• Volume 38, Issue 6

October 2015,   pages  1473-1671

• Low temperature synthesis of nanocrystalline scandia-stabilized zirconia by aqueous combustion method and its characterizations

Zirconia stabilized with 11 mol% scandia (11ScSZ) has been successfully synthesized by novel alanine-assisted soft chemical aqueous combustion method. The reaction kinetics during combustion synthesis has been studied in detail by analysing thermal behaviour of different metal–alanine complexes. A single phase 11ScSZ powder is achieved at significantly low calcination temperature of 500° C. Field emission scanning electron micrograph reveals an agglomerated morphology with particle size ranging from 80 to 100 nm. The thermal expansion coefficient is found to be 11.03 × 10−6 °C−1 in the temperature range between room temperature and 1000° C. Optical bandgap of 5.19 eV has been determined using UV–Vis spectroscopy and results are compared with the help of theoretical density of states. The total electrical conductivity of sintered pellet is found to be 7.3 × 10−3 S cm−1 at 700° C as measured by impedance spectroscopy.

• Influences of protective atmosphere on the characterization and properties of NaSr2Nb5O15 lead-free piezoelectric ceramics by sol–gel method

NaSr2Nb5O15 lead-free piezoelectric ceramics were prepared by the sol–gel method; they were sintered at different temperatures with or without protective atmosphere. The influences of sintering temperature and protective atmosphere on the characterization and properties of the ceramics were investigated. All the ceramics showed the pure tungsten bronze structure and an intermediate relaxor-like behaviour between normal and ideal relaxor ferroelectrics according to the modified Curie–Weiss law. The sintering temperature affected significantly the properties of ceramics, with the sintering temperature increased both with and without protective atmosphere, the 𝜀r, 𝑑33, 𝐾p and 𝑃r of these ceramics initially increased and decreased finally, whereas the variation of 𝑄m and 𝐸c showed the opposite tendency. Furthermore, the protective atmosphere also significantly affected the properties of these ceramics, 𝜀r, 𝑑33, 𝐾p and 𝑃r of such ceramics sintered with protective atmosphere were superior to those of the ceramics sintered without protective atmosphere, while the tan 𝛿, 𝑄m and 𝐸c gave the contrary results.

• Anomalous properties of chloroborosilicate glasses in the K2O–BaO–Al2O3–B2O3–SiO2–BaCl2 system

A series of chloroborosilicate glass having composition (in mol%) (100−x)(42SiO2–30B2O3–20BaO–4K2O–4Al2O3)–xBaCl2 (where 𝑥 = 0−30) has been prepared by the melt quench technique yielding transparent monolithic glasses up to 𝑥 = 22.5. Structural investigation by infrared reflection and UV–vis–NIR absorption revealed the bridging action of Cl atom and decrease in non-bridging oxygens with the increase in BaCl2 content. Thermal properties (𝑇g, 𝑇d and 𝑇s) were measured by the dilatometry and softening point measurement. Viscosity was calculated using the Vogel–Fulcher–Tammann equation. Elastic constants were measured by the ultrasonic method. Other mechanical properties like hardness, fracture toughness were also measured. All of the thermal and mechanical properties exhibited a similar trend of anomalous variation as a function of the BaCl2 content, showing maxima at 10 mol% and a sharp increase at 25 mol% BaCl2 content. The anomaly has been explained by the structural point of view with the help of the aforementioned spectroscopic data.

• Sintering of magnesia: effect of additives

Effect of different additives, namely Cr2O3, Fe2O3 and TiO2, up to 2 wt% was studied on the sintering and microstructural developments of the chemically pure magnesia using the pressureless sintering technique between 1500 and 1600° C. Sintering was evaluated by per cent densification and microstructural developments were studied by electron microscopy and elemental distribution of the additives in the sintered products was also investigated for their distribution in the matrix. Cr2O3 and TiO2 were found to deteriorate the densification associated with grain growth. Fe2O3 was found to improve the densification and well-compacted grain distribution was observed in the microstructure.

