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      Volume 40, Issue 2

      April 2017,   pages  253-425

    • Electrical and optical properties of ZnO–WO$_3$ nanocomposite and its application as a solid-state humidity sensor


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      This study reports the humidity sensing characteristics of ZnO–WO$_3$ nanocomposite. Pellet samples of 0–5 weight% ZnO in WO$_3$ were sintered from 300 to 600$^{\circ}$C. When exposed to humidity, the resistance of the sensing samples was found to decrease with increase in relative humidity (RH). Five percent ZnO-doped WO$_3$ showed maximum sensitivity of 20.95 M$\Omega$/%RH in 15–95% RH range. Sensor parameters like reproducibility, aging, hysteresis, response and recovery times were also studied. Sensing mechanism is discussed in terms of sintering temperature, composition and crystallite size of the sensing element. It was observed that sensing mechanism is strongly based on annealing temperature and percentage of doping. The sensing samples have also been investigated by X-ray diffraction, scanning electron microscope (SEM) and Raman spectroscopy. The crystalline size of the sample was identified by powder X-Ray Diffraction data. The SEM analysis was used to study the surface morphology. The structure, phase and the degree of crystallinity of the materials were examined by Raman spectroscopy.

    • Design and development of sustained-release glyburide-loaded silica nanoparticles


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      The aim of this study was to develop sustained-release glyburide-loaded silica nanoparticles. Silica nanoparticles were synthesized by the sol–gel method using tetra-ethyl ortho-silane as a precursor. Glyburide was successfully entrapped in synthesized silica nanoparticles. To identify the effect of independent variables (concentration of silica and concentration of glyburide) on encapsulation efficiency and drug release (dependent variables), 3$^2$ (three level-two factors) response surface methodology was employed. Silica nanoparticles and glyburide-loaded silica nanoparticles were characterized by scanning electron microscopy, BET surface area, X-ray diffraction andFourier transformed infrared spectroscopy. The optimum values of encapsulation efficiency and drug release were 70.21 and 87.8% over 24 h, respectively; these values agree well with predicted values obtained by response surfacemethodology. Glyburide-loaded silica nanoparticles were successfully prepared without any incompatibility and seem to be promising for sustained-release drug delivery application and better patient compliance.

    • Anatase–CMK-3 nanocomposite development for hydrogen uptake and storage


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      The nanometric carbon CMK-3 modified with TiO$_2$ in anatase phase was synthesized and applied to energy uptake and storage. TiO$_2$ nanoclusters are important for hydrogen energy harvesting. The creation of porousstructures or large surface with TiO$_2$ nanoclusters inside can potentially face the challenge of improving their efficiency. In the present work, we report the synthesis and characterization of TiO$_2$–CMK-3 material assembled fromanatase nanoparticles dispersed in the nanometric carbon CMK-3. The resulting nanocomposite was characterized by X-ray diffraction, Raman spectroscopy, transmission electron microscopy, X-ray photoelectron spectroscopy,energy-dispersive X-ray spectroscopy and N$_2$ adsorption–desorption analysis. The newly synthesized hybrid composites exhibited significantly enhanced H$_2$ storage, in which CMK-3-ordered porous carbon modified with anatase nanoclusters proved to be a material for hydrogen uptake. The nanoparticles of anatase ($\sim$5 nm) incorporated ontoCMK-3 showed higher hydrogen uptake at low and high pressures (2.9wt% of H$_2$ sorption at 10 bar and 77 K) thanCMK-3. The approach includes a discussion of H2 adsorption process and storage properties.

    • Investigating the tension load of rubber composites by impact dynamic testing


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      This work deals with establishing the tension load by impact dynamic testing of rubber composite conveyor belts. The value of tension load affects the shape of the used impactor and use of a support system as well as the weight of the ram and the impact height. An increase in the allowable stress when the belt is tensioned was examined during the test, to determine the effect of impact on the tension load. The obtained values of tension load are assessed using basic mathematical and statistical methods. Using the Design of Experiments method, factors that significantly affect the value of the tension load are identified.

