• Volume 42, Issue 5

October 2019

• Investigating silk yield and morphological changes in silk fibres obtained from silkworms fed with Ag and/or TiO$_2$ nanoparticles

Natural polymers like silk can be augmented in vivo with metallic elements to improve their intrinsic properties and stability. This study demonstrates the uptake of Ag and/or TiO$_2$ nanoparticles as diet supplements by silkworms. Nanoparticles dose on morphological changes in silk fibroin fibres and a change in overall silk yield was investigated. Though significant fibre reinforcement with Ag and/or TiO$_2$ was not noticed; an increase of 6% in the silk production was observed when silkworms fed with a particular composition of Ag $+$ TiO$_2$ nanoparticles (0.37 mM each) in their diet. Here, an average diameter of the degummed silk fibre was $\sim$10.91 $\mu$M with a roughness parameter value $R_{\rm q}$ being 134. This valueis comparable to silk fibres obtained from silkworms fed with Ag $+$ TiO$_2$ ($0.22 + 0.53$ mM) nanoparticles and this $R_{\rm q}$ value was also low when compared to the other tested compositions with nanoparticles. Silks from the control samples (devoid of nanoparticles in their feed) had high diameter fibres and are with low $R_{\rm q}$ values and silk yield. However, nanoparticlesupplementation to the silkworm’s diet resulted in low diameter silk fibres with varying roughnessess and with improved silk yield for the tested doses.

• Hydrothermal synthesis of strontium-doped ZnS nanoparticles: structural, electronic and photocatalytic investigations

Strontium-doped ZnS nanoparticles (NPs) (1.5, 5 and 9 wt%) were synthesized through a surfactant free hydrothermal method. The structural characterization by X-ray diffraction confirms the synthesis of ZnS, with its twocrystalline phases (cubic and hexagonal), without apparition of any peaks related to Sr phases. The crystallite size is affected by Sr doping concentration and was estimated in the range of 2.24–2.51 nm. Furthermore, transmission electron microscopy images show that the NPs have great tendency to aggregate into spherical shapes. Spectroscopy analysis revealed vibration modes specific to ZnS materials on the Raman spectra at about 260 and 345 cm$^{−1}$ and on Fourier-transform infrared spectra at 668.9 cm$^{−1}$. Electronic investigation performed by UV–Visible diffuse reflectance spectroscopy showed that thesynthesized ZnS NPs are optically transparent in the visible domain and their band gap energy decreases from 3.42 to 3.38 eV with increasing Sr concentration. Finally, the methyl orange degradation rate increases with Sr concentration, revealing an improvement in the photocatalytic properties of Sr-doped ZnS NPs.

• Hydrothermal synthesis of spindle-like SrMoO$_4$:Ln$^{3+}$ (Ln $=$ Eu and Tb) microarchitectures for selectively detecting Fe$^{3+}$ ions

In this work, spindle-like micrometre SrMoO$_4$:Ln$^{3+}$ (Tb, Eu) phosphors have been synthesized and designed as a fluorescent sensor for Fe$^{3+}$ ions assay. The structural information, morphologies and luminescence properties of the samples were characterized by X-ray diffraction, Fourier-transform infrared, Raman analysis, field-emission scanning electronmicroscopy and photoluminescence patterns. Furthermore, Fe$^{3+}$ ions could be immediately detected using fluorescence quenching methods, and this method shows excellent and satisfying sensitivity. This facile method could be extended to environmental and biological applications.

• Dielectric properties of Ag/Ru$_{0.03}$–PVA/$n$-Si structures

Ag/Ru$_{0.03}$−PVA/$n$-Si structures were successfully prepared and their morphological and electrical properties were investigated. The obtained electrical results suggested that the complex dielectric constant ($\epsilon^* = \epsilon^{\prime} − j\epsilon^{\prime\prime}$), complex electric modulus $M^∗ = M^{\prime} + jM^{\prime\prime}$, loss tangent ($\tan \delta$) and alternating current (ac) electrical conductivity ($\sigma_{\rm ac}$) are all a strong function of the frequency ($f$) and applied voltage. The changes in these parameters are the results of the existence of the surface states ($N_{\rm ss}$) or interface traps ($D_{\rm it} = N_{\rm ss}$), interfacial polymer layer, surface and dipole polarizations and hopping mechanisms. The values of $\epsilon^{\prime}$ and $\epsilon^{\prime\prime}$ show a steep decline with increasing frequency and then reach a constant value at high frequency, whereas the increments of $M^{\prime}$ and $M^{\prime\prime}$ with frequency are exponential. The $\tan \delta$ vs. $\log f$ plot has a strong peak behaviour, especially in the accumulation region. These experimental results suggested that the Ru$_{0.03}$−PVA interfacial layer could be used as a high dielectric material instead of conventional materials.

