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      Volume 41, Issue 6

      December 2018

    • Effect of surface modification of TiO$_2$ on the electrochemical performance of lithium–sulfur cell


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      Surface of TiO$_2$ is known to chemically bind the polysulfides in Li–S cell. In the present study, the effect of surface defects or oxygen vacancies in TiO$_2$ present as a composite with sulfur cathode on the performance of Li–S cell wasinvestigated by using NaBH$_4$ reduced (black colour) TiO$_2$ and pristine (white) TiO$_2$ in cathode. Results show that former is superior in performance.

    • Structure, electrical and nonlinear optical properties of M@C$_{20}$ (M$=$Li, Na, K, Be, Mg and Ca) nanoclusters


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      The decoration of Li, Na, K, Be, Mg and Ca metal atoms on C$_{20}$ fullerene was studied using the density functional theory (DFT) method. It was shown that the structure of the fullerene was intensely affected by the metal atompresent. All metal atoms have exothermic adsorption on C$_{20}$ fullerene, while Be has the highest value of adsorption energy, enthalpy and free energy. The presence of the metal atom also has a slight effect on Eg while the lowest value of Eg was obtained for Ca@C$_{20}$. The calculations of polarizability and the first hyperpolarizability show that the metal atoms highly influence fullerenes. Among metal atoms, Ca atom had the highest effect and the other metal atoms led to an increase of the first hyperpolarizability to a value of approximately 42000 a.u. The time-dependent (TD)-DFT studies showed that Ca@C$_{20}$has the lowest excitation energies which is in agreement with the calculated first hyperpolarizability.

    • Biomass carbon materials derived from macadamia nut shells for high-performance supercapacitors


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      The new biomass carbonaceous materials were obtained from macadamia nut shells (MNS) by immersion method and high-temperature activation (MNSCA) for high-performance supercapacitors.The morphologies and microstructuresare investigated by X-ray diffractometer, Raman spectrometer, scanning electron microscopy and transmission electron microscopy. The experimental results show that the obtained activated carbon (MNSCA) exhibits perfect porous structurefilled with more micropores and mesopores.MNSCA displays high specific surface area of 1057 m$^2$ g$^{−1}$. The porous carbon delivers an impressive specific capacitance of 325.7 F g$^{−1}$ and has no capacitance loss at the current density of 2 A g$^{−1}$ after 10,000 cycles, which demonstrates the excellent cycle stability and high specific capacitance. The biomass carbonaceousmaterials derived from MNS can be expected for the widespread application of supercapacitors.

    • Comparative study of structural, optical and magnetic properties of Fe–Pt, Fe–Cu and Fe–Pd-codoped WO$_3$ nanocrystalline ceramics: effect of annealing in hydrogen atmosphere

      A A DAKHEL

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      Tungsten oxide(W-oxide) nanoparticles doped and codopedwith different transition-metal (TM) ions (Fe, Pt, Cu and Pd) were synthesized by hydrochloric acid-assisted precipitation. The synthesized powders were characterized by X-raydiffraction (XRD), diffuse reflectance spectroscopy (DRS) and magnetic characterization methods. The room temperature (RT) monoclinic (P21/n) structure founded for pristine WO$_3$ nanopowder was converted into orthorhombic (Pbam) structure by Fe-doping, while codoping, (Fe–Pt) and (Fe–Cu) preserved the P21/n space group (SG) structure. It was found that thehydrogenation of the synthesized doped-samples corroded the crystallites without changing the crystalline SG structure. Moreover, controllable room temperature ferromagnetic (RT-FM) properties were created by hydrogenation of the codoped W-oxide samples. The oxygen vacancies-mediated ferromagnetic (FM) interaction could be responsible for the observed FM. The relative highest RT-FM energy was created with hydrogenated Fe–Pd codopedW-oxide. Therefore, Fe–Pd-codoped W-oxide nanopowder could be considered as a potential candidate for many applications involving partial FM properties,such as catalysts and optical phosphors.

    • Metal-chelated cryogels for amyloglucosidase adsorption: application for continuous starch hydrolysis


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      In the present work, a newmetal-chelating platformwas designed by using IDA as a chelating agent and Cu(II) as an affinity component for amyloglucosidase adsorption. Poly(AAm-GMA) cryogels were used as structural elements, whileGMA monomer served reactive epoxy groups for IDA immobilization. Synthesized cryogels were characterized by FTIR, SEM and EDX studies. Pore diameter of the whole polymeric structure was 3–10 $\mu$m. Effects of medium pH, temperature,ionic strength along with amyloglucosidase concentrationwere also investigated for more effective amyloglucosidase adsorption and maximum adsorbed amount of amyloglucosidase was 2.93 mg g$^{−1}$ cryogel by the optimum conditions. Reusability profile of the poly(AAm-GMA)-IDA-Cu$^{2+}$ cryogels was also studied and it was found that the synthesized cryogels could be used repeatedly for many times without any significant decrease on their adsorption capacity. Also continuous hydrolysis of starch by using immobilized form of amyloglucosidase in a column system was studied.

