• Volume 38, Issue 5

September 2015,   pages  1119-1472

• Synthesis of functionalized pyrazolopyran derivatives: comparison of two-step vs. one-step vs. microwave-assisted protocol and X-ray crystallographic analysis of 6-amino-1,4-dihydro-3-methyl-4-phenylpyrano[2,3-c]pyrazole-5-carbonitrile

A library of pyrazolopyran heterocycles was synthesized first by the traditional heating techniques using two-step and one-step procedures and then by microwave-assisted (MWA) multicomponent condensation of ethyl acetoacetate, hydrazine, malonodinitrile and a variety of substituted aldehydes. A comparison of the foregoing methods was first done based on the yields and then based on the time taken for the completion of the reactions. It was found that although the traditional methods gave slightly better yields, the MWA syntheses lead to substantial reduction in reaction timings. The title compound crystallizes in the triclinic crystal system with space group P–1. The crystal structure as elucidated by X-ray diffraction methods shows the presence of different intermolecular interactions, and the nature and energetics associated with these interactions have been characterized using PIXEL software.

• Synthesis and characterization of a binary oxide ZrO2–TiO2 and its application in chlorophyll dye-sensitized solar cell with reduced graphene oxide as counter electrodes

Natural dyes have been used to sensitize TiO2 nanocrystalline solar cells, but they still require pigment purification and co-adsorption of other compounds. In this study, nanocrystalline ZrO2–TiO2 films sensitized with the bioorganic dye, chlorophyll extracted from green leaves of Chromolaena odorata were investigated. The nanocrystalline ZrO2–TiO2 films were synthesized by the precipitation synthesis. The samples were characterized using X-ray diffraction, UV–vis absorption spectroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. The photoelectrodes were prepared using ZrO2–TiO2 sensitized with the chlorophyll dye and the counter electrodes using reduced graphene oxide. The shift in the absorption wavelength of chlorophyll showed an increase of adsorption of dye. The conversion efficiency was also studied.

• Facile hydrothermal synthesis of CeO2 nanopebbles

Cerium oxide (CeO2) nanopebbles have been synthesized using a facile hydrothermal method. X-ray diffraction pattern (XRD) and transmission electron microscopy analyses confirm the presence of CeO2 nanopebbles. XRD shows the formation of cubic fluorite CeO2 and the average particle size estimated from the Scherrer formula was found to be 6.69 nm. X-ray absorption spectrum of CeO2 nanopebbles exhibits two main sharp white lines at 880 and 898 eV due to the spin orbital splitting of 𝑀4 and 𝑀5. Optical absorption for the synthesized CeO2 nanopebbles exhibited a blue shift (𝐸g = 3.35 eV) with respect to the bulk CeO2 (𝐸g = 3.19 eV), indicating the existence of quantum confinement effects.

• Positron annihilation and tribological studies of nano-embedded Al alloys

Positron annihilation studies of aluminium alloys with nanodispersions of insoluble elements, i.e., In, Sn, Pb and Au were reported. The alloys were obtained using a rapid solidification process. For all alloys, except that with Au, the average diameter of nanoparticles in aluminium matrix was 100 nm, and variance of the size distribution was above 50 nm. Positron annihilation studies reveal the presence of monovacancies or divacancies, which were located at the interface between nanoparticles and the matrix. In the as-cast reference pure aluminium sample as well as the aluminium and gold alloy dislocations were identified as well. The isothermal annealing of the obtained alloys and measurement of the annihilation characteristic, i.e., S-parameter, allow us to determine the activation energy of grain boundary migration, which for the alloys was higher by the factor of four than for the reference sample. The measurements of friction parameters for the alloys confirmed the results reported by the other authors that, the friction coefficient was lower by the factor of about two and the specific wear rate was by the factor of about fifty higher than the reference sample. The present study confirmed the attractive positron affinity of the nanoparticles of In, Sn, Pb and Au compared to aluminium matrix.

• One-step synthesis of samarium-doped ceria and its CO catalysis

The samarium-doped ceria (SDC) nanospheres were prepared by the one-step hydrothermal method and characterized by transmission electron microscope, scanning electron microscope, powder X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive spectrometer and Raman spectra. According to the results, samarium was doped into the lattice successfully. The as-prepared samples were dispersed well and the average diameter was 60 nm. It showed better catalytic performance than pure ceria and the most appropriate concentration of doping was found.

• Synthesis and characterization of castor oil-based polyurethane for potential application as host in polymer electrolytes

Polyurethane (PU) based on polyol, derived from castor oil has been synthesized and characterized for potential use as a base material for electrolytes. Transesterification process of castor oil formed a polyol with hydroxyl value of 190 mg KOH g–1 and molecular weight of 2786 g mol–1. The polyols together with 4,4′-diphenylmethane diisocyanate were used to synthesize the desired bio-based PU. The molecular structure of PU was investigated by Fourier transform infrared (FTIR) spectroscopy. The disappearance of NCO peak in the FTIR spectrum at 2270–2250 cm–1 showed that diisocyanate has completely reacted to form PU. Morphological characteristic of the PU film was analysed using scanning electron microscopy, whereas thermal characteristics of the materials were characterized using dynamic mechanical analysis and thermal gravimetric analysis. The cross-sectional micrograph showed that the prepared film was highly amorphous and homogeneous. Thermal studies revealed that the film had low glass transition temperature, –15.8°C, and was thermally stable up to 259°C. These observations indicated the synthesized PU possessed favourable properties to act as a base material in polymer electrolytes.

