One-pot synthesis of Polyindole–Au nanocomposite and its nanoscale electrical properties

Nanosized gold (Au) and polyindole (PIn) composite was prepared via in-situ polymerization of indole, using metal salt chloro-auric acid as an oxidant, in a microemulsion system. The oxidization of indole and the reduction of Au³⁺ ions occurred simultaneously in a single step, which resulted in a core shell structure having a coating of polyindole over monodispersed, size-controlled, highly populated, and stable gold nanoparticles. Indole polymerization governed by chloro-auric acid, was monitored using UV–vis absorption spectroscopy. Nanoscale electrical characterization of polyindole nanocomposite was performed using current-sensing atomic force microscopy. The investigated properties of the composite proved its enormous potential in electronic applications and fabrication of nanoscale organic devices.     

Synthesis and properties of rhenium–polyethylene nanocomposite

New rhenium-containing composites were synthesized by thermodestruction of different rhenium complexes. The composites consist of rhenium-containing nanoparticles stabilized by low-density polyethylene matrix. The structure of composites was characterized by means of TEM, EDS, XRD, EXAFS and EMR. Transmission electron microscope images illustrate that the rhenium-containing nanoparticles are 15.0 ± 0.3 nm in size. The particles consist of Re, Re₂O₇, ReO₃ and ReO₂. In the electrophysical measurements it was found that permittivity and attenuation of microwave radiation correlate with composition of rhenium-containing nanoparticles.     

Synthesis and properties of rhenium–polyethylene nanocomposite

New rhenium-containing composites were synthesized by thermodestruction of different rhenium complexes. The composites consist of rhenium-containing nanoparticles stabilized by low-density polyethylene matrix. The structure of composites was characterized by means of TEM, EDS, XRD, EXAFS and EMR. Transmission electron microscope images illustrate that the rhenium-containing nanoparticles are 15.0 ± 0.3 nm in size. The particles consist of Re, Re₂O₇, ReO₃ and ReO₂. In the electrophysical measurements it was found that permittivity and attenuation of microwave radiation correlate with composition of rhenium-containing nanoparticles.     

Age-hardening by miscibility limit of Au–Pt and Ag–Cu systems in an Au–Ag–Cu–Pt alloy

The age-hardening by miscibility limit of Au–Pt and Ag–Cu systems in an Au–Ag–Cu–Pt alloy was examined by characterizing the hardening behavior, phase transformations and changes in microstructure, and elemental distribution during aging. The hardness increased by the transformation of the parent α₀ phase into the α₁ and metastable AuCu I′ phases, but not by the further transformation of the metastable AuCu I′ phase into the stable AuCu I phase due to the simultaneously initiated lamellar-forming grain boundary reaction. The replacing ratio of matrix by lamellar structure was not directly proportional to the AuCu I phase formation. The relatively high Pt content caused the severe exclusion of Au from the Cu-rich layer of the lamellar structure due to the overlapped miscibility limit of both Au–Pt and Ag–Cu systems.     

Molecular dynamics simulation of SWCNT–polymer nanocomposite and its constituents

Elastic and engineering properties of nanoparticle enhanced composites and their constituents (matrix, reinforcement and interface) are calculated. The nanocomposites considered in this study consist of a single-wall carbon nanotube (SWCNT) embedded in polyethylene matrix. Molecular dynamics simulations are used to estimate the elastic properties of SWCNT, interfacial bonding, polyethylene matrix and composites with aligned and randomly distributed SWCNTs. The elastic properties of bundles with 7, 9, and 19 SWCNTs are also compared using a similar approach. In all simulations, the average density of SWCNT–polymer nanocomposite was maintained in the vicinity of CNTs, to match the experimentally observed density of a similar nanocomposite. Results are found to be in good agreement with experimentally obtained values by other researchers. The interface is an important constituent of CNT–polymer composites, which has been modeled in the present research with reasonable success.     