    • Viscoelasticity, mechanical properties, and in vitro biodegradation of injectable chitosan-poly(3-hydroxybutyrate-co-3- hydroxyvalerate)/nanohydroxyapatite composite hydrogel


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      A novel injectable composite hydrogel based on chitosan and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) reinforced with nanohydroxyapatite particles was synthesized. The chemical structure and morphology of the composite hydrogel were characterized. The composite hydrogel porosity, swelling, mechanical properties, viscoelasticity and in vitro biodegradation were also examined. Compared with the non-reinforced hydrogel, the composite hydrogel showed increased compressive strength, elastic modulus, viscous modulus, stiffness and had shear-thinning behaviour proving the injectability of the system. Swelling and biodegradation studies revealed that the composite scaffold possesses proper hydrophilicity and biodegradability. These properties make this composite hydrogel a promising injectable scaffold for bone regeneration.

    • Composite of AuNPs@SiO$_2$NPs@[(NIPAM)-$b$-(Ala)] and its activity on leukemia cells


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      Synthesis and characterization of thermo-sensitive block copolymer of N-isopropyl acryl amide-$b$-Alanine [(NIPAM)-$b$-(Alanine)] thin film and its doping with (AuNPs)–(SiO$_2$NPs), (gold and silica nanoparticles) were reported. Further, composite effect on K562 (leukemia) cells was examined based on in vitro cell-based studies. The synthesis of SiO$_2$NPs was followed through facile Stober’s sol–gel synthesis methods. The individual morphology of [(NIPAM)-$b$-(Alanine)] thin film, AuNPs and SiO$_2$NPs including [(NIPAM)-$b$-(Alanine)]@(Au)-(SiO$_2$NPs) composite was confirmedby using TEM instrumentation. [(NIPAM)-$b$-(Alanine)] thin film was embedded with gold and silica nanoparticles followed by the sonication. The average size of AuNPs is 16 nm and for SiO$_2$NPs, it is $\sim$368 nm (in diameter). Synthesized composite [(NIPAM)-$b$-(Alanine)]@(Au)@(SiO$_2$NPs) is biocompatible for mankind use. However, composite used to examine theinhibitory activity on K562 cells and it shows $\sim$78% inhibition, which is significant value for 24 h treatment under humidified atmospheric conditions.

    • Ammonolysed LiNi$_{0.8}$Co$_{0.15}$Al$_{0.05}$O$_2$ as a cathode material for Li-ion batteries with improved rate capability


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      In this work, ammonolysed LiNi$_{0.8}$Co$_{0.15}$Al$_{0.05}$O$_2$ (NCA) prepared by co-precipitation and subsequent ammonolysis was investigated as a cathode material for Li-ion batteries with enhanced rate capability. Detailed structural and morphological property characterization demonstrated that ammonolysis results in the incorporation of a small amount of nitrogen into the surface layer of the afore-mentioned material. The electrochemical performances of NCA electrodes were measured by galvanostatic charging–discharging of the corresponding Li-ion cells, revealing that ammonolysed NCA exhibited higher capacity and rate capability than those of the pristine sample, i.e., after 20 cycles, the discharge capacity of the former equalled 176 mA h g$^{−1}$ at a current density of 18.4 mA g$^{−1}$, remaining as high as 107 mA h g$^{−1}$ at a high current density of 1840 mA g$^{−1}$. This improved performance was ascribed to ammonolysis-induced surface changes, which reduced cell polarization during cycling and enhanced the electrochemical stability and reaction kinetics of NCA electrodes.

    • Synthesis and characterization of silver-loaded mesoporous alumina antibacterial agents by hydrothermal and adsorption methods


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      In view of the compatibility between carriers of antimicrobial agents and ceramic glaze, mesoporous alumina was employed as the carrier of silver ions and silver-loaded mesoporous alumina was synthesized by hydrothermaland adsorption methods. The liquid medium microdilution method and the spread plate methods were studied to evaluate antimicrobial efficiency of silver-loaded mesoporous alumina. N$_2$ adsorption/desorption, HRTEM images and low angle X-ray diffraction experiment prove the existence of fine mesoporous structure of mesoporous alumina and silver-loaded mesoporous alumina. The chelation of ammonia can improve the adsorption capacity of silver nitrate on mesoporous alumina and adsorption capacity increases by 18 times in the presence of ammonia. The adsorption behaviour of silver nitrate canbe described by a multilayer adsorption isotherm of BET and the adsorption principle of silver nitrate on mesoporous alumina is multilayer adsorption in the presence of ammonia. The surface area, pore volume and pore-size distribution of silver-loaded mesoporous alumina are obviously smaller than those of mesoporous alumina due to the blockage of channel by silver-ammonia complex. The antibacterial test results indicate that silver-loaded mesoporous alumina have favourable antibiotic property and MIC $\leq$ 240 $\mu$g ml$^{−1}$ against Escherichia coli, Staphylococcus aureus and Salmonella. The diameter of inhibition zone of silver-loaded mesoporous alumina is 26 mm against Escherichia coli, 24 mm against Staphylococcus aureus and 22 mm against Salmonella enterica.