    • Synthesis, structure and Hirshfeld surface analysis, vibrational and DFT investigation of (4-pyridine carboxylic acid) tetrachlorocuprate (II) monohydrate


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      The new organic–inorganic hybrid compound [C$_6$H$_6$NO$_2$]$_2$CuCl$_4$$\cdot$H$_2$O has been grown from an aqueous mixture by the solvent evaporation method. X-ray diffraction, Hirshfeld surface analysis, FT-IR and FT-Raman spectroscopy were applied to characterize the composition and crystal structure of the complex. It is crystallized in a triclinic system ($P\bar{1}$ space group). The structure of this compound might be described as layered with two parallel anionic and cationic layers. The first layer is composed of isolated square planar [CuCl4]2− and the second layerof [C$_6$H$_6$NO$_2$]$^{2+}$. The water molecule is placed between the layers formed by organic cations along the $b$ axis. Network hydrogen-bonding and $\pi–\pi$ interactions lead to the formation of a three-dimensional architecture. Hirshfeld surface analysis for visually analysing intermolecular interactions in crystal structures employing molecular surfacecontours and 2D fingerprint plots has been used to scrutinize molecular shapes. The vibration properties of this structure were studied by IR spectroscopy and Raman scattering. Vibration spectra were also calculated theoreticallyby means of Gaussian 03 package of programs within the density functional theory (DFT) framework using the B3LYP/LanL2DZ level of theory. To sum up, good consistency is found between the calculated results on onehand and the IR and Raman spectra and experimental structure on the other. This study confirms the presence of the organic cations [C$_6$H$_6$NO$_2$]$^{2+}$, the inorganic anions [CuCl$_4$]$^{2−}$ and H$_2$O.

    • Reduced-graphene-oxide-and-strontium-titanate-based double-layered composite: an efficient microwave-absorbing material


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      Microwave-absorbing materials based on reduced graphene oxide (r-GO)/ strontium titanate were prepared by embedding in epoxy matrix. R-GO and strontium titanate were synthesized and characterized before composite fabrication. Microstructures of the constituent elements were studied by scanning electron microscopy and X-ray diffraction (XRD). Microwave absorption capabilities of the composite absorbers were investigated using a Vector Network Analyser in the range 8–12 GHz. A maximum reflection loss of $−$7.5 and $−$16.4 dB was obtained at 9.3 and 12.08 GHz, respectively, for 2% (w/w) r-GO-loaded epoxy composites. A maximum attenuation of $−$12.8 dB at 9.3 GHz was obtained for the strontium titanate/epoxy composite. However, double-layer composite with r-GO/strontium titanate/epoxy composition showed the maximum reflection loss of $−$15.1 dB at 9.47 GHz and $−$9.65 dB at 12.3 GHz. All the results are discussed in terms of complex permeability and permittivity. The study revealed that intrinsic conductivity and polarization of the r-GO particles and dielectric polarization of the strontium titanate within epoxy matrix contribute to the microwave absorption.

    • Mechanical and morphological investigation of virgin polyethylene and silver nanoparticle-loaded nanocomposites film: comprehensive analysis of kinetic models for non-isothermal crystallization


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      This research was accomplished to examine the mechanical, morphological and crystallization kinetics study of polyethylene/silver nanoparticles (Ag-NPs) nanocomposite films. In this research, low-density polyethylene (LDPE) nanocomposite films were prepared containing Ag-NPs using maleic-anhydride-grafted low-density polyethylene (LDPE-g-MAH) as a compatibilizer by the melt mixing process. From mechanical property evaluation, it is revealed that the LDPE/LDPE-g-MAH/Ag-NPs nanocomposite films showed decreased tensile strength as compared with virgin LDPE matrix. Thermal characteristics of the prepared virgin LDPE and its nanocomposite films were studied by differential scanning calorimetry (DSC). Comprehensive analysis of different kinetic modelssuch as the Avrami and Mo model on non-isothermal crystallization kinetics was performed in order to correlate the rate of crystallization and its various kinetic parameters. Further, the macrokinetic equation as proposed by Malkinhas been applied to describe the kinetics of crystallization in the light of the Avrami equation. Concerning virgin LDPE and Ag-NP-reinforced LDPE, the former shows primary crystallization, whereas the later exhibits both primaryand secondary crystallization with varying Avrami exponents. Kinetic parameters are recognized, and confirm the influence of Ag-NPs on crystallization kinetics. X-ray diffraction spectroscopy and transmission electron microscopicanalysis of the nanocomposite films were conducted to verify the dispersion of inorganic filler particles in the resulting hybrids.

