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      Volume 41, Issue 3

      June 2018

    • Synthesis and electrochemical analysis of AlVMoO$_7$ oxide prepared via sol–gel method


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      In this study, AlVMoO$_7$ phase was fruitfully synthesized by sol–gel method and investigated as electrode material. The role of trivalent cation Al on the position of V and Mo redox couples in a three-dimensional framework ofAlVMoO$_7$ promoted us to use this compound. The electrochemical insertion of Li in this phase was characterized by both solid solution and two-phase regimes. In the voltage range of 3.2–1.5, the first cycle discharge capacity value was found to be 310 mAh g$^{−1}$. It showed very good capacity of 180 mAh g$^{−1}$ even after 20 cycles.

    • Synthesis, characterization and antimicrobial studies of bio silica nanoparticles prepared from Cynodon dactylon L.: a green approach


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      The present study reports on a green approach method for synthesis of silica nanoparticles (SiNPs) from Cynodon dactylon. These SiNPs were characterized by using ultraviolet–visible (UV–Vis) spectrophotometer, Fouriertransform infrared (FT-IR), dynamic light scattering (DLS) and Zeta, X-ray diffractometer (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM) and evaluated its growth inhibitory efficacy against differentmicroorganisms. These SiNPs showed a colour change pattern upon synthesis and indicated a broad peak at 350 nm when analysed by UV–Vis spectrophotometer. FT-IR analysis revealed the presence of Si content, and the appearance of phytochemicals such as primary amines of proteins, phenols were mainly responsible for capping and stabilization of SiNPs. DLS and Zeta potential studies revealed average size of 62.1 nm and −23.3 mV zeta potential value of nanoparticles. An XRD study showed a broad peak at 22$^{\circ}$ of 2$\theta$ value and confirmed that the nanoparticles were amorphous in nature with60nm average size of particles. Higher magnification studies with SEM and TEM analysis revealed that the particles were poly-dispersed, spherical in shape and have the size range from 7 to 80 nm without any agglomeration among the particles. Energy dispersive X-ray analysis showed a 52.84 weight percentage of silica content in the sample, which indicates towering purity of the sample. The obtained nanoparticles were tested for growth inhibitory activity on different microbial pathogens, resulting in potential inhibitory activity. This study concluded that the plant C. dactylon was an excellent and reliable greensource for production of potential bio antimicrobial SiNPs.

    • Influence of Si$_3$N$_4$ layer on the electrical properties of Au/n-4H SiC diodes


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      In this study, the effect of Si$_3$N$_4$ insulator layer on the electrical characteristics of Au/n-4H SiC diode was investigated. The current–voltage ($I−V$), capacitance–voltage ($C−V$) and conductance–voltage ($G/w−V$) measurements were carried out at room temperature condition. Under thermionic emission model, electrical parameters as zero-bias barrier height ($\Phi_{B_o}$), ideality factor ($n$), interface states ($D_{\rm it}$), and series ($R_{\rm s}$) and shunt ($R_{\rm sh}$) resistances were estimated from forward bias $I−V$ analyses. The values of $n$ and $\Phi_{B_o}$ were about 1.305 and 0.796 eV for metal–semiconductor (MS) rectifying diode, and 3.142 and 0.713 eV for metal–insulator–semiconductor (MIS) diode with the insertion of Si$_3$N$_4$ layer, respectively. Since the values of n were greater than the unity, the fabricated diodes showed non-ideal $I−V$ behaviour. The energy distribution profile of $D_{\rm it}$ of the diodes was calculated by taking into account of the bias dependence of the effective barrier height ($\Phi_{\rm e}$) and $R_{\rm s}$. The obtained $D_{\rm it}$ values with $R_{\rm s}$ are almost one order of magnitude lower than those without $R_{\rm s}$ for two diodes. According to Cheung’s model, Rs were calculated and these values were found in increasing behaviour with the contribution of Si$_3$N$_4$ insulator layer. In addition, the $J_{\rm R}−V$ plot behaviours with linear dependence between $\ln(J_{\rm R})$ vs. $V^{0.5}$ indicated that the dominant conduction mechanism in the reverse bias region was Schottky effect for both MS and MIS diodes. In the room temperature $C−V$ measurements, different from the results of MIS diode, the values of $C$ for MS diode was observed in decreasing behaviour from ideality with crossing the certain forward bias voltage point ($\sim$2.5 V). The decrease in the negative capacitance corresponds to the increase of $G/w$.

