Tunable shapes in supported metal nanoparticles: From nanoflowers to nanocubes

The facile preparation of a range of supported nanoparticles on porous materials was successfully accomplished through the use of a range of environmentally friendly protocols including a modified impregnation/reduction methodology, ultrasounds and microwave irradiation. Materials were characterised by transmission electron microscopy (TEM) and XPS. Different morphologies including conventional nanospheres, nanoflower aggregates, nanorod-like structures and nanocubes were achieved under different conditions. The reported supported nanoparticles are envisaged to have interesting applications in various areas including catalysis, optics and sensors.     

From individual to collective chirality in metal nanoparticles

Recent reports have illustrated the promising potential of chiral metal nanostructures, which exploit the characteristic localized surface plasmon resonance of metal colloids, to produce intense optical activity. In this article we review the concepts, synthetic methods, and theoretical predictions underlying the chirality of metal colloids with a particular emphasis on the size range of 10–100 nanometers. The formation of individual colloidal nanoparticles with a chiral morphology and a plasmonic response remains elusive; however, collective chirality and the associated optical activity in nanoparticle assemblies is a promising alternative that has seen a few recent experimental demonstrations. We conclude with a perspective on chiral nanostructures built up from achiral anisotropic metal particles.     

Arabinogalactan from the Western larch tree: A new, purified and highly water-soluble polysaccharide-based protecting agent for maintaining precious metal nanoparticles in colloidal suspension

TEM and non-contact atomic force microscopy studies conducted on unprotected and protected platinum, palladium and silver nanoparticle suspensions provide evidence for the protective ability of a newly available polysaccharide known as arabinogalactan. The arabinogalactan offers advantages over conventionally used gum arabic in being highly water soluble, capable of being prepared in higher purity and not settling out insoluble material over time. Nanoparticle suspensions prepared in the presence of this protecting agent show a change in overall particle morphology and reduction in the necklace like aggregation typical of unprotected particles on the TEM grids. It is believed that the protective action exerted by the arabinogalactan on the metal nanoparticles arises out of its unique spheroidal structure adopted in aqueous solution which is thought to sequester individual metal particles by virtue of surface interactions between oxide functionalities on the colloid and hydroxyl groups on the arabinogalactan.     

Route to transition metal carbide nanoparticles through cyanamide and metal oxides

We have designed an efficient route to the synthesis of transition metal carbide nanoparticles starting from an organic reagent cyanamide and transition metal oxides. Four technologically important metal carbide nanoparticles such as tungsten carbide, niobium carbide, tantalum carbide and vanadium carbide were synthesized successfully at moderate temperatures. It is found that cyanamide is an efficient carburization reagent and that the metal oxides are completely transmitted into the corresponding carbide nanoparticles. A possible mechanism is proposed to explain the results of the reaction between cyanamide and the metal oxides.     

Using nano-QSAR to predict the cytotoxicity of metal oxide nanoparticles

It is expected that the number and variety of engineered nanoparticles will increase rapidly over the next few years, and there is a need for new methods to quickly test the potential toxicity of these materials. Because experimental evaluation of the safety of chemicals is expensive and time-consuming, computational methods have been found to be efficient alternatives for predicting the potential toxicity and environmental impact of new nanomaterials before mass production. Here, we show that the quantitative structure-activity relationship (QSAR) method commonly used to predict the physicochemical properties of chemical compounds can be applied to predict the toxicity of various metal oxides. Based on experimental testing, we have developed a model to describe the cytotoxicity of 17 different types of metal oxide nanoparticles to bacteria Escherichia coli. The model reliably predicts the toxicity of all considered compounds, and the methodology is expected to provide guidance for the future design of safe nanomaterials.     

Magnetic nanoparticles/graphitic carbon nanostructures composites: Excellent magnetic separable adsorbents for precious metals from aqueous solutions

A facile, low-cost and high-yield route was used for synthesis of magnetic nanoparticles/graphitic carbon nanostructures (MNPs/GCNs) adsorbents with adjustable GCNs structues, in which the cheap ion-exchanged resins and iron salts were adopted as the precursors. The synthesized MNPs/GCNs composites could be used as effective mobile adsorbents for removal of precious metal ions (Ag⁺ and Au³⁺). The adsorption quantity of the adsorbents for Ag⁺ and Au³⁺ ions is up to 7.88 mg/g and 7.92 mg/g, respectively, which is much higher than that of activated carbon. Notably, the adsorbents could be easily separated from solution with a commercial magnet due to the magnetic property, which is very beneficial to their practical application. The kinetics for Ag⁺ and Au³⁺ ions adsorption on MNPs/GCNs composites followed the pseudo-second-order kinetics. The XPS analyses demonstrated that the adsorbed Ag⁺ and Au³⁺ ions exsited in the form of the zero valence state silver and gold, respectively.     