• Efficiency of sapota leaf extract against aluminium corrosion in a 3 M sodium hydroxide hostile fluid atmosphere: a green and sustainable approach

The present study focussed on the performance of a sapota leaf extract in controlling the aluminium (Al) corrosion in 3 M sodium hydroxide (NaOH) medium thoroughly investigated through gasometric, atomic absorption spectroscopy,electrochemical Tafel diagrams and impedance spectroscopy techniques. The outcome shows that small amounts of the sapota leaf extract are sufficient for the effective mitigation of the Al corrosion process in 3 M NaOH solution. The gasometric data revealed that four different concentrations of the plant extract inhibit the Al corrosion process and the protection efficiency of the inhibitor varies with time of the system.Type of inhibition was studied by an electrochemical potentiodynamic polarizationtechnique. The alternating current impedance spectroscopy results show that the plant extract inhibits the corrosion process by forming a defensive layer on the Al surface through an adsorption process, which confirms the inhibition properties of the plant extract. The presence of electron rich groups in the sapota leaf extract was confirmed by the Fourier transform infrared and energy-dispersive X-ray spectroscopy techniques. The particle size of the sapota leaf extract can be analysed by an X-ray diffraction technique. Further, atomic force microscopy and contact angle results evidence the adsorption of the sapota leaf extract on the Al surface. The morphology of the Al surface in protected and unprotected systems was examined through scanning electron microscopy techniques.

• Preparation of copper–silver alloy with different morphologies by a electrodeposition method in 1-butyl-3-methylimidazolium chloride ionic liquid

Electrodeposition of a copper–silver alloy based on a 1-butyl-3-methylimidazolium chloride (BMIC) ionic liquid was studied. The electrochemical behaviour of copper and silver ions was characterized by cyclic voltammogram.The morphologies and phase compositions of copper–silver alloy coating under different electrodeposition conditions were investigated by scanning electronmicroscopy and X-ray diffraction. The results show that copper–silver alloys with different micro-morphologies can be obtained under different potential conditions in BMIC. Co-deposition of the copper–silver alloy followed a two-step reduction process, the first step is the reduction of the cupric ion to the cuprous ion and the second step is the simultaneous reduction of the cuprous ion and the silver ion to form an alloy. A dendritic alloy can be obtained at $−$0.60 V, a bract alloy can be obtained at $−$0.80 V and a granular alloy can be obtained at $−$1 V. The coating particle size at 60$^{\circ}$C was smaller than the particle size obtained at 40$^{\circ}$C. The Cu–Ag alloy prepared by electrodeposition in ionic liquids consists of single-phase copper and single-phase silver.

• Corrosion behaviour of the Al-2.1–Mg-1.8–Si alloy in chloride solution

The corrosion behaviours of Al–Mg–Si alloys were studied in different Cl$^−$ concentrations by means of scanning electron microscopy, transmission electron microscopy and electrochemical experiments. The results show that the corrosionbehaviours of Al–Mg–Si alloys are closely related to the Cl$^−$ concentration. With an increase in Cl$^−$ concentration, the corrosion rate increases sharply by facilitating the process of chemical and electrochemical reactions. In 2.0 wt.% NaCl solution, slight pitting corrosion occurred around theMgSi phase, but corrosion trenching was not found around the Fe–Mn–Si phase. In 3.5 wt.% NaCl solution, the alloy appeared localized corrosion dominated by intergranular corrosion attack. In 5.0 wt.% NaCl solution, the alloy presented serious overall corrosion, and the passivation platform of the polarization was not obvious. Furthermore, an appropriate corrosion mechanism according to polarization and electrochemical impedance spectroscopy was proposed for the Al–Mg–Si alloy in NaCl solution. In addition, the corrosion rate influenced by differentCl$^−$ concentrations was discussed in detail.