• Synthesis and characterization of silicon-doped polycrystalline GaN films by r.f. sputtering

Silicon-doped polycrystalline GaN films were successfully deposited at temperatures ranging from 300 to 623 K on fused silica and silicon substrates by radio frequency (r.f.) magnetron sputtering at a system pressure of ~ 5 Pa. The films were characterized by optical as well as microstructural measurements. The optical properties were studied by UV–vis–NIR spectrometer and photoluminicence (PL) measurements. The microstructural information was obtained from scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM) and X-ray diffraction (XRD) studies. PL measurement at 80 K exhibited two strong transitions located at ~ 2.1 and ~ 2.7 eV along with lower intensity peaks for luminescence at the higher energy side at ~ 3.45 and ~ 3.3 eV for all the films deposited here, and the peaks at ~ 3.45 and ~ 3.3 eV could be ascribed to transitions related to excitons bound to a neutral donor for h-GaN and c-GaN, respectively. A broad peak at ~ 2.1 eV indicated the presence of yellow luminescence in all the films. The SEM and AFM images revealed that the films are compact with well-dispersed polycrystalline constituting the films. The XRD traces contained the signature of both the hexagonal and cubic phases of GaN.

• Facile synthesis of porous Co3O4 nanoplates for supercapacitor applications

Porous tricobalt tetraoxide (Co3O4) nanoplates with large aspect ratio have been obtained by annealing Co(OH)2 precursor nanoplates synthesized by a facile reflux method without the need for any template or surfactant. After the heat treatment, the as-obtained phase-pure Co3O4 nanoplates with a wellretained structure were applied as the electrode material for supercapacitors, and the sample exhibits excellent performance with a high specific capacitance of 225 F g–1 after 2000 charge–discharge cycles at 2 A g–1, corresponding to a retention of 97% of the initial capacitance.

• Effect of TiO2–graphene nanocomposite photoanode on dye-sensitized solar cell performance

In this research work, graphene–TiO2 photoanodes with various graphene concentrations (0, 0.5, 1, 1.5 and 2 wt%) were deposited on fluorine tin oxide glass substrates as working electrodes for dyesensitized solar cells. The structure, morphology, surface composition and dye adsorption of the photoanodes were investigated by X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy and UV–VIS–NIR spectroscopy, respectively. The photocurrent–voltage characteristics of the dye-sensitized solar cells were examined using a solar simulator. The results indicated that the dye adsorption on photoanode surfaces increases with the increase in the graphene content. In addition, dye-sensitized solar cells efficiency increases with the increase in the graphene content to 1.5 wt% and then decreased. The efficiency of the dyesensitized solar cell, based on the TiO2–1.5 wt% graphene nanocomposite, increased by 42% with respect to the pristine sample.

• Evaluation on mechanical properties of woven aloevera and sisal fibre hybrid reinforced epoxy composites

Natural fibres as reinforcement in polymer composite for making low-cost materials are growing day by day. Researcher’s main attention is to apply appropriate technology to utilize these natural fibres as effectively and economically as possible to produce good quality fibre-reinforced polymer composites for various engineering applications. In this research, the experiments of tensile, flexural and impact tests were carried out for woven aloevera and sisal fibre hybrid-reinforced epoxy composites. The hand layup method of fabrication was employed in preparing the composites. The surface morphology of the composites was examined through scanning electron microscope. Due to the low-density and high-specific properties of sisal fibre composites, it offer cost savings when compared with synthetic fibres. Hence it has very good implications in the automotive and transportation industry.

• CoCl2 reinforced polymeric nanocomposites of conjugated polymer (polyaniline) and its conductive properties

Polyaniline (PANI) was synthesized by chemical oxidative polymerization of aniline using ammonium persulphate as an oxidant in acidic aqueous medium. Cobalt chloride hexahydrate (CoCl2⋅6H2O)-doped PANI composite was synthesized by in-situ oxidative polymerization process by using various concentrations of CoCl2. Its chemical, structural and morphological properties were examined by X-ray diffraction, energydispersive X-ray spectroscopy, Fourier transform infrared spectroscopy and field-emission scanning electron microscopy techniques. These results confirmed the successful formation of PANI and CoCl2-doped PANI nanocomposites. The morphology of CoCl2-doped PANI nanocomposite was found to be spherical in nature. The dielectric properties were examined using LCR-HITESTER in the frequency range 50 Hz–5 MHz. The optical properties were examined by UV–visible spectroscopic techniques in the wavelength range of 200–800 nm. The high dielectric properties and alternating current conductivity of the composite was studied in the temperature range 313–373 K. It was found that the synthesized polymeric nanocomposite owned fairly suitable dielectric and optical properties for its application in actuators, conductive paints and for many other purposes.

• Effect of ECAP and extrusion on particle distribution in Al-nano–Al2O3 composite

In this study equal channel angular pressing (ECAP) and conventional extrusion were used as two different techniques for consolidation of attritioned aluminium powder (45 𝜇m) with varying concentrations of nanoalumina powders (35 nm). The evolution of the homogeneity of the particle distribution in the material during ECAP and conventional extrusion was investigated by the quadrat method with image analysis software. The frequency histograms of the number of alumina particles per quadrat, 𝑁q, for each investigated condition were plotted and the effect of particle distribution on fracture surface and wear resistance of the composite was investigated.

• Temperature-dependent ionic conductivity and transport properties of LiClO4-doped PVA/modified cellulose composites

This paper presents the investigation on physicochemical properties and ionic conductivity of LiClO4-doped poly(vinyl alcohol) (PVA)/modified cellulose composites. The percolative behaviour of LiClO4 with dc conductivity (𝜎dc) for different LiClO4 weight fractions (p) related to transport dimensionality was also focused. The highest ionic conductivity of 9.79 × 10–6 S cm–1 was observed for 20 wt% LiClO4 doping level at room temperature. The activation energies (𝐸g) were estimated using temperature-dependent conductivity, which follows the Arrhenius and Vogel–Tammann–Fulcher (VTF) relation. The dynamic fragility (𝑓) and activation energy (𝐸g) vs. 𝑇g of polymer composites using equivalence of the both Williams–Landel–Ferry (WLF) and VTF equations were also correlated. Transport properties such as travel time of ions between sites (𝜏o), mobility (𝜇), diffusion coefficient (𝐷) and number of transitions per unit time 𝑃(𝐸) for normal cationic (Li+) hopping process of LiClO4-doped PVA/mCellulose composites have been investigated using the Rice and Roth model.