    • Cobalt nanoparticles as reusable catalysts for reduction of 4-nitrophenol under mild conditions


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      Facile reduction of p-nitrophenol to p-aminophenol by sodium borohydride catalysed by cobalt nanoparticles (CoNPs) has been discussed. A simple approach has been made to synthesize highly active and ordered structures of CoNPs. The air-stable nanoparticles were prepared from cobalt sulphate using tetrabutyl ammonium bromide as surfactant and sodium borohydride as reductant. The cobalt nanocolloids in aqueousmedium were foundto be efficient reusable catalysts for the p-nitrophenol reduction. Palladium nanoparticles prepared from palladium chloride and the same surfactant were found to reduce p-nitrophenol but lose their catalytic efficiency after recovery.Based on chemical and kinetic studies, an attempt has been made to elucidate the mechanism of p-nitrophenol reduction using these nanoclusters.

    • Visible-light-induced hydrogen evolution reaction with WS$_x$Se$_{2−x}$


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      WS$_2$ is a promising catalyst for the hydrogen evolution reaction.We have explored photocatalytic properties of ternary sulphoselenides of tungsten (WS$_x$Se$_{2−x}$) by the dye-sensitized hydrogen evolution.WSxSe2−x solidsolutions are found to exhibit high activity reaching 2339 $\mu$mol h$^{−1}$ g$^{−1}$ for WSSe, which is three times higher than that of WS2 alone (866 $\mu$mol h$^{−1}$ g$^{−1}$). The turnover frequency is also high (0.7 h$^{−1}$). Such synergistic effect of selenium substitution in WS2 is noteworthy.

    • Comparative study of synthesized silver and gold nanoparticles using leaves extract of Bauhinia tomentosa Linn and their anticancer efficacy


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      Nanotechnology is an emerging field in science and technology, which can be applied to synthesize new materials at the nanoscale level. The present investigation aimed at comparing the synthesis, characterization andin vitro anticancer efficacy of synthesized silver and gold nanoparticles using leaves extract of Bauhinia tomentosa Linn. Silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) were synthesized using aqueous extractof leaves with solution of silver nitrate (AgNO$_3$, 1 mM) and chloroauric acid (HAuCl$_4$·3H$_2$O, 1 mM), respectively. The synthesized nanoparticles were characterized using UV–visible spectrophotometry, Fourier transform infraredspectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive analysis of X-rays, X-ray diffraction, thermogravimetric analysis and cyclic voltammetry, which confirmed the reduction of Ag$^+$ ions to Ag$^0$ and Au$^{3+}$ ions to Au$^{0}$. The in vitro anticancer efficacy of AgNPs, AuNPs and aqueous extract of leaves confirmed by MTT assay exhibited IC50 concentrations of 28.125, 46.875 and 50 $\mu$gml$^{−1}$ for lung A-549 cells, 103.125, 34.375 and 53.125 $\mu$gml$^{−1}$ for HEp-2 cells and 62.5, 23.4 and 13.26 $\mu$gml$^{−1}$ for MCF-7 cells, respectively. The concentrations indicate that both silver and gold nanoparticles as well as aqueous extract of leaves exhibited high anticancer efficacy.

    • Gel-combustion-synthesized ZnO nanoparticles for visible light-assisted photocatalytic hydrogen generation

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      Zinc oxide nanoparticles (ZnO NPs) synthesized by the gel combustion technique using a bio-fuel, cassava starch (root tubers of Manihot esculenta), have been characterized by various techniques. The X-ray diffractionpattern reveals hexagonal wurtzite structure. The particle size averaged around 45nm with an excellent band gap of 2.5 eV. The scanning electron and transmission electron microscopic images confirm the ZnO NPs to be agglomerated with loop- and chain-like morphology. The ZnO NPs prepared by this method is a promising candidate for photocatalytic hydrogen generation (41 $\mu$mol h$^{−1}$ g$^{−1}$) under UV light illumination and (140 $\mu$mol h$^{−1}$ g$^{−1}$) under visible light illumination.

