Spectroscopic characterizations of molecularly linked gold nanoparticle assemblies upon thermal treatment

The understanding of surface properties of core-shell type nanoparticles is important for exploiting the unique nanostructured catalytic properties. We report herein findings of a spectroscopic investigation of the thermal treatment of such nanoparticle assemblies. We have studied assemblies of gold nanocrystals of approximately 2 nm core sizes that are capped by alkanethiolate shells and are assembled by covalent or hydrogen-bonding linkages on a substrate as a model system. The structural evolution of the nanoparticle assemblies treated at different temperatures was probed by several spectroscopic techniques, including UV-visible, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS). The results show that the capping/linking shell molecules can be effectively removed to produce controllable surface and optical properties. The data further revealed that the thermally induced evolution of the surface plasmon resonance property of gold nanoparticles is dependent on the chemical nature of the linker molecule. The spectral evolution is discussed in terms of changes in particle size, interparticle distance, and dielectric medium properties, which has important implications for controlled preparation and thermal processing of core-shell nanostructured metal catalysts.     

Array of molecularly mediated thin film assemblies of nanoparticles: correlation of vapor sensing with interparticle spatial properties

The ability to tune interparticle spatial properties of nanoparticle assemblies is essential for the design of sensing materials toward desired sensitivity and selectivity. This paper reports findings of an investigation of molecularly mediated thin film assemblies of metal nanoparticles with controllable interparticle spatial properties as a sensing array. The interparticle spatial properties are controlled by a combination of alpha,omega-difunctional alkyl mediators (X-(CH(2))(n)-X) such as alkyl dithiols, dicarboxylate acids, and alkanethiol shells capped on nanoparticles. Alkanethiolate-capped gold and gold-silver alloy nanoparticles (2-3 nm) were studied as model building blocks toward the thin film assemblies, whereas the variation of alkyl chain length manipulates the interparticle spacing. The thin films assembled on an interdigitated microelectrode array platform are characterized for determining their responses to the sorption of volatile organic compounds (VOCs). The correlation between the response sensitivity and the interparticle spacing properties revealed not only a clear dependence of the sensitivity on alkyl chain length but also the occurrence of a dramatic change of the sensitivity in a region of chain length for the alkyl mediator comparable with that of the capping alkyl chains. This finding reflects a balance between the interparticle chain-chain cohesive interdigitation and the nanostructure-vapor interaction which determines the relative change of the electrical conductivity of the inked nanoparticle thin film in response to vapor sorption. The results, along with statistical analysis of the sensor array data in terms of sensitivity and selectivity, have provided important insights into the detailed delineation between the interparticle spacing and the nanostructured sensing properties.     

Assembly of gold nanoparticles mediated by multifunctional fullerenes

The understanding of the interparticle interactions of nanocomposite structures assembled using molecularly capped metal nanoparticles and macromolecular mediators as building blocks is essential for exploring the fine-tunable interparticle spatial and macromolecular properties. This paper reports the results of an investigation of the chemically tunable multifunctional interactions between fullerenes (1-(4-methyl)-piperazinyl fullerene, MPF) and gold nanoparticles. The interparticle spatial properties are defined by the macromolecular and multifunctional electrostatic interactions between the negatively charged nanoparticles and the positively charged fullerenes. In addition to characterization of the morphological properties, the surface plasmon resonance band, dynamic light scattering, and surface-enhanced Raman scattering (SERS) properties of the MPF-mediated assembly and disassembly processes have been determined. The change of the optical properties depends on the pH and electrolyte concentrations. The detection of the Raman-active vibration modes (Ag(2) and Hg(8)) of C60 and the determination of their particle size dependence have demonstrated that the adsorption of MPF on the nanoparticle surface in the MPF-Au nm assembly is responsible for the SERS effect. These findings provide new insights into the delineation between the interparticle interactions and the nanostructural properties for potential applications of the nanocomposite materials in spectroscopic and optical sensors and in controlled releases.     

