Effect Of Nanoparticle Shape Research Articles

Application of alternative energy forms in catalytic reactor engineering

This review provides a general overview of recent applications of magnetic nanoparticles for controlled radiofrequency (RF) heating in catalytic synthesis, mass transfer enhancement in laminar flow and magnetic separation. By directly delivering RF energy to magnetic materials, issues such as long heating periods and energy losses can be minimized. The main mechanisms of RF heating are briefly reviewed. The effect of nanoparticles size, shape and composition on the efficiency of RF heating is discussed. RF energy has been shown to be effective in many applications, however, it is still not used in chemicals due to high equipment costs.

Catalytic application of shape-controlled Cu2O particles protected by Co3O4nanoparticles for hydrogen evolution from ammonia borane

Cu2O particles are active catalysts for hydrogen evolution from ammonia borane (AB) by hydrolysis, however, Cu2O particles easily form agglomerates as a result of highly reduced conditions during the reaction. In order to suppress agglomerate formation, capping of Cu2O with organic reagents or inorganic materials was performed and the catalytic reactivity in AB hydrolysis was examined. Among the examined methods, capping of Cu2O particles with Co3O4 nanoparticles was the most effective to avoid agglomerate formation of Cu2O particles. The finding enabled us to examine the shape effect of Cu2O particles on the catalytic reactivity in AB hydrolysis in the presence of Co3O4 nanoparticles. Comparisons of turnover frequencies for hydrogen evolution of Cu2O–Co3O4 composites, in which Cu2O particles were in the shape of 50-facets, cube, octahedron or rhombicuboctahedron, indicated that the composite with Cu2O with the shape of 50-facets showed more than 7-fold higher hydrogen evolution rate normalized by surface area than the composite with Cu2O with the octahedral shape. The size and shape effects of Co3O4 nanoparticles were also investigated on their ability to protect Cu2O from agglomeration. Comparisons of the catalytic reactivity of Cu2O particles decorated with Co3O4 nanoparticles of different sizes and shapes in terms of amounts and rates of hydrogen evolved by AB hydrolysis indicated that the size of Co3O4 nanoparticles is more important than the shape to exhibit high catalytic reactivity.

A review of multiscale modeling of metal-catalyzed reactions: Mechanism development for complexity and emergent behavior

We review and provide a perspective on multiscale modeling of catalytic reactions with emphasis on mechanism development and application to complex and emergent systems. We start with an overview of length and time scales, objectives, and challenges in first-principles modeling of reactive systems. Subsequently, we review various methods that ensure thermodynamic consistency of mean-field microkinetic models. Next, we describe estimation of reaction rate constants via quantum mechanical and statistical–mechanical methods as well as semi-empirical methods. Among the latter, we discuss the bond-order conservation method for thermochemistry and activation energy estimation. In addition, we review the newly developed group-additivity method on adsorbate/metal systems and linear free energy or Brønsted–Evans–Polanyi (BEP) relations, and their parameterization using DFT calculations to generate databases of activation energies and reaction free energies. Linear scaling relations, which can enable transfer of reaction energetics among metals, are discussed. Computation-driven catalyst design is reviewed and a new platform for discovery of materials with emergent behavior is introduced. The effect of parameter uncertainty on catalyst design is discussed; it is shown that adsorbate–adsorbate interactions can profoundly impact materials design. Spatiotemporal averaging of microscopic events via the kinetic Monte Carlo method for realistic reaction mechanisms is discussed as an alternative to mean-field modeling. A hierarchical multiscale modeling strategy is proposed as a means of addressing (some of) the complexity of catalytic reactions. Structure-based microkinetic modeling is next reviewed to account for nanoparticle size and shape effects and structure sensitivity of catalytic reactions. It is hypothesized that catalysts with multiple sites of comparable activity can exhibit structure sensitivity that depends strongly on operating conditions. It is shown that two descriptor models are necessary to describe the thermochemistry of adsorbates on nanoparticles. Multiscale and accelerated methods for computing free energies in solution, while accounting explicitly for solvent effects in catalytic reactions, are briefly touched upon with the acid catalyzed dehydration of fructose in water as an example. The above methods are illustrated with several reactions, such as the CO oxidation on Au; the hydrogenation of ethylene and hydrogenolysis of ethane on Pt; the glycerol decomposition to syngas on Pt-based materials; the NH 3 decomposition on single metals and bimetallics; and the dehydration of fructose in water. Finally, we provide a summary and outlook.

