Monodispersed Pt nanoparticles on reduced graphene oxide by a non-noble metal sacrificial approach for hydrolytic dehydrogenation of ammonia borane

Downsizing noble metal nanoparticles,such as Pt,is an essential goal for many catalytic reactions.A non-noble metal sacrificial approach was used to immobilize monodispersed Pt nanoparticles (NPs) with a mean size of 1.2 nm on reduced graphene oxide (RGO).ZnO co-precipitated with Pt NPs and subsequently sacrificed by acid etching impedes the diffusion of Pt atoms onto the primary Pt particles and also their aggregation during the reduction of precursors.The resulting ultrafine Pt nanoparticles exhibit high activity (a turnover frequency of 284 min-1 at 298 K) in the hydrolytic dehydrogenation of ammonia borane.The non-noble metal sacrificial approach is demonstrated as a general approach to synthesize well-dispersed noble metal NPs for catalysis.     

Bright Surface‐Enhanced Raman Scattering with Fluorescence Quenching from Silica Encapsulated J‐Aggregate Coated Gold Nanoparticles

Plexitonic nanoparticles offer variable optical properties through tunable excitations, in addition to electric field enhancements that far exceed molecular resonators. This study demonstrates a way to design an ultrabright surface‐enhanced Raman spectroscopy (SERS) signal while simultaneously quenching the fluorescence background through silica encapsulation of the semiconductor–metal composite nanoparticles. Using a multistep approach, a J‐aggregate‐forming organic dye is assembled on the surface of gold nanoparticles using a cationic linker. Excitonic resonance of the J‐aggregate–metal system shows an enhanced SERS signal at an appropriate excitation wavelength. Further encapsulation of the decorated particles in silica shows a significant reduction in the fluorescence signal of the Raman spectra (5× reduction) and an increase in Raman scattering (7× enhancement) when compared to phospholipid encapsulation. This reduction in fluorescence is important for maximizing the useful SERS enhancement from the particle, which shows a signal increase on the order of 10⁴ times greater than J‐aggregated dye in solution and 24 times greater than Oxonica S421 SERS tag. The silica layer also serves to promote colloidal stability. The combination of reduced fluorescence background, enhanced SERS intensity, and temporal stability makes these particles highly distinguishable with potential to enable high‐throughput applications such as SERS flow cytometry.     

Nanofence Stabilized Platinum Nanoparticles Catalyst via Facet‐Selective Atomic Layer Deposition

A facet‐selective atomic layer deposition method is developed to fabricate oxide nanofence structure to stabilize Pt nanoparticles. CeO_x is selectively deposited on Pt nanoparticles' (111) facets and naturally exposes Pt (100) facets. The facet selectivity is realized through different binding energies of Ce precursor fragments chemisorbed on Pt (111) and Pt (100), which is supported by in situ mass gain experiment and corroborated by density functional theory simulations. Such nanofence structure not only has exposed Pt active facets for carbon monoxide oxidation but also forms ceria–metal interfaces that are beneficial for activity enhancement. The composite catalysts show excellent sintering resistance up to 700 °C calcination. CeO_x anchors Pt nanoparticles with a strong metal oxide interaction, and nanofence structure around Pt nanoparticles provides physical blocking that suppresses particles migration. The study reveals that forming oxide nanofence structure to encapsulate precious metal nanoparticles is an effective way to simultaneously enhance catalytic activity and thermal stability.     

A study of nanoparticle manufacturing process using vacuum submerged arc machining with aid of enhanced ultrasonic vibration

This article presents the development of an innovative approach using the vacuum submerged arc machining with aid of enhanced ultrasonic vibration to manufacture nanoparticles. The Arc Spray Nanoparticle Synthesis System (ASNSS) previously designed by the NTUT’s Nano Laboratory has been successfully developed to generate nanoparticles. In this proposed process, a titanium bar, as the electrode, is melted and vaporized in distilled water, used as an insulating liquid. Meanwhile, the ultrasonic vibration is applied to the electrode to remove the vaporized metal powders rapidly from the melting zone. The vaporized metal particles are then rapidly quenched by the designed cooling system, thus nanocrystalline particles nucleated and formed. This study discusses the the influence of the ultrasonic amplitude and various process variables such as pulse duration, peak current, and dielectric liquid temperature on TiO₂nanoparticles suspension.     