• Effects of LiF on microwave dielectric properties of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics

The effects of LiF addition on sinterability, microstructure and microwave dielectric properties of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics were investigated. The LiF addition enhanced the sintering temperature of 0.25Ca0.8Sr0.2TiO3–0.75Li0.5Nd0.5TiO3 ceramics from 1200 to 1300°C, because the LiF addition could compensate the evaporation of Li during the sintering process. It was found that the bulk density and dielectric constant (𝜀r) gradually decreased, the quality factor (𝑄f) greatly increased and the temperature coefficient of resonant frequency (𝜏f) shifted to a near-zero value with the increase in LiF addition. Obviously, excess Li addition could efficiently improve the microwave dielectric properties. In addition, 0.25Ca0.8Sr0.2 TiO3–0.75Li0.5Nd0.5TiO3 + 4.0 wt% LiF ceramics sintered at 1350°C for 4 h exhibited good microwave dielectric properties of 𝜀r ∼ 123.4, 𝑄f ∼ 2209 GHz (at 2.43 GHz) and 𝜏f ∼ 12.3 ppm °C–1.

• Effect of Ca doping on thermally activated flux flow in the Y3Ba5Cu8O18 superconductor

Y3Ba5Cu8O18 (Y-358) and Y3Ba5Ca2Cu8O18 (YCa-358) compounds were prepared by the so-called sol–gel method. The effect of doping Ca atoms into the Y3Ba5Cu8O18 superconductor is studied by employing the electrical resistivity measurements at various magnetic fields. The possible degradation in microstructural and superconducting properties due to the addition of Ca was discussed. The resistivity as a function of temperature measurements shows that the depression in superconducting temperature is more pronounced for both samples. A systematic analysis of the magnetoresistivity of the Y-358 and YCa-358 compounds has been carried out by using the thermally activated flux flow (TAFF) model. The TAFF activation energy, 𝑈, is field dependent and obeys the power law 𝑈 = 𝑐𝐻–𝛼, where 𝛼 increases while 𝑐 decreases with the addition of Ca. Furthermore, 𝑈 and the calculated upper critical field, 𝐻𝑐2, decrease with the addition of Ca.

• Effect of sintering temperature and time on the mechanical properties of Co–Cr–Mo/58S bioglass porous nano-composite

In the present study, Co–Cr–Mo/58S bioglass porous nano-composite samples were successfully produced using 30 wt% carbonate hydrogen ammonium and polyvinyl alcohol solution as space holder and binder, respectively. The cold compacted samples were heated at 175°C for 2 h and then were heated to sinter at 1100, 1150, 1200 and 1250°C for 3, 6, 9 and 12 h. True porosity of samples was measured and the samples were characterized using the X-ray diffraction (XRD) technique, scanning electron microscopy (SEM) and compressive test. Although the results of compression test for samples sintered at 1200 and 1250°C showed that the shape of stress–strain curves were similar to each other, compacted powders sintered at 1100 and 1150°C exhibited some fluctuations. Moreover, the compressive strength increased by decreasing the true porosity, indicating the role of high temperature on the sintering process. In addition, volume diffusion was predominant mechanism for these samples at sintering temperature of 1250°C. SEM images of the porous sample sintered at 1250°C for 3 h showed an appropriate range of pore sizes and interconnectivity. The XRD results showed that there are no contaminations and new phase is detectable in the sintered porous samples.

• Effect of capping agents on optical and antibacterial properties of cadmium selenide quantum dots

Cadmium selenide quantum dots (CdSe QDs) were synthesized in aqueous phase by the freezing temperature injection technique using different capping agents (viz. thioglycolic acid, 1-thioglycerol, L-cysteine). Absorption spectra of CdSe QDs exhibited a blue shift as compared to its bulk counterpart, which is an indication of quantum confinement effect. The photoluminescence spectra of CdSe QDs confirmed that the particles are poly-dispersed and possess enhanced luminescent property, depending upon the chemical nature of capping agents. The QDs have been characterized by Fourier-transform infrared spectroscopy, atomic absorption spectroscopy and transmission electron microscopy. Further, antimicrobial activity of as-prepared QDs has also been investigated using the disk diffusion method.

• Biological and electrical properties of biosynthesized silver nanoparticles

In this work, silver nanoparticles (AgNPs) were synthesized biochemically at room temperature using aqueous extract of rhizome of Rheum australe plant. The as-synthesized AgNPs were further studied for their morphological, biological and electrical characterization. The morphological studies, such as scanning electron microscopy, X-ray diffraction and UV–vis spectrum confirmed their successful synthesis. Biological analysis revealed their antioxidant activity by 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Electrical characterization showed that the conductivity of the mixture of AgNPs with DPPH assay is more than the AgNPs dispersed in distilled water. The obtained results may have potential applications as sensors.

• Nb-doped TiO2 thin films as photocatalytic materials

Amorphous undoped and Nb-doped films were obtained by the spin coating method. The films have a compact structure, as revealed by scanning electron microscopy, and are very thin, with thickness values under 100 nm. The photocatalytic activity of the films was evaluated by observing the decomposition of an oleic acid solution under UV irradiation, and by studying the change in the optical transmittance of an aqueous solution containing methylene blue, in the presence of the UV-irradiated films. More than 30 h, depending on doping, are needed to recover their initial contact angles before applying oleic acid. The increase of the optical transmittance of the methylene blue solution confirms the photocatalytic degradation of methylene blue on the Nb-doped TiO2 films. X-ray photoelectron spectroscopy studies, performed to detect the presence of the carbon on the irradiated surface of the films, drive to the conclusion that at the surface of the films, even for contact angles close to 0°, the presence of carbon still can be detected, which demonstrates that hydrophilicity is ruled by a different mechanism than photocatalysis.

