrasting evolution of the dissolution temperatures with increasing probe size in Aab and Aa-Ab mixtures as observed experimentally.     

Development of a charge-perturbed particle-in-a-sphere model for nanoparticle electronic structure

The complex surface structure of gold-thiolate nanoparticles is known to affect the calculated density functional theory (DFT) excitation spectra. However, as the nanoparticle size increases, it becomes impractical to calculate the excitation spectrum using DFT. In this study, a new method is developed to determine the energy levels of the thiolate-protected gold nanoparticles [Au(25)(SR)(18)](-), Au(102)(SR)(44) and Au(144)(SR)(60). A 3 nm thiolate-protected nanoparticle is also modeled. The particle-in-a-sphere model is used to represent the core while the ligands are treated as point charge perturbations. The electronic structures obtained with this model are qualitatively similar to DFT results. The symmetry of the arrangement of the perturbations around the core plays a major role in determining the splitting of the orbitals. The radius chosen to represent the core also affects the orbital splitting. Increasing the number of perturbations around the core shifts the orbitals to higher energies but does not significantly change the band gaps and orbital splitting as long as the symmetrical arrangement of the perturbations is conserved. This model can be applied to any gold nanoparticle with a spherical core, regardless of its size or the nature of the ligands, at very low computational cost.     

Enhancing cell recognition by scrutinizing cell surfaces with a nanoparticle array

We report a dual-ligand nanoparticle array approach for discerning cells that have different surface receptor profiles surrounding a common primary receptor expressed at high or low levels. The achieved differentiation provides nanoparticles the ability for potential applications in treatment of patients at a personalized medicine level for drug delivery and radiation therapy with a much better safety profile.     

Synthesis of a new nanoparticle system based on electrostatic alginate‐piperazine interactions

Advanced drug delivery system development is very important for the cancer therapies. The fixing of specific targeting ligands onto biodegradable carriers can add specificity to the usual chemotherapeutical treatments that current chemotherapies lack of. This study describes the preparation of a new nanoparticle system based on electrostatic interactions between alginate and piperazine. Nanoparticles with a negative surface charge were prepared through the electrostatic interaction between alginate and piperazine under acid aqueous condition. This kind of interactions and materials has never been used before to produce nanoparticles. This nanoparticle system has been designed to be used as a carrier where superficial carboxylate groups are the binding site for different kind of molecules, for example, proteins and organic molecules. Afterwards, surface engineering was performed on the nanoparticles produced; cisplatin and epidermal growth factor (EGF) were covalently linked on the surface of the nanoparticle using reagents by carbodiimide chemistry to give a covalent bond between EGF and nanoparticles and between cisplatin and nanoparticles. As a result, this study reports the development of a potential advanced drug delivery system, which in the future will enable clinical trials in animals and humans. Copyright © 2015 John Wiley & Sons, Ltd.