• Volume 38, Issue 4

August 2015,   pages  817-1118

• Viscoelastic nature of Au nanoparticle–PDMS nanocomposite gels

A stable gel of Au nanoparticles in polydimethylsiloxane (PDMS) nanocomposite is prepared by employing the curing agent of PDMS elastomer as a reducing agent for the formation of Au nanoparticles by an in-situ process. The viscoelastic nature of these gels is very sensitive to the Au nanoparticle loading and the synthetic temperature conditions. Even a very low Au content of 0.09 wt% is sufficient enough to bring in the transition from sponge state to gel state at room temperature. Higher synthetic temperature also forms sponge formation. Infrared and ultraviolet–visible spectroscopy measurements have provided insight into PDMS crosslinking and nanoparticle formation, respectively. The optimization of the gel properties can have direct influence on the processability of Au nanoparticle–PDMS nanocomposite gels, with interesting implications in electronic, optical and microfluidic devices.

• Effect of electron beam irradiation on the structure and optical properties of nickel oxide nanocubes

This work reports the effect of electron beam (EB) irradiation on the structure and optical properties of nanocrystalline nickel oxide (NiO) cubes. NiO nanocubes were synthesized by the chemical precipitation method. The characterization was carried out by employing analytical techniques like X-ray diffraction, transmission electron microscopy, UV–visible and photoluminescence (PL) spectroscopy. The present investigation found that non-stoichiometry, defects and particle size variation caused by EB irradiation have a great influence on optical band gap, blue shift and band modification of absorption and PL spectra. Moreover, EB irradiation can result enhanced optical absorption performance and photo-activity in NiO nanocubes for optoelectronics and photo-catalytic applications. The study of International Commission on Illumination chromaticity diagram indicates that NiO can be developed as a suitable phosphor material for the application in near ultraviolet excited colour LEDs.

• VRH investigation of polyaniline–multiwalled carbon nanotube nanocomposite network

Polyaniline and polyaniline/multi-walled carbon nanotube (PAni/MWCNT) nanocomposites were synthesized by in-situ chemical oxidative polymerization of aniline. Ammonium peroxydisulphate and p-toluenesulphonic acid were used as an initiator and surfactant dopant, respectively. The molar ratio of monomer unit to initiator and dopant was 1:1:1 and the percentage of MWCNT in PAni varied from 1 to 10 wt%. The structure of the resulting nanocomposite was characterized by scanning electron microscopy, X-ray diffraction and Fourier transform infrared spectroscopy. The effects of MWCNT concentration on the electrical properties of the resulting nanocomposites were studied at temperatures between 90 and 300 K. Conductivity increases with the combination of MWCNT in the PAni environment. The strong coupling between the MWCNT and the PAni chains enhances the average localization length and hence conductivity increases for the nanocomposites.

• Investigations on the microstructure and mechanical properties of multi-pass PCGTA welding of super-duplex stainless steel

This paper addresses the weldability, microstructure and mechanical properties of the multi-pass welding of super-duplex stainless steel (SDSS). Pulsed current gas tungsten arc welding (PCGTAW) was carried out employing ER2553 and ERNiCrMo-4 fillers. Microstructure examination showed the presence of austenite in different forms at the weld zone of ER2553 whereas multi-directional grain growth was observed for ERNiCrMo-4 welds. Tensile and impact studies corroborated that the weldments employing ER2553 exhibited better results compared with ERNiCrMo-4 weldments. Detailed structure–property relationships of the weldments have been reported in the present study. The results corroborated that the enhanced properties could be achieved with the matching filler wire compared with the over-alloyed filler.

• Studies on the preparation and the photoelectrochemical properties of the nanoporous titania films attached with and without photosensitizer TCPP

Fabrication of TiO2 nanoporous films was carried out by anodic oxidation using two-step voltage mode while the subsequent attaching of the photosensitizer 5,10,15,20-tetra(4-carboxyphenyl) porphyrin (TCPP) on the prepared TiO2 nanoporous films was carried out by the electrochemical method. Photoelectrochemical properties of TiO2 nanoporous films attached with and without photosensitizer TCPP were analysed by fluorescence spectroscopy and electrochemical test. Effects of process parameters on the photoelectrochemical properties of TiO2 nanoporous films were also investigated. The optimized process parameters for the preparation of TiO2 nanoporous films with the best photoelectrochemical property can be concluded as follows: oxidation potentials is 70–140 V, oxidation temperature is 25°C, H2SO4 electrolyte concentration is 0.5 mol l−1 and oxidation time is 60 min. The results also show that attaching of the photosensitizer TCPP on the TiO2 nanoporous films can indeed improve the properties of TiO2 nanoporous films, and the optimized attaching temperature and attaching voltage are 25°C and 60 V, respectively.

• Effect of milling time on the formation of carbon nanotube by mechano-thermal method

Mechano-thermal method was used for synthesizing the carbon nanotubes (CNTs) in this study. In this method, graphite powders in the elemental form were firstly exposed to milling process in high-energy ball milling and then the milled powders were annealed at high temperatures. As a result of milling of the graphite, ultra-active disordered carbon structures were obtained. This structure serves as a carbon source for the formation of nanotubes during the annealing process. This study investigated the effect of the milling process. For this purpose, graphite powders were milled at different periods such as 5 and 150 h and then annealed at 1600°C. The transmission electron microscopy and scanning electron microscopy examinations demonstrated that CNTs formed in samples milled both for 5 and 150 h. However, the difference in the milling time influenced the amount of CNTs, their size and the formation of other structures except from nanotubes.

