Nanoparticle Networks Research Articles

Impact of Silica Nanoclusters on Furfuryl Alcohol Polymerization and Molecular Mobility

Nanocomposite materials present attractive properties and are widely employed in various applications. Most of the time, the insertion of nanoparticles in a polymer matrix induces an enhancement of its performances, yet the effect of the filler on the polymerization mechanisms and the glass transition is less often investigated. In the present study, the PFA/silica nanocomposite was studied to highlight the variation of its polymerization behavior, thermomechanical properties and glass transition induced by the presence of a clustered silica nanoparticles network. The structure of nanosilica clusters was studied by thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR). The furfuryl alcohol (FA) polymerization was studied via its activation energy variation in the presence of nanosilica clusters and anhydride maleic (MA) that led to some modifications of the polymerization mechanism. An enhancement of thermal stability and an increase of glass transition temperature have been put...

Facile synthesis of Pd-Ru-P ternary nanoparticle networks with enhanced electrocatalytic performance for methanol oxidation

Liquid fuel cells have attracted broad research interests for past several decades, especially for direct methanol fuel cells (DMFCs) because of their compact volume, environmentally benign and easy storage. Exploring cost-effective electrocatalysts toward methanol electrooxidation is meaningful for the development of (DMFCs). Herein, a series of PdRu/P network catalysts have been fabricated and modified via a facile and reproducible method taking benzyl alcohol, hydrazine hydrate as solvent and reducing agents, respectively. Profiting from the 3D network structure, the synergistic effect together with the increased electron mobility induced by the addition of nonmetal phosphorous (P). The PdRu/P catalysts display markedly improved efficient electrocatalytic activity with excellent current peak, more negative onset potential, as well as superior long-term stability compared to commercial Pd/C, PdRu and Pd/P prepared under the same condition. In this work, we highlight the effect of the incorporation of nonmetals P on the electrocatalytic performance of PdRu binary catalysts, which will contribute to broadening the application of nonmetal P or even for other nonmetals for electrooxidation. Our efforts will dedicate to accelerating the commercialization of efficient and stable anode catalysts in fuel cells by means of doping transition metals or nonmetals into Pd.

Nanoparticles alloying in liquids: Laser-ablation-generated Ag or Pd nanoparticles and laser irradiation-induced AgPd nanoparticle alloying

Laser irradiation of a mixture of single-element micro/nanomaterials may lead to their alloying and fabrication of multi-element structures. In addition to the laser induced alloying of particulates in the form of micro/nanopowders in ambient atmosphere (which forms the basis of the field of additive manufacturing technology), another interesting problem is the laser-induced alloying of a mixture of single-element nanoparticles in liquids since this process may lead to the direct fabrication of alloyed-nanoparticle colloidal solutions. In this work, bare-surface ligand-free Ag and Pd nanoparticles in solution were prepared by laser ablation of the corresponding bulk target materials, separately in water. The two solutions were mixed and the mixed solution was laser irradiated for different time durations in order to investigate the laser-induced nanoparticles alloying in liquid. Nanoparticles alloying and the formation of AgPd alloyed nanoparticles takes place with a decrease of the intensity of the surface-plasmon resonance peak of the Ag nanoparticles (at ∼405 nm) with the irradiation time while the low wavelength interband absorption peaks of either Ag or Pd nanoparticles remain unaffected by the irradiation for a time duration even as long as 30 min. The nanoalloys have lattice constants with values between those of the pure metals, which indicates that they consist of Ag and Pd in an approximately 1:1 ratio similar to the atomic composition of the starting mixed-nanoparticle solution. Formation of nanoparticle networks consisting of bimetallic alloyed nanoparticles and nanoparticles that remain as single elements (even after the end of the irradiation), joining together, are also formed. The binding energies of the 3d core electrons of both Ag and Pd nanoparticles shift to lower energies with the irradiation time, which is also a typical characteristic of AgPd alloyed nanoparticles. The mechanisms of nanoparticles alloying and network formation are also discussed.