• A 1 V supercapacitor device with nanostructured graphene oxide/polyaniline composite materials

Polyaniline and graphene oxide composite on activated carbon cum reduced graphene oxide-supported supercapacitor electrodes are fabricated and electrochemically characterized in a three-electrode cell assembly. Attractive supercapacitor performance, namely high-power capability and cycling stability for graphene oxide/polyaniline composite, is observed owing to the layered and porous-polymeric-structured electrodes. Based on the materials characterization data in a three-electrode cell assembly, 1 V supercapacitor devices are developed and performance tested. A comparative study has also been conducted for polyaniline and graphene oxide/polyaniline composite-based 1 V supercapacitors for comprehending the synergic effect of graphene oxide and polyaniline. Graphene oxide/polyaniline composite-based capacitor that exhibits about 100 F g−1 specific capacitance with faradaic efficiency in excess of 90% has its energy and power density values of 14 Wh kg−1 and 72 kW kg−1, respectively. Cycle-life data for over 1000 cycles reflect 10% capacitance degradation for graphene oxide/polyaniline composite supercapacitor.

• Shape tunable synthesis of Eu- and Sm-doped ZnO microstructures: a morphological evaluation

Facile and low-cost aqueous chemical bath deposition route has been demonstrated to fabricate Eu- and Sm-doped ZnO microstructures. The effect of Eu and Sm ions on the morphology of the ZnO was investigated. The synthesized doped ZnO microstructures were systematically characterized by field-emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman and Fourier transform infrared spectra. FESEM images depicted the formation of Eu-doped ZnO microsphere and Sm-doped ZnO microplates. XRD spectra showed single crystalline nature of the undoped ZnO microdisks, whereas Eu- and Sm-doped ZnO exhibited the polycrystalline nature. The presence of Eu and Sm ions in the ZnO matrix was confirmed by XPS. This means that all the Eu ions substituted Zn2+ as Eu2+ into the ZnO matrix, whereas most of Sm ions were being in the trivalent state. This was probably due to the segregation of Sm2O3 species on the surface of ZnO microstructures.

• Combustion synthesis and preliminary luminescence studies of LiBaPO4 : Tb3+ phosphor

The polycrystalline sample of LiBaPO4 : Tb3+ (LBPT) was successfully synthesized by solution combustion synthesis and studied for its luminescence characteristics. The thermoluminescence (TL) glow curve of LBPT material consists of two peaks at 204.54 and 251.21°C. The optimum concentration was 0.005 mol to obtain the higher TL intensity compared to commercial TLD-100 phosphor. The peak shape method was used to calculate kinetic parameter (activation energy and frequency factor). In CW-OSL mode its sensitivity for beta exposure was found to be 50% compared to commercially available 𝛼-Al2O3 : C and 40% than LMP (BARC), and photoluminescence spectrum of LBPT shows green emission when excited with 225 nm UV source.

• Phytosynthesized iron nanoparticles: effects on fermentative hydrogen production by Enterobacter cloacae DH-89

In recent years the application of metal nanoparticles is gaining attention in various fields. The present study focuses on the additive effect of `green’ synthesized iron nanoparticles (FeNPs) on dark fermentative hydrogen (H2) production by a mesophilic soil bacterium Enterobacter cloacae. The FeNPs were synthesized by a rapid green method from FeSO4 using aqueous leaf extract of Syzygium cumini. The synthesized FeNPs showed a characteristic surface plasmon resonance peak at 267 nm. The transmission electron microscopy images confirm that the formation of FeNPs was mainly porous and irregular in shape, with an average particle size of 20–25 nm. The presence of iron (Fe) in the synthesized FeNPs was confirmed by energy-dispersive X-ray spectroscopy. The comparative effect of FeSO4 and FeNPs on batch fermentative H2 production from glucose was investigated. The fermentation experiments reveal that the percentage and yield of H2 in FeNPs supplementation were increased significantly than the control (no supplementation) and FeSO4 containing media. The maximum H2 yield of 1.9 mol mol−1 glucose utilized was observed in 100 mg l−1 FeNPs supplementation, with two-fold increase in glucose conversion efficiency. Thus, the result suggests that FeNPs supplementation in place of FeSO4 could improve the bioactivity of H2 producing microbes for enhanced H2 yield and glucose consumption.