Influence of Nanoparticle Size and Shape on Oligomer Formation of an Amyloidogenic Peptide.

Understanding the influence of macromolecular crowding and nanoparticles on the formation of in-register β-sheets, the primary structural component of amyloid fibrils, is a first step towards describing in vivo protein aggregation and interactions between synthetic materials and proteins. Using all atom molecular simulations in implicit solvent we illustrate the effects of nanoparticle size, shape, and volume fraction on oligomer formation of an amyloidogenic peptide from the transthyretin protein. Surprisingly, we find that inert spherical crowding particles destabilize in-register β-sheets formed by dimers while stabilizing β-sheets comprised of trimers and tetramers. As the radius of the nanoparticle increases crowding effects decrease, implying smaller crowding particles have the largest influence on the earliest amyloid species. We explain these results using a theory based on the depletion effect. Finally, we show that spherocylindrical crowders destabilize the ordered β-sheet dimer to a greater extent than spherical crowders, which underscores the influence of nanoparticle shape on protein aggregation.

Study of the effect of size and clay structural parameters on the yield and post-yield response of polymer/clay nanocomposites via a multiscale micromechanical modelling

In order to predict the nanostructure as well as the particle size dependence of the elastic–plastic stress–strain response of polymer/clay nanocomposites, a micromechanical model based upon a multiscale approach starting from the nanostructure is proposed. The multiscale micromechanical model takes into account the interphase between the polymeric matrix and the inorganic reinforcement, and the intercalated nanostructure. Considering the interphase thickness as a characteristic length scale, the nanoparticle size effect is explicitly introduced in the present model. The intercalated nanostructure is taken into account according to an equivalent stiffness method in which the clay stacks are replaced by homogeneous nanoparticles with predetermined equivalent anisotropic stiffness. The physical and mechanical properties of nylon-6/montmorillonite nanocomposites (with clay weight fractions ranging from 1 up to 7.5%) are investigated by means of differential scanning calorimetry, dynamic mechanical analysis, thermogravimetric analysis and video-controlled tensile mechanical tests. The microstructure was characterized by transmission electron microscopy. The amount of interphase was estimated from the thermal analysis. The reinforcing effect of clay is discussed with respect to the multiscale micromechanical model. A parametric study is carried out to investigate the effect of nanoparticle shape and size and nanoparticle structural parameters (i.e. number of clay layers in the nanoparticle and interlayer spacing) on the elastic–plastic stress–strain response of polymer/clay nanocomposites. Comparison of the model results with the experimental data demonstrates that the evaluation of the reinforcing effect of clay involves considering the elastic stiffness and yield stress simultaneously. It was further found that the model correctly predicts the elastic–plastic stress–strain data.

Evaluation of the effects of gold nanoparticle shape and size on contrast enhancement in radiological imaging

There has been increasing interest in the use of a nanoparticle-based media as a contrast-enhancement agent in medical imaging, particularly with gold Nanoparticles in radiography. Particularly attractive, is the prospect of modifying the surface of these materials with monoclonal antibodies to preferentially bind the nanoparticles to tumour sites. These materials differ from conventional molecular agents in their ability to be modified with cell specificity, or tailored for size and shape for maximum uptake. We investigated the consideration that quantum confinement electronic effects in nanometre-sized metals might have an effect on the integrated photon attenuation of gold atoms; in the same manner as these materials affect X-ray absorption and scattering as seen in X-ray absorption spectroscopy. This experiment has been designed to identify any effect on contrast enhancement that might result from employing gold nanoparticles with a variety of sizes. Spherical particles and nanorods were synthesised for this application. Image contrast enhancement was quantified by contrast-to-noise ratio in computed radiography. Results are consistent with existing measurements of gold nanoparticle contrast enhancement in radiography. No significant variation in attenuation depending on particle size was observed. Findings indicate that nanoparticle-based contrast agents in the size range 4-30nm-can be synthesised for maximum stability or cell specificity (directed cellular uptake) without consideration of effect of size on contrast enhancement.

