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      Volume 42, Issue 4

      August 2019

    • Synthesis, structural and optical properties of K$_{0.5}$Na$_{0.5}$NbO$_3$ thin films prepared by spin coating route


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      In this paper, lead-free sodium potassium niobate thin films have been prepared by using a chemical solution deposition-based spin coating route. The effect of different anealing temperatures on structural and optical properties hasbeen studied. The phase analysis of thin films was investigated by using X-ray diffraction analysis. The microstructure and surface roughnes of thin films were studied by using atomic force microscopy. Raman spectroscopy analysis revealed that increase in annealing temperature gives rise to better crystallinity and perovskite phase. Optical parameter of thin films has been studied by using reflectance spectroscopy at room temperature. Photoluminescence analysis has been conducted by using an exciting wavelength of 300 nm at room temperature.

    • Substrate free synthesis of graphene nanoflakes by atmospheric pressure chemical vapour deposition using Ni powder as a catalyst


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      Graphene nanoflakes (GNFs) were synthesized by atmospheric pressure chemical vapour deposition of propane (C$_3$H$_8$) employing Ni (salen) powder without the introduction of a substrate. The graphitic nature of the GNFs was examined by an X-ray diffraction method. Scanning electron microscopy results revealed that GNFs were stacked on top of one another and had a high aspect ratio. Transmission electron microscopy studies suggested that the GNFs were made up of a number of crystalline graphene layers, some of which were even single crystalline as evident from the selected area diffraction pattern.Finally, Raman spectroscopy confirmed the high quality of the GNFs.

    • Catalytic degradation of real-textile azo-dyes in aqueous solutions by using Cu–Co/halloysite


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      Catalytic degradation of textile dyes in diluted aqueous solutions with minimal consumption of energy is a great challenge for wastewater treatment and environmental protection. Efficient heterogeneous catalysts are needed tocompletely oxidize azo-dyes under soft conditions. In this work, catalysts of Cu–Co oxide (1:2 molar ratio) supported on halloysite (Ha) nanotubes (CuCo(5%)/Ha and CuCo(10%)/Ha) were synthesized and used in the catalytic wet peroxideoxidation of reactive yellow 145 (RY-145) and basic red 46 (BR-46). The catalysts were characterized by chemical analysis, X-ray diffraction, Raman spectroscopy, N$_2$ adsorption isotherms, scanning electron microscopy and transmission electron microscopy. The results showed that the synthesized catalysts possess nanotubular structure with good mesoporosity, andthe spinel structure CuCo$_2$O$_4$ was identified as the active phase deposited on Ha. The catalysts degraded these azo-dyes in diluted solutions (22 mg l$^{−1}$ of RY-145 and 35 mg l$^{−1}$ of BR-46) under mild reaction conditions (25$^{\circ}$C, atmospheric pressure, pH 4 and minimum amounts of both catalyst and H2O2). Significant levels of dye conversion (93.1 $±$ 2.2% forRY-145 and 54.4 $±$ 2.0% for BR-46) were achieved in a relatively short time. In addition, significant values of total organic carbon removal (59.5 $±$ 1.8% for RY-145 and 33.9 $±$ 1.4% for BR-46) were obtained, indicating the total oxidation of a significant fraction of these dyes to CO$_2$ and H$_2$O.

    • Flame retardant properties of oil palm trunk particleboard with addition of epoxy resin as a binder and aluminium hydroxide and magnesium hydroxide as additives


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      This research aimed at investigating the effect of epoxy resin and flame retardant additives on oil palm trunk particleboard. The oil palm trunk was used as a raw material with epoxy resin as a binder, which was synthesized by a reaction of epichlorohydrin and phenolphthalein, while aluminium hydroxide and magnesium hydroxide were used as flame retardant additives to manufacture particle boards. Four different types of particle boards were produced, control board, board with 10% epoxy resin, board with 10% epoxy resin and 6% aluminium hydroxide and board with 10% epoxy resin and 6% magnesiumhydroxide, based on a target density of 0.80 g cm$^{−3}$, at a temperature of 180$^{\circ}$C, a pressure of 5 MPa and a pressing time of 20 min. The mechanical, physical, functional group, spectroscopic, morphological and elemental analysis properties were determined in comparison with control particleboard. Thermal degradation and flame retardant analyses were also carried out to analyse the thermal properties of particle boards. The results indicated that particleboard bonded with epoxy resin and flame retardant additives had improved mechanical, physical, thermal and flame retardant properties compared to control oil palm trunk particleboard. Overall results showed that epoxy resin as a binder and aluminium hydroxide and magnesiumhydroxide as additives have the potential to be incorporated into the particleboard to improve flame retardant properties.

    • Study of collective motion in liquid alkali metals


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      Study of collective motion in the liquid alkali metals is provided through the current article. Phonon dispersion curves for liquid alkali metals are presented using a second order approach in conjunction with the Hubbard–Beeby (HB)equation. Both longitudinal and transverse components of the collective motion are obtained through the present model. A classical approximation approach of the pseudopotential is used to describe the core interaction of the electronic configuration. Screening as well as exchange and correlation effect are determined by local field correction functions given by Hartree (H), Ichimaru–Utsumi (IU) and Sarkar et al. (S). Related parameters and constants are reported in line with the current computation to make the study comprehensive.

    • Effects of calcination temperatures on the morphology, architecture and dielectric properties of BCZT ceramics


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      (Ba$_{0.85}$Ca$_{0.15}$)(Zr$_{0.1}$Ti$_{0.9}$)O$_3$ (BCZT) ceramics were prepared by a simple sol–gel method. The effects of calcining temperature on the formation of BCZT ceramics were investigated in detail. The morphological changes and phase transformation of BCZT ceramics were analysed by X-ray diffraction and scanning electron microscopy. It is found that the calcined temperature determines the formation of a crystal phase, crystallinity and grain size. For dielectric properties, dielectric constant was increased first, and then decreased with increasing calcination temperature, in which the maximumdielectric constant of 2732 was achieved at 650$^{\circ}$C under a low-frequency alternating electric field. This may be attributed to the high crystallinity, density and fewer surface defects of BCZT ceramics. The optimum calcination temperature helps to understand the dielectric properties, which indicates that BCZT ceramics are promising lead-free candidates for widely used lead-based piezoelectric materials.

    • Visible light photocatalysis of methylene blue using cobalt substituted cubic NiO nanoparticles


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      This study reports the facile co-precipitation synthesis of pure and cobalt substituted NiO nanoparticles. The cubic crystalline structure of the synthesized NiO nanoparticles was confirmed through X-ray diffraction. Structuralbehaviour, morphological, elemental composition and optical properties of the prepared nanoparticles are investigated by Fourier transform infrared spectroscopy, scanning electron microscopy-energy dispersive spectrum, transmission electron microscopy and UV–Vis spectroscopy. The optical band gap is determined using UV spectra and is observed to decrease with an increase in cobalt ion concentration. Furthermore, methylene blue dye solution has been used to investigate the photocatalytic ability of the synthesized nanoparticles in the presence of sunlight. It is found that percentage degradation in dye concentration increases with irradiation time and also with the increase in the concentration of doping of cobalt in NiO. The dye solution is found to degrade to 94% within 50 min in the presence of solar radiation and the Ni$_{0.6}$Co$_{0.4}$O sample.

    • A comparative study of potential energy curves with RKRV curves for the ground states of I2, F2 and CO molecules


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      The latest molecular constant potential energy curves used for the electronic ground states of I2, F2 and CO molecules are constructed by the Rydberg–Klein–Rees–Vanderslice (RKRV) method. The Morse, Rydberg, Hulbert–Hirschfelder and extended Rydberg potential functions compare each other and have good agreement with RKRV curves for these molecules. The percentage deviations from RKRV curves are drawn at the same abscissa scale. These curves show that the extended Rydberg potential energy curve deviation is <0.5−2% error to dissociation limit.

