• Volume 42, Issue 3

June 2019

• Fabrication of Pt–Re atomic alloy catalysts by alloying of atomically dispersed Pt with Re inside the $\beta$-zeolite pores for an oxygen reduction reaction

The Pt–Re atomic alloy is fabricated by alloying of atomically dispersed Pt with Re inside the $\beta$-zeolite pores with a size of 0.5–0.6 nanometres. The atomically dispersed Pt–Re alloy species exhibit a surprisingly high mass activity of about 60 A g$^{−1}_{\rm Pt}$ for the oxygen reduction reaction, which is much higher than that of the existing Pt nanoparticle catalysts with a Pt particle size of several nanometres.

• Negative thermal expansion and cationic migration in zeolite Y used in FCC catalysts

The influence of extra-framework cations on the intrinsic negative thermal expansion (NTE) of calcined ultrastable and lanthanum-exchanged zeolites Y was analysed. High-temperature thermal behaviour, cationic migration and dealumination were examined by in situ high temperature X-ray powder diffraction and thermogravimetric (TG) analyses. We analysed protonated ultrastable zeolite Y and zeolite Y containing 13% La$_2$O$_3$ (LaY), and investigated howthe presence of La$^{3+}$ influences thermal behaviour of zeolite Y. Uncalcined LaY was also analysed to observe the La$^{3+}$ migration before calcination. Mass loss up to 990$^{\circ}$C was accompanied by TG analyses. X-ray powder diffraction data were analysed by Rietveld method. Our data show that lanthanum migration from supercages to sodalitic cavities is not reversible. However, some La$^{3+}$ migration occurs above 400$^{\circ}$C and we observe emptying of site I$^{\prime}$, migration to site I and to some extent to site II$^{\prime}$. Furthermore, we examined the dealumination process as well. Both samples showtwo distinct thermal behaviours, positive or near-zero thermal expansion up to 500$^{\circ}$C and NTE above this temperature. Together with intrinsic NTE in faujasite type zeolites, the dealumination process is largely responsible for NTE at high temperatures.

• Effect of strain on GaAs$_{1−x−y}$N$_x$Bi$_y$/GaAs to extract the electronic band structure and optical gain by using 16-band $kp$ Hamiltonian

GaAs$_{1−x−y}$N$_{x}$Bi$_y$ is a suitable candidate for 1.06 $\mu$m solid state lasers and high-efficiency solar cells. Mathematical models such as 16-band kp model is used to study the band structure, strain generated effect, band offset and variation of their parameters with Bi and N concentrations. Lattice constants of alloy GaAs$_{1−x−y}$N$_{x}$Bi$_y$ with $x/y = 0.58$ can match those of GaAs with the incorporation of Bi and N into GaAsNBi. Arsenic atom substitution due to the incorporation of N and Bi impurity atoms causes a significant band gap reduction of $\sim$200 meV for GaAs$_{0.937}$N$_{0.023}$Bi${{0.04}$ alloys under lattice-matched conditions and in addition, by tuning the concentrations of N and Bi, the electrical and optical properties of GaAsNBi can be controlled. Optical gain of GaAs$_{1−x−y}$N$_x$Bi$_y$ quantum well (QW) and GaAs as a barrier are calculated in generalized mode and observed the effect of the energy level of GaAs barrier on the GaAsNBi QW.

• Synthesis of V$_2$O$_5$ nanoparticles: cathode materials for lithium-ion batteries

Vanadium oxide-based nanomaterials have been showing great promise as cathode materials for lithium-ion batteries (LIBs). Among these, nanostructured V2O5 shows a high discharge capacity due to its layer structure and thermodynamically stable form. This work reports the synthesis of V$_2$O$_5$ nanoparticles via a simple low temperature hydrothermal method using ammonium vanadate and quinol. The reduced size of V$_2$O$_5$ has resulted in the blue shift of the absorption spectrum. The material has been examined as a cathode material to study lithium intercalation/deintercalation. It shows aninitial discharge capacity of 310 mAh g$^{−1}$ at a current density of 0.1 mA g$^{−1}$ at 1.5–4 V and retains a specific discharge capacity of 184 mAh g$^{−1}$ even after 58 cycles. The present study manifests how the nanostructured size V$_2$O$_5$ could be applied as a high-energy cathode material for LIBs.

• Investigation of electrical properties of In/ZnIn$_2$Te$_4$/n-Si/Ag diode

In/ZnIn$_2$Te$_4$/n-Si/Ag diode structure was fabricated by the thermal deposition of a ZnIn$_2$Te$_4$ thin film on n-Si wafer substrate with Ag metal back contact. The structural characteristics of the film were investigated in terms ofcomposition, X-ray diffraction and topographic measurements. The diode structure was completed by evaporating In metal on the film surface as a top contact. The diode parameters as saturation current, barrier height, ideality factor and seriesresistance values were determined from the semi-logarithmic forward bias current–voltage characteristics of the diode. According to the assumption of the thermionic emission model, the ideality factor was found higher than unity and it wasalso observed that the barrier height and ideality factor showed a temperature-dependent profile resulting from the nonideality in the current–voltage behaviour of the diode. As a result, the model was modified by considering inhomogeneousbarrier formation and Gaussian distribution was expected to be dominant on 1.37 eV mean barrier height with a deviation of 0.18. In addition, the voltage dependence of these Gaussian diode parameters was investigated. The forward and reverse bias capacitance and conductance measurements showed that there was a slight change in capacitance values with frequency whereas the conductance values decreased with increase in frequency. In addition to the current–voltage analysis, the distribution of density of interface states and the values of series resistance were evaluated as a function of bias voltage andfrequency.

• Understanding the role of glucose oxidase on carbon felt as electrodes in biocapacitor studies

In this work, we have reported glucose oxidase incorporated carbon felt bioelectrodes (GOx/CFE) as biocapacitors for energy storage. Glucose oxidase (GOx) was incorporated into a carbon felt electrode (CFE) and the electrodewas characterized using X-ray diffraction, scanning electron microscope and Fourier transform infrared spectroscopy. As a result, it was found that GOx was successfully incorporated into a bare CFE and enhances the specific capacitance of the electrode and it was stable up to 500 charge–discharge cycles. Consequently, it was observed that GOx/CFE exhibits enhanced energy storage capacitance compared to that of pristine carbon felt. The capacitance of GOx/CFE is found to be 4.21 mF cm$^{−2}$ (23 F g$^{−1}$) while the bare CFE shows 3.68 mF cm$^{−2}$ in a phosphate buffer solution (pH $=$ 7.0). Albeit thecapacitance values are small compared to conventional supercapacitors, the utility of these biocapacitors is expected to have a significant impact on glucose monitoring. Columbic efficiency obtained with the GOx/CFE matrix is 89%, and the electrode is stable up to 225 cycles with 100% retention of capacitance. After 225 cycles, the electrode loses the capacitance up to 12% retaining the capacitance of 88% up to 500 cycles. Cyclic voltammetric studies revealed that GOx/CFE is capable of energy storage with a 200 $\mu$A higher capacitive loop than the bare CFE at a scan rate of 10 mV s$^{−1}$. Electrochemical impedanceanalysis measurements also confirmed that GOx/CFE possess minimum resistivity. Moreover, it is very eco-friendly due to which unwanted pollution can be avoided. From the proposed matrix, it is believed that a green, eco-friendly, clean, renewable material for energy storage could be realized.