Silver nanoparticles as low-emissivity coating materials

The application potential of silver (Ag) nanoparticles as low-emissivity (low-e) coating materials has been discussed. Ag nanoparticles with an average diameter of about 50 nm were prepared via a wet-chemical method and applied on the surface of glass by spin coating. The as-prepared Ag nanoparticle films showed a typical surface emissivity of about 0.793, compared to about 0.837 of the plain glass substrate. After a mild heat treatment at 200 °C, the annealed Ag nanoparticle films showed a substantially reduced surface emissivity value as low as 0.015. The corresponding structural evolution of Ag nanoparticle films during the heat treatment and its effect on the surface emissivity were discussed by means of scanning electron microscopy. The results indicated that forming an interconnected, porous network of Ag nanoparticles is essential for achieving the low-e effect for this material. By applying such low-e coatings, the heat loss through a double-glazed window can be reduced by about 35% (U-value reduction from 2.75 to 1.78 W (m2K)−1). This work may inspire further efforts to address the energy efficiency issues in the building sector by taking the advantage of nanomaterials and nanotechnology.

Peptide A4 based AuAg alloyed nanoparticle networks for electrocatalytic reduction of oxygen

Peptide based methods create new revenues to fabricate stable, multifunctional noble metal nanomaterials under mild and green synthesis conditions. Peptide sequence A4 stabilized AuAg alloyed nanomaterials were fabricated through a facile and straightforward approach. The as-prepared alloyed nanomaterials demonstrated effective catalytic activity toward oxygen electroreduction in alkaline media. Both the metal-to-A4 ratio and Au-to-Ag ratio were optimized to enrich the electrocatalytic performance, and the sample of Au:Ag:A4 = 10:30:1 exhibited the highest activity among the series. The performance of Au:Ag:A4 = 10:30:1 is comparable with that of commercial Pt/C, within the context of onset potential, diffusion-limited current density as well as long-term stability. The as-prepared samples were characterized by UV–visible absorbance, transmission electron microscopy (TEM), as well as X-ray photoelectron microscopy (XPS). The improved activity is probably attributed to the alloying induced ensemble effects and electronic effects. This discovery may shed light on fabricating peptide based alloys as highly efficient catalysts with enhanced stability for oxygen reduction reaction (ORR).

A rapid synthesis of high surface area PdRu nanosponges: Composition-dependent electrocatalytic activity for formic acid oxidation

Here, PdRu nanoparticle networks (NPNs) with various compositions were synthesized through an inexpensive method in water as a green solvent, at different ratios of the H2PdCl4 and RuCl3 precursors. This is a fast, room temperature and surfactant free strategy which is able to form high surface area metal nanosponges with a three-dimensional (3D) porous structure. The structure of as-prepared nanosponges was characterized using the techniques of field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS) and cyclic voltammetry (CV). Then, the electrocatalytic activities of PdRu NPNs towards formic acid oxidation were examined by electrochemical measurements including CV, chronoamperometry, and electrochemical impedance spectroscopy (EIS). Based on studies, it was found that the current density of formic acid oxidation (FAO) is strongly dependent on the composition of PdRu NPNs. The best performance was realized for Pd4Ru1 NPNs compared to monometallic Pd counterpart and other bimetallic NPNs which might be ascribed to the role of Ru in the decrease of CO adsorption strength on the catalyst and consequently the priority of formic acid oxidation through the direct pathway. The Pd4Ru1 NPNs also showed the maximum current density and stability in chronoamperometric measurements. In addition, comparative studies were performed between as-prepared NPNs and CNTs-supported Pd nanoparticles (Pd NPs/CNTs). The present results demonstrated the unique structural advantages of NPNs compared to individual Pd NPs supported on the CNT which leads to the promising performance of NPNs as supportless catalysts for the oxidation of formic acid.

Using Torsion for Controllable Reconfiguration of Binary Nanoparticle Networks.

Mechanical deformation can potentially provide an effective means of controlling the nanoscale morphology in hybrid materials. The challenge, however, is establishing optimal couplings of the deformation and mechano-responsive components in the material to achieve nanoscopic structural reorganization without causing catastrophic damage. Through computational modeling, we investigate how torsion can be utilized to induce controllable structural changes in networks formed from binary mixtures (A and B) of polymer-grafted nanoparticles (PGNs). The nanoparticles' rigid cores are decorated with a corona of grafted polymers, which contain reactive functional groups at the chain ends. With the overlap of the neighboring coronas, these reactive groups form labile bonds, which can reform after breakage. The labile bond energy between similar PGNs (UAA, UBB) is different than the energy between dissimilar species (UAB). By tailoring the relative values of these bond energies and the boundary conditions acting on the system, the application of a torsional deformation can result in a controllable reconfiguration of the network, leading to intertwining helical structures, or homogeneously mixed nanocomposites. In effect, our mechano-mutable system resembles a "Rubik's cube" material, whose nanostructure, and hence global properties, can be tailored by mechanically twisting the sample.