Noble metal nanoparticles for water purification: A critical review

Water is one of the essential enablers of life on earth. Beginning with the origin of the earliest form of life in seawater, it has been central to the evolution of human civilizations. Noble metals have been similarly associated with the prosperity of human civilizations through their prominent use in jewellery and medical applications. The most important reason for the use of noble metals is the minimal reactivity at the bulk scale, which can be explained by a number of concepts such as electrochemical potential, relativisitic contraction, molecular orbital theory, etc. Recently, water quality has been associated with the development index of society. A number of chemical and biological contaminants have endangered the quality of drinking water. An overview of important events during last 200 years in the area of drinking water purification is presented. Realizing the molecular nature of contamination in drinking water, significant progress has been made to utilize the chemistry of nanomaterials for water purification. This article summarizes recent efforts in the area of noble metal nanoparticle synthesis and the origin of their reactivity at the nanoscale. The application of noble metal nanoparticle based chemistry for drinking water purification is summarized for three major types of contaminants: halogenated organics including pesticides, heavy metals and microorganisms. Recent efforts for the removal, as well as ultralow concentration detection of such species, using noble metal nanoparticles are summarized. Important challenges during the commercialization of nano-based products are highlighted through a case study of pesticide removal using noble metal nanoparticles. Recent efforts in drinking water purification using other forms of nanomaterials are also summarized. The article concludes with recent investigations on the issue of nanotoxicity and its implications for the future.     

Optical properties of metal nanoparticles in chrysotile channels

Technical Physics Letters - Chrysotile samples with macroscopically ordered channels filled by gold and silver have been studied using optical transmission spectroscopy. The channels had inner...     

Thermal stability of embedded metal nanoparticles elongated by swift heavy ion irradiation: Zn nanoparticles in a molten state but preserving elongated shapes

Solid Zn and V nanoparticles (NPs) embedded in silica were elongated by swift heavy ion (SHI) irradiation with 200 MeV Xe(14+) ions to a fluence of 5.0 × 10(13) ions cm(-2). Isochronal annealing was carried out in a vacuum from 200 to 1000 °C in steps of 100 °C for 10 min each. The degree of shape elongation was evaluated at room temperature (RT) by two different optical methods: linear dichroism spectroscopy and birefringence spectroscopy. In the as-irradiated state, the samples showed an absorption band at 5 eV due to radiation-induced defects in the silica in addition to the anisotropic absorption due to the elongated metal NPs. After annealing at 400 °C the defect band had completely disappeared, while the degree of shape elongation was almost unchanged or rather slightly increased in both the Zn and V NPs. The elongation of the Zn NPs slightly decreased but maintained a certain value after annealing at 500 °C, which is much higher than the melting point (MP) of Zn NPs (~420 °C). This observation indicates that shape elongation is mostly maintained even if the Zn NPs are in the molten state to some extent during annealing. The elongation of the Zn NPs was almost eliminated after annealing at 600 °C. In the case of the V NPs, elongation was maintained up to 800 °C but mostly eliminated at 900 °C. Since the recovery temperature of 900 °C from the elongated to the spherical shape is much lower than the MP of bulk V (1890 °C), we consider that the elongation is eliminated without melting of V NPs, i.e. via solid state mass transportation. The melting of NPs is not the key factor for the recovery to the spherical shape.     

Gold nanoparticles reduced in situ and dispersed in polymer thin films: optical and thermal properties

Optical and thermal activity of plasmon-active nanoparticles in transparent dielectric media is of growing interest in thermal therapies, photovoltaics and optoelectronic components in which localized surface plasmon resonance (LSPR) could play a significant role. This work compares a new method to embed gold nanoparticles (AuNPs) in dense, composite films with an extension of a previously introduced method. Microscopic and spectroscopic properties of the two films are related to thermal behavior induced via laser excitation of LSPR at 532?nm in the optically transparent dielectric. Gold nanoparticles were incorporated into effectively nonporous 680?μm thick polydimethylsiloxane (PDMS) films by (1) direct addition of organic-coated 16?nm nanoparticles; and (2) reduction of hydrogen tetrachloroaurate (TCA) into AuNPs. Power loss at LSPR excitation frequency and steady-state temperature maxima at 100?mW continuous laser irradiation showed corresponding increases with respect to the mass of gold introduced into the PDMS films by either method. Measured rates of temperature increase were higher for organic-coated NP, but higher gold content was achieved by reducing TCA, which resulted in larger overall temperature changes in reduced AuNP films.     

Peculiarities of metal oxide nanoparticles obtained in acoustoplasma discharge

Nanoparticles of tungsten, copper, iron, and zinc oxides were synthesized in acoustoplasma discharge. Their size distribution was studied by electron microscopy and laser correlation spectroscopy. Ultrasound was found to narrow significantly the size distribution width of zinc oxide nanoparticles. Water suspensions of zinc oxide nanoparticles showed photoluminescence in red and near infrared spectral ranges, which makes them a promising material for luminescent diagnostics of biological systems.     