• Linkage modification of a zinc oxide photoelectrode prepared with polyethylene glycol for electron transport improvement in dye-sensitized solar cells

The purpose of this study is to synthesize ZnO aggregate films using simple precipitation with polymer modification for linkage improvement of the ZnO photoelectrode. The starting materials of zinc acetate solution and ammoniasolution were mixed under violent stirring conditions. A portion of the polymer (polyethylene glycol) was slowly added into the mixed solution to obtain the viscous ZnO precursor. The precursor was then coated onto a fluorine-doped tin oxide substrate and annealed to form ZnO films. The scanning electron microscopy results revealed the formation of ZnO aggregates with flower-like microstructures. The appearance of Zn and O elements indicated a fair ZnO formation. The X-ray diffraction patterns and Raman shift confirmed the hexagonal wurtzite crystal structure of the ZnO aggregates. For dye-sensitized solarcell (DSSC) application, power conversion efficiency was enhanced because of the improved photovoltaic characteristics including the open-circuit voltage, fill factor, series resistance, shunt resistances and recombination resistance, perhaps, dueto the large particle size of the ZnO aggregates and their flower-like microstructures. The flower-like microstructure likely acts as a bridge to link each ZnO particle. The flower-like microstructure plays the role of an express pathway in electron transport in the DSSC. Therefore, the ZnO aggregation with a flower-like microstructure has the potential to improve the electron transport for efficiency enhancement of a DSSC.

• Effect of different parameters on the tribological performance of polypropylene/thermoplastic polyurethane blends under dry sliding conditions

In this study, polypropylene/thermoplastic polyurethane (PP/TPU) blends (weight ratios of 75/25 and 25/75) were produced by melt blending, and a maleic anhydride-grafted polypropylene (PP-g-MA) copolymer was used as a coupling agent. The effect of the concentration of the coupling agent (5–11 phr), TPU concentration (25–75%), normal load (2–4 N) and sliding velocity (60–72 rpm) on the wear properties of the blends were characterized through a pin-on-discabrasive wear test. A 2$4^$ full-factorial experimental design was chosen to screen the significant factors and their interactions influencing the tribological performance of the blends. After the tests, the morphology of the worn surface of the samples was observed using scanning electron microscopy. Shore D hardness tests were also conducted and the relationships between these behaviours were analysed on the basis of the findings. According to the wear test results, the factors that have the greatest effect on the wear rates are as follows: normal load, TPU concentration, sliding velocity and PP-g-MA concentration,respectively. The wear rate of the blends increases by increasing the normal load, TPU concentration and sliding speed, and slightly decreases by increasing the PP-g-MA concentration. As expected, the wear and hardness results showed the apparent superiority of the PP$_{75}$/TPU$_{25}$ blends over the PP$_{25}$/TPU$_{75}$ blends, because of the higher content of rigid segments in the blends.

• Fe/Fe$_3$O$_4$ nanocomposite powders with giant high magnetization values by high energy ball milling

The present work reports on the relatively higher saturation magnetization values of Fe/Fe$_3$O$_4$ nanocomposites. For example, the nanocomposites of Fe obtained after milling for 10 h with 5, 10 and 15 wt% of Fe$_3$O$_4$ had displayed saturation magnetization values of 210, 238 and 216 Am$^2$ kg$^{−1}$, respectively, in contrast to 218 Am$^2$ kg$^{−1}$ of bulk Fe. Similarly, themaximum magnetization values for the nanocomposites after 20 and 30 h of milling were 215 and 190 Am$^2$ kg$^{−1}$ for the sample containing 5 and 15 wt% of Fe$_3$O$_4$, respectively. The values of $H_{\rm C}$ and $Mr$ suggest that nanocomposites exhibit soft ferromagnetic behaviour. The ball milling also reduced the crystallite and particle size of Fe from microndimension tonanometres. This was confirmed from X-ray diffraction, transmission electron microscopy and scanning electron microscopy analyses. The crystallite size of pure Fe decreased to 35, 20 and 19 nm, respectively, for the samples having 5, 10 and 15 wt% of Fe$_3$O$_4$ after 10 h of milling. The crystallite size decreased further with increased milling time.

• Molecular dynamics of acetate-based ionic liquids

A radial distribution analysis of pairs between the constituent atoms of protic ionic 2-(hydroxy)ethylammonium acetate was performed with molecular dynamics technique (MDT). The ionic liquid structure will help us in different engineeringapplications, as emulsification process (petroleum industry). The results presented here show that the development of force field to predict the high interaction behaviour between the cation and the anion, as well as the formation of ion-pair dispersed aggregates. These results can contribute to help the different applications of ionic liquids.

• Enhanced magnetic performance of bulk nanocrystalline MnAl–C prepared by high pressure compaction of gas atomized powders

High density MnAl–C magnets with enhanced coercivity and remanent magnetization were prepared by high pressure compaction of the $\tau$-phase obtained by annealing the as-prepared gas-atomized powders, which are spherical in shape with size in the range of 1–7 $\mu$m. The as-prepared gas-atomized powders were composed of $\epsilon$- as the major phase and $\gamma_2$- as the minor phase. The massive phase transformation of $\epsilon \to \tau$ in the gas-atomized powders occurs at 720 K and accomplishes at 806 K, both of which are lower than those of the water-quenched $\epsilon$-MnAl–C alloys with the same composition. An optimized temperature of 760 K, at which the decomposition of metastable $\tau$-phase was minimized, was selected to prepare the ferromagnetic $\tau$- from the $\epsilon$-phase. The spherical $\tau$-phase powders were pressed at room temperatureinto two dimensional plates that stack along the direction of compaction, forming high density (98.6%) bulk magnets that exhibit larger coercivity and higher remanentmagnetization than that of the τ-phase powders. The grain size of the compacted samples was observed to be in the range of 10–100 nm. The coercivity (0.34 T) of the dense samples is twice as large as that of the $\epsilon$-phase powders, owing to the refined grain size and enlarged dislocation density resulting from high-pressure compaction.

• Synthesis of Tb$^{3+}$ ion doped ZnWO$_4$ phosphors and investigation of their photoluminescence properties: concentration effect

In this paper, the effects of Tb$^{3+}$ ion concentration on the structural and photoluminescence properties of ZnWO$_4$:Tb$^{3+}$ have been reported. X-ray diffraction studies indicated that the monoclinic structure of the samples and thecrystallinity were found to decrease with the increase of Tb$^{3+}$ ion concentration due to the distortion in the crystal lattice. The formation of the monoclinic structure was further supported by high resolution transmission electron microscopy and Fourier transform infrared analyses. The transmission electron microscopy image of ZnWO$_4$:Tb$^{3+}$ (7%) showed a spherical morphology with crystallite sizes in the range of $\sim$8–12 nm. The excitation spectrum showed a strong broad band originated from the electronic transition within the WO$^{6−}_6$ group. Upon excitation at 270 nm, the prepared ZnWO$_4$:Tb$^{3+}$ phosphors exhibited sharp and narrow emission peaks, characteristic of the f–f transitions of Tb$^{3+}$ ions besides a broad band with themaximum at around 460 nm due to the host lattice. The intensity of the broad emission band was found to decrease gradually with the increase of Tb$^{3+}$ ion concentration and reached minimum at 7 at%. The decay time of the prepared phosphors was investigated in detail and the maximum average lifetime value is found to be 1.187 ms.

• A hollow Fe$_3$O$_4$-based nanocomposite anode for lithium-ion batteries with outstanding cycling performance

The fabrication of hybrid electrodes with conversion-type electrode materials has drawn growing interest in improving the capacity performance of lithium-ion batteries (LIBs) for many high-energy applications. However, as a typical conversion-type electrode material, Fe$_3$O$_4$ is usually restricted by large amount of volume change during repeated lithiation/delithiation course, which dramatically hinders the cycling stability of the constructed LIBs. We design a hybrid electrode of Fe$_3$O$_4$ nanospheres with a hollow structure wrapped by MnO$_2$ nanosheets (H-Fe$_3$O$_4$/MnO$_2$ NSs nanospheres).As a result of the synergetic effect of a high-capacity material coating and a robust hollow core, the H-Fe$_3$O$_4$/MnO$_2$ NS hybrid electrode delivers reversible capacity as high as 590 mAh g$^{−1}$ at a current rate of 0.1C and maintains 92% of the initial reversible capacity after 1000 cycles at 1C.