Synthesis and characterization of cellulose acetate–calcium carbonate hybrid nanocomposite

A hybrid nanocomposite composed of calcium carbonate (CaCO₃) and cellulose acetate (CA) was fabricated by bubbling CO₂ gas into the mixture of CA and Ca(OH)₂ solution. Cellulose acetate–calcium carbonate (CA–CC) nanocomposite was characterized by spectral, thermal and optical methods. FTIR and XRD analysis confirmed the formation of the hybrid nanocomposite and XRD confirmed the formation of CaCO₃ with calcite polymorph. Thermal analysis showed CA–CC nanocomposite has better thermal stability than pristine CA. The CaCO₃ nanoparticles were in sphere shape with 100–1000 nm diameter.     

Electronic structures and related properties of Ag–Au bulks and surfaces

First-principles calculation reveals that the Ag–Au bulks are energetically favorable with negative heats of formation within the entire composition range, and the Ag–Au interaction has a negligible effect on electronic structures of Ag–Au bulks. Moreover, it is found out that surface segregation of Ag atoms could reduce the work function of Ag–Au surfaces to an extent of about 0.13–0.60 eV, and composition as well as surface state would be fundamental factors in determining surface segregation of the Ag–Au system, which could clarify the controversy regarding surface segregation of Ag–Au in the literature.     

Biosynthesis and stabilization of Au and Au–Ag alloy nanoparticles by fungus,Fusarium semitectum

Abstract

Crystallized and spherical-shaped Au and Au–Ag alloy nanoparticles have been synthesized and stabilized using a fungus, F . semitectum in an aqueous system. Aqueous solutions of chloroaurate ions for Au and chloroaurate and Ag⁺ ions (1 : 1 ratio) for Au–Ag alloy were treated with an extracellular filtrate of F . semitectum biomass for the formation of Au nanoparticles (AuNP) and Au–Ag alloy nanoparticles (Au–AgNP). Analysis of the feasibility of the biosynthesized nanoparticles and core–shell alloy nanoparticles from fungal strains is particularly significant. The resultant colloidal suspensions are highly stable for many weeks. The obtained Au and Au–Ag alloy nanoparticles were characterized by the surface plasmon resonance (SPR) peaks using a UV-vis spectrophotometer, and the structure, morphology and size were determined by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and transmission electron microscopy (TEM). Possible optoelectronics and medical applications of these nanoparticles are envisaged.     

Biosynthesis and stabilization of Au and Au–Ag alloy nanoparticles by fungus,Fusarium semitectum

Crystallized and spherical-shaped Au and Au–Ag alloy nanoparticles have been synthesized and stabilized using a fungus, F. semitectum in an aqueous system. Aqueous solutions of chloroaurate ions for Au and chloroaurate and Ag⁺ ions (1 : 1 ratio) for Au–Ag alloy were treated with an extracellular filtrate of F. semitectum biomass for the formation of Au nanoparticles (AuNP) and Au–Ag alloy nanoparticles (Au–AgNP). Analysis of the feasibility of the biosynthesized nanoparticles and core–shell alloy nanoparticles from fungal strains is particularly significant. The resultant colloidal suspensions are highly stable for many weeks. The obtained Au and Au–Ag alloy nanoparticles were characterized by the surface plasmon resonance (SPR) peaks using a UV-vis spectrophotometer, and the structure, morphology and size were determined by Fourier transform infrared spectroscopy (FTIR), x-ray diffraction (XRD), and transmission electron microscopy (TEM). Possible optoelectronics and medical applications of these nanoparticles are envisaged.     

Optical properties and microstructures of Pd-free Ag–Au–Pt–Cu dental alloys

Nine experimental Pd-free Ag–Au–Pt–Cu dental alloys containing 10 at.% Pt and 10–35 at.% Au were prepared and their optical properties and microstructures were investigated by means of spectrophotometric colorimetry, optical microscopy, and electron probe microanalysis. All the alloys were annealed at 850 °C and mirror-polished to observe their reflectance curves in the visible spectrum and three-dimensional color coordinates. All the alloys were composed of a major phase of Ag–Au-rich matrix and a minor and almost colorless Pt–Cu-rich phase. It was found that the color of the alloys was substantially controlled by the Ag–Au-rich matrix and that with increasing Au/Ag atomic ratio from 0.130 to 0.996, the yellow-blue chromaticity index b ^* increased from 8.0 to 14.4, giving a pale yellow color. This systematic increase in yellowness was caused by a continuous shift of the absorption edge of reflectance curve toward longer wavelengths with increasing Au/Ag atomic ratio.     

