Bulk gold with hierarchical macro-, micro- and nano-porosity

Millimeter-sized, free-standing gold structures were created with three levels of multiscale porosity. First, macro- and microporosity, which are useful for mass and heat transport within the structure, are formed within an Ag-19 at.% Au alloy by salt powder replication during powder densification and by entrapped gas expansion during sintering, respectively. Nanoporosity, which provides high surface area, is then produced by silver dealloying of these Ag-19 at.% Au foams. The resulting hierarchical gold structures are annealed at 100-800 °C, thus coarsening the ligaments, increasing relative density, and healing cracks produced during dealloying. The first effect weakens the structure, while the other two make it stronger. A bulk Au sample with hierarchical porosity annealed at 600 °C shows good compressive ductility and a strength in agreement with models.     

Evaluation of interactions between functionalised multi-walled carbon nanotubes and ligand-stabilised gold nanoparticles using surface element integration

We report here on the application of Surface Element Integration (SEI) to evaluate the potential energy of interactions between alkane-modified multiwalled carbon nanotubes (MWCNTs) and tetraoctylammonium bromide (TOAB) stabilised gold nanoparticles. The interacting objects are treated as cylinders and spheres, respectively, with corresponding alkyl chains extending perpendicularly from their surfaces. In such case the widely used Derjaguin approximation is invalid. Thus SEI was used to calculate the van der Waals, osmotic and elastic interactions. The results show that it is possible to control the self-assembly process of the gold nanoparticles at the surface of modified MWCNT in terms of size- and type-selectivity.     

Determination of cyanide in wastewaters using modified glassy carbon electrode with immobilized silver hexacyanoferrate nanoparticles on multiwall carbon nanotube

The sensitive determination of cyanide in wastewaters using modified GC electrode with silver hexacyanoferrate nanoparticles (SHFNPs) immobilized on multiwall carbon nanotube (MWCNT) was reported. The immobilization of SHFNPs on MWCNT was confirmed by transmission electron microscopy (TEM). The TEM image showed that the SHFNPs retained the spherical morphology after immobilized on MWCNT. The size of SHFNPs was examined around 27 nm. The GC/MWCNT-SHFNPs was used for the determination of cyanide in borax buffer (BB) solution (pH 8.0). Using square wave voltammetry, the current response of cyanide increases linearly while increasing its concentration from 40.0 nM to 150.0 μM and a detection limit was found to be 8.3 nM (S/N=3). The present modified electrode was also successfully used for the determination of 5.0 μM cyanide in the presence of common contaminants at levels presenting in industrial wastewaters. The practical application of the present modified electrode was demonstrated by measuring the concentration of cyanide in industrial wastewater samples. Moreover, the studied sensor exhibited high sensitivity, good reproducibility and long-term stability.     

Gold nanoparticle/single-walled carbon nanotube film on the surface of glassy carbon electrode and its application

A sensor based on gold nanoparticle/single-walled carbon nanotube film on the surface of glassy carbon electrode is prepared. Electrochemical behavior of adrenaline hydrochloride (AH) on the surface of gold nanoparticle/single-walled carbon nanotube modified glassy carbon electrode is investigated. A simple, sensitive, and inexpensive method for determination of AH is proposed. The oxidation peak currents is proportional to adrenaline hydrochloride concentrations in the range of 0.20 mg L^? 1 to 1.80 mg L^? 1 in 0.1 M phosphate buffer solution of pH 7.3, the detection limit for AH is 0.06 mg L^? 1, and the recoveries are in the range from 100.0 to 110.0% with RSD of 1.2–1.9% (n = 6).     

