Alumina and Silica based Epoxy Nano-composites for Electrical Insulation

Plain epoxy resins or resin impregnated cellulose have found application as electrical insulation in power equipment. In the past, their performance was improved by the use of inorganic oxide fillers of microscopic dimensions. In the recent past nano-particle doped epoxy insulation came into use with a view to further enhance the dielectric properties. This paper reports dielectric investigations into epoxy nano-composites based on a class of metal oxides, Al2O3 and SiO2. In particular, consideration has been given to the partial discharge performance and electrical breakdown under different voltage profiles as a function of the volumetric composition of the nano-particles in epoxy resin.

Optical bio-sensing devices based on etched fiber Bragg gratings coated with carbon nanotubes and graphene oxide along with a specific dendrimer

We demonstrate that etched fiber Bragg gratings (eFBGs) coated with single walled carbon nanotubes (SWNTs) and graphene oxide (GO) are highly sensitive and accurate biochemical sensors. Here, for detecting protein concanavalin A (Con A), mannose-functionalized poly(propyl ether imine) (PETIM) dendrimers (DMs) have been attached to the SWNTs (or GO) coated on the surface modified eFBG. The dendrimers act as multivalent ligands, having specificity to detect lectin Con A. The specificity of the sensor is shown by a much weaker response (factor of similar to 2500 for the SWNT and similar to 2000 for the GO coated eFBG) to detect non specific lectin peanut agglutinin. DM molecules functionalized GO coated eFBG sensors showed excellent specificity to Con A even in the presence of excess amount of an interfering protein bovine serum albumin. The shift in the Bragg wavelength (Delta lambda(B)) with respect to the lambda(B) values of SWNT (or GO)-DM coated eFBG for various concentrations of lectin follows Langmuir type adsorption isotherm, giving an affinity constant of similar to 4 x 10(7) M-1 for SWNTs coated eFBG and similar to 3 x 10(8) M-1 for the GO coated eFBG. (C) 2014 Elsevier B.V. All rights reserved.

Enhanced photocatalytic efficiency of AuPd nanoalloy decorated ZnO-reduced graphene oxide nanocomposites

Inhibition of electron-hole pair recombination is the most desirable solution for stimulating photocatalytic activity in semiconductor nanostructures. To implement this, herein we study the photocatalytic efficiency of elemental Au, Pd and bimetallic AuPd nanoalloy decorated pristine and reduced graphene oxide (RGO) hybridized ZnO nanorods for degrading rhodamine 6G (R6G) dye. Fabrication of Au, Pd and AuPd nanoalloy on pristine and RGO modified ZnO nanorods is simple and more importantly surfactant or polymer free. AuPd nanoalloyed ZnO-RGO nanocomposites exhibit higher photocatalytic activity for degrading dye than both Au and Pd hybridized ones, indicating the promising potential of bimetallic nanoalloys over elemental components. A non-monotonic dependence on the composite composition was found by analyzing photodegradation efficiency of a series of ZnO-RGO-AuPd hybrid nanostructures with different weight percentages of RGO. The hybrid nanostructure ZnO-RGO (5 wt%)-AuPd (1 wt%) exhibits highest photodegradation efficiency (similar to 100% degradation in 20 min) with an improvement in rate constant (k) by a factor of 10 compared to that of the ZnO-RGO nanocomposite. The enhancement of the photocatalytic activity is attributed to the better separation of photogenerated charge carriers in photocatalysts thereby suggesting possible usefulness in a broad range of applications, such as sensing, photocatalysis and solar energy conversion.

Multifunctional magnetic reduced graphene oxide dendrites: Synthesis, characterization and their applications

In this paper, for the first time, we have reported the novel synthesis of reduced graphene oxide (r-GO) dendrite kind of nanomaterial. The proposed r-GO dendrite possesses multifunctional properties in various fields of sensing and separation. The dendrite was synthesized by chemical reaction in different steps. Initially, the r-GO sheet was conjugated with silane group modified magnetic nanoparticle, resulting in nanoparticle decorated r-GO. The above r-GO sheet was further reacted with a new r-GO sheet, resulting in the formation of r-GO dendrite type of structure. Multifunctional behavior of this r-GO dendrite structure was studied by different methods. First, magnetic properties were studied by vibrating sample magnetometer (VSM) and it was found that dendrite structure shows good magnetic susceptibility (180.2 emu/g). The proposed r-GO dendrite also shows a very good antibacterial behavior for Escherichia coli and excellent electrochemical behavior towards ferrocyanide probe molecule. Along with these, it also acts as a substrate for the synthesis of molecularly imprinted polymer for europium metal ion, a lanthanide. The proposed imprinted sensor shows a very high selectivity and sensitivity for europium metal ion (limit of detection= 0.019 mu g L-1) in aqueous as well as real samples. (C) 2015 Elsevier B.V. All rights reserved.