    • Improvement of the chemical, thermal, mechanical and morphological properties of polyethylene terephthalate–graphene particle composites


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      The graphene powder was used as a reinforcement in polyethylene terephthalate (PET) with various weight percentages 0.1, 0.5, 1 and 2 wt%. To prepare PET/graphene powder composites, melt-mixing process was followed.The crosslinking degree between PET and functionalized graphene increased, which was indicated by carbonyl indexes (Fourier transform infrared spectra) when interfaced with PET. The results of thermal properties showed that adding 2 wt% of graphene composites improved the thermal stability, transition glass temperature $T_{\rm g}$, crystallinity temperature pointand chemical properties of PET. The results of thermal gravimetric analysis showed that the highest addition of graphene (2 wt%) into the PET slightly improves both the residue yields and thermal stability. The tensile strength of PET was highly increased with the increased loading of graphene, and the elongation was reduced, compared with PET without filler. The results of X-ray diffraction curves showed that 2% incorporation of graphene into PET has good interfacial interaction and higher intensity. The scanning electron microscopy micrographs showed a high compatibility between the pure PET andgraphene composite chains.

    • Microstructure and mechanical properties of carbon fibre-reinforced alumina composites fabricated from sol


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      Alumina matrix composites reinforced with the laminated and stitched carbon fibre cloth preform were fabricated through the infiltration–drying–heating route using the Al$_2$O$_3$ sol with a high solid content as raw materials. The investigation was focussed on the characteristics of sol and the mechanical properties and high-temperature resistance of C/Al$_2$O$_3$ composites. $\alpha$-Al$_2$O$_3$ with favourable sintering activity can be obtained after heat treatment of sol at 1200$^{\circ}$C. The as received C/Al$_2$O$_3$ composites with a total porosity of 16.8% exhibit a flexural strength of 271.3 MPa and a notch toughness of 13.0 MPa m$^{1/2}$, respectively. As a result of the evolution of interface and matrix, the flexural strength of C/Al$_2$O$_3$composites is decreased by 28.5% after heat treatment at 1600$^{\circ}$C for 1 h under inert atmosphere. At the same time, fracture mode of composites is transformed from tough to brittle behaviour.

    • Effect of basalt, silica sand and fly ash on the mechanical properties of quaternary polymer concretes


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      The aim of this study is to manufacture quaternary polymer concretes (PCs) and optimize the weight percentages of the epoxy resin, ultrafine fly ash, silica sand and basalt aggregates. For this, we first manufactured binary PCs ofepoxy/basalt, epoxy/silica sand and epoxy/fly ash and then studied the mechanical properties such as compressive, flexural and splitting tensile strength. The mixture design method was used as an approach for design of experiment to reduce the number of tests and optimize the mechanical strength of the PC. The best weight percentages of the PC components were 25 (epoxy), 5 (fly ash), 52.5 (silica sand) and 17.5 (basalt). The compressive, flexural and splitting tensile strength of the quaternary PC were equal to 94.1, 39.0 and 11.8, which were 3.76, 11.1 and 6.5 times higher than those of ordinary Portlandcement, respectively. Finally, a scanning electron microscopy test was implemented to study the microstructure of the PC.