Tetrazoles: Unique Capping Ligands and Precursors for Nanostructured Materials

Capping agents play an important role in the colloidal synthesis of nanomaterials because they control the nucleation and growth of particles, as well as their chemical and colloidal stability. During recent years tetrazole derivatives have proven to be advanced capping ligands for the stabilization of semiconductor and metal nanoparticles. Tetrazole‐capped nanoparticles can be prepared by solution‐phase or solventless single precursor approaches using metal derivatives of tetrazoles. The solventless thermolysis of metal tetrazolates can produce both individual semiconductor nanocrystals and nanostructured metal monolithic foams displaying low densities and high surface areas. Alternatively, highly porous nanoparticle 3D assemblies are achieved through the controllable aggregation of tetrazole‐capped particles in solutions. This approach allows for the preparation of non‐ordered hybrid structures consisting of different building blocks, such as mixed semiconductor and metal nanoparticle‐based (aero)gels with tunable compositions. Another unique property of tetrazoles is their complete thermal decomposition, forming only gaseous products, which is employed in the fabrication of organic‐free semiconductor films from tetrazole‐capped nanoparticles. After deposition and subsequent thermal treatment these films exhibit significantly improved electrical transport. The synthetic availability and advances in the functionalization of tetrazoles necessitate further design and study of tetrazole‐capped nanoparticles for various applications.     

Modification of magnetic properties of metal nanoparticles using nanotemplate approach

We demonstrate a nanotemplate approach by which different metal magnetic nanoparticles (Ni–Co, Ni–Fe and Co–Pt alloy particles) can be fabricated on a polyimide (PI) film. The process relies on the high interfacial energy between deposited metal and the PI film which forces the deposited metal film to preferentially nucleate on the pre-existing Ni seed particles. During subsequent thermal annealing, the deposited metal film coalesced onto the Ni seed particles to form a monolayer of magnetic nanoparticles on the PI film. Furthermore, the deposition/annealing can be repeated to change both size and constituent of the nanoparticles by introducing a different metal film during deposition. Potentially, any metal film can be deposited onto the Ni seed particles provided that the metal does not react with the Ni seed particles to create a monolayer of metal nanoisland structures with desire magnetic properties.     

The surface chemistry and stability of gold nanoparticles prepared using methanol extract of Eucalyptus camaldulensis

The development of nontoxic, clean techniques for synthesising metal nanoparticles such as gold has attracted increasing attention in recent years. Many reports have been published about the synthesis of gold nanoparticles using plant extracts. However, the stability of these prepared gold nanoparticles has not been investigated. In this research, the stability of gold nanoparticles prepared by Eucalyptus camaldulensis was investigated at different temperatures (4°C, 25°C and 45°C) for 8 weeks. Transmission electron microscopy and visible absorption spectroscopy confirmed the stability of gold nanoparticles during the storage period at the mentioned condition. In addition, Fourier transform–infrared spectroscopy was used to investigate the surface chemistry of gold nanoparticles prepared by the methanol extract of E. camaldulsis. The carboxyl group was characterised on the surface of the gold nanoparticles, and this functional group may have a critical role in the stability of gold nanoparticles prepared by the mentioned plant extract at different conditions. This functional group can be used for drug delivery of amino derivative drugs using gold nanoparticles.     