• Synthesis and characterization of mullite–zirconia composites by reaction sintering of zircon flour and sillimanite beach sand

Mullite–zirconia composites containing 10–30 wt% zirconia were prepared by reaction sintering of zircon flour, sillimanite beach sand and calcined alumina. Raw materials were attrition milled, shaped into pellets and bars and sintered in the temperature range of 1450–1600°C with 2 h soaking at peak temperature. Sintered products were analysed in terms of various physical, mechanical and thermo-mechanical properties. The analyses of phases developed and microstructural analyses were carried out by X-ray diffraction (XRD) and scanning electron microscope (SEM), respectively. It was observed that the addition of ZrO2 up to 20 wt% significantly improves flexural strength and fracture toughness. The transformation of t $\rightarrow$ m zirconia was found to be the dominant mechanism for enhancement in mechanical properties. ZrO2 occupies both the intergranular as well as intragranular positions. However, intragranular zirconias are much smaller compared to intergranular zirconias.

• Influence of higher sodium substitutions on magnetic entropy change and transition temperature in lanthanum manganites

Present investigation focuses on the variation of magnetic entropy change for higher sodium substitution above 50% in lanthanum manganites. Magnetic measurements indicated that all samples exhibit a ferromagnetic ordering near room temperature. Magnetic isotherms for different temperatures above and below 300 K were recorded and the magnetic entropy change for compositions belonging to La1−𝑥Na𝑥 MnO3 for 𝑥 = 0.6 to 0.9 in steps of 0.1 was estimated for different applied magnetic fields. It has been found that the compositions having a Na substitution of 0.6 are having the largest entropy change, and the entropy change increases with applied magnetic field for all compositions. The change in entropy also decreases with increase in substitution of sodium. A notable change in transition temperature with Na concentration is also found in this sample series.

• Synthesis and characterization of thermotropic liquid crystalline polyimides

Non-symmetrical and linear dyad-based mesogens were synthesised containing imine or ester bridging group. In the present work, due to the absence of branching in diamine-based mesogen, the structure has—rigidity inversely imine/ester bridging groups between two benzene rings imparts—flexible property to the mesogen and consequently rigid–flexible property has been balanced. The synthesised mesogens were characterized by different techniques including nuclear magnetic resonance and Fourier transform infrared spectroscopy. Liquid crystalline polymers (LCPs) were synthesised using pyromellitic dianhydride and 4-[(4-aminobenzylidene)amino]aniline or 4-aminophenyl-4-aminobenzoate. Subsequently, thermotropic liquid crystalline polymers (TLCPs) have also been evaluated to obtain optical microscopy textures at different temperatures which demonstrated interesting and notable changes. It is worth noting that marble-like textures were observed upto 200 ° C.

• Layered zinc hydroxide–ibuprofen nanohybrids: synthesis and characterization

The nonsteroidal anti-inflammatory drug (NSAID), ibuprofen (IBU) anion, was intercalated into the layered zinc hydroxide (LZH) to form a new organic–inorganic nanohybrid. Then, IBU–LZH nanohybrid was dispersed into chitosan for the formation of the nanocomposite. The IBU–LZH nanohybrid was characterized by powder X-ray diffraction (PXRD) to study intercalation, scanning electron microscopy (SEM) for the investigation of surface morphology, Fourier transform infrared (FTIR) spectrophotometer to study the chemical interactions and thermal gravimetric analysis/derivative thermogravimetric analysis (TGA/DTG) for understanding the thermal stability. The PXRD patterns showed that the IBU was successfully intercalated into the interlay space of LZHs as monolayers and the basal spacing of LZH increased from 9.57 to 19.54 Å. The FTIR analyses confirmed the formation of the host–guest nanohybrid. The DTG studies revealed that the thermal stability of IBU was increased after the intercalation into LZH. The in vitro release study of IBU from IBU–LZH and IBU–LZH/chitosan nanocomposite was investigated in phosphate buffer saline (PBS) solution of pH 4.8 and 7.4. The drug release from the LZH was studied by ultraviolet–visible (UV–vis) spectroscopy.