    • Rectifying resistance-switching behaviour of Ag/SBTO/STMO/p$^+$-Si heterostructure films


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      The Sr$_{0.88}$Bi$_{0.12}TiO$_3$/SrTi$_{0.92}$Mg$_{0.08}$O$_3$ (SBTO/STMO) heterostructure films were prepared on p$^+$-Si substratesby sol–gel spin-coating technique, and the films had good crystallinity and uniform grain distribution. The heterostructure films with a structure of Ag/SBTO/STMO/p$^+$-Si exhibited a bipolar, remarkable resistance-switching characteristic, and $R_{\rm HRS}/R_{\rm LRS} \sim 10^4$. More importantly, the heterostructure films showed rectifying characteristic in the low resistance state (LRS), and the rectification ratio can reach 10$^2$ at $\pm$1 V. The dominant resistive-switching conduction mechanism of high resistance state (HRS) was Ohmic behaviour, and the LRS changed to space charge-limited current(SCLC).

    • Investigation of metallic nanoparticles adsorbed on the QCM sensor by SEM and AFM techniques


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      Quartz crystal microbalance (QCM) is known as a very sensitive device used for determination of mass quantity adsorbed on sensor surface. Its detection limits are in the range of ng cm$^{−2}$. The adsorption mechanism of metallic nanoparticles on QCM sensor was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). This study aims to highlight the importance of QCM applications in nanoparticles deposition field. The layers formed through adsorption process, induced by the oscillations of the QCM sensor, were investigated by AFM for surface topography and for particle mean size values. The morphology of layers and nanoparticles dimensions were determined by SEM. For a more complex investigation of the nanoparticles adsorption mechanism, the chemical composition of layers was achieved usingSEM coupled with energy dispersive X-ray spectrometer (SEM-EDS). This preliminary research involved a new approach in characterization of metallic nanoparticles layers to achieve functional assembled monolayers.

    • Electrospun polyvinylidene pyrolidone/gelatin membrane impregnated with silver sulfadiazine as wound dressing for burn treatment


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      Nanofibrous membranes used for burn treatment have become widely popular due to their large surface area and high porous structure. In this study, electrospinning was used to fabricate a blended nanofibrous membrane of polyvinylidene pyrolidone (PVP) and gelatin, to use as wound dressing. The physical and mechanical properties of this novel membrane were investigated using SEM, FTIR and tensile tests. Results showed that poor mechanical properties of gelatin, which are preferred in medical applications for curing burns as they allow for antigen activity and skin repair, can be enhanced byadding PVP in the solution. Silver sulfadiazine (AgSD), an antibacterial agent, was also impregnated into the PVP/gelatin nanofibrous structure during electrospinning. The membrane thus fabricated showed antibacterial activities against both the Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus. AgSD release behaviour of fabricated samplesindicated short-term drug delivery. Itwas concluded that the proposed drug-loaded membrane can be used aswound dressing, specifically, in treating skin burns.

    • Linear and nonlinear optical properties of 4-nitrobenzoic acid (4-NBA) single crystals


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      4-Nitrobenzoic acid (4-NBA) single crystals were studied for their linear and nonlinear optical properties. The crystals were grown by slow solvent evaporation method at room temperature. The structure and functional groups wereconfirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic studies. The 4-NBA crystal has an optical absorption at 263nm and a wide transparency window for the visible light. Theoretical predictions for themeasured optical absorption and charge transfer mechanism in 4-NBA were explained with HOMO and LUMO illustrations. The crystal is found to be birefringent and has produced an optical quality interference pattern. The optic plane of the crystal is observed along $\langle$100$\rangle$ direction. The crystal exhibits nonlinear optical effects viz. reverse saturable absorption and self defocussing of laser beam. Considerable nonlinear refraction ($n_2$) and nonlinear absorption ($\beta$) coefficients and third-order nonlinear optical susceptibility ($\chi^{(3)}$) were determined using Z-scan technique.

    • Surface morphology, structural and electrical properties of RF-sputtered ITO thin films on Si substrates


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      Series of indium tin oxide (ITO) thin films were deposited onto Si(100) substrate by RF sputtering. The film thickness ranges from 61 to 768 nm. X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic forcemicroscopy (AFM) experiments were performed to study the structure and the surface morphology of these films. The electrical properties were obtained by a Hall effect measurement system; the electrical resistivity $\rho$, the carrier concentration n and the mobility $\mu$ were measured. Annealing experiments were carried out in the air at 400$^{\circ}$C for 60 min. The different physical parameters were investigated as a function of thickness before and after annealing. The effects of power and deposition rate were also addressed. We noted that the behaviour of some parameters with thickness is different before and after annealing. All these results are discussed and correlated in this article. Also, the results of the present ITO/Si system were compared to those of the ITO/glass, we have previously published.