• Influence of heat treatment temperature on bonding and oxidation resistance of diamond particles coated with TiO2 film

In this paper, TiO2 films were coated on the surface of diamond particles using a sol–gel method. The effects of heat treatment temperature on the morphology, composition, chemical bonds, oxidation resistance and compressive strength of diamond particles coated with TiO2 films were characterized through scanning electron microscopy, Fourier transform infrared, Raman spectroscopy, X-ray diffraction analysis, X-ray photoelectron spectroscopy, thermogravimetric–differential scanning calorimetry and compressive strength test. The results showed that when the temperature reached 600°C, the amorphous TiO2 on the diamond particles surface exhibited as a dense anatase film and the Ti–O–C bond formed between TiO2 and the diamond substrates. When temperature reached 800°C, TiO2 films were still in anatase phase and part of the diamond carbon began to graphitize. The graphitizated carbon can also form the Ti–O–C bond with TiO2 film, although TiO2 film would tend to crack in this condition. Meanwhile, the temperature had a serious influence on the oxidation resistance of diamond particles coated with TiO2 films in air. When the heat treatment temperature reached 600°C, the initial oxidation temperature of the coated diamond particles reached the maximum value of 754°C. When the diamond particles were oxidized at 800°C for 0.5 h in air, the weight loss rate reached the minimum value of 6.7 wt% and the compressive strength reached the maximum value of 15.7 N.

• STM-induced light emission from vacuum-evaporated gold film

A vacuum evaporation system has been used to evaporate gold film on glass substrate in order to probe the scanning tunneling microscope-light emission (STM-LE) from the evaporated film. The surface morphology of the evaporated Au film has been checked by atomic force microscope (AFM). In order to estimate the appropriate thickness of the Au film, which is essential for the enhancement of STM-LE in the prism-coupled geometry, a theoretical calculation has been performed. Our theoretical simulation revealed that the light emission from the prism-coupled STM junction is strongly enhanced when the Au film has a thickness of 40 nm. AFM observation also showed that the morphology of the gold films strongly depends on the cleanliness of glass substrates and the deposition temperature. Relatively smooth surface was observed when a 40-nm-thick Au film was evaporated at room temperature on the preannealed glass substrate. Finally, the evaporated films were deposited on the flat bottom of a hemispherical glass prism, and STM-LE from the tip–sample gap into the vacuum (tip-side emission) and into the prism (prism-side emission) were measured. It was found from the experimental results that the prism-side emission is much stronger than the tip-side emission by virtue of the enhancement of the prism-coupled geometry.

• Synthesis and characterization of Sn-doped CdZnS nanoparticles

Tin (Sn)-doped cadmium zinc sulphide nanoparticles (CdZnS : Sn) were synthesized by the chemical bath deposition method with two different concentrations of Sn (2 and 4 mol%). X-ray diffraction (XRD) pattern reveals the formation of CdZnS nanoparticles with cubic and hexagonal structure. It was observed that the presence of Sn does not alter the structure of CdZnS. Average crystallite size was measured from XRD data by using Scherrer’s formula. From the study of absorption spectra, band-to-band absorption was obtained at 460 and 490 nm, respectively, for the Sn-doped (2 and 4 mol%) CdZnS nanoparticles. Energy bandgap for undoped and Sn-doped CdZnS varies from 3.5 to 2.9 eV with error ± 0.05 eV. The presence of Sn was confirmed by energy-dispersive X-ray analysis. The effect of dopant concentration on the photoluminescence (PL) intensity has also been studied. The PL emission peak has been observed at 540, 550 and 560 nm for the Sn-doped (CdZnS, CdZnS 2 mol% and CdZnS 4 mol%), respectively, nanoparticles. XRD and PL analyses demonstrate that the Sn2+ ions uniformly substitute Cd2+ sites or interstitial sites in CdZnS lattice, which influence the optical properties. Increase in the concentration of Sn shifts the UV–vis absorption spectra and PL emission spectra towards higher wavelength side. Particle size and the crystallinity of CdZnS : Sn nanoparticles were confirmed through atomic force microscopy.

• Preparation and thermal stability of nickel nanowires via self-assembly process under magnetic field

Nickel nanowires were synthesized via a template-free method in an aqueous solution system combined with chemical reduction and magnetic field. The suitable concentration of Ni ions and reaction time were controlled in order to obtain nickel wires with uniform sizes. The products were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, thermogravimetry and differential scanning calorimetry. The results showed that the Ni nanowires with large aspect ratio up to 200 had uniform size and morphology, about 200 nm. Especially, it is noteworthy that the samples were stable in air when the temperature was lower than 318°C. The study would provide a facile method to prepare nickel nanowires with homogeneous diameter and high thermal stability, which could be used in catalysing CO2 hydrogenation.

• Growth and characterization of nonlinear optical single crystals: bis(cyclohexylammonium) terephthalate and cyclohexylammonium para-methoxy benzoate

Bis(cyclohexylammonium) terephthalate (BCT) and cyclohexylammonium 4-methoxy benzoate (C4MB) single crystals were successfully grown by the slow evaporation solution growth technique. The harvested crystals were subjected to single-crystal X-ray diffraction, spectral, optical, thermal and mechanical studies in order to evaluate physiochemical properties. The Kurtz and Perry technique for second harmonic generation (SHG) study revealed that the powdered materials of BCT and C4MB exhibit SHG efficiency 0.2 times less and 1.3 times greater than that of standard reference material potassium dihydrogen phosphate. C4MB crystal exhibits high efficiency than BCT, because of methoxy group substituted in the para position of phenyl ring. With high SHG efficiency and thermal stability para substituted C4MB crystal will be a potential candidate for optical device fabrication.