• Effects of reduction time on the structural, electrical and thermal properties of synthesized reduced graphene oxide nanosheets

The reduction of graphene oxide (GO) nanosheet is a promising route to produce a stable colloidal dispersion of reduced graphene oxide (RGO) nanosheets in a large scale. The production of RGO nanosheet is one of the important topics in nanotechnology disciplines due to its contribution in various applications, such as the platinum catalyst support in direct methanol fuel cell. Therefore, in this paper, the RGO nanosheets were prepared via highly efficient chemical reduction reaction of exfoliated GO nanosheets using sodium oxalate (Na2C2O4) as the reducing agent. Extensive characterizations have been conducted in terms of structural, thermal stability and electrical conductivity properties by means of high-resolution transmission microscopy, the Fourier transform infrared spectroscopy, UV–visible spectroscopy, 13C NMR and four-point probe conductivity measurement. The results indicate that most of oxygen-containing functional groups from GO nanosheets have been removed and the RGO-3 possess greater thermal stability compared to GO nanosheets. The prepared RGO-3 shows the highest electrical conductivity at room temperature which is ∼ 2.0 × 103 S m−1. Based on these analyses, the plausible mechanism of reduction of GO to RGO by sodium oxalate is well proposed.

• PEO nanocomposite polymer electrolyte for solid state symmetric capacitors

Physical and electrochemical properties of polyethylene oxide (PEO)-based nanocomposite solid polymer electrolytes (NPEs) were investigated for symmetric capacitor applications. Nanosize fillers, i.e., Al2O3 and SiO2 incorporated polymer electrolyte exhibited higher ionic conductivity than those with filler-free composites. The composites have been synthesized by the completely dry (solution-free) hot-press method. The addition of filler in fractional amount to the solid polymer matrix at room temperature further enhances the ionic conductivity. Nature of the NPEs were studied using X-ray diffraction and energy-dispersive spectra analyses. Thermal stability of the resulting electrolyte was analysed by thermogravimetric analysis and differential scanning calorimetric studies. Morphology changes occurred during the addition of fillers was evidenced by scanning electronic microscope images. Solid polymer electrolytes exhibiting these parameters was found to be suitable for solid state capacitors. The results obtained from the electrolytes with an optimum compositions (PEO70AgI30)93 (Al2O3)7 and (PEO70AgI30)95 (SiO2)5 used in the (PEO70AgI30)70 (AC)30 electrodes for symmetric capacitor applications and their performances were analysed by impedance spectroscopic, Bode plot, cyclic voltammetry, discharge characteristics and leakage current profile.

• Crystallization and mechanical properties of biodegradable poly(p-dioxanone)/octamethyl-polyhedral oligomeric silsesquioxanes nanocomposites via simple solution casting method

In this study, biodegradable poly(p-dioxanone) (PPDO)/octamethyl-polyhedral oligomeric silsesquioxanes (ome-POSS) nanocomposites were fabricated by the simple solution casting method with various ome-POSS loadings. Scanning electron microscopic observations indicate that ome-POSS is well dispersed in the PPDO matrix. Effect of ome-POSS on the isothermal melt crystallization and dynamic mechanical properties of PPDO in the nanocomposites were studied in detail. It shows that the overall crystallization rates are faster in the nanocomposites than in neat PPDO and increase with the increase in ome-POSS loadings; however, X-ray diffraction patterns, POM and the Avrami exponent suggest that the crystal structure and the crystallization mechanism do not change despite the presence of ome-POSS. The mechanical property of PPDO/ome-POSS nanocomposites was enhanced with respect to neat PPDO.

• Study of electrical percolation phenomenon from the dielectric and electric modulus analysis

Chitosan : AgI solid polymer composite films have been prepared by the well-known solution cast technique. Electrical impedance spectroscopy was used to investigate the electrical percolation threshold phenomenon in this work. A wide dispersion can be seen in dielectric constant spectra at low frequencies. The dielectric constant at selected frequencies as a function of AgI concentration indicates the occurrence of electrical percolation threshold via the appearance of two distinguishable regions. The behaviour of dielectric constant and DC conductivity vs. AgI concentration are almost the same at low and high filler concentrations. The steep increase of dielectric constant and DC conductivity from 5 to 10 wt% of AgI was observed and a plateau was achieved from 10 to 20 wt% of AgI. The pattern of real part of electric modulus (M′) at selected frequencies is similar to dielectric constant. The existence of distinct peaks in M″ spectra with no corresponding peaks in 𝜀″ spectra indicated that ionic and polymer segmental motions are strongly coupled. Argand plots of M″ vs. M′ was used to detect the relaxation type process. The Argand plots at different temperatures exhibit incomplete semicircular arc with a diameter below the real axis.