Preparation, characterization and photocatalytic properties of CdS nanoparticles dotted on the surface of carbon nanotubes

Cadmium sulfide (CdS) nanoparticles dotted on the surface of multiwalled carbon nanotubes (MWCNTs) have been synthesized by the polyol method. The as-prepared materials were characterized by x-ray powder diffraction, transmission electron microscopy, scanning electron microscopy, and Brunauer-Emmett-Teller adsorption analysis. The results indicate that CdS nanoparticles with diameter of 5-8?nm are thickly and uniformly coated on the surface of the MWCNTs. The photodegradation of azo dye using these materials was evaluated by the degradation of Brilliant Red X-3B under visible light. The coated nanotubes show higher photocatalytic activity than both CdS alone and a CdS/activated carbon sample; in addition, there is an optimum content of MWCNTs. The presence of MWCNTs can also hamper the photocorrosion of CdS. The mechanism for the enhancement of MWCNTs on the adsorption and photocatalytic property of CdS is investigated for the first time.     

The effect of surface modification with carbon nanotubes upon the tensile strength and Weibull modulus of carbon fibers

Carbon fibers are widely used as reinforcements in composite materials because of their high specific strength and modulus. Today, a number of ultrahigh strength polyacrylonitrile (PAN)-based (more than 6?GPa), and ultrahigh modulus pitch-based (more than 900?GPa) carbon fibers have been commercially available. In contrast, carbon nanotube (CNT) with the extremely high tensile strength have attracted attention as reinforcements. An interesting technique to modify the carbon fiber is CNT grafting on the carbon fiber surface. CNT-grafted carbon fibers offer the opportunity to add the potential benefits of nanoscale reinforcement to well-established fibrous composites to create micro-nano multiscale hybrid composites. In the present study, the tensile properties of CNT grown on T1000GB PAN- and K13D pitch-based carbon fibers have been investigated. Single filament tensile test at gauge lengths of 1, 5, and 25?mm were conducted. The effect of gauge length on tensile strength and Weibull modulus of CNT-grafted PAN- and pitch-based carbon fibers were evaluated. It was found that grafting of CNT improves the tensile strength and Weibull modulus of PAN- and pitch-based carbon fibers with longer gauge length (≥5?mm). The results also clearly show that for CNT-grafted and as-received PAN- and pitch-based carbon fibers, there is a linear relation between the Weibull modulus and the average tensile strength on log–log scale.     

Corrugation of the external surface of multiwall carbon nanotubes by catalytic oxidative etching and its effect on their decoration with metal nanoparticles

It was established that partial combustion of carbon constituting the walls of multiwall carbon nanotubes (MWCNTs) catalyzed by previously deposited CaCO₃ nanoparticles converts parallel graphene layers in a multiwall structure to aggregates formed by nano-onions with a diameter of 5–12 nm. The areas with positive curvature of graphene layers on the external surface of air-etched MWCNTs played the role of docking stations for nickel nanoparticles inserted by sonochemical deposition after removal of the CaCO₃. The nickel nanoparticles were located exclusively at the tops of the onions. Formation of nanoscale curvature at the MWCNT support surfaces decreased the average size of Ni nanocrystals at similar loading of 50–60 wt% from 8 to 2 nm. Partial catalytic combustion did not change the concentration of surface carbonyl groups measured by titration, which attributes the observed phenomena directly to the corrugation of the MWCNT surfaces. The catalytic tests revealed a significant increase of catalytic activity of supported Ni catalyst due to corrugating of the external surface of the MWCNT support. After oxidative etching of the MWCNTs, the rate of chloroacetophenone hydrogenation measured with a Ni–MWCNT catalyst increased by a factor of 2 without change in selectivity yielding chlorophenylethanol as the main product.     

碳纳米管担载纳米银及其电催化甲醇氧化的研究

以水溶性离聚物聚（苯乙烯磺酸钠-co-丙烯酸）（PSA）接枝多壁碳纳米管为模板,制备了碳纳米管担载纳米银（AgNP@MWNT）,研究了在碱性条件下对甲醇氧化的电催化作用。结果表明接枝在MWNT表面的离聚物PSA有效地控制了AgNP在MWNT表面以2～4nm的尺寸均匀担载,促进了AgNP与MWNT之间的界面相互作用。制备的Ag@MWNT在水中能够稳定地均匀分散,在碱性条件下可有效地电催化甲醇氧化,抗甲醇中毒性能良好。     

A review on the effect of oxide nanoparticles,carbon nanotubes,and their hybrid structure on the toughening of epoxy nanocomposites

Journal of Materials Science - Epoxy-based polymer nanocomposite is an advanced and high-performance material with numerous applications in automobiles, railways, aerospace, and construction...     