• Effect of functionalization and concentration of carbon nanotubes on mechanical, wear and fatigue behaviours of polyoxymethylene/carbon nanotube nanocomposites

The main focus of this work is to improve the mechanical, wear and fatigue behaviours of polyoxymethylene (POM) by reinforcing with carbon nanotubes (CNTs). To improve compatibility between CNTs and POM, the surface of theCNTswas modified by various methods of functionalization like carboxylation, silanation, carbonylation and amination. The functionalized CNTs were characterized by Fourier transform infrared spectroscopy to confirm the different functional groups attached to the surface. POM/CNT nanocomposites were developed with functionalized CNTs in different concentrationsvarying from 0.25 to 2 wt%. Nanocomposites with 1 wt% of silanated CNTs resulted in maximum improvement of tensile, flexural and impact properties. Furthermore, experimental results on fatigue and dry sliding wear tests revealed that the fatigue strength, specific wear rate and friction coefficient are sensitive to functionalization and concentration of CNTs.

• Spectroscopic characterization of Er$^{3+}$ doped lead zinc phosphate glass via Judd–Ofelt analysis

Lead zinc phosphate (LZP) glass dopedwith 0.6% Er$^{3+}$ is prepared by a conventional melt quenching technique. Judd–Ofelt (JO) analysis is carried out with an absorption spectrum of the as-prepared glass generating the set of JOparameters: $\Omega_2 = 2.75 \times 10^{−20}$ cm$^{−2}$, $\Omega_4 = 2.71 \times 10^{−20}$ cm$^{−2}$ and $\Omega_6 = 0.44 \times 10^{−20}$ cm$^{−2}$. The magnitude of the spectroscopic quality factor ($\xi_p$) defined by $\Omega_4/\Omega_6$ obtained in our sample turns out to be 6.16 which is 2–10 times larger than that of other Er$^{3+}$ doped glasses. The lifetime of ${}^4$I$_{13/2}$ and ${}^4$I$_{11/2}$ levels estimated via the JO parameters is found to provide superior values of 7.25 and 5.51 ms, respectively. The elevated value of $\Omega_4/\Omega_6$ along with the estimated 100%luminescence branching ratio of ${}^4$I$_{13/2}\to {}^4$I$_{15/2}$ transition implies that Er$^{3+}$ doped LZP can be a promising material as a laser active medium.

• Effect of carrier gas pressure on structural, optical and photovoltaic properties of tin sulphide thin films prepared by nebulizer spray pyrolysis method

Tin sulphide (SnS) thin films deposited using nebulizer spray pyrolysis technique by changing pressure (0.1, 0.15, 0.2 and 0.25 Pascal) at 350$^{\circ}$C and their characterization are reported. The influence of carrier gas pressure on structural, morphological, optical and electrical properties of the film are determined using X-ray diffraction (XRD), energy-dispersiveX-ray, atomic force microscopy, UV–Vis spectrophotometry and Hall effect measurement. Structural parameters such as pole density, orientation factor, crystallite size, micro strain and dislocation density were analysed using XRD data. The scanning electron microscopy studies display superior morphology and surface roughness of the films which were found to increase with pressure. Optical studies on the films revealed a variation in band gap from 1.78 to 1.66 eV for were the raise of pressure from 0.1 to 0.2 Pa. A single strong emission peak at about 825 nm is observed in photoluminescence spectra with enhanced intensity which may be attributed to near band edge emission. Grown SnS thin film exhibits p-type conductivity, which was confirmed from the Hall effect measurement. The low resistivity and higher carrier concentration are found tobe 0.235 $\Omega$cm and $5.04 \times 1018$ cm$^{−3}$, respectively. These properties were then correlated with the deposition parameters. Furthermore, to study the photovoltaic properties of SnS thin films, a heterojunction solar cell FTO/n-CdS/p-SnS/Al was fabricated showing conversion efficiency of 0.16%.

• Evaluation of microbial inhibition properties of green and chemically synthesized ZnO nanoparticles

Nanosized particles of zinc oxide have gained much attention due to several applications which includes bacterial inhibition. Therefore, this work evaluates zinc oxide properties synthesized using reduction (chemical) and bioreduction(green) processes and their corresponding inhibition potentials. The bio-reduction process was achieved using Amaranthus spinosus at 70$^{\circ}$C while the reduction process was initiated in the chemical process using sodium hydroxide. The optical measurement of ZnO was carried out using an UV–Vis spectrophotometer. The structural and morphological properties of the synthesized ZnO were evaluated using Fourier transform infrared spectroscopy, X-ray diffractometry and scanning electron microscopy. The elemental composition was carried out using energy dispersive X-ray spectroscopy. The antimicrobial activity property of the nanoparticles was tested against Pseudomonas aeruginosa, Salmonella typhi and Shigella dysenteriae. The degree of susceptibility of ZnO nanoparticles was higher in the bio-reduction process than chemically synthesized for selected microorganisms. A sustainable pathway for development of bio-antibiotic is presented.

• Role of synthesis of upconversion nanoparticles towards surface modification and photocatalysis

TiO$_2$ being a wide band gap semiconducting material cannot use the solar insolation for photocatalysis. An interesting strategy is to dope TiO$_2$ with upconverting rare earth materials, which upon infrared (IR) or visible light irradiation can emit ultraviolet light to generate excitons in TiO$_2$ for further catalytic reactions. This manuscript reports the incorporationof Er$_2$O$_3$/Yb$_2$O$_3$ into TiO$_2$ via two synthetic methodologies. One of which yields the co-presence of rare earth oxides and TiO$_2$ on the surface, while the other synthetic route yields the rare earth oxides in the core of the TiO$_2$ shell. The detailed structural, morphological and optical properties of the laboratory synthesized materials were studied by powder XRD, FESEM,STEM, HR-TEM, BET, UV-DRS and PL. The surfaces of the materials did show some difference in their properties depending on their synthesis route, however, the two photon excitation was similar to both the set of materials.The synthesizedmaterials were studied for degradation of rhodamine B dye, and the results suggested that the presence of Er$_2$O$_3$/Yb$_2$O$_3$ on the TiO$_2$ surface was detrimental for catalytic application, while TiO$_2$ exposed on the surface with Er$_2$O$_3$/Yb$_2$O$_3$ in the core can be a choice of materials for photocatalytic application.

• Electrochemical preparation and magnetic properties of Co–Cu nanometric granular alloy films

A detailed electrodeposition of Co–Cu nanometric granular alloy films in citrate solution has been performed based on a galvanostatic technique. Electrochemical behaviour of the bath solution containing both Co$^{2+}$ and Cu$^{2+}$ was investigated by linear sweep voltammetry. Cathodic polarization curves indicated that high quality Co–Cu nanometric granular alloy films can be obtained at room temperature with a pH of 6 and current density equal to or more negative than $−$1.0 mA cm$^{−2}$. Magnetic properties of the films were measured at room temperature by the physical property measurementsystem. Magnetization curves of the as-prepared Co–Cu nanometric granular alloy films displayed superparamagnetism (SPM). However, after annealing at 450$^{\circ}$C for 1 h, magnetic property of the films changed from SPM to ferromagnetism. Meanwhile, the annealed Co–Cu nanometric granular alloy films showed an increase in saturation magnetization with the increase of the current density.