Synthesis of highly stable graphite-encapsulated metal (Fe, Co, and Ni) nanoparticles

Graphite-encapsulated metal magnetic nanoparticles have been attracted for biological applications because of their high magnetization of the encapsulated particles. However, most of the synthetic methods have limitations in terms of scalability and economics because of the demanding synthetic conditions and low yields. Here, we show that well-controlled graphite-encapsulated metal (Fe, Co, and Ni) nanoparticles can be synthesized by a hydrothermal method, simply by mixing metal source with sucrose as a carbon source. The saturation magnetization (Ms) values of Fe/C, Co/C, and Ni/C were 86.6, 43.8, and 113.1?emu/g, respectively. The Fe/C and Ni/C showed higher Ms values than bulk Fe₃O₄ (75.5?emu/g). The graphite-encapsulated metal nanoparticles showed good stability against acid and base environments.     

Confinement Impact for the Dynamics of Supported Metal Nanocatalyst

Supported metal nanoparticles play key roles in nanoelectronics, sensors, energy storage/conversion, and catalysts for the sustainable production of fuels and chemicals. Direct observation of the dynamic processes of nanocatalysts at high temperatures and the confinement of supports is of great significance to investigate nanoparticle structure and functions for practical utilization. Here, in situ high‐resolution transmission electron microscopy photos and videos are combined with dynamics simulations to reveal the real‐time dynamic behavior of Pt nanocatalysts at operation temperatures. Amorphous Pt surface on moving and deforming particles is the working structure during the high operation temperature rather than a static crystal surface and immobilization on supports as proposed before. The free rearrangement of the shape of Pt nanoparticles allows them to pass through narrow windows, which is generally considered to immobilize the particles. The Pt particles, no matter what their sizes, prefer to stay inside nanopores even when they are fast moving near an opening at temperatures up to 900 °C. The porous confinement also blocks the sintering of the particles under the confinement size of pores. These contribute to the continuous high activity and stability of Pt nanocatalysts inside nanoporous supports during a long‐term evaluation of catalytic reforming reaction.     

Generation of metal and metal oxide nanoparticles by liquid flame spray process

A liquid flame spray (LFS) process has been investigated for the generation of single component nanoparticles. In the LFS process, a solution consisting of metal nitrate dissolved in water is sprayed into a turbulent, high temperature H₂-O₂-flame. The primary spray droplets evaporate and subsequent reactions in the flame produce metal or metal oxide vapours which nucleate to final particulate form. In the study, the process characteristics were examined to produce 10–60 nm particles from silver, palladium and iron containing precursors. A systematic study using variable process parameters proved that the size of the generated nanoparticles is set by the mass flow rate of the metal precursor, only. The geometric standard deviation of the size distributions was seen to vary in a limited range of 1.35–1.4. The particle size was verified by aerosol instrumentation, the composition and morphology by X-ray diffraction (XRD) and transmission electron microscopy (TEM), correspondingly. The Ag and Pd particles were seen to consist of pure metals. For iron, the presence of all three of the following compounds were detected: Fe, Fe₂O₃ and Fe₃O₄.     

Reactive friction stir processing of AA 5052–TiO2 nanocomposite: process–microstructure–mechanical characteristics

Friction stir processing (FSP) is a solid state route with a capacity of preparing fine grained nanocomposites from metal sheets. In this work, we employed this process to finely distribute TiO₂ nanoparticles throughout an Al–Mg alloy, aiming to enhance mechanical properties. Titanium dioxide particles (30 nm) were preplaced into grooves machined in the middle of the aluminium alloy sheet and multipass FSP was afforded. This process refined the grain structure of the aluminium alloy, distributed the hard nanoparticles in the matrix and promoted solid state chemical reactions at the interfaces of the metal/ceramic particles. Detailed optical and electron microscopic studies showed that the microstructural homogeneity was improved with repetition of FSP up to four passes. The average grain size of the nanocomposite was ～2 μm, while nanometric MgO and Al₃Ti particles were formed in situ and homogenously distributed in the metal matrix. Mechanical characterisations showed that the yield strength and elongation were increased from 93±5 MPa and 13·8% to 117±3 MPa and 25·3% after employing four-pass FSP. Fractographic studies also revealed that agglomerated TiO₂ particles could operate as sites of crack initiation and propagation, which led to brittle fracture. By increasing the number of FSP passes, the agglomerates were disappeared and the ductility was enhanced remarkably.     