    • Kinetic and thermodynamic biosorption of Pb(II) by using a carboxymethyl chitosan–pectin–BADGE–Pb(II)-imprinted ion polymer adsorbent


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      Pb(II)-imprinted pectin-carboxymethyl chitosan-BADGE or Pb(II)-CPBwas synthesized by mixed pectin (Pec) and carboxymethyl chitosan (CC) and then crosslinked with a crosslinking agent bisphenol A diglycidyl ether (BADGE)to form a stable adsorbent and resistant to acidic media. As a first step, the synthesis was performed by reacting the –OH group among Pec and CC with BADGE to form CPB. The Pb(II) ion was then imprinted with the Pec–CC gel and formed Pb(II)-CPB. Furthermore, the release of Pb(II) ions from the adsorbent was performed using the chelating agent, Na$_2$EDTA. The kinetic and thermodynamic equilibrium of the batch sorption of Pb(II) onto Pb(II)-CPB were investigated. The results of this study showed that the adsorption process of the Pb(II)-CPB adsorbent could be well described by the pseudo-second order model. The thermodynamic biosorbent in adsorption of the Pb(II) ion follows Freundlich isotherm. The adsorption energy of the adsorbent was 15.59 kJ mol$^{−1}$. This proves that the mechanism process of the adsorbent to Pb(II) ions occurs by physical adsorption. The Pb(II)-CPB adsorbent shows a significantly higher capacity compared to Pec and chitosan. Adsorption capacity of Pb(II)-CPB was $664.44 \times 10^{−3}$. The Pb(II)-CPB adsorbent has higher selectivity on Pb$^{2+}$ ions compared to Pec and CC with the adsorption selectivity order Pb(II)/Zn(II)<Pb(II)/Cu(II).

    • Optical properties of TAG co-doped with Ce and Eu


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      Nanopowder samples of terbium aluminum garnet (TAG) doped with Ce and Eu were prepared by a sol–gel technique followed by sintering in air at various temperatures (maximum of 1100$^{\circ}$C). The investigated concentrations of both the dopants were 0.1, 0.5 and 1.0 mol%. Nine powder samples prepared by the permutation of the doping concentrations were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray (EDX), powder X-ray diffraction (XRD) and optical spectroscopic techniques. SEM and TEM investigations confirmed the nano-structure of the prepared powders while EDX not only confirmed the doping of Ce and Eu in TAG but also eliminated the possibility of any interfering impurities. Powder XRD showed that the basic structure of TAG did not change on doping which was further confirmed by Fourier-transform infrared studies. However, optical absorption and Raman scattering investigations showed the distortion of the TAG lattice on doping. Emission (photoluminescence) in the spectral region of400–700 nm was observed when excited by 280 nm radiation. The intensity of this emission showed interesting dopant concentration dependence. The emission from TAG co-doped with 0.5 mol% of both Ce and Eu is of particular interest as its calculated colour chromaticity coordinates ‘$x$ and $y$’ were found as $x = 0.35$ and $y = 0.35$ which are very close to that of sun light at noon indicating its potential as a material for the white light source.

    • Exploring the electronic, optical and charge transfer properties of acene-based organic semiconductor materials


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      In order to tune the optoelectronic and charge transfer properties of 4,6-di(thiophen-2-yl)pyrimidine (1), some new compounds were designed, i.e., 4,6-bis(benzo[$b$]thiophen-2-yl)pyrimidine (2), 4,6-bis(naphtho[2,3-b]thiophen-2-yl)pyrimidine (3), 4,6-bis(anthra[2,3-b]thiophen-2-yl)pyrimidine (4), 4,6-bis(tetraceno[2,3-$b$]thiophen-2-yl)pyrimidine (5) and 4,6-bis(pentaceno[2,3-$b$]thiophen-2-yl)pyrimidine (6). Compounds 2–6 were designed by assimilation of benzene, naphthalene, anthracene, tetracene and pentacene, respectively at both ends of compound 1. Integration of oligocene end cores reduces the energy gap resulting in a red shift in the absorption and fluorescence emission spectra. The legible intra-molecularcharge transfer is significant from electron-rich moieties to the electron-deficient core (pyrimidine). The elongation of $\pi$-conjugation led to escalate the electron affinity, lower the ionization potential and hole reorganization energy. The hole reorganization energies of compounds 3–6 exposed that these materials would be effective hole transport contenders to be used in diverse semiconductor devices.

    • Surfactant modulated structural modification of hybrid poly($p$-phenylenediamine)/titanium dioxide composites and investigation of their functional behaviour


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      Hybrid polymer materials obtained by combining functional polymers with metal oxides are important functional materials having significant technological implications. Herein, we have described surfactant modulated structural manipulation of hybrid poly($p$-phenylenediamine)/TiO$_2$ composites using oleic acid as the surfactant molecule and investigated functional utility of the polymer composites. Hybrid polymer composites were synthesized by an oxidative polymerization technique using H$_2$O$_2$ as the oxidant and chloroglycinato(1,10-phenanthroline) copper(II) monohydrate as the catalyst. Structural characterization was performed by using conventional techniques like Fourier-transform infrared, ultraviolet–visible spectroscopy, photoluminescence, X-ray diffraction and thermogravimetric analysis. The effect of structural modification on the functional behaviour of the hybrid polymer composites was investigated and important observations were noted. Structural modification of the hybrid polymer composites significantly improved the mechanical and thermal characteristics. Conductivity values obtained from $I$–$V$ measurement and band gap calculation indicate that there is scope for using such materials as wide band gap semiconductor materials and also as insulator materials.

    • Deconvolution of Raman spectra of disordered monolayer graphene: an approach to probe the phonon modes


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      This paper explores the phonon modes from the Raman spectrum of disordered monolayer epitaxial graphene using the deconvolution technique.The phonon density of states (PDOS) of pristine monolayer graphene has been enumerated and convoluted by a Gaussian function to check the accuracy of the deconvolution process.We show that the original PDOS is recovered by deconvolution of the convoluted spectrum with the same spread function.We propose that the PDOS of pristine monolayer graphene is similar to that of the relative intensity of the deconvoluted Raman spectrum of disordered epitaxialgraphene. These results could be used for identifying the intensity of individual phonon modes to justify the structure, and probing the mechanism of changing the phonon modes with various types of defects formed in graphene.

    • Synthesis of CdSe and CdSe:Ga nanostructures for antibacterial application


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      In this paper, the preparation of CdSe and CdSe:Ga nanoparticles using two methods: thermal evaporation and pulse laser ablation has been reported. Their structural properties were characterized using X-ray diffraction (XRD) andfield emission scanning electron microscopy (FESEM). As confirmed by the XRD curves, CdSe and CdSe:Ga nanoparticles exhibited polycrystalline and wurtzite hexagonal structures with orientation planes of (100), (101), (102), (110) and (112). Also, a homogeneous distribution of nano-rod, flower-like, cylindrical, hexagonal and both nano-rod and hexagonal shapes with different diameters was seen by FESEM images. The band gaps of CdSe and CdSe:Ga (without annealed and annealed at temperatures of 150 (6 h) and 500$^{\circ}$C (1 h)) were found to be 1.72, 1.7, 1.69 and 1.64 eV, respectively. The antibacterialactivity could be increased by annealing CdSe:Ga nanoparticles at 150$^{\circ}$C for 6 h inGram-positive bacteria (Bacillus subtilis),whereas it is decreased in Gram-negative bacteria (Enterobacter cloacae). Alternatively, annealing CdSe:Ga at 500$^{\circ}$C for 1h led to an increase in the antibacterial activity in both Gram-positive and Gram-negative bacteria. It is concluded that the antibacterial activity is highly dependent on the type of bacteria, material, preparation conditions and the used methods.

    • Capsicum-extract blended chitosan composite films and studying their antibacterial properties


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      Capsicum extract at different concentrations (0.5–3.0 ml) was blended with a chitosan polymer to obtain the composite films. It was compared with the pristine film to examine their antioxidant, mechanical, barrier, biodegradability, stability and antimicrobial properties. The morphology of the films was studied using a scanning electron microscope. From the obtained results, it was observed that the antioxidant, mechanical, biodegradability, stability and antimicrobial propertieswere enhanced when compared to the other films. The barrier properties of the composite films showed a decrease in activity when compared to the pure chitosan film. It may be due to the incorporation of a capsicum extract agent into the chitosan polymer matrix which plays a vital role in enhancing the overall properties.