• Characterization and thermal expansion of Sr2Fe𝑥 Mo2−𝑥O6 double perovskites

Double perovskite oxides Sr2Fe𝑥Mo2−𝑥O6 (𝑥 = 0.8, 1.0, 1.2, 1.3 and 1.4) (SFMO) of different compositions were prepared by sol–gel growth followed by annealing under reducing atmosphere conditions of H2/Ar flow. X-ray powder diffraction studies revealed that the crystal structure of the samples changes from tetragonal to cubic at around 𝑥 = 1.2. Lattice parameters and unit cell volume of these samples found to decrease with the increase in Fe content. The characteristics absorption bands observed in the range 400–1000 cm−1 of Fourier transform infrared spectra indicate the presence of FeO6 and MoO6 octahedra and confirm the formation of double perovskite phase. The value of g ∼ 2.00 obtained from electron spin resonance studies indicates that Fe is in 3+ ionic state in the SFMO samples. Dilatometric studies of these samples reveal that the average value of coefficient of thermal expansion ($\overline{\alpha}$) increases with the increase in temperature or Fe content in SFMO samples. The low value of coefficient of thermal expansion 1.31 × 10−6°C−1 obtained for Sr2Fe0.8Mo1.2O6 in the present study in the temperature range of 40–100°C makes it useful as anode material in fuel cells. The coefficient of thermal expansion ($\overline{\alpha}$) and the unit cell volume (𝑉) of SFMO samples vary inversely with composition in agreement with Grüneisen relation.

• Preparation, characterization and electrical study of gum arabic/ZnO nanocomposites

Gum arabic (GA)-mediated chemical synthesis was carried out for obtaining ZnO nanoparticles (ZnO-NPs) (particle size of ZnO ≈ 40 nm) which, in turn, was used for preparing ZnO–biopolymer nanocomposites. The dielectric study of this synthesized products is reported in this paper. The synthesized products were characterized by X-ray diffraction, Fourier transform infrared, and transmission electron microscopy for their structure and morphology study. The frequency dependence of dielectric constant and dielectric loss of these GA–ZnO nanocomposites were analysed in the frequency range of 100 Hz–5 kHz. In addition, the dielectric property of these nanocomposites (0–15 wt% filler concentration) was analysed with respect to frequency in the temperature range 30–80°C. A high dielectric constant of 275 is achieved for the sample with 10 wt% of ZnO filler. The dielectric property of GA–ZnO nanocomposites is attributed to the interfacial and orientation polarization.

• Formation of rod-like nanostructure by aggregation of TiO2 nanoparticles with improved performances

To improve the performance of titanium dioxide (TiO2)-based devices, many efforts have been made to prepare nanostructures with composite of TiO2 nanoparticles and nanorods. In this work, a novel rod-like TiO2 nanostructure was obtained via a controllable hydrolysis process. Morphology and structure analysis showed that the rod-like nanostructure was a well-aligned aggregate of nearly spherical TiO2 nanoparticles. Rod-like TiO2 nanoparticle aggregates were fabricated on a primary TiO2 nanoparticle-based layer without the use of template, and formed a hierarchical TiO2 composite film together. The photocatalytic activity of the TiO2 film with rod-like nanoparticle aggregates was evaluated by the degradation of methylene blue. The antibacterial activity of fabricated hierarchical TiO2 film was assessed against Staphylococcus aureus. The photoelectrochemical property of this film as the photoanode in assemble dye-sensitized solar cell was also tested. Compared with randomly distributed nanoparticle-based TiO2 film, the hierarchical TiO2 film exhibited improved performance of photocatalysis, antibacterial activity and photoelectric conversion.