• Experimental and theoretical analyses of transformation temperatures of Cu-based shape memory alloys

Binary-shape memory alloys that are based on copper, mainly copper–aluminium, copper–zinc and copper–tin alloys, either with or without ternary elemental additions, are of special interest to the industry and academia because of their good shape recovery, ease of processing, larger recovery strain and lower cost. However, unlike Ni–Ti shape memory alloys, their uses are moderately limited due to shortcomings, such as stabilization of martensite due to ageing, brittleness and low mechanical strength. Therefore, efforts have been made over the years to overcome these limitations using appropriate ternary and quaternary elemental additions. This work takes into account the data obtained from the experimental work carried out by the authors of this paper as well as the data obtained from the experimental and theoretical works carried out by earlierresearchers in this area that have been published in the literature over the years. It is observed in quaternary shape memory alloys based on copper that with an increase in the atomic radius of the quaternary element, the hysteresis width is found to increase. With the addition of ternary elements to binary Cu-based alloys (Cu–Al and Cu–Zn), and quaternary elements to ternary Cu-based alloys (Cu–Al–Fe, Cu–Al–Ni, Cu–Al–Mn, Cu–Zn–Al, Cu–Zn–Ni and Cu–Zn–Si), the $M_s$ temperature either increases or decreases. This influence is directly correlated with the $e_v/a$ ratio and $c_v$ values. It is also observed that asthe concentration of electrons decreases, the $M_s$ temperature decreases too. In addition, in this paper, we have tried to obtain relationships between the $M_s$ temperature and the mass or atomic% of different elements through multiple regressions to generalize the interpretations.

• Photo-catalytic dye degradation of methyl orange using zirconia–zeolite nanoparticles