• Mixed valence nanostructured Mn3O4 for supercapacitor applications

Nanostructured Mn3O4 with an average crystallite size of ∼19 nm was synthesized through a microwave-assisted chemical route. Structural characterization was carried out using X-ray diffraction analysis and transmission electron microscopy. Observed change in the ratio of lattice constants, 𝑐/𝑎 for the sample compared with single-crystalline Mn3O4 points to the presence of Mn4+ ions at the octahedral sites. This is attributed to the presence of cation vacancies. X-ray photoelectron spectroscopic studies confirm the presence of Mn4+ ions. Specific capacitance value of 665.08 F g−1 was obtained for symmetric supercapacitor with Mn3O4 active material at slow scan rate. Reasonably high power and energy density values, viz., 4.27 kW kg−1 and 4.36 × 10−2 Wh kg−1, respectively, were obtained for charge–discharge cycles at a constant current of 12.74 mA cm−2.

• Nanoscratch technique for aligning multiwalled carbon nanotubes synthesized by the arc discharge method in open air

Horizontally aligned and densely packed multiwalled carbon nanotubes (MWCNTs) were synthesized in an open air, without the need for a controlled atmosphere, using a rotating cathode arc discharge method with the help of a metal scraper. The physical force exerted by the scraper results in in-situ alignment of MWCNTs along the direction of scrape marks. This strategy, which enables the alignment of nanotubes in a controlled fashion to any length and direction of interest, was examined to determine the force required to align a nanotube. A model is developed to understand the alignment process. Using the nanoscratch technique to mimic this strategy, and incorporating the data obtained from the nanoscratch technique into the model developed, the minimum force required to align a MWCNT, as well as the energy required to align a gram of nanotubes, has been estimated. The method demonstrated represents an economical approach for large-scale synthesis of aligned MWCNTs at low costs.

• Sol–gel synthesis of palladium nanoparticles supported on reduced graphene oxide: an active electrocatalyst for hydrogen evolution reaction

In this work, the synthesis and characterization of palladium nanoparticle-reduced graphene oxide hybrid (Pd–rGO) material is reported. Techniques of X-ray diffraction, transmission electron microscope (TEM), energy-dispersive X-ray, FT-IR spectroscopy, thermogravimetric analysis and cyclic voltammetry were used to characterize the structure and properties of the Pd–rGO. Results demonstrate the effect of Pd on the reduced GO. The average particle size of the Pd nanoparticles supported on rGO obtained from TEM is about 12–18 nm. Moreover, glassy carbon electrode (GCE) modified with palladium nanoparticle–graphene oxide hybrid (Pd–rGO/GCE) was prepared by casting of the Pd–rGO solution on GCE. The electrochemical and catalytic activity of the Pd–rGO/GCE was studied in 0.1 M H2SO4 solution. The Pd–rGO/GCE electrode exhibited remarkable electrocatalytic activity for the hydrogen evolution reaction (HER). At potential more negative than −0.4 V vs. Ag|AgCl|KCl3M, the current is mainly due to hydrogen evolution reaction. Finally, the kinetic parameters of hydrogen evolution reaction are also discussed on the Pd–rGO/GCE.

• Effects of crystalline growth on corrosion behaviour of nanocrystalline NiAl coating

In the current work, the effect of crystalline growth on the corrosion behaviour of nanocrystalline NiAl coating was investigated. In this regard, NiAl coatings with different crystalline sizes in the range of 20–110 nm were produced by mechanical alloying, high-velocity oxy-fuel processing (HVOF) and isothermal annealing at 600°C for 0–30 h. The produced and annealed samples were characterized using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The corrosion behaviours of coatings were examined in NaCl 3/5% electrolyte by potentiostat analysis. The nanocrystalline NiAl coating with the average crystalline size of about 20 nm and the porosity content of about 2% was successfully produced by mechanical alloying and HVOF processing. By annealing the coating, the NiAl crystalline sizes increased sharply, approaching a constant value of about 110 nm. It was found that the corrosion resistance of nanocrystalline coating increased with the increase in the crystalline size.

• Defect-assisted tuning of electroluminescence from p-GaN/n-ZnO nanorod heterojunction

Growth of nanostructured ZnO by solution process always lead to the formation of various kinds of defects. Defect states also can aid in improving different properties of the material. In the case of light-emitting diodes (LEDs), major research is focused on tuning the emission colour so as to achieve white emission without the use of any phosphors. Vertically aligned ZnO nanorods were grown over Mg:GaN substrate by hydrothermal process. High-resolution X-ray diffraction (HRXRD) analysis confirms the epitaxial growth of nanorods over the substrate. The photoluminescence (PL) studies revealed a narrow near band edge emission and a broad defect-induced deep level emission. The intensity of deep level emissions related to Zni, Vo, Oi defects decreases on annealing. The 𝑉-𝐼 characteristics of the heterojunction showed excellent rectifying nature with electroluminescence emission on forward bias. Device fabricated by as-grown ZnO nanorods emits in the UV–blue region and broad emission in the visible region. While the annealed device emitted only in UV–blue region. The emission wavelengths closely matched with that of defect state emissions obtained in the PL studies. By annealing, various defect states density can be controlled, thereby emission colour tuned from white to blue.