    • Recent advances in titanium dioxide/graphene photocatalyst materials as potentials of energy generation


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      The properties of titanium dioxide (TiO$_2$)/graphene/graphene oxides (GO) are examined in this study. These views summarize the recent theoretical and experimental novel approaches in the catalytic activity of TiO$_2$/graphene interface. Imperative results at a level of detail, suitable for upcoming experimental and theoretical researchers involved an overview of the enthralling characteristics of TiO$_2$ and graphene composites were presented. Aspects like crystal lattice, electronic band structure and phonon dispersion, among others that were used to describe the properties of a TiO$_2$ interface with pristine graphene and graphene dioxide among other composites are discussed. In particular, this review covers reactivity, binding energies, geometric structures as well as the photocatalytic activity of anatase TiO$_2$ surfaces with graphene and graphene oxide with hybrid nanocomposites. These views also explore the understanding of the TiO$_2$ interactions with graphene and possible applications. Finally, highlights on the challenges and proposed strategies in developing advanced photocatalytic semiconductor-based composites for water- splitting applications are provided.

    • Influence of intermolecular interactions on the properties of carbon nanotubes


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      This study is aiming at theoretical and experimental confirmations of the deposition of oligothiophene dyes (OT) on structurally and chemically diverse surfaces of carbon materials, especially carbon nanotubes (CNTs). This study isa contribution to the wide search and design of novel hybrid materials for light-sensitive (dye solar cells) and light-emitting (LEDs) structures. The obtained materials containing OTs embedded in the pores of a carbon matrix were analysed by means of microscopic and spectroscopic techniques as well as low-temperature adsorption of nitrogen, together with an investigation of the surface area by the BET method. Confocal microscopy was employed to confirm the immobilization of oligomers on the surface of CNTs. Raman spectra, XRD and HTEM microscopies allowed to judge the quality of the carbonaceousmaterial and to compare the test material before and after the introduction of OT. Additionally, the elemental content and elemental surface species were determined by means of XPS and combustion elemental analyses. The explanation of thiophene; 2,2$^{\prime}$:5$^{\prime}$,2$^{\prime\prime}$-terthiophene and $\alpha$-sexithiophene molecular interactions with singlewall armchair CNTs was supported by theoretical calculations. In computational investigations, CNTs were modelled by tubules of different sizes, lengths and hydrogenated open ends.

    • Synthesis and characterization of calcium-doped lanthanum manganite nanowires as a photocatalyst for degradation of methylene blue solution under visible light irradiation


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      Calcium-doped lanthanum manganite (LCMO) powder was synthesized via hydrothermal method. The structural, morphological and optical properties of the resulting powder was characterized by X-ray diffraction (XRD), Fouriertransform infrared spectroscopy (FTIR), inductively coupled plasma–atomic emission spectroscopy (ICP–AES spectrometer), field emission scanning electron microscopy (FESEM) and UV–Vis spectroscopy (UV–Vis). The XRD results showed the existence of only one crystalline phase. FESEM image indicates that the LCMO sample has nanowire structure with an average diameter of $\sim$125 nm. The band gap energy of the sample was about 2.13 eV. The as-prepared nanowires showed sufficient visible-light photocatalytic activity for the water treatment from dyes and toxic organic materials. The photodegradation efficiency for decolourizing methylene blue solution (7 ppm) by LCMO nanowires (0.07g l $^{−1}$), after 360 min illumination, was about 73% with a reaction rate constant of 0.003 min$^{−1}$. The six times cycled results suggested the great long-term stability of the photocatalyst.