• Thermotropic liquid crystalline polyesters derived from bis-(4-hydroxybenzoyloxy)-2-methyl-1,4-benzene and aliphatic dicarboxylic acid chlorides

A series of thermotropic liquid crystalline polyesters derived from bis-(4-hydroxybenzoyloxy)-2-methyl-1,4-benzene (BHBOMB) and aliphatic dicarboxylic acid chlorides were investigated. All these polyesters were synthesized by interfacial polycondensation method and characterized by differential scanning calorimetry and wide-angle X-ray diffractometer. These polyesters consist of BHBOMB as a mesogenic diol and aliphatic diacid chlorides were used as flexible spacers. The length of oligomethylene units in polymer was varied from the trimethylene to the dodecamethylene groups. The transition temperatures and thermodynamic properties were studied for all these polymers. All these polyesters were soluble in chlorinated solvents such as chloroform, dichloromethane, dichloroethane, etc. More importantly, all these polyesters exhibited very large mesophase stability.

• Ionic liquid intercalated V2O5 nanorods: synthesis and characterization

In this work, ionic liquid (IL) intercalated V2O5 (IL-V2O5) nanorods have been synthesized through the IL-assisted hydrothermal method using imidazolium-based functionalized IL at 130°C for 3 days. The structure and morphology of the obtained product was characterized using various techniques. X-ray diffraction pattern reveals the intercalation of IL at 2𝜃 = 7° in orthorhombic V2O5. The Fourier transform infrared spectrum shows a band at 1044 cm–1, which could be assigned to stretching vibration of terminal vanadyl (V=O), sensitive to cation intercalation between vanadium oxide layers. UV–vis absorption spectrum of IL-V2O5 nanorods and calcined V2O5 nanoparticles show a maximum absorbance at 402 and 420 nm, respectively. The morphology of the product was investigated by scanning electron microscopy and transition electron microscopy (TEM). TEM analysis reveals the nanorods with thickness of 30–50 nm.

• Non-isothermal crystallization kinetics and thermal behaviour of PA12/SEBS-g-MA blends

The thermal behaviour and crystallization kinetics of PA12/SEBS-g-MA blends were investigated under non-isothermal and isothermal conditions using thermogravimetric analysis and differential scanning calorimetry, respectively. The macrokinetic model given by Avrami was used to analyse both the nonisothermal and isothermal crystallization kinetics of the blends. The value of the Avrami exponent during non-isothermal crystallization predicted that pure PA12 and PA12/SEBS-g-MA blends show spherulitic growth with random nucleation of crystal structures as the n-values lie between 3 and 4. The slight nucleating effect of SEBS-g-MA was showed by nucleating activity calculated by the Dobreva and Gutzowa method.

• Observation of the nano-effect on the SHG in moderately Cu-doped CdI2 thin nanocrystals

Nanocrystals take into account the nano-sized quantum-confined effect, where k-space bulk-like dispersion disappears and discrete excitonic-like nanolevels occur within the forbidden energy gap of the material processes. Nanocrystals of cadmium iodide both un-doped and doped with copper, synthesized and grown by the standard Bridgman method, were analysed by scanning electron microscopy for the investigation of the nano-confined effect on the optical nonlinearity. The second harmonic generation (SHG) of the crystals was measured and studied. The second-order optical susceptibilities in dependences of the size of the nanocrystals and of their copper contents within low levels were calculated. The results showed a clear increase in the SHG with the decrease in the thickness of the nanocrystals. The observed size dependence, however, demonstrates the nano-confined effect or nano-effect on the SHG, where the quantum confinement dominates the material’s optical properties. A significant change in the second-order optical response with copper content of the nanocrystals was also observed. The observed results are discussed by exploring the photo-induced electron–phonon anharmonic interaction for the noncentrosymmetry of the nanocrystallite’s process.

• Transformation from amorphous to nano-crystalline SiC thin films prepared by HWCVD technique without hydrogen dilution

Silicon carbide (SiC) thin films were deposited on Si(111) by the hot wire chemical vapour deposition (HWCVD) technique using silane (SiH4) and methane (CH4) gases without hydrogen dilution. The effects of SiH4 to CH4 gas flow ratio (R) on the structural properties, chemical composition and photoluminescence (PL) properties of the films deposited at the different gas flow ratios were investigated and compared. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectra revealed a structural transition from amorphous SiC to cubic nano-crystalline SiC films with the increase in the gas flow ratio. Raman scattering confirmed the multi-phased nature of the films. Auger electron spectroscopy showed that the carbon incorporation in the film structure was strongly dependent on the gas flow ratio. A similar broad visible room-temperature PL with two peaks was observed for all SiC films. The main PL emission was correlated to the band to band transition in uniform a-SiC phase and the other lower energy emission was related to the confined a-Si : H clusters in a-SiC matrix. SiC nano-crystallites exhibit no significant contribution to the radiative recombination.

• Carbon nanotube-based coatings on titanium

This paper reports results of the modification of titanium surface with multiwalled carbon nanotubes (CNTs). The Ti samples were covered with CNTs via electrophoretic deposition (EPD) process. Prior to EPD process, CNTs were functionalized by chemical treatment. Mechanical, electrochemical and biological properties of CNT-covered Ti samples were studied and compared to those obtained for unmodified titanium surface. Atomic force microscopy was used to investigate the surface topography. To determine micromechanical characteristics of CNT-covered metallic samples indentation tests were conducted. Throughout electrochemical studies were performed in order to characterize the impact of the coating on the corrosion of titanium substrate. In vitro experiments were conducted using the human osteoblast NHOst cell line. CNT layers shielded titanium from corrosion gave the surface-enhanced biointegrative properties. Cells proliferated better on the modified surface in comparison to unmodified titanium. The deposited layer enhanced cell adhesion and spreading as compared to titanium sample.