• Detection of methane using multi-walled carbon nanotubes

A sensor for detecting and estimating methane using multi-walled carbon nanotubes (MWCNTs) as the sensing element has been developed for the first time. Silver electrodes have been ink-jet printed on glass substrate over which MWCNT is brush coated to fabricate the sensor element which is of chemoresistive type. The sensitivity of the sensor (increase in the resistance of the sensor on exposure to analyte) increases linearly with concentration of methane and a maximum sensitivity of about 20% has been observed for 160 ppm of methane. A prototype device has been fabricated with this sensor and tested for its performance. It could be used to detect methane on site.

• NiCr𝑥Fe2-𝑥O4 ferrite nanoparticles and their composites with polypyrrole: synthesis, characterization and magnetic properties

Nanocrystalline nickel chromium ferrite (NiCr𝑥Fe2-𝑥O4, 𝑥 = 0.1, 0.2) have been prepared by the chemical co-precipitation method. Half of the samples have been sintered at 620°C and the other at 1175°C. Then polypyrrole (PPy)–NiCr𝑥Fe2-𝑥O4 composites have been synthesized by polymerization of pyrrole monomer in the presence of NiCr𝑥Fe2-𝑥O4 nanoparticles. The structure, morphology and magnetic properties of the samples have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infrared (FT-IR) spectroscopy and vibrating sample magnetometer. Also, the initial magnetic permeability measurements as functions of temperature and frequency have been performed. The XRD and FT-IR studies have confirmed the well crystalline phase of ferrite nanoparticles, and the presence of amorphous PPy in the composite samples. The SEM and TEM images have obviously clarified the coating of ferrite nanoparticles by PPy in the composite samples. The hysteresis loop of the samples has proved that the samples are soft magnetic material because of their low coercivity.

• Molecular transport behaviour of organic solvents through halloysite nanotubes filled ethylene–vinyl acetate copolymer

The transport behaviour of three organic solvents (benzene, toluene and xylene) through halloysite nanotubes (HNTs) filled ethylene–vinyl acetate (EVA) copolymer composites have been investigated in the temperature range 303–323 K. The effects of HNTs loading, nature of solvent and temperature on the transport behaviour of solvents through composites were studied. It has been observed that all the systems follow a Fickian mode of transport on increasing temperature. The solvent uptake and sorption coefficient decreases with the increase in halloysite loading while diffusion coefficients and permeation coefficients were found to be dependent on the concentration of filler. The percentage of bounds rubber content and swelling ratio decreases up to 7.5 phr filler content, whereas above 7.5 phr filler loading were found to be increased due to poor dispersion of halloysite in EVA copolymer matrix. The transport behaviour of three organic solvents was further validated by their crosslink density values. The thermodynamic parameters such as enthalpy, entropy and free energy of sorption were evaluated. The positive values of free energy indicate the non-spontaneity of the sorption of HNTs filled EVA in aromatic solvents at 303 K.

• Effect of nanocrystalline surface of substrate on microstructure and wetting of PEO coatings

In this research, effect of surface mechanical attrition treatment (SMAT) was studied on characteristics of the coatings formed using plasma electrolyte oxidation (PEO) on AA1230 aluminium. To do so, first, the samples were coated with and without SMAT pre-process. Coating by PEO method was carried out in two phosphate-based and silicate-based suspensions of silicon nitride nanoparticles for 10 min. Next, to study the distribution of the nanoparticles and elements inside the coating, surface morphology of the samples was examined using scanning electron microscopy and energy dispersive spectroscopy. In addition, wettability test was performed on all samples using the deionized water. Also, droplet expansion manner on the porous oxide coating surface and its relation with fine structure of the coating was investigated. The results indicated that samples coated in silicate-based electrolyte have a relatively rougher microstructure as compared to samples coated in phosphate-based electrolyte. The average surface pores area percentage of the samples coated in silicate-based electrolytes was 13.9% greater than that of samples coated in phosphate-based electrolyte. Moreover, the average height to diameter (h/d) value obtained from wettability test for samples coated in silicate-based electrolyte was 13.3% greater than that of phosphate-based electrolyte.

• Biosynthesis of Yttrium oxide nanoparticles using Acalypha indica leaf extract

In this study, the synthesis of Yttrium oxide (Y2O3) nanoparticles was carried out from Acalypha indica leaf extract. The synthesized nanoparticles were characterized by using X-ray diffraction, scanning electron microscope, energy-dispersive X-ray spectrometer and transmission electron microscope for structural confirmation. The studies clearly indicate that the synthesized Y2O3 nanoparticle is a crystalline material with a particle size from 23 to 66 nm. Further analysis was carried out by Fourier transform infrared spectroscopy, to provide the evidence for the presence of Y–O–Y and O–Y–O stretchings in the synthesized Y2O3 nanoparticles. Thermogravimetric and differential scanning calorimetry analyses gave the thermal stability of Y2O3 nanoparticles. The results of the antibacterial studies conducted by using the synthesized Y2O3 revealed an increasing rate of antibacterial behaviour with pathogens.