A unique strategy towards high dielectric constant and low loss with multiwall carbon nanotubes anchored onto graphene oxide sheets

Multiwall carbon nanotubes (MWNTs) were anchored onto graphene oxide sheets (GOs) via diazonium and C-C coupling reactions and characterized by spectroscopic and electron microscopic techniques. The thus synthesized MWNT-GO hybrid was then melt mixed with 50/50 polyamide6-maleic anhydride-modified acrylonitrile-butadiene-styrene (PA6-mABS) blend to design materials with high dielectric constant (30) and low dielectric loss. The phase morphology was studied by SEM and it was observed that the MWNT-GO hybrid was selectively localized in the PA6 phase of the blend. The 30 scales with the concentration of MWNT-GO in the blends, which interestingly showed a very low dielectric loss (< 0.2) making them potential candidate for capacitors. In addition, the dynamic storage modulus scales with the fraction of MWNT-GO in the blends, demonstrating their reinforcing capability as well.

Effect of Pt doping on the gas sensing properties of porous chromium oxide films through a kinetic response analysis approach

The effect of doping trace amounts of noblemetals (Pt) on the gas sensing properties of chromium oxide thin films, is studied. The sensors are fabricated by depositing chromium oxide films on a glass substrate using a modified spray pyrolysis technique and characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. The films are porous and nanocrystalline with an average crystallite size of similar to 30 nm. The typical p-type conductivity arises due to the presence of Cr vacancies, formed as a result of Cr non-stoichiometry, which is found to vary upon Pt doping. In order to analyze the effect of doping on the gas sensing properties, we have adopted a kinetic response analysis approach, which is based on Langmuir Adsorption isotherm (LA) theory. The sensor response is analyzed with equations obtained from LA theory and time constants as well as energies of adsorption-desorption are evaluated. It is seen that, Pt doping lowers the Schottky barrier height of the metal oxide semiconductor sensor from 222 meV to 172 meV. Subsequently the reduction in adsorption and desorption energies led to enhancement in sensor response and improvement in the kinetics of the sensor response i.e. the response time as well as recovery times of the sensor.

Synthesis of cadmium oxide and carbon nanotube based nanocomposites and their use as a sensing interface for xanthine detection

Xanthine oxidase (XOD) extracted from bovine milk was immobilized covalently via N-ethyl-N'-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxy succinimide (NHS) chemistry onto cadmium oxide nanoparticles (CdO)/carboxylated multiwalled carbon nanotube (c-MWCNT) composite film electrodeposited on the surface of an Au electrode. The nanocomposite modified Au electrode was characterized by Fourier transform infrared (FTIR), cyclic voltammetry (CV), scanning electron microscopy (SEM) and electrochemical impedance spectroscopy (EIS) before and after immobilization of XOD. Under optimal operation conditions (25 degrees C, + 0.2 V vs. Ag/AgCl, sodium phosphate buffer, pH 7.5), the following characteristics are attributed to the biosensor: linearity of response up to xanthine concentrations of 120 mu M, detection limit of 0.05 mu M (S/N = 3) and a response time of at most 4 s. After being used 100 times over a period of 120 days, only 50% loss of the initial activity of the biosensor was evaluated when stored at 4 degrees C. The fabricated biosensor was successfully employed for the determination of xanthine in fish meat.

Enhancing the mechanical and biological performance of a metallic biomaterial for orthopedic applications through changes in the surface oxide layer by nanocrystalline surface modification

Nanostructured metals are a promising class of biomaterials for application in orthopedics to improve the mechanical performance and biological response for increasing the life of biomedical implants. Surface mechanical attrition treatment (SMAT) is an efficient way of engineering nanocrystalline surfaces on metal substrates. In this work, 316L stainless steel (SS), a widely used orthopedic biomaterial, was subjected to SMAT to generate a nanocrystalline surface. Surface nanocrystallization modified the nature of the oxide layer present on the surface. It increased the corrosion-fatigue strength in saline by 50%. This increase in strength is attributed to a thicker oxide layer, residual compressive stresses, high strength of the surface layer, and lower propensity for intergranular corrosion in the nanocrystalline layer. Nanocrystallization also enhanced osteoblast attachment and proliferation. Intriguingly, wettability and surface roughness, the key parameters widely acknowledged for controlling the cellular response remained unchanged after nanocrystallization. The observed cellular behavior is explained in terms of the changes in electronic properties of the semiconducting passive oxide film present on the surface of 316L SS. Nanocrystallization increased the charge carrier density of the n-type oxide film likely preventing denaturation of the adsorbed cell-adhesive proteins such as fibronectin. In addition, a net positive charge developed on the otherwise neutral oxide layer, which is known to facilitate cellular adhesion. The role of changes in the electronic properties of the oxide films on metal substrates is thus highlighted in this work. This study demonstrates the advantages of nanocrystalline surface modification by SMAT for processing metallic biomaterials used in orthopedic implants.