Nanostructured PtVFe catalysts: Electrocatalytic performance in proton exchange membrane fuel cells

This paper reports new findings of an investigation of the electrocatalytic performance of nanostructured PtVFe catalysts in proton exchange membrane fuel cells (PEMFC). The membrane electrode assembly was prepared using nano-engineered PtVFe nanoparticles with controlled composition and size supported on carbon as the cathode electrocatalysts. The results reveal that the PtVFe/C catalysts exhibited excellent fuel cell performance, better than that using the commercial Pt/C catalyst. This finding provides the first example demonstrating the viability of the PEMFC application of the nanostructured trimetallic catalysts.     

Nanostructured Pt/GC model electrodes prepared by the deposition of metal-salt-loaded micelles

Novel, nanostructured, carbon-supported Pt model electrodes with homogeneously distributed Pt nanoparticles of uniform size were fabricated and analyzed with respect to their electrochemical properties. For this purpose, Pt-salt-loaded micelles were deposited on a glassy carbon substrate and subsequently exposed to an oxygen plasma and a H2 atmosphere for removal of the polymer carriers and reduction of the Pt salt. The morphology of the resulting nanoparticles and their electrochemical/electrocatalytic properties were characterized by high-resolution scanning electron microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and differential electrochemical mass spectrometry for CO electrooxidation. The data demonstrate that this method is generally suited to the production of nanostructured model electrodes with well-defined and independently adjustable particle size and interparticle distance distributions, which are specifically suited for quantitative studies of transport processes in electrocatalytic reactions.     

Mediator-template assembly of nanoparticles

The ability to construct size- and shape-controllable architectures using nanoparticles as building blocks is essential for the exploration of nanoparticle-structured properties. This paper reports findings of an investigation of a mediator-template strategy for the size-controllable assembly of nanoparticles. This strategy explores multidentate thioether ligands as molecular mediators and tetraalkylammonium-capped gold nanoparticles (5 nm) as templates toward the preparation of size-controllable and monodispersed spherical assemblies ( approximately 20-300-nm diameters). The combination of the mediation force of the multidentate thioether and the hydrophobic force of the tetraalkylammonium template establishes the interparticle linkage and stability. The morphological properties of the spherical assemblies have been characterized using TEM, AFM, and SAXS techniques. The finding of the soft-hard nature of the nanoparticle assemblies and their interactions with contacting substrates could form the basis of a new strategy for manipulating nanoscale linkages between nanoparticle assemblies, soldering nanoelectronics, and constructing nanosensor devices. The intriguing light scattering and optical absorption properties in response to assembly, disassembly, sizing, and interparticle spacing parameters have been characterized by dynamic light scattering and spectrophotometric measurements. The discovery of the controlled disassembly into individual nanoparticles and the size regulation by a third capping component could form the basis for applications in controlled drug delivery. The fundamental basis for the mediator-template strategy as a versatile assembly technique is further discussed in terms of experimental and theoretical correlations of the morphological and optical properties.     

Surfactant‐Assisted Stabilization of Au Colloids on Solids for Heterogeneous Catalysis

The stabilization of surfactant‐assisted synthesized colloidal noble metal nanoparticles (NPs, such as Au NPs) on solids is a promising strategy for preparing supported nanocatalysts for heterogeneous catalysis because of their uniform particle sizes, controllable shapes, and tunable compositions. However, surfactant removal to obtain clean surfaces for catalysis through traditional approaches (such as solvent extraction and thermal decomposition) can easily induce the sintering of NPs, greatly hampering their use in synthesis of novel catalysts. Such unwanted surfactants have now been utilized to stabilize NPs on solids by a simple yet efficient thermal annealing strategy. After being annealed in N₂ flow, the surface‐bound surfactants are carbonized in situ as sacrificial architectures that form a conformal coating on NPs and assist in creating an enhanced metal‐support interaction between NPs and substrate, thus slowing down the Ostwald ripening process during post‐oxidative calcination to remove surface covers.     

An EQCN assessment of electrocatalytic oxidation of methanol at nanostructured Au–Pt alloy nanoparticles

Alloy nanocrystals encapsulated with alkyl dithiolates (“core-shell” nanoparticles) serve as an intriguing class of nanostructured catalysts. This paper reports the preliminary results of an electrochemical quartz-crystal nanobalance (EQCN) investigation of mass transport associated with the catalytic activation and methanol oxidation at nanostructured Au–Pt nanocrystals. It is demonstrated that the catalytic activation and oxidation of methanol are accompanied by mass fluxes across the nanostructured film. The mass transport involves oxidation–reduction of surface oxygenated species, methanol adsorption and oxidation, solvent breath and product release. The implication of the EQCN results to the understanding of the core-shell nanostructured catalytic mechanism is discussed.     