• Corrosion, haemocompatibility and bacterial adhesion behaviour of TiZrN-coated 316L SS for bioimplants

TiZrN coating was deposited on 316L stainless steel (SS) by the reactive magnetron co-sputtering technique. Cubic phase of TiZrN with uniform surface morphology was observed by X-ray diffraction and atomic force microscopy. Bacterial adhesion, haemocompatibility and corrosion behaviour of TiZrN coating were examined in order to evaluate the coating’s compatibility for ideal implant. Results revealed that TiZrN coatings exhibited less bacterial attachment against Staphylococcus aureus and Escherichia coli bacteria, negligible platelets activation and superior corrosion resistance than the uncoated 316L SS.

• Bioactivity and mechanical behaviour of cobalt oxide-doped bioactive glass

Bioactive glasses are materials capable of bonding implants to tissues. 45S5 Bio-glass® is one such material capable of bonding strongly to bone within 6 weeks. It develops a hydroxy-carbonate apatite layer on the implant that is chemically and crystallographically equivalent to the mineral phase of bone. However, it suffers from a mechanical weakness and low fracture toughness due to an amorphous glass network and is not suitable for load-bearing applications. In order to improve its mechanical strength and bioactivity, the present work explores the effects of cobalt oxide additions. Bioactivity of the glass samples was assessed through their hydroxyapatite formation ability by immersing them in the simulated body fluid for different soaking periods. The formation of hydroxyapatite was confirmed by Fourier transform infrared spectrometry, pH measurement and microstructure evaluation through scanning electron microscopy. Densities and mechanical properties of the samples were found to increase considerably with an increase in the concentration of cobalt oxide.

• Biological synthesis and characterization of silver nanoparticles using Eclipta alba leaf extract and evaluation of its cytotoxic and antimicrobial potential

With increasing global competitions there is a growing need to develop environmentally benevolent nanoparticles without the use of toxic chemicals. The biosynthesis of silver nanoparticles (AgNPs) using plant extracts became one of the potential areas of research. The bioreduction of metal ion is quite rapid, readily perform at room temperature and easily scale up. The present study describes a rapid and eco-friendly synthesis of AgNPs using Eclipta alba plant extract in a single pot process. The efficiency and the influence of various process variables in the biosynthesis of AgNPs analysed include redundant concentration, temperature and time. AgNPs were rapidly synthesized using aqueous leaf extract of E. alba and was observed when the medium turned to brown colour with the addition of silver ion. Biosynthesized AgNPs were characterized by the help of UV–visible spectroscopy for their stability and physicochemical parameters were studied by dynamic light scattering, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy. The obtained results confirmed that recorded UV spectra show the characteristic surface plasmon resonance band for AgNPs in the range of 400–440 nm and physiochemical structural analysis shown that obtained AgNPs were crystalline in nature. Further, cytotoxic and antimicrobial activities of biosynthesized AgNPs against RAW 254.7, MCF-7 and Caco-2 cells as well as Gram positive and Gram negative bacteria were assessed. In-vitro cytotoxicity activity of characterized AgNPs against tested cell lines showed significant anti-cell-proliferation effect in nanomolar concentrations. The antibacterial activity of synthesized AgNPs showed effective inhibitory activity against human pathogens, including, Escherichia coli, Staphylococcus aureus and Pseudomonas aeruginosa. Thus, the significant outcome of this study would help to formulate value added herbal-based nano-materials in biomedical and nanotechnology industries.

• Reactive alumina–LaPO4 composite as machinable bioceramics

Sintered Al2O3–LaPO4 composites were prepared using commercially available reactive alumina and phase pure lanthanum phosphate (LP), prepared by the reaction synthesis technique. LP content was varied between 10 and 50 wt% and sintering was carried out between 1400 and 1600°C. Sintered composites were characterized for phase analysis, densification, strength, machinability, microstructure and bioactivity (in SBF solution) and biocompatibility (MTT assay protocol) studies. Composite nature was confirmed by phase analysis and LP was found to reduce the densification and strength values but imparted machinability. Again positive bioactivity and biocompatibility character were observed for all the compositions.

• Conductivity studies on microwave synthesized glasses

Conductivity measurements have been made on 𝑥𝑉2O5 − (100 − 𝑥) [0.5 Na2O + 0.5 B2O3] (where 10 ≤ 𝑥 ≤ 50) glasses prepared by using microwave method. DC conductivity (𝜎) measurements exhibit temperature-and compositional-dependent trends. It has been found that conductivity in these glasses changes from the predominantly ‘ionic’ to predominantly ‘electronic’ depending upon the chemical composition. The dc conductivity passes through a deep minimum, which is attributed to network disruption. Also, this nonlinear variation in 𝜎dc and activation energy can be interpreted using ion–polaron correlation effect. Electron paramagnetic resonance (EPR) and impedance spectroscopic techniques have been used to elucidate the nature of conduction mechanism. The EPR spectra reveals, in least modified (25 Na2O mol%) glasses, conduction is due to the transfer of electrons via aliovalent vanadium sites, while in highly modified (45 Na2O mol%) glasses Na+ ion transport dominates the electrical conduction. For highly modified glasses, frequency-dependent conductivity has been analysed using electrical modulus formalism and the observations have been discussed.