Catalytic mechanisms of hydrogen evolution with homogeneous and heterogeneous catalysts

This perspective focuses on reaction mechanisms of hydrogen (H2) evolution with homogeneous and heterogeneous catalysts. First, photocatalytic H2 evolution systems with homogeneous catalysts are discussed from the viewpoint of how to increase the efficiency of the two-electron process for the H2 evolution via photoinduced electron-transfer reactions of metal complexes. Two molecules of the one-electron reduced species of [RhIII(Cp*)(bpy)(H2O)](SO4) (bpy = 2,2′-bipyridine) and [IrIII(Cp*)(H2O)(bpm)RuII(bpy)2](SO4)2 (bpm = 2,2′-bipyrimidine) produced by photoinduced electron-transfer reactions are converted to the two-electron reduced complexes suitable for H2 generation by disproportionation. The photocatalytic mechanism of H2 evolution using Pt nanoparticles as a catalyst is also discussed based on the kinetic analysis of the electron-transfer rates from a photogenerated electron donor to Pt nanoparticles, which are comparable to the overall H2 evolution rates. The electron-transfer rates become faster with increasing proton concentrations with an inverse kinetic isotope effect, when H+ is replaced by D+. The size and shape effects of Pt nanoparticles on the rates of hydrogen evolution and the electron-transfer reaction are examined to optimize the catalytic efficiency. Finally, catalytic H2 evolution systems from H2storage molecules are described including shape dependent catalytic activity of Co3O4 particles for ammonia borane hydrolysis and a large tunneling effect observed in decomposition of formic acid with [IrIII(Cp*)(H2O)(bpm)RuII(bpy)2](SO4)2.

Plasmonic Responses of Gold Nanoparticles on Organic Vapor: Shape Effect

This paper reports the study on the shape effect of gold nanoparticles on their plasmonic responses to the vapor samples, such as methanol, ethanol and propanol. In typical process, it was observed that the plasmonic of gold nanoparticles was very sensitive to the presences of the vapor samples by giving the change in the absorption as well as the shift in the SPR peaks position. It was also found that the plasmonic responses to the vapor indicated a significant improved if the gold nanoparticles prepared in the form of nanorods morphology. The plasmonic response of the spherical and nanorods gold nanoparicles to the gasses will be discussed.

Nanoparticle Shape Effect Study as an Efficient Tool to Reveal the Structure Sensitivity of Olefinic Alcohol Hydrogenation

Monodisperse Pd nanocubes of 20 nm rib length and Pd nanospheres of 3.0 nm diameter were synthesized in the presence of cetyltrimethylammonium bromide and used to investigate the structure sensitivity of three-phase 2-methyl-3-buten-2-ol hydrogenation. Turnover frequencies per all surface atoms were found as 2.58 s−1 for the cubes and 3.86 s−1 for the spheres at 313 K, indicating that (100) atoms of the cubes comprising ∼98% of all surface atoms have lower activity than other surface atoms of the spheres, composed of atoms on (111), (100) terraces, edges, and vertices. Apparent activation energies of 23 kJ/mol for the cubes and 17 kJ/mol for the spheres in the verified kinetic regime confirmed the reaction structure sensitivity. Assuming that only (100) and (111) atoms are active on the sphere surface, a hypothetical most active Pd nanostructure was predicted as a tetrahedron allowing twice higher activity per Pd loading as compared to a spherical particle.