Antibacterial and tribological properties of TaN–Cu,TaN–Ag,and TaN–(Ag,Cu) nanocomposite thin films

In this study, attempts were made to prepare and characterize TaN–(Cu,Ag) nanocomposite films by using a hybrid approach combining reactive co-sputtering and rapid thermal annealing at various temperatures to induce the formation of soft metal particles in the matrix or on the surface. The films’ properties and their antiwear and antibacteria behaviors were compared with those previously studied TaN–Cu and TaN–Ag films. All three types of TaN–(soft metal) films showed good tribological properties due to the lubricious Ag and/or Cu layers. It was also found that the antibacteria efficiency of TaN–(Ag,Cu) film against either Escherichia coli or Staphylococcus aureus could be much improved, comparing with that of TaN–Ag or TaN–Cu film. The synergistic effect due to the coexistence of Ag and Cu is obvious. The annealing temperature used to develop TaN–(Cu,Ag) films with good antibacterial and antiwear behaviors could be as low as 250 °C. The lowering of the annealing temperature made these films applicable onto low-melting-point materials, such as polymers.     

Wear behavior of Au–ZnO nanocomposite films for electrical contacts

Electrical contact switches require low contact resistance for efficient passage of signals, while withstanding repetitive cycling. Hard gold with alloy additions of Ni, Co, or Ag can increase the wear resistance of Au films, however, this causes a significant decrease in conductivity and alloying elements can segregate during long-term aging leading to property evolution. The current work demonstrates that Au–zinc oxide (ZnO) nanocomposites can create a hard Au coating with a uniform, stable structure under frictional loading. Addition of ZnO particles decreases the grain size and texture of the film by 35 and 40–75 %, respectively, indicating a change in growth behavior of the film. The nanoindentation hardness increased directly with increasing ZnO concentration. Atomic force microscopy examination of wear-tested films demonstrated morphological stability after frictional contact and thus showed the potential for these films to replace current hard Au used on contact terminals.     

Synthesis of Au microwires by selective oxidation of Au–W thin-film composition spreads

Abstract

We report on the stress-induced growth of Au microwires out of a surrounding Au–W matrix by selective oxidation, in view of a possible application as ‘micro-Velcro’. The Au wires are extruded due to the high compressive stress in the tungsten oxide formed by oxidation of elemental W. The samples were fabricated as a thin-film materials library using combinatorial sputter deposition followed by thermal oxidation. Sizes and shapes of the Au microwires were investigated as a function of the W to Au ratio. The coherence length and stress state of the Au microwires were related to their shape and plastic deformation. Depending on the composition of the Au–W precursor, the oxidized samples showed regions with differently shaped Au microwires. The Au₄₈W₅₂ composition yielded wires with the maximum length to diameter ratio due to the high compressive stress in the tungsten oxide matrix. The values of wire length (35 μm) and diameter (2 μm) achieved at the Au₄₈W₅₂ composition are suitable for micro-Velcro applications.     

Pulse plating of Ni–B/WC nanocomposite coating and study of its corrosion and wear resistance

The aim of this study is to investigate the impact of WC content on the properties of the Ni–B/WC nanocomposites deposited by the pulse method. It is obtained that, although by addition of WC nanoparticles to the bath in initial steps (WC 4 and 8 g?l^?1), the grain size was increased and hence mechanical and electrochemical properties got worse, but at the higher amount of WC (WC 12 g?l^?1), due to the formation of the fine and packed structures, the great corrosion and wear resistance was achieved. The corrosion resistance of the Ni–B/WC12 g?l^?1 coating is 59,967?Ω and wear weight loss is 2.1 mg?cm^?2 with the friction coefficient of 0.64.     

Titanium dioxide–cellulose hybrid nanocomposite and its glucose biosensor application

This paper investigates the fabrication of titanium dioxide (TiO₂)–cellulose hybrid nanocomposite and its possibility for a conductometric glucose biosensor. TiO₂ nanoparticles were blended with cellulose solution prepared by dissolving cotton pulp with lithium chloride/N,N-dimethylacetamide solvent to fabricate TiO₂–cellulose hybrid nanocomposite. The enzyme, glucose oxidase (GOx) was immobilized into this hybrid nanocomposite by physical adsorption method. The successful immobilization of glucose oxidase into TiO₂–cellulose hybrid nanocomposite via covalent bonding between TiO₂ and GOx was confirmed by X-ray photoelectron analysis. The linear response of the glucose biosensor is obtained in the range of 1–10 mM. This study demonstrates that TiO₂–cellulose hybrid nanocomposite can be a potential candidate for an inexpensive, flexible and disposable glucose biosensor.     