Instantaneous formation of metal and metal oxide nanoparticles on carbon nanotubes and graphene via solvent-free microwave heating

Microwave irradiation was shown to be an effective energy source for the rapid decomposition of organic metal salts (such as silver acetate) in a solid mixture with various carbon and noncarbon substrates under completely solvent-free conditions. The rapid and local Joule heating of microwave absorbing substrates (i.e., carbon-based) resulted in the instantaneous formation of metal and metal oxide nanoparticles on the substrate surfaces within seconds of microwave exposure. Other less absorbing substrates (such as hexagonal boron nitride) required longer exposure times for the salt decomposition to occur. Details of the effects of microwave reaction time, temperature, power, and other experimental parameters were investigated and discussed. The solvent-free microwave method was shown to be widely applicable to various organic metal salts with different substrates including single- and multiwalled carbon nanotubes, graphene, expanded graphite, hexagonal boron nitride and silica-alumina particles, forming substrate-supported metal (e.g., Ag, Au, Co, Ni, Pd, Pt) or metal oxide (e.g., Fe?O?, MnO, TiO?) nanoparticles in high yields within short duration of microwave irradiation. The method was also successfully applied to large structural substrates such as nanotube yarns, further suggesting its application potential and versatility. To demonstrate one potential application, we successfully used both carbon nanotube powder and yarn samples decorated with Ag nanoparticles prepared via the above method to improve data acquisition in surface enhanced Raman spectroscopy.     

Controlled fabrication of noble metal nanoparticles loaded on the surfaces of cyclotriphosphazene-containing polymer nanotubes

We report on the fabrication of noble metal nanoparticles loaded on the surfaces of cross-linked poly(cyclotriphosphazene-co-4,4′-sulfonyldiphenol) (PZS) nanotubes of high stability. PZS nanotubes were first synthesized by precipitation polymerization between hexachlorocyclotriphosphazene and 4,4′-sulfonyldiphenol based on in situ template mechanism. Then the PZS nanotubes were directly used as scafford to load metal Au, Ag, and Pd nanoparticles, respectively, through cation complexation followed by gentle reduction. The structure and morphology of the metal/PZS nanocomposites were determined by means of Fourier transform infrared spectra, energy dispersive X-ray spectroscopy, elemental analysis, X-ray diffraction, scanning electron microscope, transmission electron microscope, and thermogravimetric analysis (TGA). Results showed that the metal/PZS nanocomposites possessed 460 °C of initial thermal decomposition temperature under air atmosphere and the loading amount of metal nanoparticles on the PZS nanotube surfaces could be controlled easily. As-fabricated metal/PZS nanocomposites are expected to have potential applications in catalysis.     

Bio‐Derived Co2P Nanoparticles Supported on Nitrogen‐Doped Carbon as Promising Oxygen Reduction Reaction Electrocatalyst for Anion Exchange Membrane Fuel Cells

Recently, nonnoble‐metal catalysts such as a metal coordinated to nitrogen doped in a carbon matrix have been reported to exhibit superior oxygen reduction reaction (ORR) activity in alkaline media. In this work, Co₂P nanoparticles supported on heteroatom‐doped carbon catalysts (NBSCP) are developed with an eco‐friendly synthesis method using bean sprouts. NBSCP can be easily synthesized through metal precursor absorption and carbonization at a high temperature. It shows a very large specific surface area with various dopants such as nitrogen, phosphorus, and sulfur derived from small organic molecules. The catalyst can exhibit activity in various electrochemical reactions. In particular, excellent performance is noted for the ORR. Compared to the commercial Pt/C, NBSCP exhibits a lower onset potential, higher current density, and superior durability. This excellent ORR activity and durability is attributable to the synergistic effect between Co₂P nanoparticles and nitrogen‐doped carbon. In addition, superior performance is noted on applying NBSCP to a practical anion exchange membrane fuel cell system. Through this work, the possibility of applying an easily obtained bio‐derived material to energy conversion and storage systems is demonstrated.     