    • Effect of process parameters on coating composition of cathodic-plasma-electrolysis-treated copper


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      Cathodic plasma electrolysis is a novel technique to form nanostructured layers on metallic surfaces by application of high voltage in a suitable aqueous electrolyte. In the present study, copper is treated by plasma electrolysisin 50 vol% ethanol electrolyte and coatings comprising carbon nanostructure and copper oxide are formed on the copper. The effect of some process parameters such as electrical conductivity, volume and temperature of electrolyte and ratio of anode to cathode surface area on current–voltage behaviour and subsequently coating compositions are investigated at 150V deposition voltage. The composition and morphology of these coatings are characterized by X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Different current–voltage behaviours, temperatures of substrate and the contents and energies of radicals and ions around the substrate by changes in the mentioned parameters cause different compositions from 100 vol% copper oxide to different ratios of copper oxide to carbon, the structure changing from amorphous to graphitic structure in carbon and amorphous to cubic morphology in copper oxide on the substrate. Therefore, the understanding of cathodic plasma electrolysiscan be developed.

    • Effect of magnetite nanoparticles on dye absorption properties of magnetite@carbon composites


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      Magnetite@carbon (Fe$_3$O$_4$@C) composites were prepared using three kinds of Fe$_3$O$_4$ nanoparticles (NPs). All the Fe$_3$O$_4$@C composites could be easily separated from water by an external magnet. The Fe$_3$O$_4$ NPs synthesized by a microreactor system have the smallest size and narrowest size distribution among the three kinds of Fe$_3$O$_4$ NPs. The saturated capacity of the Fe$_3$O$_4$@C composite originating from microreactor-prepared Fe$_3$O$_4$ NPs to absorb Rhodamine B at 20$^{\circ}$C exceeds 135 mg g$^{−1}$, which is 1.35 times as much as the value of the Fe$_3$O$_4$@C composite originating from traditional Fe$_3$O$_4$ NPs. This value for the Fe$_3$O$_4$@C composite using commercial Fe$_3$O$_4$ NPs as core is only 76 mg g$^{−1}$. The Fe$_3$O$_4$@C composite using microreactor-prepared Fe$_3$O$_4$ NPs also has good retrievability and reusability

    • Effect of sol–gel method on colour properties of the classical cobalt olivine (Co$_2$SiO$_4$) ceramic pigment


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      A sol–gel method based on (H$_2$S$_2$O$_5$)$_{aq}$ as silicon precursor in the presence of NaCl and KCl mineralizers was used for the synthesis of the classical cobalt olivine (Co2SiO4) ceramic pigment. The effect of this synthesisroute on the colour properties was studied. Highly pure olivine phase was obtained after firing at 1200$^{\circ}$C for 3 h. The resulting powders exhibited very intense violet colour, while their addition at only 1 wt% to an industrial transparent glaze was enough to produce a very intense blue–violet colouration. Based on the aspect of glazed ceramics, addition of pigments even at 0.5 wt% to the glaze resulted in a very interesting colour and opacity. By this appropriateminimization of the used pigment amount without compromising the colouring properties required during application, the obtained Co olivine could be more efficient, less toxic and less expensive.

    • Biocomposites from polyhydroxybutyrate and bio-fillers by solvent casting method