Robust Gold Nanoparticle Sheets by Ligand Cross-Linking at the Air-Water Interface.

We report the results of cross-linking of two-dimensional gold nanoparticle (Au-NP) assemblies at the air-water interface in situ. We introduce an aqueous soluble ruthenium benzylidene catalyst into the water subphase to generate a robust, elastic two-dimensional network of nanoparticles containing cyclic olefins in their ligand framework. The most striking feature of the cross-linked Au-NP assemblies is that the extended connectivity of the nanoparticles enables the film to preserve much of its integrity under compression and expansion, features that are absent in its non-cross-linked counterparts. The cross-linking process appears to "stitch" the nanoparticle crystalline domains together, allowing the cross-linked monolayers to behave like a piece of fabric under lateral compression.

Low-Voltage High-Performance UV Photodetectors: An Interplay between Grain Boundaries and Debye Length.

Accurate detection of UV light by wearable low-power devices has many important applications including environmental monitoring, space to space communication, and defense. Here, we report the structural engineering of ultraporous ZnO nanoparticle networks for fabrication of very low-voltage high-performance UV photodetectors. A record high photo- to dark-current ratio of 3.3 × 105 and detectivity of 3.2 × 1012 Jones at an ultralow operation bias of 2 mV and low UV-light intensity of 86 μW·cm-2 are achieved by controlling the interplay between grain boundaries and surface depletion depth of ZnO nanoscale semiconductors. An optimal window of structural properties is determined by varying the particle size of ultraporous nanoparticle networks from 10 to 42 nm. We find that small electron-depleted nanoparticles (≤40 nm) are necessary to minimize the dark-current; however, the rise in photocurrent is tampered with decreasing particle size due to the increasing density of grain boundaries. These findings reveal that nanoparticles with a size close to twice their Debye length are required for high photo- to dark-current ratio and detectivity, while further decreasing their size decreases the photodetector performance.

Preparation, antimicrobial and antioxidant evaluation of indole-3-acetic acid-based pH-responsive bio-nanocomposites

Nanocomposites were synthesized among citric acid, ethylene glycol and indole-3-acetic acid by condensation followed by incorporating silver nanoparticles (AgNPs) in a hydrogel. The formation of parent hydrogel and their nanocomposites were identified by Fourier transform infrared spectroscopy. The incorporation of silver nanoparticles in the hydrogel network, surface morphology and size of nanoparticles were established by ultraviolet spectroscopy, scanning electron microscopy and transmission electron microscopy, respectively. The thermal properties of the hydrogels were studied by TGA–DTA analysis. The parent hydrogel (ICE) and nanocomposites revealed a good pH-sensitive swelling behavior at acidic media than in basic media. In vitro examination of fungal activity revealed all prepared hydrogels as effective against Aspergillus fumigatus, Rhizopus oryzae and Candida albicans. Further, the antibacterial properties of the optimum sample were successfully evaluated against Gram-positive (Bacillus aureus, Staphylococcus aureus) and Gram-negative (Escherichia coli) bacteria. The prepared nanocomposites showed a higher antimicrobial activity than that of the parent hydrogel. Further, the radical scavenging ability of the hydrogel and nanocomposites were estimated using DPPH (2,2-diphenyl-1-picryl-hydrazyl) and nitric oxide radicals. The prepared nanocomposites with tuned antibacterial, antifungal and antioxidant properties can be used for wound healing, burn dressing, treatment of topical fungal infections and for other biomedical applications.

Effects of morphology on the mechanical properties of heterogeneous polymer-grafted nanoparticle networks

The layered binary nanoparticle networks exhibit superior tensile properties and remarkable resilience in comparison with the random binary mixtures.

Nanostructured 3D porous hybrid network of N-doped carbon, graphene and Si nanoparticles as an anode material for Li-ion batteries

A facile and scalable process to prepare nanostructured 3D porous networks combining graphene, N-doped carbon and silicon nanoparticles (G@Si@C) as a promising anode material for lithium ion batteries.

One-step synthesis and self-assembly of a luminescent sponge-like network of gold nanoparticles with high absorption capacity

One-step strategy to fabricate a luminescent sponge-like network of AuNPs with a high capacity for heavy metal ion absorption.