    • Crystal structure, thermal behaviour, vibrational spectroscopy and optical properties of new compounds K$_2$Ca(HAsO$_4$)$_2$·2H$_2$O with kröhnkite-type chain


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      The newkröhnkite compound called potassium calcium-bis-hydrogen arsenate dihydrate K$_2$Ca(HAsO$_4$)$_2$·2H$_2$O was obtained by hydrothermal method and characterized by X-ray diffraction, infrared spectroscopy, Raman scattering, thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis and optical (photoluminescence and absorption) properties. It crystallizes in the triclinic space group P$\bar{1}$ and unit cell parameters $a = 5.971(3)$ \AA, $b = 6.634(3)$ \AA, $c = 7.856(4)$ \AA, $\alpha = 104.532(9)^{\circ}$, $\beta = 105.464(9)^{\circ}$ and $\gamma = 109.698(9)^{\circ}$. The structure of K$_2$Ca(HAsO$_4$)$_2$·2H$_2$O builtup from this infinite, (Ca(HAsO$_4$)$_2$(H$_2$O)$_2$)$^{2+}$, was oriented along an axis resulting from the association of CaO$_6$ octahedra alternating with each two HAsO$_4$ tetrahedra by sharing corners. Each potassium atom links two adjacent chains by three oxygen atoms of HAsO$_4$ tetrahedra. TGA and DSC have shown the absence of phase transition. The existence of vibrational modes corresponding to the kröhnkite is identified by the IR and Raman spectroscopies in the frequency ranges of 400–4000 and 20–4000 cm$^{−1}$, respectively. The photoluminescence measurement show one peak at 507 nm, which is attributed to band–band (free electron–hole transitions) and (bound electron–hole transitions) emissions within the AsO$^4$ inorganicpart.

    • Physical, optical and structural studies of copper-doped lead oxychloro borate glasses


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      Bluish coloured glasses are obtained from the composition PbCl$_2$–PbO–B$_2$O$_3$ doped with Cu$^{2+}$ ions. Basic physical properties and spectroscopic studies (optical absorption, electron paramagnetic resonance, Fourier transform infrared and Raman spectroscopies) were carried out on these samples. The increase in PbCl2 content resulted in the decrease in density and increase in molar volume. At optical frequencies, band gaps and Urbach energies were evaluated and their variation is explained. Spin-Hamiltonian parameters (SHP) obtained from the EPR spectra suggest that the ligand environmentaround Cu$^{2+}$ is tetragonally distorted octahedral sites and the orbital $d_{x^2−y^2}$ is the ground state. The characteristics broad bands in the optical absorption spectra are assigned to the ${}^2B_{1g} \to {}^2B_{2g}$ transition. The bonding coefficient values were evaluated using optical data and SHP. FTIR studies suggested that the glass structure is built up of BO$_3$ and BO$_4$ units. The presence of diborate, pyroborate, pentaborate groups, etc. in the glass network was confirmed from Raman spectra.

    • Eco-friendly method to synthesize and characterize 2D nanostructured (1,2-bis(diphenyl-phosphino)ethyl) tungsten tetracarbonyl methyl red/copper oxide di-layer thin films


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      Three-layer thicknesses ($T_1 = 50$, $T_2 = 75$ and $T_3 = 100$ nm) of 1,2-bis(diphenylphosphino)ethyl tungsten tetracarbonyl methyl red (DPE-W-MR) were deposited onto the CuO thin film (50 nm) to produce DPE-W-MR/CuOdi-layer thin films by sol–gel spin-coating technique. The composition and the chemical structure of the as-prepared thin films were characterized using various techniques including elemental analysis, Fourier transform infrared spectroscopy,${}^1$H-NMR and X-ray diffraction (XRD). Scanning electron microscopy was used to investigate the size and shape of the CuO nanoparticles and the fabricated thin films. The films are crystalline as evidenced by the XRD pattern and DPE-W-MR has an orthorhombic crystal system. The crystallite size was calculated from an analysis of the line broadening features using theScherrer formula; the average crystallite sizes of DPE-W-MR/CuO di-layer thin films are 52.92, 56.24 and 72.26 nm for $T_1$, $T_2$ and $T_3$, respectively. Thermogravimetric analysis and the thermal curve of DPE-W-MR complex were studied. Optical properties of DPE-W-MR/CuO di-layer thin films are discussed. The optical band gap energies of DPE-W-MR di-layer thin films/CuO decreased (2.25, 2.1 and 1.88 eV) as the film thickness increased (from $T_1$ to $T_3$). Based on the optical results and the quantum confinement effects, the DPE-W-MR/CuO di-layer thin films may be candidates as semiconductor materialsfor optoelectronic devices.