• Factors affecting the pH and electrical conductivity of MgO–ethylene glycol nanofluids

The pH and electrical conductivity are important properties of nanofluids that have not been widely studied, especially with regard to temperature and ultrasonication energy. To study the factors that affect the pH and electrical conductivity of magnesium oxide–ethylene glycol (MgO–EG) nanofluid, the effects of temperature, volume fraction, particle size and ultrasonication energy were investigated. Two different sizes of MgO were dispersed in EG base fluid up to the volume fraction of 3%, and the pH and electrical conductivity were monitored between the temperatures of 20 and 70°C. Characterization by transmission electron microscopy and size analyses revealed the morphology and sizes of the nanoparticle samples. The pH values dropped consistently with the increase of temperature, while electrical conductivity value increased with the increase of temperature. The experimental result showed that the increase in the MgO volume fraction increased both the pH and electrical conductivity values of the MgO–EG nanofluid. There was no recognizable influence of ultrasonication energy density on the pH and electrical conductivity of the nanofluid; therefore, it was concluded that temperature, volume fraction and particle size are the predominant factors affecting both the pH and electrical conductivity of MgO–EG nanofluid within the present experimental conditions.

• Red luminescence from ZnO : Cr3+ nanophosphors under visible excitation

ZnO : Cr3+ (1 mol%) nanophosphor is synthesized by the wet chemical solution combustion method at the temperature of 400°C. Powder X-ray diffraction results confirmed that Cr3+-doped and undoped ZnO nanophosphors exhibit hexagonal wurtzite structure. The average crystallite size calculated from Scherrer’s method is 25 nm for undoped and 14 nm for Cr3+-doped ZnO. The UV–visible absorption spectra shows red shift in Cr3+-doped ZnO. Photoluminescence studies of undoped ZnO show violet emission peak at 400 nm and blue emission peak at 447 nm. Cr3+-doped ZnO shows red emission peaks at 642, 694 and 746 nm, which are mainly attributed to spin forbidden transitions of $^2$Eg $\to {}^4$A2g of Cr3+ ion in ZnO : Cr3+ nanophosphor. Thermoluminescence (TL) studies recorded at a heating rate of 6°C s$^{–1}$ show two well-resolved glow peaks at 124 and 284°C. It is found that the TL intensity increases with the gamma irradiation dose (500 Gy–10 kGy).

• Fabrication and characterization of hydroxyapatite-coated forsterite scaffold for tissue regeneration applications

In this study, a novel hydroxyapatite (HA)-coated forsterite scaffold with a desired porous structure, high mechanical properties and good bioactivity was successfully fabricated via gel-casting and sol–gel in low pressure methods. X-ray diffraction, scanning electron microscopy, transmission electron microscopy and X-ray map techniques were utilized in order to evaluate the phase composition, dimension, morphology, interconnectivity of the pores and state of the coating on the porosities of the synthesized scaffold. The porosity and compressive strength of the scaffolds were measured and the bioactivity was investigated by soaking the scaffolds in simulated body fluid (SBF). The results show that the prepared scaffolds had highly interconnected spherical pores with size in the range of 65–245 μm. Additionally, compressive strength and elastic modulus were 7.5 ± 0.2 and 291 ± 10 MPa, respectively. The crystallite size of the scaffolds was less than 60 nm. True (total) and apparent (interconnected) porosity of the scaffolds were in the range of 75–80 and 65–70%, respectively. In vitro tests in the SBF also confirmed good bioactivity of the prepared scaffolds. While bone-like apatite formation started from the first day of soaking and apatite covered the entire surface and inner wall of the scaffolds pores at long immersion time. Conclusion suggested that HA coating on forsterite scaffolds could significantly improve the mechanical properties and bioactivity, which might be promising for tissue engineering applications.

• Effect of increasing lanthanum substitution and the sintering procedures on the properties of SrBi4Ti4O15 ceramics

Lanthanum-substituted SrBi4Ti4O15 (SBTi) ceramic, that is SrBi4–𝑥La𝑥Ti4O15 (SBLTi), samples were calcined by solid-state reaction and densified using the microwave sintering and conventional sintering techniques. Their structural, morphological and mechanical properties were investigated. The microwave sintered samples showed high densities like 95% of the theoretical density with short duration exposures. Compared with SBTi ceramics and other lanthanide-substituted compositions, the incorporation of La3+ results in clear improvement in properties for SBLT (𝑥 ∼ 0.75) with respect to the values of hardness and Young’s modulus of the microwave sintered samples (8.8–12.5 and 160–180 GPa) are higher than that for conventional sintered (8–10 and 135–155 GPa) samples.

• Influence of europium (Eu3+) ions on the optical properties of silver lead borate glasses

The influence of europium (Eu3+) ions on the optical properties of silver lead borate glasses of the 𝑥Eu2O3–(1 – 𝑥)Ag2O–29PbO–70B2O3 (𝑥 = 0, 0.1, 0.2, 0.3, 0.4 and 0.5 mol%) glass system prepared by the conventional melt quenching technique and their physical and optical properties were investigated. The UV absorption spectra were recorded at room temperature in the wavelength range of 200–600 nm. From the absorption edge data, it is found that both the direct and indirect transitions and their values are ranging from 3.19 to 3.54 and 2.50 to 3.07 eV, respectively. The Urbach energy values for these glasses were found to be in the range of 0.39–0.52 eV. The refractive indices have also been evaluated with respect to different molar concentrations of Eu2O3 and their calculated values are ranging from 1.598 to 1.654.

• Hydrothermal synthesis of LiFePO4 nanorods composed of nanoparticles from vivianite precursor and its electrochemical performance for lithium ion battery applications

LiFePO4 nanorods composed of nanoparticles were synthesized from precursor phase Fe3(PO4)2(H2O)8 (vivianite) via hydrothermal reaction. Nanorods consisting of nanoparticles were formed by using L-(+)- ascorbic acid as reducing and capping agent. Near-theoretical specific capacity is achieved at 0.1 C rate with excellent retention capacity of up to 50 cycles. Morphology of as-synthesized samples favours fast intercalation/deintercalation process with easy mass and charge transfer.