    • Investigations on the ZnO- and Cr-doped ZnO powders


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      Among the metal–oxide nanoparticles, pure and doped zinc oxide (ZnO) has been widely studied due to their potential applications, such as electrical, thermal and optical materials. In this context, samples of undoped ZnO and Cr-dopedZnO powders were prepared using a solution-combustion route. The formation of the combustion products was confirmed by X-ray diffraction analysis. The samples were well characterized using the Fourier transform infrared spectroscopy and scanning electron microscopy techniques. In the sample, photoluminescence studies showed that ZnO could be excited at267 nm, while an ultraviolet emission centred at $\sim$383 nm was exhibited. Antibacterial-activity testing was carried out using the disc-diffusion method.

    • An ultrafast laser micromachined broadband terahertz frequency selective surface


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      The purpose of this paper is to focus on the frequency selective surface (FSS) filter structure which exhibits a broadband frequency response operating in the terahertz (THz) frequency regime. The achievement of the broadbandfrequency response has been accomplished by means of only invoking the FSS structure excluding the presence of a ground plane and also excluding the multilayered FSS technique. The FSS filter is simulated using CST Microwave Studio. This simulation has been carried out using Teflon as the substrate which is a dielectric over which the conductive material gold with a thickness of 2 $\mu$m is coated in which the FSS filter structure is designed with periodic hexagonal aperture unit cells. The structure of the proposed frequency selective surface filter helps in achieving a broadband frequency response witha bandwidth of 300 GHz centred at 0.36 THz. The designed FSS structure is a bandpass filter and it exhibits the most imperative properties of angle resolvability and polarization insensitivity. The fabrication of the same has been carried outusing the laser micromachining process.

    • Influence of pyramid size on reflectivity of silicon surfaces textured using an alkaline etchant


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      Surface texturing of p-type monocrystalline silicon (100) is well known as one of the best methods to reduce reflection losses and to increase light trapping and light absorption probability. Pyramid surface textures play a major role in reducing the reflectance of monocrystalline silicon surfaces. In this paper, the size of pyramids formed on the surface of p-type silicon substrates and by changing the etching characteristics during the texturing process of silicon were studiedand evaluated. The pyramids that formed on the crystalline silicon surface formed light traps that led to increased light absorption efficiency. The pyramid size effects on the percent reflectivity were evaluated at normal incidence and an inverse relationship between the percent reflectivity and the pyramid size was found. The size of the pyramids was controlled by controlling the texturing process by changing the concentrations of potassium hydroxide (KOH) and isopropyl alcohol (IPA) and by controlling the etching process time. In this work, the optimized etching conditions were determined as a solutionprepared with 20 wt% KOH and 3 wt% IPA for wet etching at a reaction temperature of 80$^{\circ}$C and an etching time of 40 min. The lowest value for percent reflectivity of the patterned surfaces was 9.7% and it was achieved for pyramid bases close to 4 $\mu$m as measured at a wavelength of 650 nm.

    • Preparation and characterization of graphite/thermosetting composites


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      Graphite/thermosetting composites were prepared via a melt blending and compression–curing process using epoxy and phenolic resins as polymer matrices. The flexural strength, flexural modulus and electrical conductivity of thecomposites were investigated. The composites containing 55wt% graphite showed the maximum flexural strength and modulus. Scanning electron microscopy results showed that the thermosetting resins and graphite were uniformly dispersed on the fractured surface of the composites. The electrical conductivity of the composites increased with an increase in the graphite content. The flexural and electrical properties of the composites improved significantly by the addition of a carbon fibre cloth (CFC) or a CFC and carbon nanotubes.

    • Reaction of YBa$_2$Cu$_3$O$_{7−x}$ (YBCO) and fused silica in YBCO glass fibres


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      This work introduces the first reported experiments on drawing YBa$_2$Cu$_3$O$_{7−x}$ (YBCO) into fibres with a fused silica cladding using a fibre draw tower to manufacture YBCO glass fibres. These fibre draw experiments allowed manufacturing fibre sections with core diameters between 50 and 200 $\mu$m and a length of around 1.2 m. However, reactionsbetween the fused silica cladding and the YBCO core were revealed by the fibre drawing process. Therefore, this study focusses on investigating these reactions (in as-drawn fibres as well as after additional heat-treatments) using energy dispersive spectroscopy analyses on an environmental scanning electron microscope as well as using X-ray photoelectron spectroscopyanalyses and a cross-polarized light study. The results showed the formation of silica precipitations inside the as-drawn YBCO core, forming an interface layer between the core and the cladding regions, as well as the presence of a high silicon content inside the core with a possible silicate formation. Additional heat-treatments have shown the formation of silica and copper oxide co-precipitations at 900$^{\circ}$C. In addition, heat-treatments at higher temperatures have shown the occurrence of further reactions, which led to a degradation of the core and the formation of new phases.

    • Plant-based synthesis of silver nanoparticles in Handelia trichophylla and their biological activities


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      In this research, silver nanoparticles (AgNPs) were prepared via a ‘green’ procedure using an aqueous extract of Handelia trichophylla. The formation of AgNPs was confirmed by its light brown colour. The AgNPs were formed in silver nitrate (1 mM) via a bioreduction process in spherically shaped NPs with a mean diameter in the range of 20–50 nm. Moreover, the green synthesized AgNPs seemed to demonstrate a higher antibacterial activity against human pathogenic bacteria. In addition, the in vitro cytotoxicity effect of biosynthesized AgNPs was also investigated, which was detected tobe up to 15.62 $\mu$gml$^{−1}$ in the treated Neuro2A cells. Low toxicity and high antibacterial activity of biosynthesized silvernanoparticles can be utilized in different biological, biomedical and industrial applications.

    • Al-doped Nb$_3$O$_7$F nanosheets: preparation, characterization and photocatalytic performance under visible light irradiation


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      Doping can result in energy band rearrangement, high carrier concentration and fast carrier separation in semiconductor materials. Consequently, great enhancement in the photocatalytic performance can be achieved. In this work,Al3+-doped niobium oxyfluoride (Nb$_3$O$_7$F) was synthesized by a facile hydrothermal approach for the first time. A series of characterization tools were used to investigate the phase, composition, microstructure, chemical state, spectrum response and band gap. The influence of Al doping on the photocatalytic performance was also investigated by varying the molarratios of Al/Nb. The results confirmed that Al atoms have been successfully incorporated into the Nb$_3$O$_7$F lattice. Al doping led to slightly lowering of the band gap of Nb$_3$O$_7$F from 3.08 to 2.99 eV. Moreover, Nb$_3$O$_7$F with 0.06 mol% Al doping exhibited the highest degradation efficiency for methyl blue under visible light irradiation. Crystal defects generated by appropriate Al-doping increased the specific surface area and the optimized band gap could be responsible for the improved photocatalytic activity.

    • First principles calculation of electronic, phonon and thermal properties of hydrogenated germanene


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      Germanene is a basic building block of two-dimensional materials of germanium and it exhibits many unique electronic properties. It is necessary for germanene to tuning its electronic band structure for future applications. Theelectronic and vibrational properties of germanene, germanane, single-sided semi-hydrogenated germanene and single-sided full-hydrogenated germanene (FHgermanene) were analysed by density function theory. It was found that hydrogenation effectively leads to germanene transition from metallic to semiconductors. Meanwhile, phonon dispersion showed that germanane and FHgermanene are stable. For the same Ge/H ratio in the structure, the thermal properties of germanane and FHgermanene are consistent. The hydrogenation process provides a novel method to tune the properties of germanene withunprecedented potentials for future nanoelectronics.

    • Enhanced photocatalytic activity of SnO$_2$ NPs by chromium (Cr) concentration


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      This study reports the synthesis of un- and chromium (Cr)-doped tin dioxide (SnO$_2$) nanoparticles (NPs) through chemical precipitation and their application for photodegradation of methylene blue dye. The obtained NPs were characterized by X-ray diffraction (XRD) analysis, transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, elemental mapping and ultraviolet–visible (UV–Vis) spectroscopy. The TEM and XRD results demonstrated that the SnO$_2$ NPs are spherical and contain polycrystalline tetragonal crystals. UV–Vis spectra showed that increasing the concentration of the Cr dopant enhances the light absorption potential of the SnO$_2$ NPs. Finally, the findings of the photocatalytic experiments performed for 120 min in ultraviolet irradiation under ambient conditions revealed an improvement inthe degradation efficiency of the SnO$_2$ NPs by Cr doping.