    • Highly dispersed PVP-supported Ir–Ni bimetallic nanoparticles as high performance catalyst for degradation of metanil yellow


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      Bimetallic nanoparticles, a new class of materials for catalysis, were intensively investigated. Highly dispersed Ir–Ni bimetallic nanoparticles with varying mole fractions were synthesized by modified polyol reduction method from the solution of iridium trichloride and nickel chloride in ethylene glycol, which acts as both solvent and reducing agent. The particles were characterized for their size, morphology and composition using various techniques like UV–Vis, Fourier transform infrared (FT-IR), X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) and X-ray photo electron spectroscopic (XPS) techniques. The synthesized nanoparticles were in pseudo-spherical morphology and utilized as catalyst for the degradation of dyes. The feasibility of degradation of an azo dye i.e., metanil yellow (MY) in aqueous alkaline medium by hexacynoferrate (III) ions using Ir–Ni bimetals as catalyst, prepared in different molar ratios, was investigated. Results show that Ir–Ni (2:1) bimetals have good catalytic activity and degradation as compared to Ir–Ni (1:2) due to their small size and high stability for the oxidation of MY.

    • A comparative study on dielectric behaviours of Au/(Zn-doped PVA)/$n$-4H-SiC (MPS) structures with different interlayer thicknesses using impedance spectroscopy methods


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      Three different thicknesses (50, 150 and 500 nm) Zn-doped polyvinyl alcohol (PVA) was deposited on $n$-4HSiC wafer as interlayer by electrospinning method and so, Au/(Zn-doped PVA)/$n$-4H-SiC metal–polymer–semiconductorstructures were fabricated. The thickness effect of Zn-doped PVA on the dielectric constant ($\epsilon^{\prime}$), dielectric loss ($\epsilon^{\prime\prime}$), losstangent ($\tan \delta$), real and imaginary parts of electric modulus ($M^{\prime}$ and $M^{\prime\prime}$) and ac electrical conductivity ($\sigma_{\rm ac}$) of them were analysed and compared using experimental capacitance ($C$) and conductance ($G/\omega$) data in the frequency range of 1–500 kHz at room temperature. According to these results, the values of $\epsilon^{\prime}$ and $\epsilon^{\prime\prime}$ decrease with increasing frequency almost exponentially, σac increases especially, at high frequencies. The $M^{\prime}$ and $M^{\prime\prime}$ values were obtained from the $\epsilon^{\prime}$ and $\epsilon^{\prime\prime}$ data and the $M^{\prime}$ and $M^{\prime\prime}$ vs. $f$ plots were drawn for these structures.While the values of $\epsilon^{\prime}$, $\epsilon^{\prime\prime}$ and $\tan \delta$ increase with increasing interlayer thickness, the values of $M^{\prime}$ and $M^{\prime\prime}$ decrease with increasing interlayer thickness. The double logarithmic $\sigma_{\rm ac}$ vs. $f$plots for each structure have two distinct linear regimes with different slopes, which correspond to low and high frequencies, respectively, and it is prominent that there exist two different conduction mechanisms. Obtained results were found as a strong function of frequency and interlayer thickness.