Improved Performance of All-Inorganic Perovskite Light-emitting Diodes via Nanostructured Stamp Imprinting

Halide perovskites are emerging emitters with excellent optoelectronic properties. Contrary to the large grain fabrication goal in perovskite solar cells, perovskite light-emitting diodes (PeLEDs) based on small grain enable efficient radiative recombination because of relatively higher charge carrier densities due to spatial confinement. However, achieving small-sized grain growth with superior crystal quality and film morphology remains a challenge. In this work, we demonstrated a nanostructured stamp thermal imprinting strategy to boost the surface coverage and improve the crystalline quality of CsPbBr₃ film, particularly confine the grain size, leading to the improvement of luminance and efficiency of PeLEDs. We improved the thermal imprinting process utilizing the nanostructured stamp to selectively manipulate the nucleation and growth in the nanoscale region and acquire small-sized grain accompanied by improved crystal quality and surface morphology of the film. By optimizing the imprinting pressure and the period of the nanostructures, appropriate grain size, high surface coverage, small surface roughness and improved crystallization could be achieved synchronously. Finally, the maximum luminance and efficiency of PeLEDs achieved by nanostructured stamp imprinting with a period of 320 nm are 67600 cd/m² and 16.36 cd/A, respectively. This corresponds to improvements of 123 % in luminance and 100 % in efficiency, compared to that of PeLEDs without the imprinting.     

Nanoparticle Growth in Supported Nickel Catalysts during Methanation Reaction—Larger is Better

A major cause of supported metal catalyst deactivation is particle growth by Ostwald ripening. Nickel catalysts, used in the methanation reaction, may suffer greatly from this through the formation of [Ni(CO)₄]. By analyzing catalysts with various particle sizes and spatial distributions, the interparticle distance was found to have little effect on the stability, because formation and decomposition of nickel carbonyl rather than diffusion was rate limiting. Small particles (3–4 nm) were found to grow very large (20–200 nm), involving local destruction of the support, which was detrimental to the catalyst stability. However, medium sized particles (8 nm) remained confined by the pores of the support displaying enhanced stability, and an activity 3 times higher than initially small particles after 150 h. Physical modeling suggests that the higher [Ni(CO)₄] supersaturation in catalysts with smaller particles enabled them to overcome the mechanical resistance of the support. Understanding the interplay of particle size and support properties related to the stability of nanoparticles offers the prospect of novel strategies to develop more stable nanostructured materials, also for applications beyond catalysis.     

From the Lindlar Catalyst to Supported Ligand‐Modified Palladium Nanoparticles: Selectivity Patterns and Accessibility Constraints in the Continuous‐Flow Three‐Phase Hydrogenation of Acetylenic Compounds

Site modification and isolation through selective poisoning comprise an effective strategy to enhance the selectivity of palladium catalysts in the partial hydrogenation of triple bonds in acetylenic compounds. The recent emergence of supported hybrid materials matching the stereo‐ and chemoselectivity of the classical Lindlar catalyst holds promise to revolutionize palladium‐catalyzed hydrogenations, and will benefit from an in‐depth understanding of these new materials. In this work, we compare the performance of bare, lead‐poisoned, and ligand‐modified palladium catalysts in the hydrogenation of diverse alkynes. Catalytic tests, conducted in a continuous‐flow three‐phase reactor, coupled with theoretical calculations and characterization methods, enable elucidation of the structural origins of the observed selectivity patterns. Distinctions in the catalytic performance are correlated with the relative accessibility of the active site to the organic substrate, and with the adsorption configuration and strength, depending on the ensemble size and surface potentials. This explains the role of the ligand in the colloidally prepared catalysts in promoting superior performance in the hydrogenation of terminal and internal alkynes, and short‐chain alkynols. In contrast, the greater accessibility of the active surface of the Pd–Pb alloy and the absence of polar groups are shown to be favorable in the conversion of alkynes containing long aliphatic chains and/or ketone groups. These findings provide detailed insights for the advanced design of supported nanostructured catalysts.     