    • Microstructure and transport properties of multiwall carbon nanotube-reinforced barium zirconium titanate ceramics


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      The influence of multiwall carbon nanotubes (MWCNTs) reinforced on microstructures and their transport properties on pure and cerium-substituted barium zirconium titanate (BZT) ceramics are reported in this study. The MWCNTswere prepared by a low-temperature sonochemical/hydrothermal method using dichloromethane as a carbon source. These MWCNTs were mixed with the as-prepared ceramic powders before heat treatment to obtain a reinforced product. The scanning electron micrographs reveal the successful incorporation of carbon nanotubes in BZT ceramics. The temperature dependent direct current (dc)-resistivity was less for MWCNT-reinforced ceramics in contrast to that of pure ceramics. The decrease in the dc resistivity was due to the superior electrical behaviour of MWCNTs, which act as a connector between ceramic grains. The Seebeck coefficient of cerium-substituted-BZT improved after reinforcing the MWCNTs.

    • Mechanical and corrosion performance of multilayer ceramic coatings deposited on an austenitic stainless steel using plasma spray


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      This research investigated consecutive multilayer thermal barrier coatings, including Ni$_3$Al–Al$_2$O$_3$–Al$_2$O$_3$/MgO, produced by plasma spray with outer layer thicknesses of 50, 100 and 150 $\mu$m deposited on an AISI 316 stainless steel. X-ray diffraction, scanning electron microscopy, Rockwell-B hardness measurements, pin-on-disk wear test and potentiodynamic polarization test were performed to evaluate the specimens. The results revealed that the structure of the produced coatings was completely crystalline. An increase in the coating thickness formed a smooth surface and a lowdegree of roughness and promoted grain growth. According to the Hall–Petch equation, the degree of hardness decreased from 99 to 92 HRB, and the friction coefficient decreased from 1.25 to 0.6 because of low surface roughness. An adherence test performed with a Brinell hardness test showed that an increase in the layer thickness improved the coating adherence coefficient (d$p$/d$r$) from 0.083 to 0.118 kg $\mu$m$^{−1}$. The corrosion test results indicated that the increase in the coating thickness caused a decrease in corrosion current density from 1.1 to 0.008 mA cm$^{−2}$.

    • Magnetic behaviour of ${}^{57}$Fe/Co/Al multilayers deposited on a glass substrate


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      Multilayers of ${}^{57}$Fe/Co/Al 20 and 40 trilayers (TLs) prepared on a glass substrate using ion beam sputtering deposition techniques have been studied. Magnetization curves obtained at different angles show the anisotropic nature of both the samples. Both samples show strong in-plane uniaxial anisotropy. Negative $\delta m$ values suggest that dipolar type interactions between grains contribute to the in-plane uniaxial anisotropy. Angular dependence of coercivity indicates that the magnetization reversal mechanism is different for both samples. The variation in coercivity with azimuthal angle is wellreproduced in the 20 TL sample using the modified Kondorsky model and by the Stoner–Wohlfarth model in the 40 TL sample.

    • The influence of carbon nanotube addition on the properties of shear thickening fluid


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      The properties of shear thickening fluid (STF), based on polypropylene glycol and amorphous silica, modified by the addition of multiwalled carbon nanotubes (MWCNTs), were studied. The STF’s viscosity increases abruptly during impact tests. The addition of a small amount of carbon nanotubes (CNTs) to the STF, leads to an increase of the maximal viscosity from 2128 to 12,213 Pa·s. To show the differences between various compositions, the microstructures of fluids wereobserved by scanning electron microscopy. A pronounced influence of the CNTs on the ability of impact force absorption was noticed. The protective structure containing 55 and 0.25 vol% of fumed silica and CNTs, respectively, is able to absorb up to 74% of impact force.

    • Influence of Ni doping on the structural, ferroelectric, magnetic and optical properties of Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ thin films


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      Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ ($x = 0.025–0.125$) thin films were synthesized by applying a sol–gel method on fluorine-doped tin oxide substrates. The influence of Ni doping concentration on the structure, leakage current, ferroelectric, magnetic and optical properties of Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ thin films was investigated. Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ thin films are polycrystalline films that present a single perovskite structure without any impurity phase when the Ni doping concentration is below 0.1 and present a Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ phase when the Ni doping concentration is above 0.1. The grain size of the films and their holes gradually decrease with an increase in the Ni doping amount. The saturation magnetization of Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ thin films increases with Ni content.However, appropriate Ni doping concentration can decrease the leakage current and enhance the ferroelectric polarization and optical transmittance of the films. Meanwhile, the absorption edge has a slight red shift. Bi$_{0.85}$Nd$_{0.15}$Fe$_{1−x}$Ni$_x$O$_3$ thin films possess better combination properties at a leakage current density of $4.27 \times 10^{−9}$ A cm$^{−2}$, ferroelectric polarization of 28.58 $\mu$C cm$^{−2}$, saturation magnetization of 2.08 emu cm$^{−3}$ and transmittance of over 85% when the Ni doping concentration, $x$ is 0.05.

    • Effect of vanadyl doping on relative intensities of factor group split Raman bands in potassium oxalate monohydrate


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      We report Raman spectral studies of pure potassium oxalate monohydrate, K$_2$C$_2$O$_4$$\cdot$H$_2$O (POM) and its doped varieties with 1 and 5% vanadyl concentrations at room temperature. Apart from many other interesting changes in the Raman spectra on doping with VO$^{2+}$, one of the most intriguing observations is the change in relative intensities of factorgroup split components of several Raman bands including some bands in the lattice mode region. We have explained the relative intensity changes of factor group split components in terms of locking of adjacent C$_2$O$_4$−H$_2$O−C$_2$O$_4$−H$_2$O chains due to vanadyl doping in the POM lattice. The reduction in the intensities of water bands on vanadyl doping also supports this view.

    • A detailed parametric study on the operating frequency of chloride ion-electrically charged carbon nanotube oscillators


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      Fabrication of new types of nanoscale oscillators with enhanced operating frequency has become the focal centre of interest. The aim of this paper is to explore the mechanical oscillatory behaviour of chloride ion tunnelling through carbon nanotubes (CNTs) decorated with identical functional groups at both ends. To this end, our previously proposed analytical expression for total potential energy between an ion and a functionalized CNT is used to derive a new semi-analytical expression for the accurate evaluation of oscillation frequency. With respect to the proposed frequency formula obtainedfrom the conservation of mechanical energy principle, a comprehensive study is conducted to gain an insight into the effects of different parameters such as, sign and magnitude of functional group charge, nanotube length and initial conditions on the operating frequency of chloride ion-electrically charged CNT oscillators. It is revealed that the presence of functional groups, especially ones with the opposite charges to the chloride ion, leads to enhancement of the maximum achievable frequency. It is further observed that optimal frequency is attained when the ion oscillates near the ends of a positively charged nanotube.

    • Investigation of photodegradation of rhodamine B over a BiOX (X$=$Cl, Br and I) photocatalyst under white LED irradiation


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      In this study, a low temperature precipitation method was applied to prepare BiOX (X$=$Cl, Br and I) nanostructures using HCl, HBr and HI as halogen sources. The as-prepared samples were characterized by various techniques such as X-ray diffraction, field emission scanning electron microscopy, energy dispersive spectroscopy, Fourier-transform infrared spectroscopy, diffuse reflectance spectroscopy and nitrogen adsorption–desorption analysis. The photoactivity of BiOX samples to degrade rhodamine B (RhB) molecules in aqueous solution was investigated under white LED irradiation. The results indicated that BiOCl exhibits a higher photodegradation performance in comparison with BiOBr and BiOI. Ninety six percent of the RhB molecules was degraded over BiOCl after 25 min light irradiation, whereas under the same conditions, the degradation efficiencies of BiOBr and BiOI samples are 62 and 24%, respectively. The enhanced photodegradation activity of BiOCl is ascribed to the higher specific surface area which increases the physical adsorption of RhB molecules on the Vphotocatalyst surface.Moreover, the photodegradation mechanism and the main radical species in the degradation reactionsover BiOCl were investigated.