Direct electrochemistry for the imidazole complex of microperoxidase-11 in dimethyl sulfoxide solution at naked electrode substrates including glassy carbon, gold, and platinum

The effect of the total water content on the persistence and rate of direct heterogeneous electron transfer between the imidazole complex of microperoxidase-11 (im-MP-11) and naked gold, platinum, and glassy carbon (GC) in dimethyl sulfoxide (DMSO) solutions containing 0.1 M tetra-n-butylammonium perchlorate was investigated using cyclic voltammetry. Electron transfer between im-MP-11 and Au, Pt, and GC has been found to be persistent for more than 1 h and at least quasi-reversible [k(s)' = (8.7 ± 0.1) × 10(-4) cm/s (Au), k(s)' = (7.2 ± 1.3) × 10(-4) cm/s (Pt), and k(s)' = (5.7 ± 1.0) × 10(-4) cm/s (GC)] in dimethyl sulfoxide containing an absolute water content between 0.1 and 1.8%. The heterogeneous electron transfer rate constant is independent of the total water content of the DMSO solution when between 0.1 and 1.8% water is present.     

Quantitative detection of individual cleaved DNA molecules on surfaces using gold nanoparticles and scanning electron microscope imaging

Single-nucleotide polymorphisms (SNPs) are the most frequent type of human genetic variation. Recent work has shown that it is possible to directly analyze SNPs in unamplified human genomic DNA samples using the surface-invasive cleavage reaction followed by rolling circle amplification (RCA) labeling of the cleavage products. The individual RCA amplicon molecules were counted on the surface using fluorescence microscopy. Two principal limitations of such single-molecule counting are the variability in the amplicon size, which results in a large variation in fluorescence signal intensity from the dye-labeled DNA molecules, and a high level of background fluorescence. It is shown here that an excellent alternative to RCA labeling is tagging with gold nanoparticles followed by imaging with a scanning electron microscope. Gold nanoparticles have a uniform diameter (15 +/- 0.5 nm) and provide excellent contrast against the background of the silicon substrate employed. Individual gold nanoparticles are readily counted using publicly available software. The results demonstrate that the labeling efficiency is improved by as much as approximately 15-fold, and the signal-to-noise ratio is improved by approximately 4-fold. Detection of individual cleaved DNA molecules following surface-invasive cleavage was linear and quantitative over 3 orders of magnitude in amount of target DNA (10(-18)-10(-15) mol).     

Highly conducting poly(methyl methacrylate)/carbon nanotubes composites: Investigation on their thermal, dynamic-mechanical, electrical and dielectric properties

Nanocomposites of poly(methyl methacrylate) (PMMA) containing various multi-walled carbon nanotubes (MWCNT) contents were prepared using melt mixing. Several techniques were employed to study the influence of the MWCNT addition on the thermal, mechanical, electrical and dielectric properties of the PMMA matrix. The electrical percolation threshold (p_c) was found to be 0.5 vol.% by performing AC and DC conductivity measurements. Significantly high conductivity levels (σ_dc) were achieved: σ_dc exceeds 10⁻² S/cm already at 1.1 vol.%, the criterion for EMI shielding (σ_dc > 10⁻¹ S/cm) is fulfilled at 2.9 vol.%, and the highest loaded sample (5.2 vol.%) gave a maximum value of 0.5 S/cm. Dielectric relaxation spectroscopy measurements in broad frequency (10⁻¹−10⁶ Hz) and temperature ranges (−150 to 170 °C) indicated weak polymer-filler interactions, in consistency with differential scanning calorimetry and dynamic-mechanical analysis findings. Weak polymer-filler interactions and absence of crystallinity facilitate the achievement of high conductivity levels in the nanocomposites.     