Self‐Assembling of Er2O3–TiO2 Mixed Oxide Nanoplatelets by a Template‐Free Solvothermal Route

An easy solvothermal route has been developed to synthesize the first mesoporous Er₂O₃–TiO₂ mixed oxide spherical particles composed of crystalline nanoplatelets, with high surface area and narrow pore size distribution. This synthetic strategy allows the preparation of materials at low temperature with interesting textural properties without the use of surfactants, as well as the control of particle size and shape. TEM and Raman analysis confirm the formation of nanocrystalline Er₂O₃–TiO₂ mixed oxide. Mesoscopic ordered porosity is reached through the thermal decomposition of organic moieties during the synthetic process, thus leading to a template‐free methodology that can be extended to other nanostructured materials. High specific surface areas (up to 313 m² g^?1) and narrow pore size distributions are achieved in comparison to the micrometric material synthesized by the traditional sol–gel route. This study opens new perspectives in the development, by solvothermal methodologies, of multifunctional materials for advanced applications by improving the classical pyrochlore properties (magnetization, heat capacity, catalysis, conductivity, etc.). In particular, since catalytic reactions take place on the surface of catalysts, the high surface area of these materials makes them promising candidates for catalysts. Furthermore, their spherical morphology makes them appropriate for advanced technologies in, for instance, ceramic inkjet printers.     

Kinetic Control via Binding Sites within the Confined Space of Metal Metalloporphyrin-Frameworks for Enhanced Shape-Selectivity Catalysis

One striking feature of enzyme is its controllable ability to trap substrates via synergistic or cooperative binding in the enzymatic pocket, which renders the shape-selectivity of product by the confined spatial environment. The success of shape-selective catalysis relies on the ability of enzyme to tune the thermodynamics and kinetics for chemical reactions. In emulation of enzyme's ability, we showcase herein a targeting strategy with the substrate being anchored on the internal pore wall of metal-organic frameworks (MOFs), taking full advantage of the sterically kinetic control to achieve shape-selectivity for the reactions. For this purpose, a series of binding site-accessible metal metalloporphyrin-frameworks (MMPFs) have been investigated to shed light on the nature of enzyme-mimic catalysis. They exhibit a different density of binding sites that are well arranged into the nanospace with corresponding distances of opposite binding sites. Such a structural specificity results in a facile switch in selectivity from an exclusive formation of the thermodynamically stable product to the kinetic product. Thus, the proposed targeting strategy, based on the combination of porous materials and binding events, paves a new way to develop highly efficient heterogeneous catalysts for shifting selectivity.     

Tailoring the refractive indices of thin film polymer metallic nanoparticle nanocomposites

We demonstrate how to tailor the spatial distribution of gold nanoparticles (Au-NPs) of different sizes within polystyrene (PS) thin, supported, film hosts, thereby enabling the connection between the spatial distribution of Au-NPs within the polymer film and the optical properties to be determined. The real, n, and imaginary parts, k, of the complex refractive indices N = n(λ)+ik(λ) of the nanocomposite films were measured as a function of wavelength, λ, using multivariable angle spectroscopic ellipsometry. The surface plasmon response of films containing nearly homogeneous Au-NP distributions were well described by predictions based on classical Mie theory and the Drude model. The optical spectra of samples containing inhomogeneous nanoparticle distributions manifest features associated with differences in the size and interparticle spacings as well as the proximity and organization of nanoparticles at the substrate and free surface.     