    • Fabrication and characterization of transparent nanocrystalline ZnO thin film transistors by a sol–gel technique


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      A nanocrystalline zinc oxide (ZnO) thin film-based metal–insulator–semiconductor thin film transistor (MISTFT) was fabricated by a facile sol–gel technique onto silicon di-oxide/indium tin oxide-coated glass substrates. Themicrostructural study of the ZnO thin films indicated uniform crystalline growth with typical (002) X-ray diffraction peaks for h-ZnO with a wurtzite structure. The optical transmittance of the ZnO thin films was >80% in the visible region of theelectromagnetic spectrum. The field effect transistor (FET) aluminium top contacts were fabricated using suitable shadow masking. The transfer characteristics of a typical ZnO MIS FET revealed nonlinearity in a linear plot. From the slope and crossover, we obtained a first estimate of field effect mobility ($\mu$) and threshold voltage ($V_T$) of 0.13 cm$^2$ V$^{−1}$ s$^{−1}$ and1.03 eV, respectively. The ZnO TFT operated in enhanced mode with n-channel characteristics and the drain current on–off ratio was 105. The deposition parameter needs to be optimized to obtain TFTs with a higher modulation ratio and larger field-effect mobility.

    • Decrystallization of cellulose under the influence of elastomer-assisted mechanical and mechanochemical shear


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      Microcrystalline cellulose (MCC) was subjected to mechanical and mechanochemical shear in a rubber mixing milling. Nitrile rubber (NBR) and ethylene–propylene–diene monomer (EPDM) rubber were used to induce shearon cellulose during treatment. Solid-state interactions between $N,N^{\prime}$-dimethylacetamide/lithium chloride (DMAc/LiCl)and cellulose particles were facilitated during mechanochemical shear. Fourier transform infrared spectroscopy, X-ray diffraction analysis, thermogravimetric analysis, scanning electron microscopy and swelling studies were carried outon MCC, DMAc/LiCl-treated MCC, MCC subjected to mechanical shear and DMAc/LiCl-treated MCC subjected to mechanochemical shear. Crystallinity and swelling behaviour of the untreated and merely DMAc/LiCl-treated MCC samples, in the absence of any shear, were found to be similar. However, when MCC was subjected to mechanical shear assisted by NBR and DMAc/LiCl-treated MCC subjected to mechanochemical shear assisted by EPDM, the resultant MCC samples exhibited significant reduction in their crystalline index with increased swelling. When DMAc/LiCl-treated MCC was subjected to mechanochemical shear assisted by NBR and mechanical shear alone on MCC, assisted by EPDM, did not exhibit any appreciable change in the crystalline index and swelling behaviour of the resultant MCC samples. While NBR-assisted mechanical shear was found to reduce crystallinity in untreated MCC, crystallinity in DMAc/LiCl-treated MCC was found to be reduced significantly with EPDM rubber-assisted mechanochemical shear.

    • A study of electromagnetic light propagation in a perovskite-based solar cell via a computational modelling approach


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      Recently, there has been huge surge of scientific interest in organic–inorganic hybrid perovskite solar cells by virtue of their high efficiency and low cost fabrication procedures. Herein, we examine the light propagation inside a planar perovskite solar cell structure (ITO/TiO$_2$/ZnO/CH$_3$NH$_3$PbI$_3$/Spiro-OMeTAD/Al) by solving the Helmholtz equation inthe finite element-frequency domain. The simulations were conducted using the COMSOL multiphysics finite element solver to carry out the two-dimensional optical modelling of simulated solar cells in the visible region. It has been observed that shorter wavelengths of light are significantly absorbed by the top region of the photoactive perovskite layer. Specifically, at a wavelength of 400 nm, the effective optical power penetration decays to zero at only 40% of the overall length of the photoactive layer. This observation has been attributed to the high absorption coefficient of the CH$_3$NH$_3$PbI$_3$ perovskitematerial at shorter wavelengths. However, at longer wavelengths, the incident light propagates deeper into the photoactive layer, reaching 100% penetration. Based on the numerical computation, a maximum generation rate of $\sim 3.43\times 10^{23}$ m$^3$ s$^{−1}$ has been observed in the photoactive layer at a wavelength of 550 nm.

    • Numerical investigation of temperature distribution and melt pool geometry in laser beam welding of a Zr–1% Nb alloy nuclear fuel rod end cap


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      Zr–Nb alloys are used in the nuclear and chemical industries, in which the welding of an end cap to a fuel rod is a critical issue in manufacturing processes. To identify the optimal process parameters for achieving good-quality welds, it is necessary to investigate the thermal environment in the fusion and heat-affected zones. A three-dimensional computational fluid dynamics analysis is performed with a volumetric heat source by simulating the interaction of the heat source and the material and by accounting for the phase change during welding. The model incorporates the buoyancy force and Marangoni stress and generates the temperature distribution, weld bead geometry and fluid flow in the weld pool during the laser welding process.

    • Understanding solubility, spinnability and electrospinning behaviour of cellulose acetate using different solvent systems


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      The purpose of this study is to understand the solubility and spinnability of cellulose acetate (CA) and its electrospinning behaviour in different solvents. As the process of electrospinning and the corresponding fibre propertiesare primarily governed by the solvents used, a systematic study of the selection of solvent systems using the solubility parameters of Hildebrand and Hansen along with a Teas chart for a particular polymer is essential for the better optimization of the process. It appeared from the Teas chart that higher dispersion force ($f_d$) and lower hydrogen bonding force ($f_h$) areconvenient for both the solubility and spinnability of CA in single solvent of acetone and binary solvent of 2:1 acetone/$N$,$N$ dimethylacetamide(DMAc). The viscosity of the solutions escalated with increasing concentration of CA due to polymer chain entanglement which in turn favoured fibre formation. Among the solvent systems used in this work, field emission scanning electron microscopy arrayed the electrospun CA fibres using pure acetone as a solvent produced both cylindricaland ribbon-shaped fibres of a diameter of 1 $\mu$m, whereas CA in 2:1 acetone/DMAc yielded smooth bead-free cylindricalfibres of diameter in the range of 250–350 nm and CA in 3:1 acetic acid/water formed fibres with beads. Rheological analysis showed that fibre formation improved with increasing viscosity of CA solution. Electrical conductivity measurement of the CA solutions depicted that with an increase in CA concentration, fibre diameters were increased, whereas the conductivitydecreased. Also, attenuated total reflectance–Fourier transform infrared spectroscopy confirmed the major peaks of CA for all the electrospun samples.

    • Structural and catalytic properties of Ni–Co spinel and its composites


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      Pure nickel–cobalt (Ni–Co) spinel and its two composites with active carbon and multi-walled carbon nanotubes (MWCNTs) were synthesized. X-ray diffraction confirmed the nickel cobaltites of cubic syngony and lattice constants fornanosized crystallites. Fourier transform infrared spectra confirmed an inverse spinel consisting of a tetrahedral site Co$^{2+}$ and octahedral sites Ni$^{2+}$ and Co$^{2+}$. Scanning electron microscopy images demonstrated a surface texture typical for spinels and agglomerates of composite particles with active carbon and MWCNTs. All the synthesized samples have a surface areaand porosity that are sufficient for the flow of heterogeneous catalytic processes. The micropore volume of the composite with MWCNTs constituted only 4% of the total porosity, while this percentage represented 25% for the composite on thebasis of active carbon. The high catalytic activity of Ni–Co spinel is proved in the model reaction of borohydride hydrolysis. To create composite spinel catalysts, active carbon showed itself to be a more efficient carrier for the catalytically active mass of spinel, as compared to MWCNTs.

    • Surface modification of Kevlar fibre fabric and its influence on the properties of Kevlar/epoxy composites


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      The present study addresses the enhancement of interfacial interaction between Kevlar and epoxy through surface modification of Kevlar fabric using various chemical treatments. The chemically modified aramid surface wasexamined by Fourier transformed infrared spectroscopy, energy dispersive spectroscopy, scanning electron microscopy (SEM), dynamic mechanical analysis and wettability characteristics. The Kevlar/epoxy composites were prepared using the hand lay-up process. Furthermore, the influence of surface modification was validated through the mechanical characteristics of Kevlar/epoxy composites. The study reveals that the chemical treatment of the Kevlar surface increases the polar functional groups and improves the interfacial adhesion between fibre and epoxy. The surface energy,work of adhesion and performance of Kevlar composites were studied for treated and untreated fibres. The tensile and flexural moduli were increased up to 38% in treated Kevlar fibre compared with untreated fibre. It was observed from SEM analysis that adhesive failure bondsrely on chemical bonds at the interface of fibre matrix composites and cohesive failure at the fibre matrix was decreased.