• Preparation and characterization of low cost flat ceramic membranes from easily available potters’ clay for dye separation

In the present day scenario, the crisis of safe drinking water is an extremely serious issue across many parts of the globe and needs efficient methods to overcome this problem. The effort made in this study is to develop a methodto prepare a ceramic membrane with locally available cheap compositions such as potters’ clay, stone dust and tea waste materials for efficient adsorptive dye removal from water. The preparation of ceramic membrane was carried out by a paste pressing method and sintered at an optimized temperature of 900$^{\circ}$C to obtain flat ceramic membranes of 42 mm in diameterand $3\pm 0.5$ mm thickness with good thermal and chemical stabilities with 52.51% porosity and average pore size of 0.49 $\mu$m. The membrane was capable of decolouring methylene blue and congo red from water with good efficiency and the used membrane was regenerated by calcining at 400$^{\circ}$C for 30 min without much loss of its efficiency. Development of newer advanced products with the available local resources may be another way to sustain the small scale industry and livelihood of the people around.

• Compositional dependence of properties in calcium substituted sodium borophosphate glasses containing VO$^{2+}$ ions

Synthesis of calcium-substituted sodium borophosphate glasses with compositions $x{\rm CaO} − (30 − x){\rm Na}_2{\rm O} −35{\rm B}_2{\rm O}_3−35{\rm P}_2{\rm O}_5$ ($x = 0$, 2, 5, 7 and 10 mol%, abbreviated as CNV$x$) containing additional 1.0 mol% of V$_2$O$_5$ following a melt-quench method has been carried out. Different analytical techniques viz. wide angle X-ray diffraction (to confirm noncrystallinenature), ultraviolet–visible spectroscopy (for optical band gap analysis), infrared absorption spectroscopy (for structural analysis) and differential thermal analysis (to evaluate characteristic temperatures) were employed to characterizethe synthesized compositions. The optical band gap is calculated for both indirect allowed and indirect forbidden transitions. The values of the band gap decrease with increasing concentration of CaO (from 5 to 10 mol%) at the cost of Na$_2$O. The cut-off wavelength and Urbach’s energy are determined from the optical absorption spectra and were related to the structural changes occurring in these glasses with an increase in CaO content. The results obtained from Fourier-transform infrared studies confirm that V$_2$O$_5$ and CaO play the role of network modifier oxides. Also, the significant shifting in IR bands with an increase in CaO content in the glass matrix suggests the formation of a new boron–oxygen ring. From differential scanning calorimetry measurements it is observed that substitution leads to the increase in natural bond orbitals,high degree cross-linking and thus strengthens the glass network. Glass transition temperature ($T_{\rm g}$) is found to increase from 483 to 522$^{\circ}$C. Electrical and dielectric properties are analysed using dc conductivity and impedance spectroscopy. Using impedance spectroscopy, different dielectric parameters i.e. dielectric loss ($\epsilon^{\prime}$), electrical modulus ($M^∗$) and ac conductivity ($\sigma_{\rm ac}$) etc. are evaluated as a function of frequency, temperature and composition. The frequency dependence of impedance exhibits the non-Debye relaxation behaviour and the total conductivity obeys Jonscher’s power law.

• Synthesis, characterization, optical and electrochemical band gaps of green poly(azomethine-ester)s containing oxalyl and succinyl units

A new series of poly(azomethine-ester)s (PAZ-E)s with different (turning ortho, meta and para) positions weresynthesized by condensation polymerization. The chemical structure of polymers was verified by ${}^1$H-NMR, ${}^{13}$C-NMR, FTIR and UV–Vis measurements. Electrochemical characteristics of the corresponding polymers were obtained with cyclic voltammetric (CV) analysis. Thermal characteristics of the obtained polymers were analysed by TG-DTA, DMA and DSC measurements. The first degradation temperature values of PAZ-E compounds were found between 198 and 250$^{\circ}$C from TGA measurements. Photophysical characteristics of the obtained polymers were explained with photoluminescence (PL) spectroscopy.Molecularweight distributions of (PAZ-E)s were obtained by gel permeation chromatographic (GPC) analysis. Two- and three-dimensional (2D and 3D) properties and images of the synthesized (PAZ-E)s were analysed by SEM and AFM surface analysis techniques, respectively. Electrochemical band gap ($E^{\prime}_{\rm g}$) values of (PAZ-E)s P-9, P-10, P-11, P-12,P-13 and P-14 were calculated as 2.58, 2.14, 1.90, 2.06, 1.89 and 1.69 eV, respectively. The $E^{\prime}_{\rm g}$ g values of the (PAZ-E)s werefound to be quite low.

• Wollastonite/forsterite composite scaffolds offer better surface for hydroxyapatite formation

The present work deals with a comparative study of ceramic/ceramic composites for the development of scaffolds for biomedical applications.Wollastonite and forsterite were synthesized by a sol–gel combustion method. The influence of constituents and composition on apatite deposition was studied by fabricating wollastonite/forsterite composites. The X-ray diffraction pattern explains the bone like-apatite deposition within early stages of immersion. The atomic force microscopy micrographs revealed that with an increase in wollastonite content in the composites the roughnesswas enhanced.Dissolutionstudies further confirmed the rapid consumption of Ca and P ions from the simulated body fluid. Hence, apatite formation was observed to be more on the surface of a composite containing a higher amount of wollastonite. The results suggest that composites have more influence on the biomineralization activity when compared with pure bioceramics.

• Electrical conductivity and pH modelling of magnesium oxide–ethylene glycol nanofluids

Nanofluids as new composite fluids have found their place as one of the attractive research areas. In recent years, research has increased on using nanofluids as alternative heat transfer fluids to improve the efficiency of thermal systems without increasing their size. Therefore, the examination and approval of different novel modelling techniques on nanofluid properties have made progress in this area. Stability of the nanofluids is still an important concern. Research studies on nanofluids have indicated that electrical conductivity and pH are two important properties that have key roles in the stability of the nanofluid. In the present work, three different sizes of magnesium oxide (MgO) nanoparticles of 20, 40 and 100 nm at different volume fractions up to 3% of the base fluid of ethylene glycol (EG) were studied for pH and electrical conductivity modelling. The temperature of the nanofluids was between 20 and 70$^{\circ}$C for modelling. A genetic algorithm polynomial neural network hybrid system and an adaptive neuro-fuzzy inference system approach have been utilized to predict the pH and the electrical conductivity of MgO–EG nanofluids based on an experimental data set.

• Gel combustion synthesis of fluorine-doped tin oxide and its characteristics: applying D-optimal factorial design of experiment

Fluorine-doped tin oxide (FTO) nano-powders were synthesized by a gel combustion method. To analyse the effect of processing factors and their interactions and to achieve an equation for nano-powder particle size in termsof code factors, D-optimal factorial design was used. Stannous chloride penta-hydride, ammonium fluoride and citric acid were used to synthesize the FTO nano-powders. The structure, morphology and composition of the synthesized powders were characterized by X-ray diffraction, field emission scanning electron microscopy and X-ray photoelectron spectroscopy, respectively. The results revealed the formation of homogenous FTO nano-powders with an average particle size of 20 nm and equiaxed morphology in the concentration of precursor 0.2, citric acid to precursor molar ratio of 1 and pH of 0.5. The average particle size increased as the concentration of the precursor, citric acid to precursor molar ratio and pH increased from 0.2 to 1, 1 to 3 and 0.5 to 3, respectively. Citric acid to precursor molar ratio, concentration of the precursor and the pH had the most significant effect on the synthesis of the FTO nano-powders, respectively.