Monodispersed core-shell Fe3O4@Au nanoparticles

The ability to synthesize and assemble monodispersed core-shell nanoparticles is important for exploring the unique properties of nanoscale core, shell, or their combinations in technological applications. This paper describes findings of an investigation of the synthesis and assembly of core (Fe(3)O(4))-shell (Au) nanoparticles with high monodispersity. Fe(3)O(4) nanoparticles of selected sizes were used as seeding materials for the reduction of gold precursors to produce gold-coated Fe(3)O(4) nanoparticles (Fe(3)O(4)@Au). Experimental data from both physical and chemical determinations of the changes in particle size, surface plasmon resonance optical band, core-shell composition, surface reactivity, and magnetic properties have confirmed the formation of the core-shell nanostructure. The interfacial reactivity of a combination of ligand-exchanging and interparticle cross-linking was exploited for molecularly mediated thin film assembly of the core-shell nanoparticles. The SQUID data reveal a decrease in magnetization and blocking temperature and an increase in coercivity for Fe(3)O(4)@Au, reflecting the decreased coupling of the magnetic moments as a result of the increased interparticle spacing by both gold and capping shells. Implications of the findings to the design of interfacial reactivities via core-shell nanocomposites for magnetic, catalytic, and biological applications are also briefly discussed.     

Study of the composition and morphology of new modifications of titanium‐magnesium catalysts with improved properties in ethylene polymerization

Data on new modifications of supported titanium‐magnesium catalysts (TMCs) with improved performance in ethylene polymerization are reported. These catalysts possess a high and stable activity, an enhanced ability to regulate molecular weight of the polymer by hydrogen, a controllable particle size at a narrow particle size distribution, and the ability to produce the polymer with an increased bulk density. Various physicochemical methods were used to obtain data on the chemical composition of novel supports and catalysts, their phase composition and crystal structure as well as the pore structure. The results obtained were used to discuss possible correlations between composition and structure of TMCs and their catalytic properties. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2545–2558     

Fabrication of magnetic core@shell Fe oxide@Au nanoparticles for interfacial bioactivity and bio-separation

The immobilization of proteins on gold-coated magnetic nanoparticles and the subsequent recognition of the targeted proteins provide an effective means for the separation of proteins via application of a magnetic filed. A key challenge is the ability to fabricate such nanoparticles with the desired core-shell nanostructure. In this article, we report findings of the fabrication and characterization of gold-coated iron oxide (Fe2O3 and Fe3O4) core@shell nanoparticles (Fe oxide@Au) toward novel functional biomaterials. A hetero-interparticle coalescence strategy has been demonstrated for fabricating Fe oxide@Au nanoparticles that exhibit controllable sizes ranging from 5 to 100 nm and high monodispersity. Composition and surface analyses have proven that the resulting nanoparticles consist of the Fe2O3 core and the Au shell. The magnetically active Fe oxide core and thiolate-active Au shell were shown to be viable for exploiting the Au surface protein-binding reactivity for bioassay and the Fe oxide core magnetism for magnetic bioseparation. These findings are entirely new and could form the basis for fabricating magnetic nanoparticles as biomaterials with tunable size, magnetism, and surface binding properties.     

Photoreactive nanoparticles as nanometric building blocks for the generation of self-healing hydrogel thin films

The use of reversible photo-cross-linkable nanoparticles as nano building blocks for the formulation of nanostructured self-healing thin hydrogel films is shown for the first time. This strategy for the fabrication of autonomous self-healing coatings consisted of various microgels bearing surface cinnamate moieties. The nanoparticles were formed by miniemulsion copolymerization, which was followed by surface functionalization with the cinnamate groups. These nanoparticles were then used to form films by drop-casting, followed by interparticle photo-cross-linking polymerization through the light-induced forward dimerization reaction of the previously incorporated cinnamate groups. The reversibility of this macroscopic network formation was also demonstrated by photoinducing the backward dimerization reaction and carrying out several cycles of photoinduced cross-linking and de-cross-linking. The self-healing ability through swelling of these films following surface damage was also demonstrated. Finally, the ability of these self-healing macroscopic films to incorporate additives of different chemical nature before photo-cross-linking was evaluated.     

Abnormal IR effects of Pt nanostructured surfaces upon CO chemisorption due to interaction and electron-hole damping

The abnormal IR effects (AIREs) characterized by a positive-going peak of platinum (Pt) nanostructured surface generated in a square-wave potential treatment upon CO molecule chemisorption was observed and analyzed with a consideration of the interparticle interaction and electron-hole damping between nanoislands and CO molecules. A theoretical simulation shows that the islanded nanostructured Pt surfaces, which gives rise to interparticle interaction, coupling with electron-hole mechanism, may contribute to the origins of positive-going peak (AIREs) observed by in situ Fourier transformation IR (FTIR) experiments.