Strategies for area-selective deposition of metal nanoparticles on carbon nanotubes and their applications: a review

Journal of Materials Science - Carbon nanotubes (CNTs) have a common use as a nanostructured substrate to support and stabilize metal nanoparticles (MNPs), generating hybrid materials whose...     

Polymer-encapsulated metal nanoparticles: optical, structural, micro-analytical and hydrogenation studies of a composite material

A single-step synthesis route is described for the preparation of a metal-polymer composite in which palladium acetate and meta-amino benzoic acid were used as the precursors for palladium nanoparticles and poly(meta-amino benzoic acid) (PABA). The palladium nanoparticles were found to be uniformly dispersed and highly stabilized throughout the macromolecule matrix. The resultant composite material was characterized by means of different techniques, such as IR and Raman spectroscopy, which provided information regarding the chemical structure of the polymer, whereas electron microscopy images yielded information regarding the morphology of the composite material and the distribution of the metal particles in the composite material. The composite material was used as a catalyst for the ethylene hydrogenation reaction and showed catalytic activity at higher temperatures. TEM studies confirmed the changed environment of the nanoparticles at these temperatures.     

The role of metal nanoparticles and nanonetworks in alloy degradation

Oxide scale, which is essential to protect structural alloys from high-temperature degradation such as oxidation, carburization and metal dusting, is usually considered to consist simply of oxide phases. Here, we report on a nanobeam X-ray and magnetic force microscopy investigation that reveals that the oxide scale actually consists of a mixture of oxide materials and metal nanoparticles. The metal nanoparticles self-assemble into nanonetworks, forming continuous channels for carbon transport through the oxide scales. To avoid the formation of these metallic particles in the oxide scale, alloys must develop a scale without spinel phase. We have designed a novel alloy that has been tested in a high-carbon-activity environment. Our results show that the incubation time for carbon transport through the oxide scale of the new alloy is more than an order of magnitude longer compared with commercial alloys with similar chromium content.     

磁响应性贵金属核/壳纳米复合粒子制备研究进展

磁响应的贵金属核/壳结构复合纳米粒子具有不同于单组分纳米粒子更优越的多重功能,在催化剂、光学材料、生物传感器及生物医学领域具有重要前景。从核/壳结构类型出发,综述了具有磁响应的贵金属核/壳结构纳米复合粒子的化学制备与结构特征,并简要对其应用研究进展做了讨论。     

Control of morphology in inert-gas condensation of metal oxide nanoparticles

We report preparation conditions to obtain different morphologies of as-deposited refractory metal-oxide nanoparticles using inert-gas condensation with CO₂ laser heating. The micrometer-scale morphology of the nanoparticles depends on the specific metal oxide, the buffer gas composition and pressure, and the target-to-substrate distance. These parameters control the extent to which a plume of nonagglomerated nanoparticles can reach a deposition substrate. Buffer gas pressure has the largest influence for a given material, with lower pressures producing a dense columnar morphology and higher pressures resulting in an open networked morphology. An estimate based on the geometry of the gas-phase plume and experimental results for Y₂O₃ nanoparticles produced in 4 Torr N₂ gives a critical concentration of tens of nanoparticles per μm³ for the transition of agglomerates versus isolated nanoparticles reaching a deposition substrate.     

A new route to mass production of metal hydroxide/oxide hydroxide nanoparticles

Aluminum hydroxide/oxide hydroxide nanofibers were self-assembled by hydration of highly activated aluminum powder using no surfactants or templates. The activation was performed by milling aluminum powder with sodium chloride as nano-miller. Transmission electron microscopy images and X-ray diffraction patterns confirm that this method leads to smaller size of aluminum particles (less than 50 nm) and increases the lattice strain. These factors provide conditions under which hydration procedure proceeds until it reaches the core of aluminum particles. The synthesized powder consists of nanofibers with thickness less then 10 nm and average length of 120 nm and specific surface area of 309 m² g⁻¹. The process is convenient, highly efficient and capable to be implemented in mass production. It may be extended to produce hydroxide/oxide hydroxide nanopowders of other metals, as well.     

Reduction mechanism of uniform iron oxide nanoparticles to metal used as recording media

Uniform and stable α-Fe nanoparticles of around 40 nm in width and axial ratios from 5 to 7 have been obtained from hematite (α-Fe₂O₃) without any additive. The precursor was synthesized by forced hydrolysis of a Fe(ClO₄)₃ solution in the presence of urea and different amounts of NaH₂PO₄. These particles have been reduced to metal α-Fe by heating under a hydrogen flow and the best conditions of temperature, hydrogen flow and time to preserve the morphology have been established. There is a minimum temperature (400 °C) and a minimum hydrogen flow (20 l/h) to reduce the hematite particles to metal in a reasonable time (4 h), preserving the size and the shape of the particles. The main change in the material is related to the crystallite size of the metal particles, which increases as the reduction proceeds. A detailed analysis of the magnetic properties of these particles during the reduction process and the influence of the particle axial ratio has been carried out.