The influence of nanoparticle shape on the drying of colloidal suspensions

Dried deposits of spherical Ludox silica and disk-like laponite clay nanoparticles have been examined by dark-field optical microscopy and atomic force microscopy (AFM) to investigate the effects of nanoparticle shape on the deposit structure. Dark-field optical images indicated that a higher concentration of Ludox nanoparticles was required, compared to laponite, for an optically visible deposit to be formed. Compared with the relatively simple ring-like features observed at the edges of Ludox deposits, the laponite deposits were more complex, with dendritic features appearing below 10ppm that disappeared at higher laponite concentrations. AFM images revealed that whilst the Ludox rim deposit structure gradually increased in height and width with increasing nanoparticle concentration, the laponite rim deposits increased steadily in height up to 1ppm, above which the rim height suddenly decreased and the deposit structure became smoother. The widths of the rim deposits were observed to increase in a similar manner for both nanoparticle types. Nanoparticle shape is suggested as the main reason for differences in the structural features of the rim for each nanoparticle type. The disk-like laponite forms tall thin rim profiles at low concentrations, before creating a more uniform rim profile at higher concentrations. We suggest that a critical laponite rim height is reached before partial collapse of the nanoparticle stack at the rim takes place as the particle concentration is further increased. This produces much thinner and smoother films of laponite at high particle concentrations than is found for similar concentrations of Ludox. Our work suggests that both the shape and the concentration of the nanoparticles themselves are crucial in determining the structure of the final dried nanoparticle deposit.

Shape and size effects of ceria nanoparticles on the impact strength of ceria/epoxy resin composites

Ceria nanoparticles with various shapes (rods, cubes, and plates) and sizes were controllably synthesized and then introduced into epoxy resin. Subsequently, we investigated correlations between the shape and size of ceria nanostructures and the mechanical performance of composites. The samples were characterized by transmission electron microscopy, scanning electron microscopy, and X-ray diffraction. Compared with commercial ceria filled composites, the composites made with morphology-controlled ceria nanostructures show a higher impact strength. It is found that epoxy resins made with high-aspect-ratio ceria nanorods show the highest impact strength, up to 17.27 kJ/m 2, which is about four times that of the neat epoxy resin.

Lithographically defined uniform worm-shaped polymeric nanoparticles

We report a nanoimprint lithography method combined with photolithography on abi-layer polymer setup to define nano-worms laterally in nano-gratings and produceuniform worm-shaped polymeric nanoparticles in aqueous solution by dissolving watersoluble sacrificial layer poly(vinyl alcohol) (PVA). Process control of the thin residue layer,SU-8 curing using broadband UV source, and warm development to remove any residue arenecessary to ensure success of this technique. The use of water soluble PVA as a releasinglayer and elimination of an invasive plasma etching for the releasing process makes thisprotocol highly compatible with biomaterials. Direct release and suspension of fluorescentworm-shaped nanoparticles (length to width ratio up to 75) in aqueous solution weredemonstrated. Compared to the worm-shaped nanoparticles made by self-assembly, theselithographically defined nano-worms have much better controllability and uniformityon the shape, size, and aspect ratio. The availability of these precisely definednon-spherical particles would be important to develop a comprehensive understanding ofthe shape effects of nanoparticles on their efficacy in nanomedicine applications.

Structure, scattering patterns and phase behavior of polymer nanocomposites with nonspherical fillers