• Optical and magnetic properties of Yb ion-doped cobalt-based ZnO nanoparticles for DMS applications

Well-crystalline structured ZnO nanoparticles with cobalt (Co) and ytterbium (Yb) multiple ions doping were successfully synthesized by the chemical precipitation technique. The structures, optical and magnetic properties of the samples were analysed with X-ray diffraction (XRD), UV–visible spectroscopy and magnetic measurements, respectively. In the XRD pattern of the pure ZnO and Yb co-doped samples, the formation of highly crystalline phase of pure ZnO was observed even at high Yb concentration. UV–vis spectra show a strong UV absorbance for all the samples with different absorbance maxima. Magnetic characterizations have shown that the sample with 1% Yb co-doped ZnO: Co nanoparticles exhibited a clear ferromagnetic (FM) behaviour at room temperature. The X-ray photoelectron spectral peaks for Yb 4f ions reveal Yb occupation of both Yb3+ as well as Yb2+ states. Hence, it can be confirmed that a clear FM behaviour at room temperature was exhibited by an imbalanced valence state of Yb that strongly interacted with the Co2+. When compared to the Co-doped ZnO, Yb co-doped ZnO exhibits a clear ferromagnetism at room temperature with high coercivity due to the contribution of both 3d and 4f exchange interaction with the host matrix.

• Impedance spectroscopy studies of surface engineered TiO2 nanoparticles using slurry technique

Dielectric analysis of nanometre range size ceramic particles like TiO2 is very important in the understanding of the performance and design of their polymer nanocomposites for energy storage and other applications. In recent times, impedance spectroscopy is shown to be a very powerful tool to investigate the dielectric characteristics of not only sintered and/or pelleted ceramic materials but also particulates/powders (both micron-sized and nano-sized) using the slurry technique. In the present work, impedance spectroscopy employing slurry methodology was extended to study the influence of various chemical groups on the nano-TiO2 surface on the electrical resistivity and the dielectric permittivity of nanoparticles. In this regard, different organophosphate ligands with linear, aromatic and extended aromatic nature of organic groups were employed to remediate the surface effects of nanoTiO2. It was observed that the type of chemical nature of surface engineered nanoparticles’ surface played significant role in controlling the surface electrical resistivity of nanoparticles. Surface passivated nanoTiO2 yielded dielectric permittivity of about 70–80, respectively.

• Er3+–Al2O3 nanoparticles doping of borosilicate glass

Novel borosilicate glasses were developed by adding in the glass batch Er3+–Al2O3 nanoparticles synthetized by using a soft chemical method. A similar nanoparticle doping with modified chemical vapour deposition (MCVD) process was developed to increase the efficiency of the amplifying silica fibre in comparison to using MCVD and solution doping. It was shown that with the melt quench technique, a Er3+–Al22O3 nanoparticle doping neither leads to an increase in the Er3+ luminescence properties nor allows one to control the rare-earth chemical environment in a borosilicate glass. The site of Er3+ in the Er3+–Al2O3 nanoparticle containing glass seems to be similar as in glasses with the same composition prepared using standard raw materials. We suspect the Er3+ ions to diffuse from the nanoparticles into the glass matrix. There was no clear evidence of the presence of Al2O3 nanoparticles in the glasses after melting.

• Physicochemical, electrical and optical studies of methyl-3-(2-furylmethylidene) carbazate single crystal

The current study provides an insight into the physicochemical properties of an organic single crystal methyl-3-(2-furylmethylidene) carbazate, which was grown by employing the slow evaporation solution growth technique and its results were correlated for application point of view. The grown crystal was confirmed by performing single-crystal X-ray diffraction studies and Fourier transform infrared analysis. The optical, thermal, dielectric and mechanical properties of the grown single crystal were primarily investigated. Etching study was performed to analyse the defects and growth mechanism. Kurtz–Perry powder technique was used to study the second harmonic generation efficiency of the crystal and the crystal was found to exhibit Type-I phase matching.

• Effect of pH on the morphology, mechanical and optical properties of L-arginine monohydrobromide monohydrate (LAHBr) single crystals

L-arginine monohydrobromide monohydrate (LAHBr) single crystals were grown from two molar mixtures of L-arginine and HBr acid in 1 : 2 and 1 : 3 ratios. The solution pH of the above molar ratios was measured to be 7.2 and 1.8, respectively. This drastic change in pH has modified the morphology of LAHBr single crystal and influenced the mechanical stability, optical transparency, refractive index, birefringence and laser damage threshold. The decrease in pH from 7.2 to 1.8 has enhanced the optical transparency and laser damage threshold of LAHBr crystal.

• Nucleation and evaporation of domains due to electric field at room temperature in BaTiO3 single crystals

A study of nucleation and evaporation of 90° and 180° domains by external direct current (dc) electric field at room temperature in barium titanate single crystals has been carried out using reflecting microscope. It was observed that both the 90° and 180° domains were nucleated at some sites, while evaporated at some other sites of the crystal surface. The 90° domain follows the mechanism of micro-domain wall nucleation as well as the evaporation based on impurity dipoles, like reported for KNbO3. The mechanism of the 180° domain nucleation is not established yet. However, in both cases, nucleation and evaporation are operative simultaneously by the same electric field, which seems to be quite interesting and which can be attributed to the different critical lengths of the domains.