High performance sol-gel spin-coated titanium dioxide dielectric based MOS structures

High-kappa TiO2 thin films have been fabricated using cost effective sol-gel and spin-coating technique on p-Si (100) wafer. Plasma activation process was used for better adhesion between TiO2 films and Si. The influence of annealing temperature on the structure-electrical properties of titania films were investigated in detail. Both XRD and Raman studies indicate that the anatase phase crystallizes at 400 degrees C, retaining its structural integrity up to 1000 degrees C. The thickness of the deposited films did not vary significantly with the annealing temperature, although the refractive index and the RMS roughness enhanced considerably, accompanied by a decrease in porosity. For electrical measurements, the films were integrated in metal-oxide-semiconductor (MOS) structure. The electrical measurements evoke a temperature dependent dielectric constant with low leakage current density. The Capacitance-voltage (C-V) characteristics of the films annealed at 400 degrees C exhibited a high value of dielectric constant (similar to 34). Further, frequency dependent C-V measurements showed a huge dispersion in accumulation capacitance due to the presence of TiO2/Si interface states and dielectric polarization, was found to follow power law dependence on frequency (with exponent `s'=0.85). A low leakage current density of 3.6 x 10(-7) A/cm(2) at 1 V was observed for the films annealed at 600 degrees C. The results of structure-electrical properties suggest that the deposition of titania by wet chemical method is more attractive and cost-effective for production of high-kappa materials compared to other advanced deposition techniques such as sputtering, MBE, MOCVD and AID. The results also suggest that the high value of dielectric constant kappa obtained at low processing temperature expands its scope as a potential dielectric layer in MOS device technology. (C) 2015 Elsevier Ltd. All rights reserved.

Amine Functionalized polyaniline grafted to exfoliated graphite oxide: Synthesis, characterization and multi-element sensor studies

An amine functionalized polyaniline (AMPANI) derivative has been grafted onto exfoliated graphite oxide (EGO). The synthesis involved the in-situ chemical oxidative polymerization of functionalized aniline monomer in the presence of EGO with diaminobenzene acting as a bridging ligand to yield EGAMPANI. The synthesized compound was characterized by FT-IR and FT-Raman spectroscopy as well as thermogravimetric and X-ray diffraction analysis. The EGAMPANI was then used to modify a carbon paste electrode (CPE), which was applied for multi-elemental sensing of Pb2+, Cd2+ and Hg2+ ions using differential pulse anodic stripping voltammetty. The limits of detection achieved using the EGAMPANI modified CPE were 22 x 10(-6) M for Hg2+ ion, 1.2 x 10(-6) M for Cd2+ ion and 9.8 x 10(-7) M for Pb2+ ion. (C) 2015 Elsevier B.V. All rights reserved.

Optical and Morphological Properties of Sol Gel derived Titanium dioxide Films

Titanium oxide (Titania) thin films were synthesized on different substrates via the sol-gel dip-coating method using alkoxide solution. Some selected samples were also prepared with different percentage of Lead (Pb). The influence of Pb addition in precursor sol on the optical properties of titanium dioxide thin films was studied. The optical transmittance in the visible region has increased with increase in weight percentage of lead. The refractive index was slightly decreased with Pb addition. Crystallization of these coatings was achieved through thermal annealing at temperatures above 400 degrees C. The structural properties and surface morphology of the crystallized coatings were studied by Scanning Electron Microscopy. Increase in average grain size from 250 nm to 350 nm with increase in Pb concentration is observed. Films were appeared to more coarse with increase in Pb addition. An increase in Pb addition resulted increase in average roughness from 12 nm to 25 nm.

Unimpeded permeation of water through biocidal graphene oxide sheets anchored on to 3D porous polyolefinic membranes

3D porous membranes were developed by etching one of the phases (here PEO, polyethylene oxide) from melt-mixed PE/PEO binary blends. Herein, we have systematically discussed the development of these membranes using X-ray micro-computed tomography. The 3D tomograms of the extruded strands and hot-pressed samples revealed a clear picture as to how the morphology develops and coarsens over a function of time during post-processing operations like compression molding. The coarsening of PE/PEO blends was traced using X-ray micro-computed tomography and scanning electron microscopy (SEM) of annealed blends at different times. It is now understood from X-ray micro-computed tomography that by the addition of a compatibilizer (here lightly maleated PE), a stable morphology can be visualized in 3D. In order to anchor biocidal graphene oxide sheets onto these 3D porous membranes, the PE membranes were chemically modified with acid/ethylene diamine treatment to anchor the GO sheets which were further confirmed by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and surface Raman mapping. The transport properties through the membrane clearly reveal unimpeded permeation of water which suggests that anchoring GO on to the membranes does not clog the pores. Antibacterial studies through the direct contact of bacteria with GO anchored PE membranes resulted in 99% of bacterial inactivation. The possible bacterial inactivation through physical disruption of the bacterial cell wall and/or reactive oxygen species (ROS) is discussed herein. Thus this study opens new avenues in designing polyolefin based antibacterial 3D porous membranes for water purification.