• Synthesis, characterization and electrical properties of visible-light-driven Pt-ZnO/CNT

This paper deals with synthesis of ZnO doped with different concentrations of platinum (Pt) and its deposition on the surface of multi-walled carbon nanotube (MWCNT). The synthesized nanocomposite material was characterized by standard analytical techniques like X-ray diffraction (XRD), UV–vis spectroscopy, scanning electron microscopy, transmission electron microscopy and energy-dispersive spectroscopy. The XRD analysis confirms two things; first, synthesized nanocomposite shows no impurity peaks indicating products being crystalline in nature, second, the phase structure of composite remains unchanged during doping of Pt into ZnO crystal. Results indicate that the incorporation of dopant into ZnO coated on the surface of MWCNT was found to shift the fundamental absorption edge towards the longer wavelength side. The impedance analysis was carried out to distinguish between the grain and grain boundary contributions to the system. The dielectric property was strongly affected by increasing the dopant concentration. The dielectric constant (𝜖) and dielectric loss (tan 𝛿) factors decrease with the increase in frequency only upto a certain limit. The a.c. conductivity also increases with the increase in frequency.

• Mechanical, dielectric and optical assessment of glass composites prepared using milling technique

In the present investigation, mechanical and spectroscopic properties of glass composites have been investigated. The glass composites have been prepared by the milling technique instead of using any filler particle. Due to the presence of different alkaline earth modifiers in composites, marked difference in their strength and optical properties is observed. The band gap, Urbach energy and the extinction coefficient of the glass composites have been calculated using UV–visible spectroscopy. Moreover, the real and imaginary dielectric constants have also been calculated for all the composites in addition to the Weibull statistics and cumulative probability of failure. The results have been discussed in light of comparison between the glass composites and the individual glasses. The mechanical and optical properties indicate marked effect on the mechanical strength, band gap and Urbach energy for glass composites as compared with the individual glasses.

• Synthesis and evaluation of effective parameters in thermal expansion coefficient of Ln0.6Sr0.4Co0.2M0.8O3−𝛿 (Ln = La,Nd and M = Mn,Fe) perovskite oxide

In this study, oxides Ln0.6Sr0.4Co0.2M0.8O3−𝛿 (Ln = La,Nd and M = Mn,Fe) have been prepared and characterized to study the influence of the different cations on thermal expansion coefficient (TEC). TEC decreases favourably with replacement of Nd3+ and Mn3+ ions in the lattice. Nd3+ leads to decreasing ionicity of the Ln–O bond and phase transition from rhombohedral to orthorhombic. Structural parameters of compounds have been determined by X-ray diffraction (XRD). FT-IR analysis has been used to compare the bond strength of different cations in the lattice. Variations of lattice parameters of compounds have been monitored by in-situ XRD at different temperatures in order to study the thermo-chemical expansivity. Concentration of oxide ion vacancy has been determined by high temperature gravimetry. The results show more stability of Mn4+ ions in high temperature in comparison with Fe4+ ions, which suppreses the tendency to lose oxygen from the lattice with the increase in temperature.

• Synthesis and analysis of Fe3+, Co2+ and Ni2+ : PEO + PVP blended polymer composite films for multifunctional polymer applications

Blended polymer films of polyethylene oxide + polyvinyl pyrrolidone (PEO + PVP) containing transition metal (TM) ions like Fe3+, Co2+ and Ni2+ have been synthesized by a solution casting method. For these films, structural, thermal, magnetic and optical properties have been studied. X-ray diffraction results reveal the semi-crystalline nature of the polymer films. Thermal stability of the host (undoped) polymer film has been investigated from its thermogravimetric–differential thermal analysis profiles. Raman spectral profiles indicate a complex formation trend owing to the addition of TM ions into the host matrix. Co2+, Fe3+ and Ni2+ ions doped polymer films have revealed ferromagnetism based on their vibrating sample magnetometre profiles. However, the host polymer film has exhibited a paramagnetic nature. Further, ionic conductivities have been calculated using an impedance analyser at different temperatures for all the samples. Among these films, a maximum ionic conductivity (𝜎 = 7.5 × 10−6 S cm−1) has been noticed from PEO + PVP : Ni2+ polymer film at 373 K. Emission analysis of Co2+ : PEO + PVP polymer film has exhibited a strong red emission under an UV source and from both PEO + PVP : Fe3+; PEO + PVP: Ni2+, green emissions have commonly been noticed under an UV source. Thus, based on these results, it could be suggested that these TM ions doped PEO + PVP polymer films are found to be potential multifunctional materials for magneto-electric, magneto-optic fields with encouraging electrical, dielectric and optical properties as well as displaying with ferromagnetic nature from the doped films.