Engineering high-temperature stable nanocomposite materials

The low thermal stability of nanoparticles typically restricts their use in catalytic and other applications to low-?to moderate-temperature conditions. We present a novel approach to the stabilization of nanosized noble metal particles by embedding them in a high-temperature stabilized hexa-aluminate matrix. The simple 'one-pot' approach is based on a microemulsion-templated sol-gel synthesis and yields mesoporous nanocomposite materials with pure textural porosity and excellent high-temperature stability up to about 1200?°C. To our knowledge, this is the first time that metal nanoparticles have been stabilized to such high temperatures. We furthermore find that the microemulsion templating allows a tailoring of the ceramic matrix without influencing the size of the embedded Pt particle. This opens up the possibility of a true multiscale engineering of nanocomposite materials. We see these novel materials therefore not only as very promising candidates for a broad range of high-temperature catalytic applications, but generally view this versatile synthesis route as a first step towards expanding the parameter range for nanoparticle applications.     

Crosslinking Metal Nanoparticles into the Polymer Backbone of Hydrogels Enables Preparation of Soft,Magnetic Field‐Driven Actuators with Muscle‐Like Flexibility

The combination of force and flexibility is at the core of biomechanics and enables virtually all body movements in living organisms. In sharp contrast, presently used machines are based on rigid, linear (cylinders) or circular (rotator in an electrical engine) geometries. As a potential bioinspired alternative, magnetic elastomers can be realized through dispersion of micro‐ or nanoparticles in polymer matrices and have attracted significant interest as soft actuators in artificial organs, implants, and devices for controlled drug delivery. At present, magnetic particle loss and limited actuator strength have restricted the use of such materials to niche applications. We describe the direct incorporation of metal nanoparticles into the backbone of a hydrogel and application as an ultra‐flexible, yet strong magnetic actuator. Covalent bonding of the particles prevents metal loss or leaching. Since metals have a far higher saturation magnetization and higher density than oxides, the resulting increased force/volume ratio afforded significantly stronger magnetic actuators with high mechanical stability, elasticity, and shape memory effect.     

Ultrasmall Metal Nanoparticles Confined within Crystalline Nanoporous Materials: A Fascinating Class of Nanocatalysts

Crystalline nanoporous materials with uniform porous structures, such as zeolites and metal–organic frameworks (MOFs), have proven to be ideal supports to encapsulate ultrasmall metal nanoparticles (MNPs) inside their void nanospaces to generate high‐efficiency nanocatalysts. The nanopore‐encaged metal catalysts exhibit superior catalytic performance as well as high stability and catalytic shape selectivity endowed by the nanoporous matrix. In addition, the synergistic effect of confined MNPs and nanoporous frameworks with active sites can further promote the catalytic activities of the composite catalysts. Herein, recent progress in nanopore‐encaged metal nanocatalysts is reviewed, with a special focus on advances in synthetic strategies for ultrasmall MNPs (<5 nm), clusters, and even single atoms confined within zeolites and MOFs for various heterogeneous catalytic reactions. In addition, some advanced characterization methods to elucidate the atomic‐scale structures of the nanocatalysts are presented, and the current limitations of and future opportunities for these fantastic nanocatalysts are also highlighted and discussed. The aim is to provide some guidance for the rational synthesis of nanopore‐encaged metal catalysts and to inspire their further applications to meet the emerging demands in catalytic fields.     