Polymer nanocomposites made with carbon nanotubes, clay platelets, laponite disks and other novel nonspherical fillers have been the focus of many recent experiments. However, the effects of nanoparticle shape on statistical structure, polymer-mediated effective interactions, scattering patterns, and phase diagrams are not well understood. We extend and apply the polymer reference interaction site model liquid state theory to study the equilibrium properties of pseudo one-, two- and three-dimensional particles (rod, disk, cube) of modest steric anisotropy and fixed space-filling volume in a dense adsorbing homopolymer melt up to relatively high volume fractions. The second virial coefficient, nanoparticle potential-of-mean force, osmotic compressibilities, and isotropic spinodal demixing boundaries have been determined. The entropic depletion attraction between nanoparticles is dominant for weakly adsorbing polymer, while strongly adsorbing chains induce a bridging attraction. Intermediate interfacial cohesion results in the formation of a steric stabilizing adsorbed polymer layer around each nanoparticle, which can partially damp inter-filler collective order on various length scales and increase order on an averaged length scale. The details of depletion, stabilization, or bridging behavior are shape-dependent and often, but not always, trends are monotonic with increasing filler dimensionality. Distinctive nanoparticle shape-dependent low angle features are predicted for the collective polymer structure factor associated with competing macrophase fluctuations and microphase-like ordering. The influence of nonzero mixture compressibility on the scattering profiles is established.

Shape effects of nanoparticles conjugated with cell-penetrating peptides (HIV Tat PTD) on CHO cell uptake.

In order to probe the nanoparticle shape/size effect on cellular uptake, a spherical and two cylindrical nanoparticles, whose lengths were distinctively varied, were constructed by the selective cross-linking of amphiphilic block copolymer micelles. Herein, we demonstrate that, when the nanoparticles were functionalized with the protein transduction domain of human immunodeficiency virus type 1 Tat protein (HIV Tat PTD), the smaller, spherical nanoparticles had a higher rate of cell entry into Chinese hamster ovary (CHO) cells than did the larger, cylindrical nanoparticles. It was also found that nanoparticles were released after internalization and that the rate of cell exit was dependent on both the nanoparticle shape and the amount of surface-bound PTD.

Effects of Nanoparticle Shape on the Morphology and Properties of Porous CdSe Assemblies (Aerogels)

We demonstrate the effect of differently shaped CdSe nanoscale building blocks (dots, rods, branched nanoparticles, and hyperbranched nanoparticles) on the morphologies, surface characteristics, and optical properties of resultant porous CdSe nanostructured aerogels. Monolithic CdSe aerogels were produced by controlled oxidative removal of surface thiolate ligands from differently shaped CdSe nanoparticles to yield a wet gel, followed by CO(2) supercritical drying. The X-ray diffraction data show that the resultant CdSe aerogels maintain the crystalline phase of the building blocks without significant grain growth. However, the transmission electron microscopy images indicate that the morphology of CdSe aerogels changes from a colloid-type morphology to a polymer-type morphology when the building block changes from dot to rod or the branched nanoparticle. The morphology of the CdSe aerogel assembled from hyperbranched nanoparticles appears to be intermediate between the colloid-type and the polymer-type. Nitrogen physisorption measurements suggest that the surface areas and porosity are a direct function of the shape of the primary building blocks, with aerogels formed from rods or branched particles exhibiting the greatest surface areas (>200 m(2)/g) and those prepared from hyperbranched nanoparticles exhibiting the least (<100 m(2)/g). Band gap measurements and photoluminescence studies show that the as-prepared CdSe aerogels retain to a large extent the intrinsic quantum confinement of the differently shaped building blocks, despite being connected into a 3D network.

The effect of nanoparticle shape on polymer‐nanocomposite rheology and tensile strength

AbstractNanoparticles can influence the properties of polymer materials by a variety of mechanisms. With fullerene, carbon nanotube, and clay or graphene sheet nanocomposites in mind, we investigate how particle shape influences the melt shear viscosity η and the tensile strength τ, which we determine via molecular dynamics simulations. Our simulations of compact (icosahedral), tube or rod‐like, and sheet‐like model nanoparticles, all at a volume fraction ϕ ≈ 0.05, indicate an order of magnitude increase in the viscosity η relative to the pure melt. This finding evidently can not be explained by continuum hydrodynamics and we provide evidence that the η increase in our model nanocomposites has its origin in chain bridging between the nanoparticles. We find that this increase is the largest for the rod‐like nanoparticles and least for the sheet‐like nanoparticles. Curiously, the enhancements of η and τ exhibit opposite trends with increasing chain length N and with particle shape anisotropy. Evidently, the concept of bridging chains alone cannot account for the increase in τ and we suggest that the deformability or flexibility of the sheet nanoparticles contributes to nanocomposite strength and toughness by reducing the relative value of the Poisson ratio of the composite. The molecular dynamics simulations in the present work focus on the reference case where the modification of the melt structure associated with glass‐formation and entanglement interactions should not be an issue. Since many applications require good particle dispersion, we also focus on the case where the polymer‐particle interactions favor nanoparticle dispersion. Our simulations point to a substantial contribution of nanoparticle shape to both mechanical and processing properties of polymer nanocomposites. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1882–1897, 2007