Synthesis and characterization of mechanically strong carboxymethyl cellulose–gelatin–hydroxyapatite nanocomposite for load-bearing orthopedic application

Novel three-dimensional hybrid polymer–hydroxyapatite nanocomposites have been developed as load-bearing synthetic bone graft through in situ mineralization process, using natural polymers carboxymethyl cellulose (CMC) and gelatin (Gel) as matrix. This process is simple and does not involve any chemical cross-linker. Detailed structural and physicochemical characterization of the samples disclosed that incorporation of gelatin with CMC assists the formation of CMC-Gel polymeric network of new conformational structure through non-covalent interactions (H-bond). The formation of hydroxyapatite (HA) in this polymeric network was occurred in such a fashion that the HA serves as bridging molecule which strengthen the polymeric network more and formed a mechanically strong three-dimensional CMC-Gel-HA nanocomposite. The synthesized CMC-Gel-HA nanocomposites have compressive strength and modulus in the range of 40–86 MPa and 0.4–1.2 GPa, respectively, analogous to human cancellous as well as cortical bone. In vitro cell interaction of the synthesized nanocomposites with osteoblast-like MG-63 cells has been evaluated. Results showed that synthesized CMC-Gel-HA nanocomposite promote cells for high alkaline phosphatase activity and extracellular mineralization. Extracellular mineralization ability of nanocomposite was investigated by alizarin red staining and von Kossa staining. Biodegradable nature and bone apatite formation ability of CMC-Gel-HA nanocomposite under simulated physiological environment were investigated by different characterization processes. Results indicated that the synthesized CMC-Gel-HA nanocomposite has great potential to be used as regenerative bone graft in major load-bearing region.     

Thermal evolution of morphological,optical, and photocatalytic properties of Au–Cu2O–CuO nanocomposite thin film

Plasmonic nanocomposite thin films find exciting applications in environmental remediation and photovoltaics. We report on thermal annealing driven development of morphology, structure and photocatalytic performance of Au–Cu₂O–CuO nanocomposite thin film. Nanocomposite thin film coatings of Au–Cu₂O–CuO, prepared by radio frequency (RF) magnetron co-sputtering, were annealed at different temperatures. Thermal annealing driven evolution of morphology of Au–Cu₂O–CuO nanocomposite was studied by field emission scanning electron microscopy (FESEM), which revealed significant growth in size of nanostructures from 10 nm to 69 nm upon annealing. X-ray diffraction (XRD) together with Raman studies confirmed the nanocomposite nature of Au–Cu₂O–CuO film. UV-visible diffuse reflectance spectroscopy (UV-vis-DRS) studies showed band gap variation from 2.44 eV to 1.8 eV upon annealing at 250 °C. Nanocomposite thin film annealed at 250 °C exhibited superior photocatalytic activity for organic pollutants [methylene blue (MB) and methyl orange (MO)] decomposition. The origins of thermal transformation of morphological, optical and photocatalytic behaviour of the Au–Cu₂O–CuO nanocomposite coating are discussed.

     

Synthesis of nanocomposite powders of γ-alumina-carbon nanotube by sol–gel method

The nanocomposite powders of γ-alumina-carbon nanotube were successfully synthesized by a sol–gel process. The homogeneous mixture of carbon nanotubes and alumina particles was obtained by mixing the carbon nanotubes within alumina solution and followed by heating into gel. The resultant gel was dried and calcined at 200 °C into boehmite-carbon nanotubes composite powders. The mean particle size of synthesized boehmite was of the order of 4 nm. The boehmite-carbon nanotubes composite powders were calcined at different temperatures and XRD investigations revealed that as the amount of carbon nanotube increases, γ- to α-alumina phase transformation is completed at higher temperatures. The specific surface area and mean particle size of resultant nanocomposite powders increased and decreased, respectively by increasing the content of carbon nanotubes.