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      Biocomposites from polyhydroxybutyrate (PHB) and some bio-fillers such as lignin (L), alpha cellulose (AC) and cellulose nanofibrils (CNFs) were prepared to investigate the effect of the bio-fillers on the properties of PHB by a solvent casting method. The thermal properties by thermogravimetry analysis (TGA–DTG and DTA) and differential scanning calorimetry (DSC) were determined; morphological characterization by scanning electron microscopy (SEM) and structural analysis by X-ray diffraction (XRD), and Fourier transform infraredspectroscopy (FTIR) of the biocomposites were performed. TGA curves showed that the highest values for T 10%, T 50% of the biocomposites were 278.2◦C for PHB+2%AC and 291.7$^{\circ}$ C for PHB+2%CNFs; however, the bestvalue for T 75% was obtained as 381.5$^{\circ}$C for PHB+2%L. According to DTG curves, the best results were found for PHB+0.5%L and PHB+0.5%CNFs. DTA showed an increase in temperature of maximum degradation withloading of lignin and CNFs. The addition of bio-fillers increases Tc and Tm for both first cooling/heating and second cooling/heating. Tc and Tm values for first cooling/healing were found to be lower as compared with second cooling/healing. Furthermore, the addition of bio-fillers acts as a nucleating agent in PHB and SEM pictures showed the porous structure in all biocomposites. SEM images revealed uniform distribution of the reinforcing particles in the polymer at low loadings (0.5wt%), while higher loadings (2 wt%) of L and CNFs contributed to easy aggregation within the PHB matrix. In XRD studies, PHB in the range 5–55$^{\circ}$ shows 6 main peaks. XRD patterns of the PHBbiocomposites revealed 3 main peaks at 13.57$^{\circ}$, 16.87$^{\circ}$ and 22.1$^{\circ}$, and the other peaks disappeared in the patterns.The largest and lowest values of Xc were found for PHB+2%AC and PHB+2%CNFs, respectively.

    • On the origins of the anisotropic mechanical behaviour of extruded AA2017 aluminium alloy

      A MAY

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      This paper presents some experimental investigations about the origins of the anisotropic behaviour in cyclic loadings of AA2017 aluminium alloy. In the first step, fatigue damage evolutions were quantified for controlled proportional cyclic loadings in axial and shear directions. In this stage, the aim was to confirm the anisotropic mechanical behaviour, which has recently been revealed. To this end, severalmodels of fatigue damage quantification were used. After a comparative study between the obtained results we confirmed the anisotropic nature of the used material. In the second step, microstructural investigations were performed in order to understand the origins of the anisotropic mechanical behaviour. We used scanning electron microscopy to analyse phases and precipitates inthe transversal and the longitudinal sections. It was deduced that the structure and the morphology of these entities are responsible for the anisotropic behaviour of the used aluminium alloy. Moreover, the results obtained usingKikushi diagrams, poles figure and inverse poles figures have also confirmed these conclusions. Indeed, these results have shown great differences in crystallographic texture of the material.

    • Corrosion protection of AM60B magnesium alloy by application of electroless nickel coating via a new chrome-free pretreatment


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      Cerium–vanadium (Ce–V) conversion coating was proposed as a new pretreatment for application of electroless Ni–P coating on AM60B magnesium alloy to replace the traditional chromium oxide pretreatment. Morphology and chemical composition of the conversion coating were investigated. The subsequent Ni–P coating deposited on the conversion coating was also characterized by morphology, chemical composition, microstructure, corrosion protection performance and micro-hardness. A uniform, compact and pore-free electroless coating with a moderate concentration of phosphorus (7.78 wt%) was obtained. The electroless coating showed a nobler opencircuitpotential than that of the bare alloy during the first 13 h of immersion in 3.5 wt% NaCl solution. Also, the sample plated with the Ce–V conversion coating showed lower corrosion current density than the sample plated with traditional chromium oxide pretreatment. The micro-hardness of the bare alloy was significantly increased after electroless coating. The electroless coating is pore-free and there is suitable adhesion between the coating and alloy substrate.

    • Hydrothermal synthesis of NiFe$_2$O$_4$ nano-particles: structural, morphological, optical, electrical and magnetic properties


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      NiFe$_2$O$_4$ nano-crystallites with an average diameter of 8.9 nm are synthesized via hydrothermal method.The single-phase spinel structure is confirmed from X-ray diffractograms. Morphology is analysed by transmissionand field emission scanning electron microscopes. High specific surface area of 55.7 m$^2$ g$^{−1}$ is obtained for nano-particles. The M–H loop and M–T curve behaviours are investigated by vibrating sample magnetometry.The optical band gap energy is estimated from the UV–visible spectrum. In addition, the frequency dependence of dielectric properties is investigated. Cole–Cole plots are drawn to study electrical conduction mechanism and thekind of relaxation—Debye or non-Debye type. Low a.c. conductivity and low magnetic losses are noticed at 5 MHz frequency, which are suitable for microwave device applications.

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