    • Influence of RGO/TiO$_2$ nanocomposite on photo-degrading Rhodamine B and Rose Bengal dye pollutants


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      Reduced graphene oxide/titanium oxide-nanostructured composite (RGO/TiO$_2$) was prepared by combining Hummer’s synthesized graphene oxide and solvothermally synthesized TiO$_2$ nanoparticles (TiO$_2) through a facile ultrasonication-mediated mechanical mixing method. Structural and morphological evidences from XRD and SEM results confirmed that the as-prepared TiO$_2$ composed of mixed phases, anatase phase with body centred tetragonal crystal structured prism-like architecture, rutile phase with primitive tetragonal crystal-structured bipyramid-like architecture and hence,RGO/TiO2 system exhibited the similar structural and morphological features. Band gap energy of RGO/TiO$_2$ was reduced from 2.98 to 2.91 eV due to the presence of RGO and hence, the light absorption range was extended to visible region. In addition, RGO acted as the electron acceptor and hence, the separation efficiency of photo-generated electron–hole pairs increased effectively, and this prevented the recombination process in RGO/TiO$_2$ system. Thus, RGO/TiO$_2$ system exhibited greater efficiency towards degrading Rhodamine B (RhB) and Rose Bengal (RB) dye pollutants than bare TiO$_2$ under sonophotocatalytic condition with natural sunlight irradiation. The possible mechanisms responsible for the enhanced efficiency are explained in this study using appropriate characterization techniques.

    • Novel dental nanocomposites: fabrication and investigation of their physicochemical, mechanical and biological properties


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      The aim of this study was to investigate biological, physicochemical and mechanical characteristics of a series of novel dental restorative nanocomposites that comprise dendritic methacrylate end-caped monomers, triethyleneglycol dimethacrylate (TEGDMA; as diluting monomer) and modified silica nanoparticles (M-SiO$_2$; as inorganic filler). The cytotoxicity effects of the monomers and fabricated nanocomposites were examined against NIH3T3 cells (the standard fibroblast cell line) through MTT and trypan blue cell viability tests, respectively. The antibacterial activities of the monomers were evaluated against Lactobacillus plantarum by standard agar disk diffusion approach.The mechanical properties (flexural strength (FS) and compressive strength (CS)) as well as some physicochemical characteristics such as water sorption (WS), sol fraction (SF) and double bond conversion (DC) were also investigated, and compared with corresponding characteristics of 3M Filtek Z250 as a reference. Thus, the fabricated nanocomposites have potential as dental restorative materials mainly due to their suitable biological, physicochemical and mechanical properties.

    • Synthesis, characterization and comparison of polythiophene–carbon nanocomposite materials as Pt electrocatalyst supports for fuel cell applications


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      A novel polymer–carbon (PTh–C) nanocomposites containing different percentages of polythiophene (10, 20 and 50% (w/w)) and carbon (Vulcan XC-72)was prepared by a facile solution dispersion method and used to support platinum nanoparticles. The effect of using different percentages of polythiophene in nanocomposites and subsequently prepared electrocatalystswas investigated. The resultant electrocatalysts were extensively characterized by physical (X-ray diffraction (XRD) and transmission electron microscopy (TEM)) and electrochemical (cyclic voltammetry (CV)) techniques. The TEM results showed that the fine Pt nanoparticles prepared by ethylene glycol (EG) method were distributed on the surface of the 50% PTh–C nanocomposites successfully. From the XRD patterns, the average size of dispersed Pt nanoparticles with the face-centered cubic (fcc) structure on 50% PTh–C, 20% PTh–C, 10% PTh–C and carbon were about 4.9, 5.2, 5.4 and6.1 nm, respectively. The conductivity of PTh–C with different percentages of pure PTh was compared with the conductivity of the corresponding support of pure PTh. It is observed that the conductivity of 50% PTh–C nanocomposites is about 600 times higher than that of pure PTh. Finally, CV measurements of hydrogen and methanol oxidations indicated that Pt/50% PTh–C had a higher electrochemical surface area and higher catalytic activity for methanol oxidation reaction compared to other electrocatalysts. These measurements showed that the Pt/50% PTh–C electrocatalyst by the value of 3.85 had higher $I_{\rm f}/I_{\rm b}$ ratio with respect to Pt/10% PTh–C and Pt/20% PTh–C by the values of 2.66 and 2.0, respectively.