• Microstructure and texture development in a polycrystal and different aluminium single crystals subjected to hydrostatic extrusion

A hydrostatic extrusion (HE) process was applied to commercial pure polycrystalline aluminium (99.9%) and two aluminium single crystals $\langle$111$\rangle$ and $\langle$110$\rangle$. On comparison, the results obtained from single crystals and polycrystalline aggregates are unique. Microstructure and crystallographic texture investigations were performed by transmission electron microscopy, electron backscatter diffraction and X-ray diffraction (XRD). Significant differences in grain refinement and texture formation were noticed depending on the starting orientation. The deformed single crystal with $\langle$110$\rangle$ starting orientation features an average grain size value of 150% higher than the second investigated single crystal (0.5 μm forthe $\langle$111$\rangle$ single crystal and 1.3 $\mu$m for the second crystal). In turn, the average grain size obtained for polycrystalline aluminium is 0.9 $\mu$m. The deformation process causes a difference in the grain sizes, while a fraction of the high angle grain boundaries have a comparable volume percentage in all the deformed microstructures—reached about 35%. The qualitative and quantitative XRD texture results proved that the HE process leads to the formation of a characteristic fibrous texture.

• Effect of short fibre orientation on the mechanical characterization of a composite material-hybrid fibre reinforced polymer matrix

Polymer matrix composites (PMCs) are widely used materials in aerospace structures, boat hulls, automotive parts, etc. Since the progression of PMCs, a single fibre composite lags the addition of one or more fibres preparedas a hybrid composite which can be used to enhance their mechanical properties. Hybrid bamboo/glass fibres as the alternative replacement for polyester composites have been fabricated with $\pm$60$^{\circ}$ orientation, and coconut shell powder in micro and nanosized particles was added as the filler materials. Mechanical properties such as tensile, flexural, and impact strength, hardness number, and fatigue behaviour were investigated. The fractured surfaces of the composites were observed by scanning electron microscopy analysis. The test results reveal that the bamboo fibres in combination withglass fibres show an enhancement in their mechanical properties like strength and stiffness, and are suitable for aerospace applications.

• Properties of group III–V semiconductor: BAs

The structural, electronic, mechanical, thermal and optical properties of boron arsenide (BAs) semiconductor, which belongs to group III–V, has been studied using the first-principles approach. BAs is a binary semiconductor compound, which has a space group $F-43m$ at ambient temperature. The structural and electronic properties of BAs are found to be in good agreement with the available experimental and theoretical results. Some of the mechanical properties are also in agreement with the data available. The thermal parameters such as Debye temperature, specific heat and Grüneisen parameterare analysed as functions of temperature and pressure.

• A molecular dynamics simulation of energetics and diffusion of point defects in a Au–Ag alloy

For revealing an aging mechanism for self-irradiation in a Pu–Ga alloy, we carried out a molecular dynamics (MD) simulation on a substitutional material, i.e., Au–Ag alloy. In this work,we estimate physical and microscopic propertiesof the Au–Ag alloy containing various point defects using a MD method, in particular, formation energy for point defects, migration energy for point defects diffusion into interstitial sites, and diffusion coefficient for the Au–Ag alloy containing point defects, such as vacancy, He atom and He-vacancy (He-V) cluster. The results indicate that volumetric heat capacity and linear expansion coefficient would decrease due to the various point defects, and He atom has the most remarkable influence on the physical properties of the Au–Ag alloy for point defects considered in this work. The formation energy of Au and Ag self-interstitial atom indicates that Octa1 is the most stable site, and structural stability of octahedral (Octa) interstitial sites for the He atom obeys Octa1 > Octa2 > Octa4 > Octa3. For the He$_n$ V$_m$ cluster, the formation energy ofthe defect structure is most stable at $n = m$. The diffusion coefficient of the He-V cluster is relatively smaller, showing that vacancy defects would further decrease atomic diffusion. An influence of various point defects on the diffusion velocity in the Au–Ag alloy obeys the He-V cluster > He > vacancy > Ag > Au.

• Dielectric studies on Sm-modified two-layered BLSF ceramics

Sm$_x$Bi$_{3−x}$TiNbO$_9$ (SBTN) with $x = 0$, 0.2, 0.4, 0.6, 0.8 and 1.0, a novel type of ceramic was prepared by a conventional solid-state reaction method. X-ray diffraction patterns confirm the formation of a single-phase, and lattice parameters were calculated based on the parent compound Bi$_3$TiNbO$_9$ (BTN). Well-defined grains were seen in the scanningelectron microscopy pictures. A kink observed near 400$^{\circ}$C for all the samples in the dielectric plot as well as in the stretched exponential parameter ($\beta$) vs. temperature plot reveals the dielectric relaxation of the samples. The tolerance factor ($t$) was found to increase with increase in the size of the A-site (Bi-site) modified ion (Sm). Impedance and modulus spectroscopicstudies were conducted to understand the plausible reason for the dielectric relaxation. The relaxation was found to be well-fit with Arrhenius equation. SBTN samples showed lower dielectric loss compared to BTN. The remnant polarization, obtained from experimental, was found to be less than that of theoretically calculated polarization, using Shimakawa’s formula. The proposed defect mechanism was interpreted using FTIR and Raman spectroscopic studies.

• Systematic investigation of parameters of an electrospinning process of poly(acrylic acid) nanofibres using response surface methodology

In this study, response surface methodology (RSM) based on the central composite design (CCD) was used for modelling the electrospinning process of polyacrylic acid (PAA) nanofibres, so as to assess simultaneously the effect ofthe most important electrospinning parameters (concentration of polymer solution, applied voltage, distance between the nozzle and collector and flow rate of solution) on the diameter of electrospun PAA nanofibres. The surface morphology was studied by scanning electron microscopy (SEM). The average diameter of PAA nanofibres obtained was from 233 to 1210 nm from SEM images with different process parameters. The results showed that the solution concentration, the applied voltage and the distance between the nozzle and collector are, in that order, the most important parameters affectingthe diameter of nanofibres. The flow rate, however, showed no significant effect on the nanofiber diameter. The RSM model predicted that under optimal electrospinning conditions (solution concentration of 3 w/v%, voltage of 16 kV, electrospinning distance of 15 cm and flow rate of 1.75 ml h$^{−1}$), the nanofibres would be 262 nm in diameter, which was proved to be veryclose to the actual measured value. Therefore, the obtained results demonstrated the good performance of the RSM model in investigating the effect of electrospinning variables and predicting the diameter of PAA nanofibres. PAA nanofibres have great potential in applications such as sensors and biosensors, removal of heavy metals and contaminants, muscle tissue engineering, etc. and the use of thinner nanofibres leads to their improved performance in these applications.

• Characterization of the antibacterial galactomannan/Zn(OH)$_2$–ZnO composite material prepared in situ from a green process using mesquite seeds as a biopolymer source

In this work, the preparation of an antibacterial galactomannan/Zn(OH)$_2$–ZnO composite material by a greenprocess is proposed and demonstrated. The galactomannan polysaccharide was extracted from the arid-native mesquite (Prosopis spp.) seeds through a hydrothermal technique, and it was used as an organic polymeric matrix for the in situ chemical precipitation of the Zn(OH)$_2$–ZnO inorganic particles from simple reactions between Zn$^{2+}$ and NaOH. Thepreparation was performed under standard conditions in aqueous solutions. The composite material, which was obtained by centrifugation of the previous preparation, was characterized by X-ray diffraction, transmission and scanning electron microscopy, infrared spectroscopy and thermal analysis. By means of these techniques, it was deduced that the composite material is highly crystalline (about 94%), composed of about 92% inorganic and 8% organic portion, and has a predominant size of 760 nm and a mean size of 800 nm. The antibacterial activity of the composite material was also studied, which resulted better against Escherichia coli (Gram-negative bacterium) than against Staphylococcus aureus (Gram-positive bacterium), which was calculated in a difference of about 30%. This work presents the high potential of galactomannans to form functional composite materials with inorganic particles.