In this research, the dye photo-catalytic removal was investigated using zirconia (ZrO$_2$) nanocatalysts, zeolite (Ze), ZrO$_2$–Ze with different percentages and optimized ZrO$_2$–Ze doped via urea, copper oxide and cerium oxide. In order to determine the optimal conditions, the effects of different catalysts and parameters such as dye concentration, UV lamp power, amount of the loaded catalyst and pH were investigated. The response surface methodology was used to obtain optimal experimental conditions. Physical and chemical properties of materials were investigated by X-ray diffraction,Fourier transform infrared, scanning electron microscopy and Brunauer–Emmett–Teller. Completely methyl orange (MO)-dye removal (100%) was achieved at optimal conditions under UV light during 80 min. The optimal operational condition for MO photo-catalytic decomposition using an optimal N-doped 10 wt% ZrO$_2$–zeolite nanocatalyst was obtained at UV lamp power, pH, catalyst loading and dye concentration of 15 W, 3, 0.4 g l$^{−1}$ and 5 mg l$^{−1}$, respectively. Photo-catalytic degradation kinetics of MO described well using pseudo-first order which is in accordance with the Langmuir–Hinshelwoodmodel ($k_{\rm app}$ = 0.031$min$^{−1}$). • Modelling of novel-structured copper barium tin sulphide thin film solar cells In this work, a novel structured Cu$_2$BaSnS$_4$(CBTS)/ZnS/Zn(O, S) photovoltaic device is proposed.Anontoxic, earth-abundant and auspicious quaternary semiconductor compound copper barium tin sulphide (Cu$_2$BaSnS$_4$) is used as an absorber layer.We propose a novel Zn(O, S) buffer layer for a high-power conversion efficiency (PCE) of CBTS-based thinfilm photovoltaic cells. Solar cell capacitance simulator software is used for device modelling and simulations are performed under a 1.5 AM illumination spectrum. The proposed device is investigated by means of numerical modelling and optimized the parameters to maximize its efficiency. Promising optimized functional parameters had been achieved from the proposed structurewith back surface field layer with a PCE of 18.18%, a fill factor of 83.45%, a short-circuit current of 16.13 mA cm$^{−2}$and an open-circuit voltage of 1.3 V. The promising results give an imperative standard for possible manufacturing of highefficiency, eco-friendly inorganic CBTS-based photovoltaic cells. • Synthesis of a high-quality NaP zeolite from epidesmine by a hydrothermal method Epidesmine as a silicon source was used to synthesize NaP zeolite by a hydrothermal method. Parameters such as SiO$_2$/Al$_2$O$_3$and H$_2$O/Na$_2$O molar ratios, reaction temperatures and reaction times were investigated for regulating the purity of the final product. The samples were characterized by X-ray diffraction, infrared spectroscopy and scanning electronmicroscope. The experimental results evidenced that a high-quality NaP zeolite was obtained at SiO$_2$/Al$_2$O$_3$and H$_2$O/Na$_2$O molar ratios of 3.7 and 55, respectively, and at a temperature of 95$^{\circ}$C for 6.5 h of ageing. The BET surface area and total pore volume of the powders were 17.1359 m$^2$g$^{−1}$and 0.006845 cm$^3$g$^{−1}$, and the pore size was$\sim$3.2$\mu$m. • Removal of hexavalent chromium from aqueous solutions using Ni–SiO$_2$nanomaterials This study describes an effective method developed for the removal of hexavalent chromium, Cr(VI), from anaqueous environment. In this study, the Ni–SiO$_2$nanomaterial was synthesized by the sol–gelmethod and then characterizedby field emission scanning electron microscopy, X-ray diffraction and energy dispersive X-ray spectroscopy. The preparednanomaterial was then employed as an adsorbent with significant properties of high surface area and uptake capacity.Adsorption conditions of Cr(VI) onto the Ni–SiO$_2$nanomaterial were optimized by altering different parameters (pH, initial Cr(VI) concentration and different periods of time). An amount of 100.75 mg g$^{−1}$was estimated as the maximum uptakecapacity of the Ni–SiO$_2$nanomaterial at pH 4.0. The experimental data of Cr(VI) adsorption onto the Ni–SiO2 nanomaterialwere fitted well to the Langmuir isotherm and pseudo second-order kinetic models.Moreover, the adsorption of Cr(VI) ontothe Ni–SiO$_2$nanomaterial was not influenced even in the presence of different coexisting ions. Finally, the recommendedmethodology was applied on several environmental water samples. • Evolution of microstructure with increasing carbon content and its effect on mechanical properties of disordered iron–aluminium alloy Correlation of microstructure and mechanical properties of hot-rolled Fe–7 wt.% Al with varying carbon contents has been investigated in detail. The microstructures of the alloys change significantly with an increase in the carboncontent. An alloy with 0.012 wt.% carbon shows a single ferrite phase, whereas with increase in carbon up to 0.65 wt.%, the microstructure evolves into a dual phase consisting of ferrite and$\kappa$-pearlite. At about 1.5 wt.% carbon, the alloy exhibits only$\kappa$-pearlite and with a further increase in carbon to 2.2 wt.%, an additional phase starts precipitating in the form of graphite. The room temperature tensile strength of the alloy increased significantly with an increase in the carbon content, which is in agreement with the microstructure. The yield strength and hardness of the steels with different carbon contents can becorrelated well with the inter-barrier spacing in different steels. • Promotion of bone repair of rabbit tibia defects induced by scaffolds of P(VDF-TrFE)/BaTiO$_3$composites In this work, scaffolds made of a novel experimental 0–3 type composite were implanted onto non-critical defects in rabbit tibiae. This work discusses the bone repair promoted by polyvinylidene fluoride-trifluoroethyleneP(VDF-TrFE)/barium titanate (BaTiO$_3$) composite that scaffolds with 10 vol% BaTiO$_3$. Prior to implant surgery, the P(VDF-TrFE)/BaTiO$_3$scaffolds, moulded into a membrane disk, were subjected to a cytotoxicity test (ASTM F895-84). A standardized transverse osteotomy was made with the following dimensions: 4.5 mm in width by 9 mm in length, at the