    • Effect of particle size distribution on thermo-mechanical properties of NiO filled LDPE composites


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      The effect of nickel oxide (micro) addition on thermo-physical and mechanical properties of low density polyethylene (LDPE) has been studied. The samples have been prepared by the melt mixing process. The X-ray diffraction(XRD) and scanning electron microscopy (SEM) of the samples have been performed for micro-structural characterization and surface morphology, respectively. The XRD result confirms that the crystallinity of LDPE is affected by NiO addition, whereas the agglomeration of nickel oxide can be seen in the SEM photographs of LDPE samples having higher NiO loading. The thermal stability of the samples has been checked from DSC and TGA analyses under nitrogen atmosphere. The thermal stability of LDPE improves with the addition of a small amount of NiO particles. However, the peak melting temperature of LDPE/NiO composites decreases due to the dispersion of nickel oxide in the LDPE matrix. Again, the thermal conductivity of LDPE/NiO composites measured by a KD$_2$ prothermal analyser increases approximately two times for 40 wt.% of NiOloaded LDPE composites. This increase in the thermal conductivity of LDPE may be explained on the basis of a model based on particle size distribution. The coefficient of linear thermal expansion (CTE) of the samples has been measuredby a thermo-mechanical analyser as a function of temperature. The experimental value of CTE is well explained by taking the inter-phase volume and interaction between the filler particles and matrix into account. The mechanical properties ofLDPE/NiO composites show an improvement with NiO addition and are explained in the light of various models and correlations.

    • Characterization of an amorphous indium tin oxide (ITO) film on a polylactic acid (PLA) substrate


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      The study presents the deposition of nanostructured indium tin oxide thin films with thicknesses of 10, 30 and 50 nm on the polylactic acid (PLA) substrate by sputtering at 30$^{\circ}$C. The absence of ITO peaks on the X-ray diffraction patterns confirms the amorphous state of ITO films and the X-ray photoelectron spectroscopy spectrum validates the deposition of ITO films on the PLA substrate. The results of atomic force microscopy of films exhibit variation in the average roughness of 0.3–1.5 nm when the thickness is increased. It was examined that optical transmission is dependent on the thickness of films which varies from 78 to 87% in the visible spectrum of 400–700 nm and the energy band gap varies from 3.95 to 4.02 eV. The films exhibit the low sheet resistance which is due to the formation of oxygen vacancies and dangling bonds.An increase in transmittance enhances the FOM of the ITO films on the PLA substrate.

    • Silica- and diatomite-modified fluorine rubber nanocomposites


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      To find the most suitable filler system for fluorine rubber, a simple and green method to introduce a limited content of silanol groups on the surfaces of silica and fluorine rubber was studied. Fluorine rubber nano-composites wereprepared by using nano-silica, diatomite and carbon black as the reinforcement and filler and the coupling agents KH550, KH590 or Si69 as the compatibilizer between the filler and fluorine rubber. The structure and morphology of the composites were investigated by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The results showed that the most suitable filler system for fluorine rubber was the diatomite and silica compound (8:12 mass ratio), the best coupling agent was KH550 at 2 parts per hundred rubber (phr). The modified compound filler was silanized with the coupling agent KH550 for fluorine rubber by FTIR analysis, the compatibility between the filler and fluorine rubber was improved by SEM analysis and further confirmed by thermogravimetric analysis to improve the thermal properties of fluorine rubber with the filler compound system.

    • Multi-walled carbon nanotubes as secondary fibre fillers for property improvement of short carbon fibre-reinforced silicone rubber


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      To improve the properties of room temperature vulcanized (RTV) silicone rubber, functional multi-walled carbon nanotubes (MWCNTs) and short carbon fibres were added into the RTV silicone rubber as hybrid fibre fillers. Thefunctionalized MWCNTs were characterized by transmission electron microscopy and X-ray photoelectron spectroscopy. The mechanical, thermal and ablative properties of the fabricated RTV silicone rubber composites were investigated. Their properties were enhanced by adding the functionalized MWCNTs with appropriate contents. The tensile strength and tear strength of the composites are improved from 4.0 MPa and 20.3 kN m$^{−1}$ to 4.3 MPa and 21.3 kN m$^{−1}, respectively, when the MWCNT content increased from 0 to 0.5 phr. In addition, the decomposition temperatures at the onset point and 50%mass loss increased from 493.4 and 564.4$^{\circ}$C to 498.8 and 612.4$^{\circ}$C, respectively. The mass and line ablation rates alsodecreased from 0.062 g s$^{−1}$ and 0.148 mm s$^{−1}$ to 0.059 g s$^{−1}$ and 0.145 mm s$^{−1}$, respectively.

    • Preparation, characterization and properties of LnSmWO$_6$ (Ln $=$ Nd and Dy) nanofunctional ceramics


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      Isovalent substitution of lanthanide ions in Ln$_2$WO$_6$ (Ln $=$ lanthanides) nanoceramics can probe into multifunctional applications due to their unique structural and electronic properties. In this work Sm$^{3+}$ ions in the Sm$_2$WO$_6$ nanoceramics were partially replaced with Nd$^{3+}$ and Dy$^{3+}$ ions and their structural, optical and ionic transport propertieswere studied. The size and structure of the nanocrystalline LnSmWO$_6$ (Ln $=$ Nd and Dy) compounds prepared through a combustion method were characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy and transmission electron microscopy (TEM). UV–Visible spectroscopy and photoluminescence spectroscopywere used for the investigation of optical and electronic properties of the nanoceramics. Bulk ceramics prepared from the nanoparticles achieved high-density during the sintering process and the surface morphology of the dense NdSmWO$_6$ was imaged using scanning electron microscopy. The electrical properties of the dense ceramics were analysed using impedancespectroscopy. XRD analysis carried out on the prepared materials showed a single-phase monoclinic structure for the nanoceramics. A combined analysis of FTIR and Raman studies showed the presence of Ln–O and O–W–O vibrations,which confirm the monoclinic structure. Particulate properties investigated through the TEM imaging showed that the prepared materials are polycrystalline aggregates. Optical studies carried out on the nanoparticles showed absorption in the UV region and emission in the visible region. Impedance spectroscopic studies conducted on bulk ceramics imply that these are good oxide ion conductors at high-temperature.

    • Effect of cerium doping on the optical and photocatalytic properties of ZnO nanoflowers


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      Photocatalytic performances of the synthesized cerium doped (Ce-doped) ZnO nanoflowers are reported in this work. A microwave-assisted sol–gel method is adopted for the synthesis of the nanomaterial and its structural andmorphological features are characterized. While doping, the Ce$^{3+}$ ions occupy the sites of Zn$^{2+}$ ions in the hexagonal ZnO lattice, which is investigated by means of X-ray diffraction studies and energy dispersive X-ray analysis. At higher Ce$^{3+}$ concentrations, ultraviolet (UV) light absorption is quite high as evidenced by the UV–Vis absorption spectra. The photoluminescence study demonstrates higher oxygen vacancy and zinc interstitials for the Ce-doped ZnO compared to the undoped ZnO. Ce-doping improves the electrical properties of the sample as well. Finally, it is established that the Ce-doped ZnO nanoflower is highly efficient in UV degrading the methylene blue organic dye.

    • Performance of a rechargeable cell using an ionic liquid gel polymer electrolyte and natural graphite electrode


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      With the concepts of green environment and the priority given on economical aspects, a great deal of research activities has been diverted towards clean and low-cost device fabrication. Central focus was on eliminating the use of toxicand expensive materials like Li and different solvents. Application of ionic liquid-based gel polymer electrolytes (GPEs) and non-Li electrodes can address many shortcomings associated with liquid, solid and GPEs. In the present study, characteristics of a rechargeable cell with 1-ethyl-3-methylimidazolium trifluoromethanesulphonate-based GPE having Zn and Sri Lankan natural graphite electrodes have been investigated. For characterization, electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic charge discharge test have been performed at room temperature. The open circuit voltage of the cell was about 1 V. Specific charge and discharge capacities of the cell were 4.66 and 2.99 mA h g$^^{−1}$, respectively. Moreover, efficiency of the specific charge was 80.2% over 500 cycles, while efficiency of specific discharge was 92% over 1000 cycles. These results proved the suitability of the electrolyte and electrodes investigated in the present study to be usedwell in rechargeable cells.