• Synthesis of acrylate guar-gum for delivery of bio-active molecules

Modification of natural polymers by graft copolymerization is a promising technique as it functionalizes these biopolymer to their potential, imparting desirable properties onto them. Grafting with vinyl monomers is the route for modifying the properties of the naturally occurring guar-gum for their better industrial exploitation and development of various commercial products. Acrylated guar-gum chain is synthesized and analysed using Fourier transform infrared, differential scanning calorimetry and X-ray diffraction techniques to gain an insight into the particle size and structural features. Chlorpyrifos is then entrapped into the polymer, and its release is studied under various conditions. Critical factors influencing the size, entrapment efficiency and release behaviour of entrapped chlorpyrifos have been studied.

• Effect of zinc oxide nanoparticles synthesized by a precipitation method on mechanical and morphological properties of the CR foam

ZnO nanoparticles were synthesized by a precipitation method in aqueous media from zinc nitrate hexahydrate and sodium hydroxide. The synthesized ZnO nanoparticles exhibited a crystalline structure with hexagonal structure of the wurtzite. The morphology of the synthesized ZnO nanoparticles presented a spherical shape with the average primary size of 54.53 nm and the specific surface area of 20.28 m2 g−1. The effect of the synthesized ZnO nanoparticles by the precipitation method as a crosslinking agent for chloroprene rubber foam (CR foam) on cure characteristics, mechanical properties and morphologies was investigated. The aim of this study is to vary the synthesized ZnO nanoparticles’ level in the range of 0.5–5 parts per hundred parts of rubber (phr) compared with the conventional ZnO at 5 phr. The rheological characterization showed that the maximum torque (𝑀H), the minimum torque (𝑀L), the differential torque (𝑀H–𝑀L) and Mooney viscosity increased with the increase in synthesized ZnO nanoparticles’ content, whereas the optimum cure time (𝑡90) and scorch time (𝑇5) decreased. On the other hand, the mechanical properties such as hardness, tensile strength and specific gravity were improved. For CR foam, the results compared to the amount of conventional ZnO, only 60 wt% (3 phr) nano-ZnO was enough to obtain similar cure characteristics and mechanical properties. The synthesized ZnO nanoparticles showed the mechanical properties higher than conventional ZnO because of small particle size and large specific surface area which led to the increase in the degree of crosslinking.

• Synthesis of iron/GAC catalyst for wastewater treatment using heterogeneous Fenton reaction

Iron catalyst dispersed on granular activated carbon (GAC) was prepared by impregnating Fe(NO3)3 solution on GAC. The mixed solution was annealed at 600°C in muffle furnace under ambient condition for 1 h. The structural property of the catalyst was investigated using X-ray diffraction (XRD). The catalyst’s activity and lifetime were tested using the degradation of 50 ppm methyl orange (MO) solution. In addition, the optimum conditions of the Fenton reaction such as initial pH, initial MO concentration hydrogen peroxide concentration and the amount of catalyst were also investigated. The XRD results showed that magnetite and haematite were two main compositions of the synthesized catalyst. The investigation of optimum conditions suggested that initial pH at 3 provided the highest efficiency of MO removal. In addition, the concentration of hydrogen peroxide at 8 ppm was the most suitable. The optimum condition of amount of catalyst was 5 g l−1. The efficiencies of MO removal reached 95% at 60 min of reaction time at low initial MO concentration (25–500 mg l−1). In the meantime, the removal efficiency was found to decrease with the increase in the initial MO concentration. The efficiency decreased to 70 and 30% at 1000 and 3000 mg l−1 of initial MO concentration, respectively. Additionally, after reuse the synthesized catalyst 3 times the MO removal efficiency still remained over 90%. In conclusion, the iron/GAC catalyst was successfully synthesized and applied to dye treatment using heterogeneous Fenton reaction. The catalyst showed high efficiency of MO removal and could be reused many times.

• Photocatalytic generation of hydrogen under visible light on La2CuO4

The semiconducting properties of La2CuO4 prepared by a chemical route are investigated for the first time by the photo-electrochemical technique. The optical gap is found to be 1.27 eV and the transition is directly allowed. p-Type conductivity is demonstrated from the Mott–Schottky plot in alkaline KOH solution (0.1 M), extrapolation of the linear region to the potential axis gives a flat band potential of −0.41 VSCE, a holes density of 1.75 × 1019 cm−3 and a space-charge region of 18 nm. The electrochemical impedance spectroscopy, measured over the frequency range (1 mHz–105 Hz), reveals the predominance of the bulk contribution with a constant phase element. The energy diagram shows the feasibility of La2CuO4 for the H2 evolution under visible light. The best performance occurs at pH 12.5 in the presence of S2O$^{2-}_{3}$ as holes scavenger. A liberation rate of 20.6 𝜇mol mn−1 (g catalyst)−1 is obtained under full light (29 mW cm−2).