Systematic investigation on the intracellular trafficking network of polymeric nanoparticles.

Polymeric nanoparticles such as PLGA-based nanoparticles are emerging as promising carriers for controlled drug delivery. However, little is known about the intracellular trafficking network of polymeric nanoparticles. Here, more than 30 Rab proteins were used as markers of multiple trafficking vesicles in endocytosis, exocytosis and autophagy to investigate in detail the intracellular trafficking pathways of PLGA nanoparticles. We observed that coumarin-6-loaded PLGA nanoparticles were internalized by the cells mainly through caveolin and clathrin-dependent endocytosis and Rab34-mediated macropinocytosis. Then the PLGA nanoparticles were transported to early endosomes (EEs), late endosomes (LEs), and finally to lysosomes. Two novel transport pathways were identified in our research: the macropinocytosis (Rab34 positive)-LE (Rab7 positive)-lysosome pathway and the EE-liposome (Rab18)-lysosome pathway. Moreover, the slow (Rab11 and Rab35 positive), fast (Rab4 positive) and apical (Rab20 and Rab25 positive) endocytic recycling endosome pathways could transport the PLGA nanoparticles to lysosomes. The PLGA nanoparticles were transported out of the cells by GLUT4 transport vesicles (Rab8, Rab10 positive), classic secretory vesicles (Rab3, Rab27 positive vesicles) and melanosomes (Rab32, Rab38 positive vesicles). Besides, the PLGA nanoparticles were observed in autophagosomes (LC3 positive), which means that the nanoparticles can be delivered by the autophagy pathway. Multiple cross-talk pathways were identified connecting autophagy and endocytosis or exocytosis by screening the co-localization of the Rab proteins with the LC3 protein. Degradation of nanoparticles through lysosomes can be blocked by autophagy inhibitors (3 MA and CQ). A better understanding of intracellular trafficking mechanisms involved in polymeric nanoparticle-based drug delivery is a prerequisite to clinical application.

Anisotropic enhancement of Yb3+ luminescence by disordered plasmonic networks self-assembled on RbTiOPO4 ferroelectric crystals.

Increasing Yb3+ absorption efficiency is currently desired in a number of applications including bio-imaging, photovoltaics, near infrared driven photocatalysis or ultra-short pulsed solid-state lasers. In this work, silver nanoparticles, which are connected forming disordered networks, have been self-assembled on Yb3+ doped RbTiOPO4 crystals to produce a remarkable enhancement of Yb3+ absorption, and hence in the photoluminescence of this ion. The results are interpreted taking into account the near-field response of the plasmonic networks, which display strong amplification of the electric field at the maximum of Yb3+ excitation at around 900 nm, together with the anisotropic character of the Yb3+ transitions in RbTiOPO4. We show that in the near field regime, the scattering of the plasmonic networks produces additional polarization field components to those of the incident field, which allows access to the largest transition dipolar moment of Yb3+ ions in RbTiOPO4. As a result, a much more efficient route for Yb3+ excitation takes place at the immediacy of the plasmonic networks. This work provides fundamental insights for improving the optical properties of rare earth ions by the suitable design of metallic nanoparticle arrangements, and constitutes a promising step towards the development of new multifunctional solid-state lasers.

Three-dimensional nano-heterojunction networks: a highly performing structure for fast visible-blind UV photodetectors.

Visible-blind ultraviolet photodetectors are a promising emerging technology for the development of wide bandgap optoelectronic devices with greatly reduced power consumption and size requirements. A standing challenge is to improve the slow response time of these nanostructured devices. Here, we present a three-dimensional nanoscale heterojunction architecture for fast-responsive visible-blind UV photodetectors. The device layout consists of p-type NiO clusters densely packed on the surface of an ultraporous network of electron-depleted n-type ZnO nanoparticles. This 3D structure can detect very low UV light densities while operating with a near-zero power consumption of ca. 4 × 10-11 watts and a low bias of 0.2 mV. Most notably, heterojunction formation decreases the device rise and decay times by 26 and 20 times, respectively. These drastic enhancements in photoresponse dynamics are attributed to the stronger surface band bending and improved electron-hole separation of the nanoscale NiO/ZnO interface. These findings demonstrate a superior structural design and a simple, low-cost CMOS-compatible process for the engineering of high-performance wearable photodetectors.

Interfacial crowding of nanoplatelets in co-continuous polymer blends: assembly, elasticity and structure of the interfacial nanoparticle network.

