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.     

Aniline as a stabilizer for metal nanoparticles

Palladium nanoparticles were synthesized by two different methods, i.e. reflux and γ-radiolysis in the presence of various monomers like aniline, N-ethyl aniline, N-methyl aniline, o-anisidine and o-toluidine as the stabilizing agent for the Pd nanoparticles. UV–Visible spectral analysis reveals that the aniline renders best stability to the Pd nanoparticles up to a period of 96 h. Nanocomposites were synthesized by polymerizing aniline stabilized Pd° nanoparticle solution by using ammonium persulphate as an oxidizing agent. The average particle size of the nanoparticles calculated from X-ray diffraction patterns were ∼24 nm (reflux method) and ∼28 nm (γ-irradiation method). The above results are supported by TEM analysis.     

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.     

Effect of EPR coefficient policy on the production decision in precious metal accessory recycling

This study examines the effect of the extended producer responsibility (EPR) coefficient policy on the production decision between a supplier and a manufacturer in a precious metal accessory recycling supply chain. EPR coefficient is a regulation proposed by the government and enterprises to balance economic profit and EPR behaviour, and refers to the production proportion of recycled products in all serviceable products. Enterprises with a large EPR coefficient have good EPR practice. This study uses the newsvendor model and numerical simulation to study a supply chain system with remanufacturing and reproduction processes. Results show that the optimal recycling mode and the optimal EPR coefficient are always present in precious metal accessory operations. The increasing market demand for recycled products and the improving whole recycling parameters are both effective in enlarging the optimal EPR coefficient. However, the improvement of single or partial recycling parameters (except the market demand parameter) has no effect on the optimal EPR coefficient. The implementation mechanism and applicable conditions of the EPR coefficient policy are also explored. This study indicates that the EPR coefficient policy is an appropriate and effective approach to promote the EPR practice of the Chinese Government.     

Tomato response to metal nanoparticles introduction into the nutrient medium

This study is aimed to explore the capacity of metal nanoparticles (NPs) iron, zinc, copper and their combinations introduced in the Murashige–Skoog (MS) nutrient medium (NM) to affect the growth and development of tomato plants (Solanum lycopersicum L.). NPs were prepared by a flow‐levitation method. Metal NPs were characterised by transmission and scanning electron microscopy, X‐ray phase analysis. Average NPs diameters were: iron – 27.0 nm, zinc – 54.0 nm, copper – 79.0 nm. MS NM was modified by substitution of common metal sulphates by neutral metal NPs instead of salts. Tomato seedlings cultivation on NM MS with NPs instead of salts assures improved seedling parameters (root length and root activity) in comparison with plants grown on standard MS. Venice cultivar tomato seedlings grown on NM with metal NPs demonstrated an increase in: seed germination by 10–180%, root length by 10–20%, and root activity by 10 –125%. After 45 days of cultivation, tomato seedlings were transplanted in a greenhouse and were grown up to the harvest. Effects in seed germination and increase of crop mass depended on metal nature and NPs concentration.Inspec keywords: copper, crops, nanoparticles, scanning electron microscopy, greenhouses, agriculture, nanofabrication, iron, zinc, transmission electron microscopyOther keywords: size 27.0 nm, size 54.0 nm, size 79.0 nm, time 45.0 d, Fe, Zn, Cu, metal nanoparticles, iron, zinc, tomato plants growth, Solanum lycopersicum L., flow‐levitation method, scanning electron microscopy, X‐ray phase analysis, metal sulphates, tomato seedlings cultivation, Murashige‐Skoog nutrient medium, Venice cultivar, copper, transmission electron microscopy, seed germination, greenhouse, seedlings transplantion     

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.     

Green nanochemistry: metal oxide nanoparticles and porous thin films from bare metal powders

A universal, simple, robust, widely applicable and cost-effective aqueous process is described for a controlled oxidative dissolution process of micrometer-sized metal powders to form high-purity aqueous dispersions of colloidally stable 3-8 nm metal oxide nanoparticles. Their utilization for making single and multilayer optically transparent high-surface-area nanoporous films is demonstrated. This facile synthesis is anticipated to find numerous applications in materials science, engineering, and nanomedicine.     

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.     

Transition metal oxide nanoparticles: Potential nano-modifier for rocket propellants

ABSTRACT

TiO₂, ZnO₂, and CrO₂ nanoparticles were prepared by novel quick precipitation method, where transition metal oxides were used as catalyst. All nanoparticles were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM). The average particle size for TiO₂, ZnO₂, and CrO₂ was 44.8, 13.4, and 77.6 nm, respectively. Catalytic properties of these nanomaterials were studied using ammonium perchlorate (AP)/hydroxy-terminated polybutadiene (HTPB) propellant by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). Both experimental results reveal that there is an increase in the thermal decomposition of propellants in the presence of transition metal oxide nanoparticles. Activation energy of high-temperature decomposition (HTD) of propellant with transition metal oxide nanoparticles was calculated by Kissinger equation. Burning rates of propellants were also calculated.     

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...     

Disabling partners in crime: Gold nanoparticles disrupt multicellular communications within the tumor microenvironment to inhibit ovarian tumor aggressiveness

The tumor microenvironment (TME) plays a key role in the poor prognosis of many cancers. However, there is a knowledge gap concerning how multicellular communication among the critical players within the TME contributes to such poor outcomes. Using epithelial ovarian cancer (EOC) as a model, we show how crosstalk among cancer cells (CC), cancer associated fibroblasts (CAF), and endothelial cells (EC) promotes EOC growth. We demonstrate here that co-culturing CC with CAF and EC promotes CC proliferation, migration, and invasion in vitro and that co-implantation of the three cell types facilitates tumor growth in vivo. We further demonstrate that disruption of this multicellular crosstalk using gold nanoparticles (GNP) inhibits these pro-tumorigenic phenotypes in vitro as well as tumor growth in vivo. Mechanistically, GNP treatment reduces expression of several tumor-promoting cytokines and growth factors, resulting in inhibition of MAPK and PI3K-AKT activation and epithelial-mesenchymal transition - three key oncogenic signaling pathways responsible for the aggressiveness of EOC. The current work highlights the importance of multicellular crosstalk within the TME and its role for the aggressive nature of EOC, and demonstrates the disruption of these multicellular communications by self-therapeutic GNP, thus providing new avenues to interrogate the crosstalk and identify key perpetrators responsible for poor prognosis of this intractable malignancy.     

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.     

Rapid room-temperature synthesis of a porphyrinic MOF for encapsulating metal nanoparticles

While metal nanoparticles(NPs)have shown great promising applications as heterogeneous catalysts,their agglomeration caused by thermodynamic instability is detrimental to the catalytic performance.To tackle this hurdle,we successfully prepared a functional and stable porphyrinic metal-organic framework(MOF),PCN-224-RT,as a host for encapsulating metal nanoparticles by direct stirring at room temperature.As a result,Pt@PCN-224-RT composites with well-dispersed Pt NPs can be constructed by introducing pre-synthesized Pt NPs into the precursor solution of PCN-224-RT.Of note,the rapid and simple stirring method in this work is more in line with the requirements of environmental friendly and industrialization compared with traditional solvothermal methods.