X-ray computed tomography imaging of a tumor with high sensitivity using gold nanoparticles conjugated to a cancer-specific antibody via polyethylene glycol chains on their surface

Contrast agents are often used to enhance the contrast of X-ray computed tomography (CT) imaging of tumors to improve diagnostic accuracy. However, because the iodine-based contrast agents currently used in hospitals are of low molecular weight, the agent is rapidly excreted from the kidney or moves to extravascular tissues through the capillary vessels, depending on its concentration gradient. This leads to nonspecific enhancement of contrast images for tissues. Here, we created gold (Au) nanoparticles as a new contrast agent to specifically image tumors with CT using an enhanced permeability and retention (EPR) effect. Au has a higher X-ray absorption coefficient than does iodine. Au nanoparticles were supported with polyethylene glycol (PEG) chains on their surface to increase the blood retention and were conjugated with a cancer-specific antibody via terminal PEG chains. The developed Au nanoparticles were injected into tumor-bearing mice, and the distribution of Au was examined with CT imaging, transmission electron microscopy, and elemental analysis using inductively coupled plasma optical emission spectrometry. The results show that specific localization of the developed Au nanoparticles in the tumor is affected by a slight difference in particle size and enhanced by the conjugation of a specific antibody against the tumor.     

Phytochemicals-mediated green synthesis of gold nanoparticles using Pterocarpus santalinus L. (Red Sanders) bark extract and their antimicrobial properties

In the present study, phytochemicals-mediated rapid, stable and eco-friendly synthesis of gold nanoparticles (GNPs) using Pterocarpus santalinus L. (Red Sanders) bark extract is reported. The powerful characteristics of different phytochemicals present in P. santalinus L. bark prompted us to determine their efficacy in the bio-reduction of gold chloride trihydrate to the corresponding GNPs. The biosynthesis of GNPs was investigated at the physiological condition (pH?=?7.4). The synthesized GNPs were characterized by UV–visible spectroscopy by measuring the peak in the range of 400–700?nm. The GNPs synthesized at physiological conditions revealed surface plasmon resonance (SPR) at 545?nm. The crystalline nature of GNPs was confirmed by using x-ray diffraction (XRD), and the functional groups adhered on the surface of the GNPs were analyzed by Fourier Transform Infrared spectroscopy (FTIR). Transmission Electron Microscopy (TEM) analysis showed spherical GNPs in the size range of 13–26?nm. The synthesized GNPs exhibited antibacterial activity against Gram-positive and Gram-negative bacterial strains.     

3D printing of ABS Nanocomposites. Comparison of processing and effects of multi-wall and single-wall carbon nanotubes on thermal,mechanical and electrical properties

The following paper reports on a comparative study of the effects of two types of carbon nanotubes,namely multiwall(MWCNT) and single-wall(SWCNT) carbon nanotube, on the properties of 3D-printed parts produced with acrylonitrile-butadiene-styrene(ABS) nanocomposites with various CNT loadings of5-10 wt.%. Quasi-static tensile properties and Vicat softening temperature of 3D-printed parts were enhanced with the increasing CNT content. The highest enhancement in tensile properties was observed for ...     

Dielectric, magnetic, and microwave absorbing properties of multi-walled carbon nanotubes filled with Sm2O3 nanoparticles

This study investigates the dielectric, magnetic, and microwave absorbing properties of Sm₂O₃-filled multi-walled carbon nanotubes (MWCNTs) synthesized by wet chemical method. The complex permittivity and permeability were measured at a microwave frequency range of 2-18 GHz. Sm₂O₃ nanoparticles encapsulated in the cavities enhance the magnetic loss of MWCNTs. The calculated results indicate that the bandwith of absorbing peak of the modified MWCNTs is much broader than that of unfilled MWCNTs. The maximum reflectivity (R) is about − 12.22 dB at 13.40 GHz and corresponding bandwidth below − 5 dB is more than 5.11 GHz. With the increase of thickness, the peak of R shifts to lower frequency, and multiple absorbing peaks appear, which helps to broaden microwave absorbing bandwidth.     