• A new form of a Halpin–Tsai micromechanical model for characterizing the mechanical properties of carbon nanotube-reinforced polymer nanocomposites

In the present work, a new form of a Halpin–Tsai (H–T) micromechanical model is proposed to characterize the elastic modulus and tensile strength of carbon nanotube (CNT)-reinforced polymer nanocomposites. To this end, three critical factors, including random dispersion, non-straight shape and agglomerated state of the CNTs are appropriately incorporated into the H–T model. A comparison of the model predictions with some experiments on the CNT/polymer nanocomposites serves to verify the applicability of the proposed approach. It is found that the present predictions are in good agreement withthe available experimental data. The results clearly reveal that for a more accurate prediction of the mechanical properties of the CNT/polymer nanocomposites, considering the random orientation, waviness and agglomeration of CNTs into the polymer matrix is critically essential. Also, some parametric studies are carried out to show the effects of volume fraction,non-straight shape, aspect ratio, mechanical characteristics and non-uniform dispersion of CNTs as well as matrix properties on the elastic modulus and tensile strength of CNT/polymer nanocomposites. The results reveal that it is necessary to eliminate the agglomeration and use the straight CNTs if the full potential of CNT reinforcement is to be realized.

• Poly(vinyl pyrrolidone)-mediated synthesis of silver nanowires decorated with silver nanospheres and their antimicrobial activity

Pathogenic infectious diseases, like bacterial infections, are one of the most prevalent types of diseases all over the world. Although antibiotics are commonly used and widely available drugs for the treatment of bacterial infections,bacteria show multiple drug resistance, have a tendency to get genetically mutated and become resistant to commonly employed antibiotic drugs. This makes the invention of novel drugs essential. One of the possible approaches is the use of nanomaterials for this purpose. The present study attempts to synthesize silver nanospheres and silver nanowires and compare their antibacterial activity. Silver nanospheres were synthesized by chemical reduction of silver nitrate in the presence of a suitable stabilizer. For the synthesis of silver nanowires, polyol method was employed. Silver nanowires neatly decorated with silver nanospheres were obtained. The antibacterial activity was estimated by separately determining the minimum inhibition concentration of the two nanostructures on Gram-positive bacteria Bacillus subtilis and Gram-negative bacteria Escherichia coli cultured on Luria Bertani agar media. The comparison shows that the antibacterial activity of silvernanospheres is better than that of silver nanowires which is attributed to its higher surface area and the difference in uptake mechanism by the bacterial cells.

• Development of an acetanilide/benzoic acid eutectic phase change material based thermal energy storage unit for a passive water heating system

In the present work, two organic phase change materials (PCMs) are used to develop a new eutectic PCM for sharp melting point with high latent heat of fusion. Optimized eutectic can be suitable for a passive water heating system(PWHS). The binary eutectic PCMs consisting of different compositions of acetanilide and benzoic acid are prepared and optimized at a composition of 30:70 by weight percentage. Optimized samples are characterized by using differential scanning calorimetry (DSC), Fourier transform infrared spectrophotometry and field-emission scanning electron microscopy.The results of DSC showed that melting temperature and latent heat of the optimized eutectic PCM is found to be 75.56$^{\circ}$C and 193.56 J g$^{−1}$. A negligible change in melting temperature and latent heat of fusion of the optimized eutectic based PCM after 100 accelerated heating and cooling cycles is observed. The prepared eutectic PCM is employed as a thermal energystorage (TES) system for PWHS. The experimental results of a eutectic PCM based TES system for the PWHS show that the use of eutectic helps in enhancing the maximum utility of solar energy during off-shine hours.

• Superoxide dismutase mimic activity of spinel ferrite MFe$_2$O$_4$ (M $=$ Mn, Co and Cu) nanoparticles

In the present study, superoxide dismutase (SOD) mimic activity of ferrite nanoparticles (NPs), having a formula MFe$_2$O$_4$ (M $=$ Mn, Co and Cu) was investigated. Spinel ferrite NPs were synthesized by employing sol–gelmethodology and characterized using scanning electron microscopy, X-ray diffraction, BET analysis and Fourier transform infrared spectroscopy techniques. BET analysis revealed that the surface area of ferrite NPs ranged from 0.43−23.49 m$2^$ g$^{−1}$. Enzyme mimic activity was compared using SOD as a model enzyme. CuFe$_2$O$_4$ NPs exhibited a maximum activity followedby CoFe$_2$O$_4$ and MnFe$_2$O$_4$ NPs. The results were correlated with a facile interconversion of the oxidation state leading to a stable electronic configuration in CuFe$_2$O$_4$ NPs. Optimum pH and contact time was 1 and 3 min respectively. Kinetic studies were performed under optimum conditions and data were analysed using the Michaelis Menten equation. The valuesof $V_{\rm max}$ (0.77 s$^{−1}$) and Km (4.20 mM) proved CuFe$_2$O$_4$ NPs as potential SOD mimic for a wide range of applications.

• A triboelectric energy harvester using human biomechanical motion for low power electronics

This article presents the conversion of human biomechanical motion into useful electricity using triboelectricity. Nylon, polytetrafluoroethylene (PTFE) and fluorinated ethylene propylene (FEP) are selected as triboelectric materials forcharge generation and aluminium/copper is selected as an electrode during vertical and sliding motions. Output voltage, energy density and power are computed across different capacitors and resistors. The maximum d.c. voltage is found to be 9.56 V across a 1 $\mu$F capacitor using a combination of nylon and PTFE during vertical motion. Also, the maximum energy density across a 100 $\mu$F capacitor is 492.47 $\mu$J cm$^{−3}$ and the maximum power across a 4.63 M$\Omega$ resistor is 6.2 $\mu$W. Such portable systems can harvest human biomechanical energy while walking or exercising and can act as an infinite lifetime energy source for conventional low power electronics.

• Magnesium/fish bone derived hydroxyapatite composites by friction stir processing: studies on mechanical behaviour and corrosion resistance

Magnesium (Mg)-based biomaterials are widely investigated for degradable implant applications. Developing Mg-based composites is one of the strategies adopted to increase the bioactivity and to reduce the degradation rate of Mg. In the present study, hydroxyapatite (fHA) has been produced from fish bones and incorporated into pure Mg sheets by friction stir processing (FSP). Microstructures of the composites clearly revealed the grain refinement in the stir zone up to 10 $\mu$m from the starting size of 2000 $\mu$m. Measurements of microhardness also indicated the effect of a smaller grain size and the presence of fHA on increasing the hardness in composites. Interestingly from the tensile tests, mechanical properties, such as yield strength and ultimate tensile strengths were measured as they decreased for the composite due to the presence of fHA particles. However, the observed % elongation of the composite was similar to that of a natural bone. From the electrochemical tests, the composite exhibited an enhanced corrosion performance. From the results, it can be concluded that the cost-effective Mg–fHA composites can be developed by FSP for degradable scaffold applications in biomedical fields.

• Optimization of RF sputtering process parameters on electrical resistivity, deposition rate and sensitivity of Al-doped ZnO thin films grown on Si substrate using grey-Taguchi technique

Increasing environmental pollution globally demands gas sensors for monitoring urban air quality, fire and exhaust from automobiles. The need for high performance gas sensors requires a good control over sensing material structure. This paper studies the suitability of Al-doped ZnO thin films for development of CO gas sensors. Deposition of Al-doped ZnO thin films on Si substrates by the radio frequency sputtering technique was carried out to study the influence of process parameters. The process parameters selected for the analysis were power, deposition time, substrate temperature and working pressure. An orthogonal array L16 (4$^4$), signal-to-noise ratio and analysis of variance (ANOVA) were performed to optimize the electrical resistivity, deposition rate and sensitivity of the thin films using the Taguchi method. Grey relational grade (GRG) was performed to obtain multiple-performance characteristics of the thin films by optimizing the process parameters. GRG analyses identified the process parameters: power 150 W, deposition time 35 min, substrate temperature 25$^{\circ}$C and working pressure 1.5 Pa showed optimal multiple-performance characteristics. ANOVA analyses indicate that power and substrate temperature show significant effect compared with other parameters. Thin films at the annealingtemperature (450$^{\circ}$C) showed a decrease in electrical resistivity and an increase in sensitivity. At the sensor operatingtemperature of 150$^{\circ}$C, Al-doped thin films exhibited the lowest resistivity $3.76 \times 10^{−3}$ $\Omega$-cm and the highest sensitivity of 59%. The optimal multiple-performance characteristic of thin film sample identified is found suitable for CO gas-sensing applications.