    • Synthesis, structural and luminescence properties of Dy$^{3+}$ activated GdAlO$_3$ phosphors by a solid state reaction method under a N$_2$ atmosphere


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      Dysprosium (Dy$^{3+}$) ion-doped GdAlO$_3$ nanophosphors were fabricated by using a high temperature solid state reaction method. X-ray diffraction measurements were used to investigate the phase and crystal size of these phosphors. The morphology of the powder was observed by scanning electron microscopy. The band structure of the phosphor was determined by recording the UV absorption spectra and Tauc plot. The optical behaviour of the phosphors was determined by measuring their photoluminescence (PL) spectra. The PL spectra show characteristic blue (489 nm) and green (567 nm)emissions corresponding to the energy level transitions of Dy$^{3+}$.

    • Structural evolution and CO$_2$ capture performance of silicon oxycarbide-derived carbon by thermal-treatment under an Ar atmosphere


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      In this paper, we investigated the effect of thermal-treatment under an Ar atmosphere on the structural evolution of silicon oxycarbide-derived carbons (SiOC-DCs) by adjusting the temperature from 1200 to 2100$^{\circ}$C, which will be characterized by means of N$_2$ adsorption, X-ray diffraction, Raman and transmission electron microscopy techniques, and studied their CO$_2$ capture performances. The results show that the structure of SiOC-DCs varied regularly with treatment temperature. The porosity and crystallinity of the as-received sample are almost stable when the thermal-treatment temperatureis <1500$^{\circ}$C. Subsequently, increasing the temperature (especially up to 1800$^{\circ}$C) will lead to an obvious improvement in the carbon crystallinity at the cost of pore structure breakage, which can be characterized by a quick decrease in the surface area and total pore volume of SiOC-DCs. Interestingly, the as-received SiOC-DC sample exhibits good CO$_2$ captureperformance at 0◦C under ambient pressure, up to 3.16 mmol g$^{−1}$. The thermal-treatment process under an Ar atmosphere in the range of 1200–1500$^{\circ}$C could further help in increasing the CO$_2$ adsorption ability by increasing the ultra-micropore ($d$ < 0.6 nm) volume.

    • First principles investigation of the structural, electronic, thermal and transport properties of new ternary auride X$_3$AuO (X $=$ K and Rb) semiconductors


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      We report the structural, electronic, thermal and transport properties of two new ternary aurides containing gold atom X$_3$AuO (X $=$ K and Rb) using the full-potential linearized augmented plane wave method, based on the density functional theory. To describe the exchange-correlation potential, we have employed the generalized gradient approximation–Perdew–Burke–Ernzerhof (GGA–PBE) scheme of the GGA. The computed ground state properties are in good accordance with the experiments. Moreover, Tran–Blaha-modified Becke–Johnson (TB–mBJ) potential improves the electronic properties andgives accurate band gaps. Both anti-perovskites X$_3$AuO are semiconductors with an indirect band gap. Furthermore, the inclusion of spin–orbit coupling effects on the band structure along with TB–mBJ approximation splits the valence band of our compounds and reduces their band gap energy. The thermodynamic properties including heat capacity ($C_V$), thermal expansion ($\alpha$) and Debye temperature ($Theta_{\rm D}$) are also estimated. The transport properties as function of temperature are calculated using the BoltzTrap code; therefore, these two materials are very appropriate for thermoelectric devices at high temperatures.

    • Structure of ice confined in carbon and silica nanopores


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      In this work, water confined in silica and carbon nanopores has been examined. The purpose of this study is to describe the melting behaviour and structure of ice confined in silica nanopores, KIT-6 and ordered carbon nanopores, CMK-3, having pore diameters of 5.9 and 5.2 nm, respectively. To determine the melting temperature of ice inside the nanopores, we performed differential scanning calorimetry measurements of the systems studied.We found that the melting temperature of confined ice is reduced relative to the bulk melting point and this shift is 16 K for water confined in KIT-6 and 21 K for water confined in CMK-3. The structural properties of water at the interfaces were analysed by using the neutron diffraction method (ND). The ND measurements for all the systems studied, showed the features of both hexagonal ice, $I_h$,and cubic ice, $I_c$. However, we show that the ice confined in nanopores does not have a structure corresponding to the typical hexagonal form or the metastable cubic form. The ice confined in nanopores has a structure made up of cubic sequences interlaced with hexagonal sequences, which produce the stacking disordered ice (ice $I_{\rm sd}$).

    • Photocatalytic activity of Zn-doped Fe$_2$O$_3$ nanoparticles: a combined experimental and theoretical study


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      Iron oxide (Fe$_2$O$_3$) nanoparticles were synthesized by a simple co-precipitation method. The effect of Zn concentration on Fe$_2$O$_3$ nanoparticles was investigated by structural and electronic properties. X-ray diffractograms indicate the formation of a hematite Fe$_2$O$_3$ structure. The calculated particle sizes for undoped-Fe$_2$O$_3$ and Zn-doped Fe$_2$O$_3$ are 31 and 15 nm, respectively. The photocatalytic test was performed against methylene blue to find the efficiency of the photocatalyticactivity of the prepared nanoparticles. From the results, it is found that compared to undoped-Fe$_2$O$_3$, the efficiency of Zn-doped Fe$_2$O$_3$ increases considerably. To understand the mechanism behind the photocatalytic activity, a DFT-based calculation was performed to measure the band edge positions of the undoped and Zn-doped Fe$_2$O$_3$ nanostructures and the results are matched well with experimentally observed values.

    • A compact CRLH metamaterial with wide band negative index characteristics


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      Metamaterials are the artificial materials that may have a negative refractive index and results in extraordinary properties which are not found in nature. This research focusses on designing a compact-sized artificial material for negativecharacteristics of permittivity, permeability and refractive index over the wide range of frequencies. The metamaterial design is evaluated for single negative, double negative and double positive behaviours over a broad range of frequencies to investigate the gap and gapless transitions from backward to forward wave propagation. The dispersion diagram of the material is also investigated for left or right hand behaviour of the material. The equivalent circuit diagrams along with circuit simulations of the parameters are also presented for detailed analysis and understanding. The designed metamaterial behaves like a double negative material for low frequencies and double positive material for high frequencies. The approach is verified using CST microwave studio simulation and the results obtained are validated using the rectangular waveguide measurement method.

    • Novel fabrication of a laccase biosensor to detect phenolic compounds using a carboxylated multiwalled carbon nanotube on the electropolymerized support


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      Biosensors research is one of the fastest growing fields in which tens of thousands of papers have been published over the years; even more, numerous biosensors have been developed for the detection of phenolic compounds, such as catechol which reacts with an appropriate enzymatic bioreceptor like laccase. A biosensing electrode for catechol detection was investigated by covalent immobilization of laccase on a glassy carbon electrode modified by conducting polymers built of poly(3,4-ethylenedioxythiophene), gold nanoparticles and carboxylated multiwalled carbon nanotubes. The fabrication process of the sensing surface was investigated by Fourier transform infrared spectroscopy, scanning electron microscopy and electrochemical procedures. The electrochemical results demonstrate that the enzyme was immobilized covalently onto the modified glassy carbon electrode by the interaction between carboxyl groups of the carboxylated multiwalled carbon nanotubes and laccase. The biosensor demonstrates a direct electron transfer between the electrode and immobilized laccase. Under optimum conditions, it presented two linear responses in the range of 0.1–0.5 and 11.99–94.11 $\mu$M. The limits ofdetection were found to be 0.11 and 12.26 $\mu$M.