The sequence of events which leads to the interfacial crowding of plate-like nanoparticles in co-continuous polymer blends is investigated through a combination of morphological and rheological analyses. Very low amounts (∼0.2 vol%) of organo-modified clay are sufficient to suppress phase coarsening in a co-continuous polystyrene/poly(methyl methacrylate) blend, while lower particle loading allows for a tuning of the characteristic size of the polymer phases at the μm-scale. In any case, an interfacial network of nanoparticles eventually forms, which is driven by the preferred polymer-polymer interface. The elastic features and stress-bearing ability of this peculiar nanoparticle assembly are studied in detail by means of a descriptive two-phase viscoelastic model, which allows isolation of the contribution of the filler network. The role of the co-continuous matrix in driving the space arrangement of the nanoparticles is emphasized by means of comparative analysis with systems based on the same polymers and nanoparticles, but in which the matrix is either a pure polymer or a blend with drop-in-matrix morphology. The relaxation dynamics of the interfacial network was found not to depend on the matrix microstructure, which instead substantially affects the assembly of the nanoplatelets. When the host medium is co-continuous, the particles align along the preferred polymer-polymer interface, percolating at a very low amount (∼0.17 vol%) and prevalently interacting edge-to-edge. The stress bearing ability of such a network is much higher than that in the case of matrix based on a homogeneous polymer or a drop-in-matrix blend, but its elasticity shows low sensitivity to the filler content.

Thermal transport enhancement in gold nanofluid containing network like structure

In this report, we have shown that gold nanofluid containing networked gold particles have much more enhancement (≈35%) in thermal transport in comparison to gold nanofluid containing conventional spherical gold nanoparticles under similar condition and loading fraction. This shows that structure or shape of the loading materials has very important effect on thermal conductivity of a nanofluid. Connected structure helps to increase the rate of heat transfer in the medium. The gold nanofluid having network of gold nanoparticles is synthesized in a single step process by pulsed laser ablation. The nanofluid (containing gold network) is stable and in addition to enhanced thermal conduction (compared to conventional gold nanofluids) shows no enhancement of viscosity unlike that seen in many nanofluids containing elongated nanomaterials (like cylinder or ellipsoids) in the dispersed phase which limits the use of nanofluids containing these kind of elongated structures in thermal transport though they have enhanced thermal conductivity than the conventional nanofluids (containing spherical nano particles). We synthesized and investigated the thermal transport in nanofluids containing network of Au nanoparticles instead of elongated nanomaterials in the dispersed phase as it retains the advantage of the spherical nanoparticles yet utilizes the enhanced heat transport by the network structure.

Mesoporous Assembled Mn3 O4 Nanoparticle Networks as Efficient Catalysts for Selective Oxidation of Alkenes and Aryl Alkanes.

The design of nanoscale materials has been considered important for enhancing their surface properties for catalysis. Metal oxide nanoparticles have a large number of exposed surface active sites, but they suffer from low reactivity and poor stability resulting from excessive aggregation into less active microscopic structures. Herein, the synthesis of mesoporous Mn3 O4 nanoparticle assemblies by polymer-assisted self-assembly is presented and their catalytic activity is demonstrated in the oxidation of various saturated and unsaturated hydrocarbons, including aromatic alkenes and aryl alkanes, in the presence of tert-butyl hydroperoxide as a mild oxidant. It is also shown through comparative studies that the high catalytic activity and stability of these Mn3 O4 assemblies arise from the unique three-dimensional open-pore structure, high internal surface area (90 m2 g-1 ) and uniform mesopores (≈6.6 nm in size).

Morphological characterization of sphere-like structured ZnO-NiO nanocomposites with annealing temperatures

Three-dimensional (3D) sphere-like structured zinc oxide (ZnO) – nickel oxide (NiO) nanocomposites were prepared via a simple one-pot solution process. Their morphological properties were investigated as a function of the annealing temperature in the range 300–700°C. Metal hydroxides (Zn(OH)2 and Ni(OH)2) were completely decomposed to metal oxides (ZnO and NiO), respectively, after annealing at 500°C. Field emission scanning electron microscopy (FESEM) images revealed that the sphere-like structures maintained their shapes during the annealing treatment. The interwoven nanowalls that constituted sphere-like structures were themselves a sheet-like assembly of nanoparticles, which increased in size with increase in annealing temperature. After annealing at 700°C, a network of interconnected nanoparticles could be observed.