proximal tibial metaphysis, in adult male rabbits, by using a cylindrical drill, cooled with a physiologic solution. These critical defects were filled with blood clot on the left tibiae (control group), whereas the right tibiae were covered with composite scaffolds, measuring 5 mm in thickness and 10 mm in diameter (experimental group);$n = 12$for each group.After 21 days, the rabbits were sacrificed and the tibiae bone fragments were conducted to demineralization routines, from fixation and stain procedures to histological analysis. The scaffolds promote the growth of the bone, resulting in an increased repair with callus formation around the scaffold and high mitotic activity at newly formed bones. • Surface micro-texturing design for improving tribological behaviour of graphene oxide thin films Effect of micro-scale surface texture with different densities on wear resistance of graphene oxide (GO) films was studied using a revolving ball-on-flat tribometer in humid environments. The micro-scale surface texture was producedby depositing about 363 nm thick GO films onto silicon substrates pre-textured with the patterns of dimples. The goal of the surface patterning was to improve the wear resistance of the GO films so that to extend lubricating life. The experimental results demonstrated excellent ability of the textured films to improve wear resistance of the silicon substrate. Furthermore, the GO films with an appropriate dimple area density (4%) were effective in reducing the friction coefficient (0.024) and exhibiting outstanding wear resistance owing to the entrapment of wear particles in the dimples. Finally, a simple frictionmechanism model was drawn to explain the frictional properties of the different textured area density GO films. • Utility of newly modified chitosan in the removal of heavy metal ions from aqueous medium: ion selectivity, XPS and TGA The purpose of this study is to evaluate the newly prepared modified chitosan, a new environmentally friendly adsorbent, in the field of wastewater treatment. Chitosan (CS) reacted with 3-chloro-2,4-pentanedione to give CS derivatives, CS-CPD. Modified CS with O–O and N–O chelating centres was treated with aqueous solution containing different metal ions to investigate its metal uptake and selectivity. The concentration of metal ions in aqueous solution was measured by inductively coupled plasma-optical emission spectrometry. The structure of the complex was identified by elemental analysis, infrared and solid-nuclear magnetic resonance. In addition, the chelating centres were determined by X-ray photoelectron spectroscopy. The morphology of the modified polymer and its metal complexes was studied to show a dramatic change incases of the CS-CPD–Pb, CS-CPD–Hg, CS-CPD–Cr and CS-CPD–Co complexes. • Villari effect in silicone/FeGa composites This paper presents the results of the Villari effect study in FeGa magnetorheological composites with very low stresses. The composites consist of a silicone matrix and Fe75Ga25 powder of size ranging from 50 to 100$\mu$m. Two types of composites, one is with 45 wt% and the other one with 30 wt% of Fe75Ga25 powder have been manufactured. The Villari effect has been measured in both samples as-manufactured and in those in which a 1 T magnetic field has been applied after curing. The results indicate that the composites with an applied field of 1 T after curing show the greatest Villari signal evenwithout any applied magnetic field. This fact allows a design of a low-cost force sensor and high performance. A simple model, based on the change in the cross-section of the composite, has been developed to explain the results obtained. • Photodegradation of methylene blue over a new down-shifting luminescence catalyst TiO$_2$nanotube arrays prepared by anodization technology are modified with a samarium ion (Sm$^{3+}$) by a hydrothermal method for use in photodegradation of methylene blue (MB). The samarium ion as a down-shifting luminescence material can improve UV radiation harvesting to increase visible light utilization. The efficiency of the photocatalytic activity for the modified-TiO$_2$nanotube arrays in degradation of MB was investigated under UV–Vis light irradiation. The results show that Sm–TiO$_2$nanotubes can increase the photocatalytic efficiency of MB. When TiO$_2$nanotubes are modified by 0.02 M Sm$^{3+}$, MB can be almost completely degraded when compared with bare TiO$_2$nanotubes. This indicates that TiO$_2$nanotubes structure, surface area and good UV radiation harvesting play important roles in the degradation of MB. • A study on zeolite-based adsorbents for CO$_2$capture In this study, zeolite-based sorbents were prepared and examined for CO$_2$adsorption from a simulated flue gas mixture using a fixed-bed flow reactor. Various amines such as monoethanolamine, ethylenediamine, diethylenetriamine and triethylenetetramine (TETA) were impregnated on support materials to prepare the adsorbents. Also, the effects of various parameters on CO$_2$adsorption capacity have been examined in this work. Further, an effort has been made to characterize various physico-chemical properties like surface area, pore volume, chemical composition, etc. of the in-house developedsorbents. Observation showed that the CO$_2$adsorption capacity enhanced with amine loading up to a certain concentration. The maximum carbon capture capacity of the 30-TETA-ZSM-5 sorbent is around 53 g of CO$_2$/kg of adsorbent. The thermochemical stability of the adsorbents has been tested by reusing the same material for multiple adsorption–desorption cycles,and no significant change in CO$_2$adsorption capacities was observed. • Synthesis and mechanism perspectives of a carbon nanotube aerogel via a floating catalyst chemical vapour deposition method HAYDER An effective and cost-effective approach to synthesize newmaterials can be determined via research on a carbon nanotube (CNT) aerogel. This review paper gives an overview of the current synthetic methodologies and routes to enhanceunderstanding. It also investigates the appropriate issues on the development of CNT-based three-dimensional (3-D) porous materials in an attempt to fill the knowledge gap regarding viability. First, an elaborate description on CNTs is provided, followed by a focus on CNT macrostructure fabrication, showcasing their key features, disadvantages, advantages and other aspects that were considered as related. Then, the methods for synthesis pertaining to the CNT aerogel are discussed with a focus on a floating catalyst chemical vapour deposition method as well as the growth mechanism pertaining to CNTsemploying the method.Key parameters, including catalyst, reaction time, carbon source, carrier gas and reaction temperature, which could cast an impact on the efficiency of the process are discussed subsequently. • Enhanced intercalation of organo-muscovite prepared via hydrothermal reaction at low temperature Muscovite clay is an ideal reinforcing filler due to its high-aspect ratio. However, it does not swell in water, making it hard to be treated and intercalated. In this study, ion exchange treatment is carried out on muscovite clay usingcetyltrimethylammonium bromide (CTAB) cations via two-step intercalation method. The intercalation steps included: inorganic–inorganic ion exchange treatment and inorganic–organic ion exchange treatment under hydrothermal conditions. The intercalation of muscovite particles was examined with various techniques to analyse the physical and chemical changes.Furthermore, the hydrothermal conditions for effective CTA$^+$ion intercalation within muscovite interlayers prepared via the hydrothermal process at low temperature, 180$^{\circ}$C, under different hydrothermal reaction times and CTAB/Li-Mus mass ratio were investigated. Fourier transform infra-red (FTIR) analysis revealed that the CTA$^+$ions are diffused into the interlayers of aluminosilicate and formed a strong electrostatic bond with the clay surface. X-ray powder diffraction analysis showed that the interplanar spacing in the organo-muscovite samples is almost identical as the hydrothermal reaction time is prolonged beyond 12 h. An optimum limit of the CTAB to Li-Mus ratio is observed as the d002 plane spacing is increased with an increase of the mass ratio of CTAB to Li-Mus up to 1.0 C and decreased with a further increase in the mass ratio. In addition, the intercalated CTA$^+$chains are homogenously distributed and formed a paraffin-like arrangement in the muscoviteclay. Besides, the structure of aluminosilicate layers is not affected or damaged after both treatments according to FTIR analysis. • Silica-supported Ni$_x$O$_y$, Zn$_x$O$_y$and Mn$_x$O$_y$nanocomposites: physicochemical characteristics and interactions with water and$n$-decane A series of M$_x$O$_y$/SiO$_2$(where M$=$Ni, Zn and Mn) nanocomposites were synthesized at different M$_x$O$_y$contents (0.2, 1 and 3 mmol per 1 g SiO$_2$) using a deposition method. The samples were characterized using nitrogen adsorption–desorption, X-ray diffraction, Fourier transform infrared spectroscopy, high resolution transmission electronmicroscopy and photon correlation spectroscopy. The heat of immersion in water ($Q_w$) and$n$-decane ($Q_d$) were measured using a microcalorimetry method, and the corresponding values of the hydrophilicity index$K_h = Q_w/Q_d$were analysed.The formation of M$_x$O$_y$on a silica surface leads to diminishing of the$Q_w$and$Q_d$values (calculated per 1 g of nanocomposites) because of the specific surface area reduction. However, the$Q_w$values calculated per 1 m$^2$increase for Zn$_x$O$_y$/SiO$_2$andMn$_x$O$_y$/SiO$_2$in comparison with the unmodified silica, and it remains unchanged for Ni$_x$O$_y$/SiO$_2$. Silica modification with M$_x$O$_y$significantly changes the pH dependence of zeta potential and affects the surface charge density. A shift of the isoelectric point (pH$_{\rm IEP}$) and a character of the zeta potential$\zeta$(pH) curve are affected by the M$_x$O$_y$phase, and pH$_{\rm IEP}$shifts toward higher values as follows Mn < Zn < Ni. • Effect of graphite particle fillers on dielectric and conductivity properties of poly(NIPAM-co-HEMA) Copolymers of 2-hydroxyethyl methacrylate (HEMA) and$N$-isopropylacrylamide (NIPAM) in different ratios were prepared by free radical polymerization using 2,2$^{\prime}$-azobisisobutyronitrile as an initiator at 60$^{\circ}$C. The copolymers were analysed by Fourier transform infrared and proton nuclear magnetic resonance. Thermal behaviours were determined bythermogravimetric analysis and differential scanning calorimetry (DSC). DSC measurements showed that the glass transition temperature ($T_g$) of poly(HEMA) and poly(NIPAM) was 100 and 140$^{\circ}$C, respectively. Electrical properties (dielectric constant, dielectric loss and alternating current conductivity) of polymers and composites prepared with graphite were investigated by using an impedance analyser, in the range of 10–20 kHz. While the dielectric constant values vary from 3.3 to 4.01 for copolymers at 1 kHz, these values are increased about 10 times for composites doped with 10 wt% graphite. Similarly, the dielectric loss and conductivity values were fairly high for composites. The conductivity values of composites doped with 10 wt% graphite showed a significant increase and the insoluble polymer became semiconducting. Itwas observed that the electrical properties of graphite-added composites at different ratios (8, 9 and 10 wt%) increased with the increase in graphite ratio for all polymers. In addition, the direct current conductivity of composites doped with10 wt% graphite was examined according to the temperature and the activation energy ($E_a$) values were calculated. • Thermodynamics of the oxidation of ZrB$_2$–TiB$_2$, ZrB$_2$–SiC and ZrB$_2$–B$_4$C ceramics The thermodynamics of the oxidation of three-high temperature ZrB$_2$-based ceramics (ZrB$_2$–TiB$_2$, ZrB$_2$–SiC and ZrB$_2$–B$_4$C) has been studied in order to find the stability domain of zirconium diboride, in terms of temperature, partial pressure of oxygen and composition, in which it is protected against oxidation. In the case of the ZrB$_2$-TiB$_2$binarysystem, a plot of$\log p$O$_2$vs.