• A conductive mechanism of PVA (Mowiol 10-98) filled with ZnO and MWCNT nanoparticles

Polyvinyl alcohol (PVA) hybrid nanocomposites are prepared via an ex situ approach with ZnO and MWCNT nanoparticle fillers and their conductive mechanisms have been investigated. The tailored hybrid nanocomposite conformation and their microstructural disparities for different filler concentrations were studied using an X-ray diffractometer. The direct current (DC) conductivity studies show an increase in the conductivity from $1.0528\times 10^{−11}$ to $2.1514\times 10^{−8}$ S cm$^{−1}$ up to a percolation threshold filler concentration of $x = 7.5$ wt%. The dielectric constant substantially indicates a decreasingtrend with increasing frequency. The exaggerated dielectric constant values of 11.8 at 5 kHz, 6.3 at 100 kHz, 5.86 at500 kHz and 2 at 1 MHz are observed for 7.5 wt% filler hybrid nanocomposites, which indicates their potential applicationas a gate material in metal-oxide-semiconductor field-effect transistors (MOSFETs). The alternating current (AC) electricalconductivity demonstrates an increasing behaviour up to $x = 7.5$ wt% filler concentration. The smaller values observedin the real part of the electric modulus ($M^{\prime}) indicates a riddance in electrode polarization. The observed higher frequencyshift in the imaginary part of the electric modulus for increasing the filler concentration up to$x = 7.5$wt%, decreases therelaxation time of the dipole orientation thereby increasing the conductivity mechanism of the hybrid nanocomposites. Apartfrom these, its small relaxation time with high electrical conductivity favours this material PVA/($x$)MWCNT($15 − x$)ZnO to have prospective application in microwave absorption appliances. The increase in the surface roughness of the film seenfrom the AFM images up to$x = 7.5$wt% concentration supports an enhancement in the crystalline nature of the filler. Differentialscanning calorimeter studies show an enhancement in glass transition temperature ($T_g$), melting temperature ($T_m$)and decomposition temperature ($T_d$) for PVA filled with MWCNTs and ZnO composites for optimum filler concentration$x = 7.5$wt%. • Effect of electrolytes on photoelectrochemical performance of a CuS–CdS heterojunction CdS–CuS heterojunction films have been grown successfully on a copper substrate using a chemical bath deposition (CBD) method. The obtained films are characterized usingX-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), optical absorption, Raman spectroscopy and photoluminescence (PL) analysis and the photo-electrochemical (PEC) properties of the CdS–CuS heterojunction have been studied using different electrolytes. The XRD pattern of CuS–CdS shows peaks corresponding to CuS (hexagonal) and CdS (cubic) structures, while the optical absorption studies revealed the presence of an absorption edge corresponding to CuS–CdS (band gap of 1.85 eV). The Raman spectra of the CuS, CdS and CuS–CdS heterojunctions were recorded and are in good agreement with the results reported in the literature. TEM and cross-sectional SEM images show an overlap between CuS rods and CdS flasks. The charge transfer across the layers was studied by using PL spectra. The measurement of the photo-electrochemical properties using a conventional two electrode system for an iodine electrolyte showed the highest conversion efficiency of 1.40% as against for potassium ferro–ferricyanide (0.38%) and polysulphide electrolytes (0.02%). • Ti–Zr coating on graphite through powder immersion reaction-assisted coating (PIRAC) and its oxidation kinetics at$T = 1000^{\circ}$C Coating of graphite with a metal alloy Ti–Zr was carried out on a block of graphite sample; the sample was initially dipped in ZrO$_2$containing a natural starch solution and then proceeded to powder immersion reaction-assisted coating (PIRAC) after drying. Ti powder containing 4 wt% iodine was used as depositing material, and the process was carried out at 850−950$^{\circ}$C for 10 h. The characterizations include X-ray diffraction, scanning electron microscopy and the hardness test. The coating thickness is proportional to the temperature of the PIRAC process, while the percentage of Zr is inversely proportional to the temperature of PIRAC treatment. All the characterizations revealed that the coated layer was a Ti–Zr alloy with hexagonal crystalline symmetry similar to$\alpha$-Ti. An oxidation kinetic assessment at 1000$^{\circ}$C of uncoated graphite shows a burns-off mechanism, while for a coated sample reveals a reaction of Ti with oxygen produces TiO$_2$; the reaction kinetics obey a diffusional mechanism. • Development of pure rutile TiO$_2$and Magneli titanium sub-oxide microstructures over titanium oxide-seeded glass substrates using surfactant-free hydrothermal process Titanium oxide seed layer was coated over glass substrates by sol–gel spin coating method. Single-step surfactant-free hydrothermal process developed titanium oxide microstructures over the titanium oxide-seeded glass substrates.Various morphologies of titanium oxide microstructures, varying from coral reefs to flower-like morphology were evolved by changing HCl concentration (1 and 3 M) in the precursor solution and growth temperature (GT) (120, 150 and180$^{\circ}$C) of the hydrothermal process. Structural studies confirmed the formation of rutile TiO2, TiO$_2+$Ti$_2$O$_3$and Ti$_4$O$_7$microstructures due to varying the concentration of HCl (1 and 3 M) in the solution and GTs. Morphological studies revealed the possibility of engineering coral reefs, cauliflower, flowers, ball, cactus and jasmine flower-shaped microstructures oftitanium oxide films by tuning the growth parameters. The indirect band gap of the titanium oxide microstructures derived from UV–Vis absorption spectra lies in the range of 2.9–3.02 eV. • Charge transport and transfer phenomena involving conjugated acenes and heteroacenes Conjugated acenes are very promising for their applicability in different optoelectronic devices. In particular, pentacene (PCn) shows some distinct behaviours, namely high optical absorption and remarkably high carrier mobility which makes it as a landmark semiconductor for use in field-effect transistors or hole transporting materials in organic photovoltaics. During the last few decades, a large number of theoretical and experimental researches has been performed showing the practical applicability of different acenes and heteroatom-doped acenes (heteroacenes). Few reviews are also made in this regard. However, correlating the molecular properties arising from their intrinsic electronic structures with their charge transfer (CT) and transport characteristics is really scattered. Furthermore, very recent understandings on the nanojunctionsmade of acenes along with suitable electrodes need to be reviewed for further development of their performances in electronic devices. At the same time, the photovoltaic applicability of acenes and heteroacenes has recently been shown as an interplay of the dynamics of CT states as well as the intrinsic charge separation within the molecules or composites. The present review aims to point out those recent observations so as to draw more attention for further development in the area of aceneand heteroacene-based optoelectronic devices. We concentrate more on the structure–property relationships which could guide the device performance. As the subject area is so vast, we put emphasis on the very recent studies on PCn and some lower S,N-heteroacenes. • A novel micro-solid oxide fuel cell ($\mu$-SOFC) for detecting methane content in biogas A novel micro-solid oxide fuel cell ($\mu$-SOFC), with a rectangular saw-tooth shape, was designed with a 50 wt% BYCF$+$50 wt% GDC$_{10}$cathode and a 60 wt% NiO$+$40 wt% GDC10 anode deposited on a GDC$_{10}$electrolyte substrate by the spray pyrolysis technique.