• Evaluation on electrical resistivity of silicon materials after electron beam melting

This research deals with the study of electron beam melting (EBM) methodology utilized in melting silicon material and subsequently discusses on the effect of oxygen level on electrical resistivity change after EBM process. The oxygen content was reduced from 6.177 to less than 0.0517 ppmw when refining time exceeded 10 min with removal efficiency of more than 99.08%. The average value of electrical resistivity of silicon before EBM processing was recorded to be 2.25 𝛺 cm but with the increase in melting time that was applied through EBM, the electrical resistivity was recorded to go high in the range of 4–13 𝛺 cm for different regions. The electrical resistivity values were greater in the top and the bottom regions, whereas lowest in the central region at all conditions of melting time. It is the result of the evaporation of oxygen during melting process and the segregation of metal impurities during solidification.

• High-performance aqueous rechargeable batteries based on zinc anode and NiCo2O4 cathode

A new aqueous Zn–NiCo2O4 rechargeable battery system with a high voltage, consisting of NiCo2O4 as cathode and metal Zn as anode, is proposed for the first time. It is cheap and environmental friendly, and its energy density is about 202.8 Wh kg–1. The system still maintains excellent capacity retention of about 85% after 100 full cycles at a current rate of 2 A g–1 between 1.5 and 1.95 V. This work not only provides a new battery system but also shows promise for application in large-scale energy storage for its low cost, good cycling and environmental friendliness.

• Characteristics of CoPc/CdS hybrid diode device

CdS/CoPc hybrid heterojunctions were fabricated and characterized. CdS films were deposited by the spray pyrolysis technique on indium tin oxide (ITO)-coated glass substrates and CoPc films coated on CdS by chemical precipitation. Ag contact metal deposited on CoPc by e-beam evaporation and glass/ITO/CdS/ CoPc/Ag structures were fabricated. Rectification ratio, ideality factor, barrier height and junction parameters of the devices were determined. It is shown that device has diode characteristics with the ideality factor (n) of 4.8, rectification ratio of 4.5 and the built-in voltage (𝑉b) of 0.48 V. Absorption energy for CoPc was found as 1.57 eV. The results encourage utilizing CoPc as absorber organic material for solar cells.

• Fabrication of CdSe quantum dots/permutite luminescent materials

Permutite incorporating CdSe in mesopores has been prepared with a simple route. Firstly, mercaptosuccinic acid-capped CdSe quantum dots (QDs) were prepared in aqueous solution by using SeO2 as selenium source and NaBH4 as reductant. Secondly, the commercial permutite was treated with acetic acid to induce a partial dealumnization, which can introduce a large number of intracrystal mesopores, and the CdSe QDs were successfully incorporated in the mesopores with the wet impregnation method. Photoluminescence spectra, X-ray diffraction and scanning electron microscopy were used for the characterization of samples. The spectra analyses results showed that the illuminant colour of QDs/permutite powder was similar to the corresponding QDs colloid. X-ray diffraction measurements indicated that the (1 0 1) diffraction peak at 2𝜃 = 27° for QDs/permutite powder was the same as the raw permutite, and the energy-dispersive X-ray spectra demonstrated that Cd and Se elements existed in the CdSe QDs/permutite powder.

• Electronic transport and magnetoresistivity of La0.4Bi0.1Ca0.5–𝑥Sr𝑥MnO3 (𝑥 = 0.1 and 0.2)

Electrical resistivity and magnetoresistive behaviour of bismuth-substituted lanthanum manganites La0.4Bi0.1Ca0.5–𝑥Sr𝑥MnO3 (𝑥 = 0.1 and 0.2) were systematically studied by varying the temperature from 2 to 300 K and the magnetic field up to 12 T. The samples were found to crystallize in rhombohedral structure and their morphology shows near-spherical nanosize crystallites. Charge ordering was observed in both the samples under zero field conditions and corresponding transition temperature 𝑇CO was found to decrease with the increase of 𝑥. Resistivity measurements with magnetic field also showed suppression of magnetoresistivity (MR) with the increase of 𝑥 and the maximum MR was found to be 98 and 93% for 𝑥 = 0.1 and 0.2, respectively, at 10 T. In the high-temperature domain, the electronic transport was observed to be dominated by the variable range hopping mechanism for both the samples, whereas in the low-temperature domain the electrical conduction of 𝑥 = 0.1 sample was observed to be contributed by various other electron scattering mechanisms.

• Facile fabrication of highly flexible graphene paper for photocatalytic reduction of 4-nitrophenol

Freestanding paper-like materials prepared from chemically derived graphene have considerable potential as a carbon-based catalyst in high-performance flexible catalytic reaction. Herein, a highly flexible graphene paper (GP) assembled from graphene oxides (GOs) with the aid of polyacrylamide (PAA) and electroless deposition of gold nanoparticles (AuNPs) was prepared. In contrast to previous reports on GOs based on a flow-directed assembly of graphene sheets, this GOs/PAA/Au composite paper exhibited a highly wrinkled and disordered morphology. The resultant GOs/PAA/Au composite paper was applied as a catalytic material for the reduction of 4-nitrophenol and showed the favour separation, recovery and cyclic utilization properties.

• Magneto-structural properties of Ni–Zn nanoferrites synthesized by the low-temperature auto-combustion method

Using nickel, zinc and ferric nitrates, and glycine in a fuel-rich composition, Ni1–𝑥Zn𝑥Fe2O4 nanoparticles were prepared by a simple low-temperature auto-combustion method without further sintering at high temperatures. The auto-combusted powders obtained were characterized by X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy, energy-dispersive X-ray (EDAX) analysis and vibrating scanning magnetometer measurements. XRD confirms the formation of pure nanocrystalline spinel phases with an average diameter of about 55 nm. Raman spectra show tetrahedral and octahedral sites in the structure of Ni1–𝑥Zn𝑥Fe2O4 and also imply the doping of Zn2+ and displacement of Fe3+ ions from the tetrahedral site. EDAX showed that the samples were close to the nominal compositions. The magnetic measurement shows that the saturation magnetization and remanence magnetization decreases with the increase in the zinc content.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 5
October 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019