$1/T$in the temperature range of 500–2000 K and another plot of$p$O$_2$($\times$10$^{14}$) vs.$x$TiB$_2$for$T = 2000$K are made taking into account the two-extreme possibilities of no solubility and 100% solid solubility between ZrB$_2$and TiB$_2$, respectively. A plot of$\log p$CO vs.$\log p$O$_2$is made for 1773 K for the systems ZrB$_2$–SiC and ZrB$_2$–B$_42$C. It was found that the ZrB$_2$–TiB$_2$ceramics does not have sufficient oxidation resistance in the temperature range of 500–2000 K. ZrB$_2$of ZrB$_2$–SiC ceramics can be protected under 1 atmosphere oxygen or in air if the liquid borosilicate(with the chosen composition, 70% B$_2$O$_3$–30% SiO$_2$), which is an intermediate product, provides a kinetic barrier to the continuation of oxidation by forming an impervious layer on the exposed surfaces. In contrast, the ZrB$_2$–B$_4$C ceramics does not produce the borosilicate upon oxidation. In view of the volatility of pure liquid B$_2$O$_3$, it is recommended that the ZrB$_2$–B$_4$C ceramics can be used at a lower temperature, perhaps below 1373 K, when the vapour pressure of B$_2$O$_3$is significantlysmall. • Thermal, mechanical and electrical properties of lithium phosphate glasses doped with copper oxide Lithium phosphate glasses with the basic composition (P$_2$O$_5$50 and Li$_2$O 50 mol%) series by the addition of copper oxide (0, 10, 15 and 20 g/100 g) were prepared by a melt quenching technique. Fourier-transform infrared (FTIR) absorption spectra and X-ray diffraction (XRD) analysis were used to characterize the glass samples. Thermal expansion and mass density were also measured. The different mechanical properties of the prepared glasses were measured by an ultrasonic non-destructive technique. Additionally, both frequency and temperature dependence of alternating-current conductivity were measured in the frequency range of 40 Hz–1 MHz and the temperature range of 308–488 K. Moreover, direct current conductivity was also measured for the same temperature range. FTIR measurements confirm the appearance ofthe bands of phosphate groups and the assumption of bonds formed between Cu and P. XRD spectra approve the amorphous nature of the studied glasses. Thermal expansion and mass density of the prepared samples show an increase in values by increasing the CuO content. The mechanical properties of the studied glasses (hardness ($H_v$), Young’s modulus ($E$), elastic modulus ($L$), bulk modulus ($K$), shear modulus ($G$) and Poisson’s ratio ($ν$)) were positively affected by the CuO content, reflecting a better packed structure. Furthermore, the electrical conductivity values of the prepared glasses are identified to increase with an increase in both temperature and CuO content. Such trends agree with the data obtained by thermal expansion and FTIR. The progressive addition of CuO is assumed to improve thermal, mechanical and electrical properties of the prepared lithium phosphate glasses. • Use of colorimetric hydrogel as an indicator for food packaging applications A novel hydrogel was synthesized from$N,N$-dimethyl acrylamide (DMAAm), gelatin, citric acid (CA) and Basilicum extract (BE). This study was aimed at creating an advanced food packaging material that allows the detectionof food spoilage, which can be monitored colorimetrically. The poly(gelatin-co-DMAAm)/CA–BE was synthesized in the form of a film on Petri dishes using a redox polymerization technique. Mechanical and water resistance properties of the hydrogel were further improved by the addition of CA and$N,N$-methylene-bis-acrylamide as crosslinkers; BE was added to the reaction mixture and entrapped in the polymer chains with the aim to introduce antimicrobial, antioxidant and anthocyanin properties for the desired utilization. The characterization of the synthesized hydrogel was carried out usinga dynamic and mechanical analyser, thermo gravimetric analyser, Fourier transform infrared spectroscopy and scanning electron microscopy. The antimicrobial activity of the hydrogel was observed as it was tested against Escherichia coli, Bacillus subtilis and Staphylococcus aureus. Furthermore, total antioxidant and anthocyanin activities of the hydrogels were also studied at different pH values to monitor the colour change capabilities. It was concluded that the hydrogel was a strong candidate for use in food packaging. • Photosensitization effect on visible-light-induced photocatalytic performance of TiO$_2$/chlorophyll and flavonoid nanostructures: kinetic and isotherm studies Preparation and performance of natural dye-sensitized photocatalysts of TiO$_2$are described in this study. Such sensitized nanostructures offer visible-light-reactive systems for the photodegradation of organic pollutants. Natural pigments of chlorophyll and flavonoid extracted from parsley leaves and Curcuma longa roots are grated on TiO$_2$nanoparticlesas photosensitizers using an incipient wetness impregnation method. The as-prepared samples are structurally characterized by combined techniques, such as X-ray diffraction, scanning electron microscopy and Fourier transform infrared. The diffuse reflectance UV–Vis spectra are also used to investigate band-gap energies. The resultant band-gap energies confirm the ability of visible light absorption and thereby the ability of more efficient generation of photoexcited charge-carriers. The photocatalytic performance of dye-sensitized nanoparticles is tested in terms of decolourization efficiency of MB dye as a function of involved operating parameters including reaction time, amount of catalyst, initial MB concentration and pH. Both samples show the excellent photocatalytic efficiencies relevant to the red shift generated and high absorption of photons in the visible region. However, the highest efficiency is obtained for TiO$_2$/chlorophyll catalysts (93%) compared to TiO$_2\$/flavonoid samples (91%), which is perfectly in agreement with their band-gap energies and visible-light absorption ability. Photodegradation process kinetics is investigated by the Langmuir–Hinshelwood model, while the adsorption equilibrium is described based on Langmuir and Freundlich isotherms.