    • Bio-inspired AgNPs, multilayers-reduced graphene oxide and graphite nanocomposite for electrochemical H$_2$O$_2$ sensing


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      A bio-mediated route for the synthesis of silver nanoparticles (AgNPs) is an area of interest in research of many scientists, and this work aims to study the electrocatalytic activity of these particles during electrochemical sensing of H$_2$O$_2$ in a phosphate buffer media. The composite electrodes were fabricated using nearly spherical AgNPs and reduced grapheneoxide (rGO) with the graphite (99.999% purity) support made of graphite paste. Graphene oxide (GO) was first synthesized using the modified Hummers method followed by rGO synthesis by chemical reduction of GO. rGO is consisting of about nine layers of rGO sheets of a wrinkled surface morphology with an intensity ratio of D to G band ($I_D/I_G$) of 1.17 and an interplanar $d$-spacing of 0.36 nm as evidenced by HRTEM micrograph. There was about 10 times increase in the cell current with the AgNPs-impregnated composite–electrode compared to without AgNPs impregnation, and an overpotential of H$_2$O$_2$ reduction was found to be $−$1.373 V with a detection limit of 19.04$\mu$M and 95.3% electrode stability with the graphite–rGO–AgNPs composite electrode. A nafion membrane cast on the rGO–AgNPs prevented the leakage of thiscomposite from the electrode surface. The interference of various electroactive compounds on the amperometric response of the graphite–rGO–AgNPs electrode was also investigated.

    • Electronic structure and magnetic studies of V-doped ZnO: ab initio and experimental investigations


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      In this study, the electronic structure of V-doped ZnO system is studied by means of density functional theory. Different concentrations of V and rising of Fermi level increase the relative occupation of majority/minority spin of 3d stateand also induce strong spin-splitting. The existence of three different states of V spin moment has been confirmed and is found to be concentration dependent. We found that O p-orbitals are responsible for the origin of the magnetic moment.Ruderman–Kittel–Kasuya–Yosida mechanism and the atomic spin polarization of V are the key factors for the appearance of ferromagnetism in V-doped ZnO system. The synthesized nanoparticles exhibit hexagonal wurtzite crystal structure, where both crystallite size and lattice parameters vary with V content. Magnetic measurements at room temperature confirm the ferromagnetic behaviour of V-doped ZnO system.

    • Synthesis of MCM-41 nanoparticles from stem of common reed ash silica and their application as substrate in electrooxidation of methanol


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      In this work, stem of common reed ash (SCRA) is introduced as a new source of silica in the preparation of mesoporous materials. Mesoporous silicate MCM-41 nanoparticles were synthesized hydrothermally using sodium silicateprepared from SCRA as a silica source. The characterization of MCM-41was carried out by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), N2 adsorption/desorption (BET) and transmission electron microscopy (TEM). SEM shows that MCM-41 nanoparticles are sphere-like with size in the range of 30–50 nm with some degree of agglomeration. TEM image of the synthesized sample shows the open framework structure of MCM-41. A type IV isotherm can be observed from adsorption/desorption curves, which is the characteristic of mesoporousmaterials. The prepared MCM-41 nanoparticles were used as substrate to facilitate the oxidation of methanol through the modification with an electroactive species. The modification was achieved by impregnation of MCM-41 pores with Ni$^{2+}$ ions (Ni-doped MCM-41). A modified carbon paste electrode (CPE) was prepared by mixing Ni-doped MCM-41 with carbon paste (NiMCM-41CPE). Cyclic voltammetry of NiMCM-41CPE shows an increment in current density of methanoloxidation in comparison with CPE in alkaline solution. Moreover, a decrease in the overpotential of methanol oxidation occurred on the surface of modified electrode. The effects of some parameters such as scan rate and methanol concentration are also investigated on the behaviour of NiMCM-41CPE. Also, the heterogeneous electron transfer rate for the catalytic reaction ($k$) of methanol is calculated.

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