    • Electrochemical, thermodynamic and theoretical study on anticorrosion performance of a novel organic corrosion inhibitor in 3.5% NaCl solution for carbon steel


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      The theoretical and electrochemical performance of a novel organic corrosion inhibitor 3,4$^{\prime}$-dihydro-3-[2$^{\prime}$-mercaptothiazolidine]indol-2-one (DMI), for API 5L Grade B carbon steel in 3.5% NaCl, was evaluated by potentiodynamic polarization (Tafel), electrochemical impedance spectroscopy (EIS) and density functional theory (DFT) for quantum chemical studies. Potentiodynamic studies confirmed that DMI was a mixed organic corrosion inhibitor type which specially affects the cathodic branch. The inhibition efficiencies of reactants, DMI and acetylcysteine followed the following order at 25$^{\circ}$C and 200 ppm: DMI (87%) > isatin (71%) > 2-thiazoline-2-thiol (62%) > acetylcysteine (54%). EIS measurementsillustrated the charge transfer controlled corrosion process. The Langmuir adsorption isotherm model of DMI was adopted. Surface studies were performed using scanning electron microscopy. Activation and adsorption thermodynamicparameters of DMI were computed. The magnitude of $\Delta G^{\circ}_{\rm ads}$ and the sign of $\Delta H^{\circ}_{\rm ads}$ concluded that the adsorption occurred through chemisorption. Quantum chemical calculations of four corrosion inhibitors were used for investigating the molecular structure effect on inhibition efficiency.

    • Electrical, mechanical and dynamic properties of ternary composites from acrylonitrile butadiene rubber and conductive fillers


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      This paper presents comparative investigations on dual and ternary composites based on nitrile butadiene rubber. These composites were filled with carbon black and nickel powder at various ratios with each filler or with a combination of both. The focus of this study is on the electrical, mechanical and dynamic properties of the materials as influenced by the loading rate, applied pressure and bending degree have on the specific volume electrical resistivity. The investigations of the dynamic properties view the effect that the amount and chemical nature of the fillers have on the storage modulus and the tangent of the mechanical loss angle. It has been established that the specific characteristics of each of the fillers (particle size, specific surface, tendency to aggregate and agglomerate, interaction with the elastomeric matrix) have the greatest impact on composite properties. Scanning electron microscopy studies of the fillers and composites also confirm the results obtained.

    • Bandgap engineering of cobalt-doped bismuth ferrite nanoparticles for photovoltaic applications


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      The bandgap energy range of multiferroic bismuth ferrite is 2.2–2.7 eV, making it a promising candidate for photovoltaic (PV) applications. But its efficiency is still very low (<2%). This report thus focusses on the application ofbismuth ferrite (BFO) engineered with cobalt (Co) doping and on the tuning of its bandgap energy ($E_g$). BiFeO$_3$ is a unique multiferroic material that simultaneously displays both ferromagnetic and ferroelectric properties at room temperature. Co doped with pure BiFeO$_3$ (BiFe$_{(1−x)}$Co$_x$O$_3$; $x = 0$, 0.05, 0.1 and 0.15) was synthesized by the sol–gel method andannealed at 600$^{\circ}$C. X-ray diffraction shows the well-arranged crystalline structure and peaks of pure and doped-BiFeO$_3$ nanoparticles. A suitable reduction of $E_g$ has been observed for Co-doped BiFeO$_3$, which may be appropriate for the effective use in PV solar cells. Thermogravimetric analysis and differential scanning calorimetry were used to investigate the thermal decomposition character of the xerogel powder and the pattern of pure and doped BiFeO$_3$ phases. Field emission scanning electron microscopy images showthe surface crystallography of pure and Co-doped BiFeO$_3$. Co-doped BiFeO$_3$ has considerably reduced the crystallite and particle size of the samples. We have calculated the $E_g$ of pure and doped BiFeO$_3$ using a UV–Vis–NIR spectrophotometer and the results show the important reduction of $E_g$ (1.60 eV) of the Co-doped samples, which may have potential applications in PV solar cells.

    • Exhibition of polarization conversions with asymmetric transmission theory, natural like chiral, artificial chiral nihility and retrieval studies for K- and C-band radar applications


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      In this study, asymmetric transmission, natural chirality phenomena and a retrieval study with chiral metamaterials (MTMs) are numerically and experimentally focussed, investigated and discussed by examining the polarization conversion effect. Suggested multi-functional designs have simple geometries ($\pi$-shaped), low losses and huge optical activities. In addition, these new designs are numerically and experimentally retrieved in the study. The proposed model has many advantages with respect to the asymmetric transmission and chiral MTM studies in the literature. These advantages arehaving simple geometries ($\pi$-shaped), large asymmetric transmissions, small chirality like natural materials and also hug chirality can also be provided by rotating one of the resonators. Besides, the proposed structure can be easily reconfigured for other frequency regimes to provide new chiral MTMs or can be adopted for different application areas from defence systems to stealth technology which will be examined in our future studies.

    • Efficient heat conducting liquid metal/CNT pads with thermal interface materials


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      Ga-Based thermal interface material (TIM) pads/sheets with high thermal conductivity ($\kappa$) are indispensable components in thermal management systems. Here, we present a feasible method to fabricate heat conduction pads, which are composed of carbon nanotubes embedded into a liquid metal (LM). This setup has resulted in a large increase of $\kappa$ reaching $\sim$14.2 W mK$^{−1}$, greater than that of most of the commercial thermal silicone pads ($\sim$5 W mK$^{−1}$). In addition, a series of experiments were conducted on smartphones to evaluate the heat dissipation performance of the CPU. It turned out that LM/nanotube pads with TIMs show distinguish thermal conductivity performance.

    • In situ forming hydrogels based on polyethylene glycol itaconate for tissue engineering application


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      Novel strategies have been proposed to enhance the quality of surgery by scheming noninvasive methods. For this reason, photo-curable in situ forming hydrogels have been well developed during advancements in the regenerative medicine. In this study, polyethylene glycol itaconate (PEGI) was synthesized by reacting polyethylene glycol (PEG) with different molecular weights (1000, 4000 and 8000 g mol$^{−1}$) and itaconyl chloride. The synthesized PEGIs were fully characterized and employed as a macromonomer for the preparation of in situ forming hydrogels using a combination of camphorquinone and dimethylaminoethyl methacrylate as a reactive photoinitiator system, and hydroxyethyl methacrylate as a reactivediluent. The physical properties of the hydrogels including gel yield, equilibrium swelling and compressive strength were determined. The hydrogel based on PEG 4000 with a gel yield of 86%, a water uptake of 103%, a compressive modulus of 11.2 MPa, an elongation at break of 9% and a curing time of 4 min was selected for the encapsulation of rabbit articular chondrocyte cells. The cytocompatibility of the in situ formed hydrogels was evaluated using 3[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide, live-dead fluorescence assays and optical microscopy observations. Glycosaminoglycanswere quantified by dimethylmethylene blue staining from the encapsulated chondrocytes after 14 days. The proposed in situ forming hydrogel can be considered as an injectable and photocurable carrier for cell delivery in cartilage tissue engineering.

    • Graphene-nanoparticle incorporated responsivity tuning of p-CuO/n-Si-based heterojunction photodetectors


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      The current work focusses on investigating the appropriate wt% of graphene-nanoparticles to be incorporated into the CuO film as a dopant for enhancing its optoelectronic properties. CuO and graphene-nanoparticle-incorporatedCuO films (CG) are grown by employing a chemical bath deposition (CBD) method. Graphene-nanoparticles have been incorporated at different wt% (1, 5 and 10%) with respect to the metal salt (CuCl$_2$·${}^2$H$_2$O), and a comparative study has been performed on the systematic change of the film morphology, chemical composition, oxidation states, crystallite structures and photo-sensing effects. It has been found that the morphology and the structural properties of CBD grown CuO films have been tuned by the incorporation of graphene-nanoparticles. The results show a significant enhancement in the optoelectronic properties of CG1 (1%) and CG5 (5%) films. The optical properties of the as-grown films have been observed to be modified by graphene-nanoparticle incorporation. Moreover, the electronic and optoelectroniccharacteristics of the fabricated p-CuO/n-Si heterojunctions have also been investigated. The enhancement of the optoelectronic properties of the CG5 sample as compared to other grown films in the present study suggests thatthe responsivity and photodetecting properties of the CBD grown CuO films can be improved by graphene-nanoparticle incorporation.

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