• Investigation of a thermoluminescence response and trapping parameters and theoretical model to explain concentration quenching for Yb³⁺-doped ZrO₂ phosphors under UV exposure

In this paper, a thermoluminescence signal centred at 129°C induced by UV radiation of Yb3+-doped ZrO2 is reported. Phosphor was prepared by a solution combustion method and annealed at 600 and 900°C to study the effect of annealing. The prepared phosphor was characterized by X-ray diffraction and scanning electron microscopy methods. Various parameters were optimized. Computerized glow curve deconvolution was employed and kinetic parameters for every deconvoluted peak were calculated. To understand the concentration quenching, a 3T1R (three trap one recombination centre) model has been proposed.

• Entropy analysis of Hall current and thermal radiation inﬂuenced by cilia with single- and multi-walled carbon nanotubes

Abstract. The present investigation explores the signiﬁcance of creeping viscous nanoﬂuids in an axi-symmetric channel inﬂuenced by metachronal waves containing magnetohydrodynamics and Hall current. Heat transport analysis is also per-formed to derive the impact of thermal radiation on internal heat source phenomena. The use of mathematical formulation resulted in a set of nonlinear coupled partial differential equations. The governed differential system is transformed into an ordinary differential system by considering similar variables. Exact solutions in the closed form have been derived for the temperature, momentum and pressure gradient. Moreover, entropy generation due to heat transfer, thermal radiation and magnetic effects has been measured. The graphical results have been presented to interpret sundry parameters of interest. Streamlines and isotherms are also plotted against the multi-walled carbon nanotube. For the validation of our results, a comparison table is presented. It is also seen that entropy of the system increases and the Bejan number decreases with an increase in the Brinkman number.

• # Bulletin of Materials Science

Current Issue
Volume 42 | Issue 5
October 2019

• # Editorial Note on Continuous Article Publication

Posted on July 25, 2019