Forces between Surfaces across Nanoparticle Solutions: Role of Size, Shape, and Concentration

Using a surface force apparatus, we have measured the normal forces between mica surfaces across various types of nanoparticles consisting of ZnS cores coated with a monolayer of physisorbed surfactant, dispersed in organic solvents. We focused on the effects of nanoparticle size, shape, and concentration on the force-distance profiles. Forces were exponentially repulsive when the surfactant layers were strongly bound to the nanoparticles and were roughly linear when there was adhesion between the nanoparticle cores, i.e., when the surfactant layers detached from the nanoparticles. In both cases, the range and magnitude of the forces were dependent upon the particle size, shape, and solution concentration. Fine details in the otherwise smooth force-distance profiles indicate specific effects due to particle chemistry and geometry and the existence of first-order disorder-order phase transitions upon confinement. Small amounts of water in the (hydrophobic) organic solvents had dramatic effects on the measured forces. Understanding and controlling the effects of particle shape, size, and concentration and the presence of water (or other surface-active solutes) on particle-particle and particle-surface interactions are important for the processing of nanoparticles into ordered superstructured materials.

Direct ordering and shape effects of FePt nanoparticles produced by nanoparticle beam technology

Partial chemically ordered FePt nanoparticles were produced by annealing the nanoparticles in transit through the furnace from the source to the substrate. The equiaxed or polyhedral morpohology of FePt nanoparticles can be produced by tuning the temperature of nanoparticle-forming chamber. The equiaxed FePt particles were amorphous whereas the polyhedral particles showed good crystallinity. Both FePt particle assemblies were superparamagnetic without on-line heating of particles. With on-line annealing, the assembled films showed ferromagnetic behavior. The coercivity of the polyhedral FePt particle assembly was about 600Oe, whereas that of equiaxed FePt particles was 450Oe. The larger coercivity was attributed to the increased particle size.

Catalysis with Transition Metal Nanoparticles in Colloidal Solution: Nanoparticle Shape Dependence and Stability

AbstractFor Abstract see ChemInform Abstract in Full Text.

Catalysis with Transition Metal Nanoparticles in Colloidal Solution: Nanoparticle Shape Dependence and Stability

While the nanocatalysis field has undergone an explosive growth during the past decade, there have been very few studies in the area of shape-dependent catalysis and the effect of the catalytic process on the shape and size of transition metal nanoparticles as well as their recycling potential. Metal nanoparticles of different shapes have different crystallographic facets and have different fraction of surface atoms on their corners and edges, which makes it interesting to study the effect of metal nanoparticle shape on the catalytic activity of various organic and inorganic reactions. Transition metal nanoparticles are attractive to use as catalysts due to their high surface-to-volume ratio compared to bulk catalytic materials, but their surface atoms could be so active that changes in the size and shape of the nanoparticles could occur during the course of their catalytic function, which could also affect their recycling potential. In this Feature Article, we review our work on the effect of the shape of the colloidal nanocatalyst on the catalytic activity as well as the effect of the catalytic process on the shape and size of the colloidal transition metal nanocatalysts and their recycling potential. These studies provide important clues on the mechanism of the reactions we studied and also can be very useful in the process of designing better catalysts in the future.