Influence of Temperature on the Colloidal Stability of Polymer‐Coated Gold Nanoparticles in Cell Culture Media

The temperature‐dependence of the hydrodynamic diameter and colloidal stability of gold‐polymer core‐shell particles with temperature‐sensitive (poly(N‐isopropylacrylamide)) and temperature‐insensitive shells (polyallylaminine hydrochloride/polystyrensulfonate, poly(isobutylene‐alt‐maleic anhydride)‐graft‐dodecyl) are investigated in various aqueous media. The data demonstrate that for all nanoparticle agglomeration, i.e., increase in effective nanoparticle size, the presence of salts or proteins in the dispersion media has to be taken into account. Poly(N‐isopropylacrylamide) coated nanoparticles show a reversible temperature‐dependent increase in size above the volume phase transition of the polymer shell when they are dispersed in phosphate buffered saline or in media containing protein. In contrast, the nanoparticles coated with temperature‐insensitive polymers show a time‐dependent increase in size in phosphate buffered saline or in medium containing protein. This is due to time‐dependent agglomeration, which is particularly strong in phosphate buffered saline, and induces a time‐dependent, irreversible increase in the hydrodynamic diameter of the nanoparticles. This demonstrates that one has to distinguish between temperature‐ and time‐induced agglomerations. Since the size of nanoparticles regulates their uptake by cells, temperature‐dependent uptake of thermosensitive and non‐thermosensitive nanoparticles by cells lines is compared. No temperature‐specific difference between both types of nanoparticles could be observed.     

Ultrafast Laser Manufacture of Stable,Efficient Ultrafine Noble Metal Catalysts Mediated with MOF Derived High Density Defective Metal Oxides

Supported metal nanoparticles (MNPs) undergo severe aggregation, especially when the interaction between MNPs and their supports are limited and weak where their performance deteriorates dramatically. This becomes more severe when catalysts are operated under high temperature. Here, it is reported that MNPs including Pt, Au, Rh, and Ru, with sub‐2 nm size can be stabilized on densely packed defective CeO₂ nanoparticles with sub‐5 nm size via strong coupling by direct laser conversion of corresponding metal ions encapsulated cerous metal–organic frameworks (Ce‐MOFs). Ce‐MOF serves as an ideal dispersion precursor to uniformly encapsulate noble metal ions in their orderly arranged pores. Ultrafast laser vaporization and cooling forms uniform, ultrasmall, well‐mixed, and exceptionally dense nanoparticles of metal and metal oxide concurrently. The laser‐induced ultrafast reaction (within tens of nanoseconds) facilitates the precipitation of CeO₂ nanoparticles with abundant surficial defects. Due to the well‐mixed ultrasmall Pt and CeO₂ components with strong coupling, this catalyst exhibits exceptionally high stability and activity both at low and high temperatures (170–1100 °C) for CO oxidation in long‐term operation, significantly exceeding catalysts prepared by traditional methods. The scalable feature of laser and huge MOF family make it a versatile method for the production of MNP‐based nanocomposites in wide applications.     

Nanoparticle-induced enhancement in fracture toughness of highly loaded epoxy composites over a wide temperature range

The fracture toughness of an epoxy molding compound (EMC) has been enhanced over a wide temperature range by the addition of a very low volume fraction of silica nanoparticles to the EMC filled with micro-silica particles, which induces macroscopic crack deflection and plastic deformation in front of the crack tip. To evaluate the fracture toughness (G _IC) of these materials, the single edge notched bending (SENB) test was performed for a wide range of temperatures (from ambient temperature to 230°C). The fracture toughness of the nano-silica filled EMCs was found to be improved in this temperature range by as much as a factor of two. Investigation of the fracture surfaces revealed that the micro-silica particles are covered with deformed matrix materials, which implies that the silica nanoparticles induced the crack to move into the interface between the micro-silica particles. Fractography results suggest that the silica nanoparticles act as surface modifiers of the micro-silica particles, which results in crack deflection and plastic deformation.