• Study of the degree of deuteration on the microhardness of deuterated potassium dihydrogen phosphate crystals

A series of deuterated potassium dihydrogen phosphate (DKDP) crystals with different degrees of deuteration are grown from aqueous solution by the point-seed technique. The microhardness of (100), (001) and so-called ‘tripler’ faces for these DKDP crystals were measured. Initially the hardness number of (001) face for each crystal increases with the increase of the applied load until it reaches 25 g. With further increase in load, the hardness number decreases gradually. The hardness numbers decline with the increase in deuterium content. These composition dependences are expected since the bond strength is weakened by the substitution of deuterium for hydrogen. The hydrogen bond is considered to play the key role in effecting the crystal’s hardness. The visible hardness anisotropy of the different faces is attributed to the inhomogeneous distribution of the oxygen–hydrogen bond on these faces.

• Study of influence on micro-fabricated resistive switching organic ZrO2 array by C-AFM measurement

In this paper, a comparison of the interfacial electronic properties between Pt/Ir conductive atomic force microscopy (C-AFM) tip and ZrO2 organic array was carried out. A uniformed ZrO2 array was fabricated with a mean diameter of around 1 𝜇m using laser interference lithography. A C-AFM measurement set-up was built up. The 𝐼-𝑉 curve was directly measured of the organic ZrO2 array which shows a resistive switching characteristic by C-AFM measurement. The set voltage is 18.0 V and the reset voltage is −5.0 V. After the Pt layer was coated on the ZrO2 array, the set voltage decreases to 0.8 V and the reset voltage decreases to −2.2 V. This result shows that Pt layer can prevent the potential drop effectively. The electron barrier height between Pt/Ir C-AFM tip and organic ZrO2 array was enhanced by sputtering Pt layer on the ZrO2 organic array.

• Crystal structure of the quaternary compounds CuFe2AlSe4 and CuFe2GaSe4 from X-ray powder diffraction

The crystal structure of the quaternary compounds CuFe2AlSe4 and CuFe2GaSe4, belonging to the system I–II2–III–VI4, were characterized using X-ray powder diffraction data. Both compounds crystallize in the tetragonal space group I42m (No. 121), 𝑍 = 2, with unit cell parameters 𝑎 = 5.609(1) Å, 𝑐 = 10.963(2) Å for CuFe2AlSe4 and 𝑎 = 5.6165(3) Å, 𝑐 = 11.075(1) Å for CuFe2GaSe4. These compounds are isostructural with CuFe2InSe4, and have a normal adamantane stannite structure.

• Structural, electronic and magnetic properties of MnB2

The self-consistent ab-initio calculations, based on density functional theory approach and using the full potential linear augmented plane wave method, are performed to investigate both electronic and magnetic properties of the MnB2 compounds. Polarized spin and spin–orbit coupling are included in calculations within the framework of the ferromagnetic state between two adjacent Mn atoms. Magnetic moment considered to lie along the (001) axes are computed. The antiferromagnetic and ferromagnetic energies of MnB2 systems are obtained. Obtained data from ab-initio calculations are used as input for the high-temperature series expansions (HTSEs) calculations to compute other magnetic parameters. The exchange interactions between the magnetic atoms Mn–Mn in MnB2 are established by using the mean field theory. The HTSEs of the magnetic susceptibility with the magnetic moments in MnB2 (𝑚Mn) through Ising model is given. The critical temperature 𝑇C (K) is obtained by HTSEs applied to the magnetic susceptibility series combined with the Padé approximant method. The critical exponent 𝛾 associated with the magnetic susceptibility is deduced as well.

• Instrumental characterization of the smectite clay–gentamicin hybrids

This paper focusses on the intercalation of clay mineral with gentamicin (an aminoglycoside antibiotic). The smectite clay–gentamicin hybrids were prepared by a solution intercalation at 60°C and the process was carried out on unmodified smectite clay and on smectite after Na+ ionic activation. The resulting structural/microstructural properties and the potential for introducing gentamicin between smectite clay layers were investigated by means of X-ray diffraction, Fourier transform infrared spectroscopic techniques and transmission electron microscopy and scanning electron microscopy with energy-dispersive spectroscopy X-ray analysis. The results confirm the successful intercalation of gentamicin into the interlayer space of smectite clay, demonstrating that the material thus obtained could potentially be used as a drug carrier.

• Contribution of sodium dodecyl sulphate and sodium lauric acid in the one-pot synthesis of intercalated ZnAl-layered double hydroxides

Anion surfactants, sodium dodecyl sulphate (SDS) and sodium lauric acid (SLA), with almost the same chain length but different anion groups were used together as intercalates to prepare intercalated ZnAl–layered double hydroxides (ZnAl–LDHs). Their composition, structure and morphology were characterized by Fourier transform infrared, X-ray fluorescence, thermogravimetric and X-ray diffraction (XRD). The results indicated SDS intended to maintain the lamellae structure of LDHs, but SLA was more likely to expand the basal spacings of LDHs in the present system. The arrangement of the surfactants in the interlayer of ZnAl–LDHs was also simulated by Materials Studio. The basal spacings of the LDHs calculated based on simulated structure consisted with that from XRD.