Comparison of different surface modification techniques for electrodes by means of electrochemistry and micro synchrotron radiation X-ray fluorescence. dimerization of cobalt(II) tetrasulfonated phthalocyanine and its influence on the electrodeposition on gold surfaces

This paper compares different electrochemical surface modification techniques with special attention to the immobilization of cobalt(II) tetrasulfonated phthalocyanine tetrasodium salt (Co(II)TSPc) on gold electrodes. Electrochemical and synchrotron radiation X-ray fluorescence (SR-XRF) microbeam analysis were performed in order to compare the amount of adsorbed CoTSPc onto the gold electrode and to determine the level of uniformity of the deposited layer. The nondestructive, quantitative characterization of CoTSPc deposition on gold electrodes by means of scanning SR-XRF on the microscopic scale has never been described before. The described methodology can be in general used for thin-film characterization. Depending on the degree of dimerization of the CoTSPc molecules, different electrochemical behavior is observed.     

Molecularly imprinted Au nanoparticles composites on Au surfaces for the surface plasmon resonance detection of pentaerythritol tetranitrate, nitroglycerin, and ethylene glycol dinitrate

Molecularly imprinted Au nanoparticles (NPs) composites are generated on Au-coated glass surfaces. The imprinting process involves the electropolymerization of thioaniline-functionalized Au NPs (3.5 nm) on a thioaniline monolayer-modified Au surface in the presence of a carboxylic acid, acting as a template analogue for the respective explosive. The exclusion of the imprinting template from the Au NPs matrix yields the respective imprinted composites. The binding of the analyte explosives to the Au NPs matrixes is probed by surface plasmon resonance spectroscopy, SPR, where the electronic coupling between the localized plasmon of the Au NPs and the surface plasmon wave leads to the amplification of the SPR responses originating from the dielectric changes of the matrixes upon binding of the different explosive materials. The resulting imprinted matrixes reveal high affinities and selectivity toward the imprinted explosives. Using citric acid as an imprinting template, Au NPs matrixes for the specific analysis of pentaerythritol tetranitrate (PETN) or of nitroglycerin (NG) were prepared, leading to detection limits of 200 fM and 20 pM, respectively. Similarly, using maleic acid or fumaric acid as imprinting templates, high-affinity sensing composites for ethylene glycol dinitrate (EGDN) were synthesized, leading to a detection limit of 400 fM for both matrixes.     

Biochemical synthesis of gold nanoparticles from leaf protein of Nicotiana tabacum L. cv. xanthi and their physiological,developmental, and ROS scavenging responses on tobacco plant under stress conditions

The stress conditions imposed by the impact of metal and non‐metal oxide nanoparticles over plant systems enhances the synthesis of reactive oxygen species (ROS), resulting in oxidative damage at cellular level. The objective of this study was to synthesise the gold nanoparticles (GNps) from the leaves protein of Nicotiana tabacum L. cv. xanthi, its characterisation, and response on plant physiology and ROS scavenging activity on plants after exposure to different stresses. The authors have treated N. tabacum L. cv. xanthi plants with 100, 200, 300, 400, and 500 ppm biochemically synthesised GNps and examined physiological as well as biochemical changes. Results showed that biochemically synthesised GNps exposure significantly increased the seed germination (P  < 0.001), root (P  < 0.001), shoot growth (P  < 0.001), and antioxidant ability (P  < 0.05) of plants depending on bioengineered GNPs concentrations. Low concentrations (200–300 ppm) of GNps boosted growth by ∼50% and significantly increase in photosynthetic parameters such as total chlorophyll content (P  < 0.05), membrane ion leakage (P  < 0.05) as well as malondialdehyde (P  < 0.05) content with respect to untreated plants under stress conditions. The high concentration (400–500 ppm) of GNps affected these parameters in a negative manner. The total antioxidant activity was also elevated in the exposed plants in a dose‐dependent manner.Inspec keywords: toxicology, nanoparticles, membranes, biotechnology, oxidation, proteins, tobacco industryOther keywords: biochemical synthesis, gold nanoparticles, leaf protein, tobacco plant, stress conditions, nonmetal oxide nanoparticles, reactive oxygen species, oxidative damage, leaves protein, plant physiology, ROS scavenging activity, xanthi plants, biochemical changes, nicotiana tabacum L. cv. xanthi