$\mu$-SOFC receives methane only (CH$_4$) as fuel gas from one side. The fuel gas was applied at a flow rate of 0.2 l min$^{−1}$. The power density obtained was 1.0$\mu$W at 800$^{\circ}$C. Voltage levels generated by the$\mu$-SOFCat 40–99.99% CH$_4$was highly accurate representing the quantity of CH$_4$. Low accuracy was observed at 10–30% of CH$_4$. Therefore,$\mu$-SOFC is an application of SOFC technology to be a sensor for economically detecting CH$_4$in a biogas system, while being capable of operating in humid conditions at high temperatures. • Functional performance evaluation of an alginate/nano-cockle shell powder nanobiocomposite bone scaffold with BMP-2 Improvement in bone tissue engineered scaffolds plays an important role in determining the healing outcome. This study aims to investigate the functional performance of previously developed nanobiocomposite bone scaffolds usingbone morphogenetic protein-2 (BMP-2) for comparative analysis. The structural morphology and porosity of the scaffolds were analysed using scanning electron microscopy prior to dividing them into two groups, BMP-2 treated and control, forthe surface mineralization study, in vitro and in vivo evaluation. The surface mineralization study showed the presence ofplate-like calcium and phosphorus apatite crystallites in both groups indicative of the mineralization process. Osteoblasts (MC3T3-E1 subclone 4) cultured on the scaffold showed changes in the surface morphology with the presence of mineralization elements and the extensive presence of collagen fibres in BMP-2 scaffolds compared to the control. This was supported by a significant increase in calcium and alkaline phosphatase (ALP) activity showing enhancement in osteoconductiveness. In vivo studies conducted on 20 male ICR albino mice through subcutaneous dorsum implantation of scaffolds for 2 and4 weeks showed a significant increase in the histological score for inflammatory cells, scaffold degradation and neovascularization at week 4 compared to week 2 for the BMP-2 scaffold. These findings are supported by a significant decreasein ALP activity indicative of scaffold mineralization. There were no significant differences between BMP-2 and control scaffolds within the period of this study. In conclusion, the functional performance of the scaffolds was mildly acceleratedin BMP-2 compared to the control scaffold which showed promising properties in supporting osteogenesis without the use of any promoting factors. • Chitosan nanoparticles containing Physalis alkekengi-L extract: preparation, optimization and their antioxidant activity Physalis alkekengi-L is a medicinal herb with a high antioxidant capacity. It is used to treat various diseases. In this study, encapsulation of the hydro-alcoholic extract of P. alkekengi-L into chitosan nanoparticles (CNPs) was optimized by using response surface methodology, and its antioxidant capacity and anticancer activity were investigated. The results ofthe antioxidant capacity evaluation showed that the antioxidant activity of the chitosan nanoparticles containing extract did not significantly decrease by increasing the time of storage (over a 12 day period) as compared to that of un-encapsulated extracts. In conclusion, CNPs can be used to encapsulate and improve the stability of P. alkekengi-L extract and its antioxidantproperties. • Synthesis and characterization of short sisal fibre polyester composites Natural fibres have the potential to replace synthetic fibres for making polymer composites because of their good engineering properties. Sisal fibres obtained from the leaves of the sisal plant exhibit high strength among various other natural fibres, but have not been yet fully explored. Nevertheless, the impact of sisal fibre in polymer composites depends on sisal fibre extraction process, characteristic of fibre, fibre binder ratios, synthesizing technique, etc. In the present study, a detailed experimental protocol was conducted for sisal cultivation, fibre extraction, processing and development of compositeboards/panels and assessed the impact of incorporation of chopped strand sisal fibre mat on the mechanical behaviour of polyester composites. The results revealed that the diameter of sisal fibre harvested after 5 years of its cultivation varied from 275 to 475$\mu$m with a tensile strength of 121–337 MPa; tensile modulus of 2.59–10.47 GPa; elongation at break varied from 3.37 to 10.86%. It is imperative to note that the mechanical properties of sisal composites significantly improved with the incorporation of chopped strand sisal fibre mat (preform). The tensile, flexural and impact strengths of composites developed using chopped short sisal fibre mat (preform) were$45.87 \pm 3.2$,$102.29 \pm 9$,$33,954 \pm 5288$J m$^{−2}$, respectively. The findings of the study revealed the effectiveness of sisal fibre as reinforcing materials in polyester composites for use in building construction products and automotive applications. • Antibacterial, antioxidant properties of Solanum trilobatum and sodium hydroxide-mediated magnesium oxide nanoparticles: a green chemistry approach A comparative study of Solanum trilobatum-mediated magnesium oxide (St-MgO) nanoparticles (NPs) and sodium hydroxide-mediated MgO (Che-MgO) NPs are synthesized using magnesium nitrate precursor. The characterization analyses, such as ultraviolet–visible spectroscopy (UV–Vis), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), energy-dispersive X-ray diffraction (EDX), scanning electron microscopy (SEM) and particle-size analysis were carried out. To determine the antioxidant activity of MgO NPs by 2,2-diphenyl-1-picrylhydrazyl (DPPH) method and antibacterial activity against Escherichia coli (MTCC: 912), Bacillus subtilis (MTCC: 121) and Streptococcus pyogenes (MTCC: 1925), was performed by the well-diffusion method. The UV–Vis analysis of St-MgO, Che-MgO confirmed the formation of MgO NPs that have a broad absorption peak at 362 and 374 nm, respectively. IR spectrum of synthesized St-MgO and Che-MgO exhibits a high-intensity band at 440 and 460 cm$^{−1}$, respectively. XRD analysis indicates that synthesized St-MgO, Che-MgO were crystal in nature and EDX confirmed the composition of MgO-NPs. SEM analysis revealed that St-MgO and Che-MgO NPs were spherical in shape without aggregation. Particle-size analysis confirmed that the average particle sizes of St-MgO and Che-MgO NPs were 30 and 42 nm, respectively. DPPH assay of St-MgO NPs has higher absorbance value, which indicates the high antioxidant capacity compared with ascorbic acid. St-MgO NPs are effective against bacterial pathogens, such as E. coli ($16.66 \pm 0.66$), B. subtilis ($16.00 \pm 0.88$) and S. pyogenes ($13.66 \pm 2.08$) at 100 mg ml$^{−1}$concentration when compared with Che-MgO and the control ($P$< 0.001). Thus, the result suggested that safer use of biologically synthesized MgO NPs can act as effective antioxidant and antibacterial agents in the field of biomedicine. • Investigation of structural and luminescence properties of nanocrystalline tungsten-incorporated molybdenum disulphide ternary compounds: an experimental and DFT study The present manuscript reports the synthesis of tungsten-incorporated molybdenum disulphide ternary compounds in particle form at the nanoscale using existing solid state reactions, followed by ultrasonication and a densityfunctional theory (DFT) investigation of the compound system. The effect of W in the W-inserted MoS$_2$ternary compound system is the subject of current research. A comparative study shows enhanced photoluminescence (PL) at room temperature in the as-synthesized transition metal dichalcogenide (TMD) ternary compound. The compositional and structural characterization studies of the materials are performed using XRD, SEM, EDX, TEM and Raman spectroscopy. We have observed that a combination of W and S leads to better crystallinity than the combination of Mo and S in the compound system. The high band gap (BG) energy also confirms the nanoscale dimension of the material system which may be attributed to the formation of excitonic states from spin splitting and band nesting effects. A theoretical investigation of the effect of Win the MoS$_2\$ system using DFT also reveals that insertion of Wleads the system toward a direct BG semiconductor (SC). Multiple BGs of the material in the visible light range as found by UV–Visible (UV–Vis) spectroscopy, suggest applicability of these materials in luminescence devices and photocatalytic activity.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 3
June 2019