• Preparation and characterization of zinc and cobalt (II, III) oxides mixture and direct red 23 diazo dye heterogeneous photocatalysis

The decolourization of the direct red 23 diazo dye, commonly used in textile industries, was investigated through the heterogeneous photocatalysis mediated by zinc oxide, n-type semiconductor combined with p-type cobalt oxide at 30°C. The mixture of n- and p-type semiconductors may form a p–n junction, which can decrease the band gap energy and thus increase the photocatalytic activity. This work reports the preparation and characterization of cobalt oxide and oxide mixtures of Zn and Co in 1, 3 and 5% proportions, respectively, as well as their photocatalytic activity, measured by direct red 23 diazo dye decolourization rate constants. These oxides were characterized through the X-ray diffraction, scanning electron microscope, energy-dispersive X-ray spectroscopy, X-ray fluorescence spectroscopy and diffuse reflectance spectrophotometry. The suspension, formed from direct red 23 diazo dye solution and oxide mixtures, was kept in the dark for 1 h at 30°C for diazo dye adsorption on the oxide surface and irradiated by UV light for diazo dye decolourization. The mixture of ZnO containing, respectively, 3 and 5% cobalt oxide showed higher decolourization rate constant in comparison to ZnO.

• Influence of solvent evaporation rate on crystallization of poly(vinylidene fluoride) thin films

The processes for obtaining crystalline and smooth poly(vinylidene fluoride) (PVDF) thin films using 2-butanone solvent are explored. The in-situ substrate temperature has been systematically controlled to observe the crystallization process. The in-situ substrate temperature is manipulated to control the rate of evaporation of 2-butanone solvent and is found to have played a vital role in the crystallization of PVDF thin films. Further, X-ray diffraction and Raman microscope were utilized to understand the crystalline phase of PDVF thin films, while atomic force microscopy and scanning electron microscopy have been utilized to investigate the surface morphology and surface roughness of the films.

• Influence of substrate and Ca substitution on multiferroic BiMnO3 thin films

BiMnO3 (BMO) and Ca (10 at%) substituted BiMnO3 (BCMO) thin films are grown on n-type Si (100) and Pt/Ti/SiO2/Si (100) substrates by RF magnetron sputtering. The structural, elemental, morphological, magnetic, dielectric and ferroelectric properties of the films are investigated by X-ray diffraction (XRD), energy-dispersive X-ray analysis (EDAX), atomic force microscope (AFM), vibrating sample magnetometer (VSM), dielectric and ferroelectric measurements, respectively. The XRD pattern shows that the films acquire monoclinic structure with C2 space group. The elemental composition and surface roughness of the films are also measured by EDAX and AFM analysis, respectively. The VSM results exhibit that all the films possess room temperature ferromagnetism and the BCMO film deposited on the Si substrate has better magnetic properties (𝑀rem = 1.8 × 10−3 emu cm−3) than the other films. The dielectric measurement also reveals that the BCMO film has the highest value of dielectric constant (497) with less dielectric loss (0.3). Similarly, the ferroelectric measurement implies that all the films possess room temperature ferroelectricity.

• Effect of RF power and gas flow ratio on the growth and morphology of the PECVD SiC thin films for MEMS applications

Low-temperature plasma enhanced chemical vapour deposition (PECVD) deposited silicon carbide (SiC) thin films are promising materials for the development of high-temperature working microelectromechanical system (MEMS) owing to their excellent mechanical properties, non-corrosive nature and ability to withstand high temperature. However, the surface roughness of such thin films is the main obstacle to achieve thicker thin films for MEMS applications as the surface becomes more rougher with the increase in the thickness of PECVD SiC thin films. Therefore, in this present study, thicker SiC thin films were deposited by PECVD process by using CH4 and SiH4 as the precursor gases in the presence of Ar as the carrier gas and two process parameters, i.e., radio frequency (RF) power with mixed frequency condition and flow ratio of silane to methane were varied by keeping the temperature and pressure constant to investigate the influence of these parameters on the growth rate, surface roughness and morphology of SiC thin films. It was observed that both the RF power (with the mixed frequency condition) and flow ratio of SiH4/CH4 can control the growth rate, surface roughness and morphology of the PECVD SiC thin films. Higher the carbon content in the thin films the surface became more smoother, whereas the surface became for rougher by increasing the RF power.

• Growth kinetics of boride layers formed on 99.0% purity nickel

The present study reports on the kinetics of borided Nickel 201 alloy. The thermochemical treatment of boronizing was carried out in a solid medium consisting of B4C and KBF4 powders mixture at 1123, 1173 and 1223 K for 2, 4 and 6 h, respectively. The boride layer was characterized by optical microscopy, X-ray diffraction technique and micro-Vickers hardness tester. X-ray diffraction analysis revealed the existence of NiB, Ni2B, Ni3B and Ni4B3 compounds at the surface of borided Nickel 201 alloy. The thickness of the boride layer increased with an increase in the boriding time and the temperature. The hardness of the nickel borides formed on the surface of the nickel substrate ranged from 1642 to 1854 HV0.05, whereas the Vickers hardness value of the untreated nickel was 185 HV0.05. The growth kinetics of boride layers forming on the borided Nickel 201 alloy was also analysed. The boron activation energy (𝑄) was estimated as equal to 203.87 kJ mol−1 for the borided Nickel 201 alloy.

• # Bulletin of Materials Science

Volume 43, 2020
All articles
Continuous Article Publishing mode

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019