• Effect of silver nanoparticle on the properties of poly(methyl methacrylate) nanocomposite network made by in situ photoiniferter-mediated photopolymerization

Here we report preparation and characterization of poly(methyl methacrylate)/silver nanoparticles (PMMA/AgNPs) nanocomposite networks prepared via in situ photoiniferter-mediated photopolymerization (in situ PMP) using tetraethylthiuram disulphide (TED) as photoiniferter and 2,2-dimethoxy-2-phenylacetophenone (DMPA) as photoinitiator. Photopolymerization was performed in the presence of allyl methacrylate, as crosslinking agent, and various amount of silver nanoparticles (AgNPs). AgNPs were synthesized via chemical reduction of silver nitrate with t-BuONa-activated sodium hydride in tetrahydrofuran. The degree of monomer conversion (DC%) during polymerization was followed quantitatively via Fourier transform infrared spectroscopy. DC% of nanocomposite networks slightly increased with AgNPs content. Moreover, differential scanning calorimetry results disclosed a decrease in glass transition temperature (𝑇g) of the nanocomposite networks in comparison with the pure polymer network, suggesting the plasticizing effect of AgNPs. Swelling behaviour was also measured in water and ethanol/water (3/1, v/v) solution at 37 ± 1°C after 30 days. The enhanced swelling ratio for nanocomposite networks with increase in the AgNPs content suggested the potential role of AgNPs in photo-crosslinking reactions. The flexural strength and modulus values resulted from three-point bending method revealed an improvement in mechanical properties of the nanocomposites in comparison with pure PMMA networks. The mechanical behaviour observations were rationalized based on the field emission scanning electron microscopy micrographs from the fractured surfaces of the nanocomposite networks. Finally, thermogravimetric analysis showed that while the AgNPs catalyse the degradation in the early stages, they subsequently act as a retardant agent against thermal degradation.

• Heating ability and biocompatibility study of silica-coated magnetic nanoparticles as heating mediators for magnetic hyperthermia and magnetically triggered drug delivery systems

The aim of this study is to prepare core–shell La0.73Sr0.27MnO3 –silica nanoparticles and evaluating their heat generation ability under the safe alternating magnetic field (𝑓 = 100 kHz and 𝐻 = 10–20 kA m−1) for potential applications in magnetic fluid hyperthermia and magnetically triggered drug delivery systems. The magnetic cores of La0.73Sr0.27MnO3 with an average particle size of 54 nm were synthesized by the citrate–gel method. Then, the Stober method was applied to encapsulate nanoparticles with 5-nm-thick silica shell. The core–shell structure of nanoparticles was confirmed by X-ray diffraction, fourier transform infrared spectroscopy and transmission electron microscopy analyses. Cytotoxicity of bare and silica-coated nanoparticles was evaluated by methyl thiazol tetrazolium bromide assay with MCF-7 cell line. The results revealed that the both samples have negligible toxicity below 500 𝜇g ml−1 and silica coating can improve the biocompatibility of nanoparticle. In addition, calorimetric measurements were used to determine the heating efficiency of the core–shell nanostructures in aqueous medium. The results showed that the heat generated of the prepared sample could be safely controlled in the range of 40–60°C which is suitable for biomedical applications.

• Studies on thermo-optic property of chitosan–alizarin yellow GG complex: a direction for devices for biomedical applications

The optical parameters including the refractive index (𝑛) and thermo-optic coefficient, TOC (d𝑛/d𝑇), the dielectric constant (𝜀) and its variation with temperature, and the thermal volume expansion coefficient (𝛽) and its variation with temperature of chitosan–alizarin yellow GG (CS–AY GG) complex were examined. The dn/dT and 𝜀- values for the polymer derivative were in the range −2.5 × 10−4 to 1.2 × 10−4° C−1 and 2.2 to 2.3, respectively. The dn/dT values were larger than that of inorganic glasses such as zinc silicate glass (5.5 × 10−6° C−1) and borosilicate glass (4.1 × 10−6° C−1) and were larger than that of organic polymers such as polystyrene (−1.23 × 10−4 ° C−1) and PMMA (−1.20 × 10−4 ° C−1). The 𝜀-values are lower than optically estimated 𝜀-values of conventional polymer (3.00), aliphatic polyimide (2.5) and semi-aromatic polyamide (2.83). The obtained results of chitosan derivative are expected to be useful for optical switching and optical waveguide areas for devices of biomedical applications.

• Effect of working pressure and annealing temperature on microstructure and surface chemical composition of barium strontium titanate films grown by pulsed laser deposition

Barium strontium titanate (BST, Ba1−𝑥Sr𝑥TiO3) thin films have been extensively used in many dielectric devices such as dynamic random access memories (DRAMs). To optimize its characteristics, a microstructural control is essential. In this paper, Ba0.6Sr0.4TiO3 thin film has been deposited on the SiO2/Si substrate by the pulsed laser deposition (PLD) technique at three different oxygen working pressures of 100, 220 and 350 mTorr. Then the deposited thin films at 100 mTorr oxygen pressure were annealed for 50 min in oxygen ambient at three different temperatures: 650, 720 and 800°C. The effect of oxygen working pressure during laser ablation and thermal treatment on the films was investigated by using X-ray diffraction (XRD), atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis methods. X-ray photoelectron spectroscopy analysis was used to determine the surface chemical composition of the samples. The results indicate that the deposited BST film at low working pressure (100 mTorr) in PLD chamber shows a lower surface roughness than other working pressures (220 and 350 mTorr). The as-deposited films show an amorphous structure and would turn into polycrystalline structure at annealing temperature above 650°C. Increase of temperature would cause the formation of cubic and per-ovskite phases, improvement in crystalline peaks and also result in the decomposition of BST at high temperature (above 800°C). In addition, rising of temperature leads to the increase in size of grains and clusters. Therefore more roughness was found at higher temperatures as a result of a more heterogeneous growth and less tensions.

• Fabrication of MgAl2Si2O8 : M0.01 (M = Ni2+, Cu2+, Pd2+, Pt2+ and Ru3+): catalytic effects for the reduction of 2- or 4-nitroanilines in water

Five new MgAl2Si2O8 : M0.01 (M = Ni2+, Cu2+, Pd2+, Pt2+ and Ru3+) materials were developed for the reduction of nitroarenes as catalysts by conventional solid state reaction at 1300°C. The prepared materials were characterized by thermal analysis, Fourier transform infrared spectroscopy, X-ray powder diffraction analysis, scanning electron microscopy, energy-dispersive X-ray analysis and nitrogen adsorption–desorption analysis. The catalytic activities of the prepared catalysts were tested in the reduction of 2- or 4-nitroanilines in aqueous media at ambient temperature in the presence of NaBH4 by UV–vis spectrophotometer. Furthermore, the MgAl2Si2O8 : M0.01 catalysts can be recovered by filtration and reused for five cycles for the reduction of 2-nitroaniline. These results show that the MgAl2Si2O8 : M0.01 catalysts can be used in practical applications in the reduction of nitroanilines.

• Fabrication of worm-like Ag2S nanocrystals under mediation of protein

A simple protein-assisted method was reported to synthesize pepsin-conjugated Ag2S nanocrystals in aqueous solution. The morphology, composition and structure of the products were characterized by transmission electron microscopy, high-resolution transmission electron microscopy, energy-dispersive spectroscopy, selected area electron diffraction and X-ray diffraction measurements. The results showed that as-prepared monoclinic Ag2S nanocrystals are worm-like nanochains in shape with sizes about 25 nm in diameter and up to hundreds of nanometres in length. The multiple coordinate bonds of pepsin molecules to the surface of Ag2S nanocrystals make as-prepared samples have good colloidal stability and biocompatibility as elucidated by Fourier transform infrared examination. Thermogravimetry–differential scanning calorimetry analysis indicated that the obtained products are inorganic–organic nanocomposites and there is strong interaction between Ag2S and pepsin. This interaction could result in the change of hydrophilic environment of pepsin and consequently intrinsic fluorescence of protein was quenched by Ag2S nanocrystals. Furthermore, the nanochains assembly of particle–particle and rod–rod oriented attachment was discussed to investigate the growth mechanism.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 6
December 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019