    • Effect of gel polymer electrolyte based on polyvinyl alcohol/polyethylene oxide blend and sodium salts on the performance of solid-state supercapacitor


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      In this work, the effect of gel polymer electrolytes (GPE) containing polyvinyl alcohol/polyethylene oxide (90/10, wt%) blend and different contents of sodium salt mixture (sodium acetate (CH$_3$COONa)/sodium sulphate (Na$_2$SO$_4$) $=$ 50/50 wt%) on the performance of solid-state supercapacitor was investigated. The active electrode of the solid-state supercapacitor was made from graphene nanoplatelets and carbon black. The results indicate that the sodium salt mixtures were easily mixed in polymer blend gel to make excellent GPE with large concentration of ionic liquid. At the sodium salt mixture content of 30%, the solid-state supercapacitor showed the best performance of electrode-specific capacitance of 93.768 F g$^{−1}$ at current density of 1 A g$^{−1}$, energy density of 3.25 Wh kg$^{−1}$ and power density of 586.166 W kg$^{−1}$.These results highly recommend the good potential of GPE for developing solid-state supercapacitor in the future.

    • Interface engineering of TiO$_2$@PANI nanostructures for efficient visible-light activation


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      Core–shell-structured TiO$_2$@PANI composites were fabricated using negatively charged titanium glycolate (TG) precursor spheres, which were decorated using hydrochloric acid; subsequently, the uniform polyaniline (PANI) layer could be attached onto the surface of the polystyrene spheres by in situ chemical oxidative polymerization and finally, the resulting PANI-grafted TG were allowed to hydrolyse by treating the material with hot water. The TGs were transformed to porous TiO$_2$, leading to the formation of core–shell TiO$_2$@PANI composites. The resulting TiO$_2$@PANI compositephotocatalysts were characterized by X-ray diffraction, scanning electron microscopy, ultraviolet–visible diffuse reflection spectroscopy and photoluminescence spectroscopy. Significantly, the TiO$_2$@PANI composite photocatalysts exhibited dramatically enhanced photo-induced electron–hole separation efficiency, which was confirmed by the results of photocurrentmeasurements. PANI was dispersed uniformly over the porous TiO$_2$ surface with an intimate electronic contact on the interface to act cooperatively to achieve enhanced photocatalytic properties, indicating that core–shell TiO$_2$@PANI composite photocatalysts could be promising candidate catalysts under visible-light irradiation. The mechanism of enhancing photocatalytic activity was proposed on the basis of the experimental results and estimated energy band positions.

    • Plastic crystal-incorporated magnesium ion conducting gel polymer electrolyte for battery application


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      Studies on a novel composition of magnesium ion conducting gel polymer electrolyte (GPE), comprising a solution of Mg-salt, magnesium trifluoromethanesulfonate (Mg-triflate or Mg(Tf)$_2$) in a plastic crystal succinonitrile (SN), entrapped in a host polymer poly(vinylidenefluoride–hexafluoropropylene) (PVdF–HFP) was reported. Small amount of anionic liquid, 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf) was added to stabilize the GPE composition. The electrolyte possesses excellent dimensional integrity in the form of free-standing thick film, which offers the ionicconductivity of $4 \times 10^{−3}$ S cm$^{−1}$ at room temperature $\sim$26$^{\circ}$C. The electrochemical potential window of the electrolyte,observed from the linear sweep voltammetry, is determined to be $\sim$4.1 V. The magnesium ion conduction in the GPE film is confirmed from cyclic voltammetry, electrochemical impedance spectroscopy and dc polarization techniques. Different structural, thermal and electrochemical studies demonstrate the promising characteristics of the polymer film, suitable as electrolyte in rechargeable magnesium batteries. The potential of the GPE as electrolyte/ separator was ascertained by fabricating a prototype magnesium battery of the configuration Mg:graphite composite anode/GPE/MnO$_2$-cathode. Thespecific discharge capacity of 40 mAh g$^{−1}$ (with respect to the MnO$_2$ cathode material) was obtained at the first discharge. The cell shows charge–discharge performance for eight cycles with a substantial fading in capacity.

    • Orientation-dependent crack-tip blunting and crack propagation in a single crystal BCC iron


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      Atomistic simulations of cracks with four different orientations in body-centered cubic single crystal iron are presented using molecular dynamics. Crystal orientation has considerable effect on the activation and evolution ofcrack propagation mechanisms. The results reveal that (a) crack-tip blunting depends on the crystallographic orientation, (b) continuous generation of dislocations form crack tip occurs for large crack-tip blunting, and (c) absence of deformation activities like dislocation generation, twin formation, etc. at the crack tip results in crack propagation in a brittle manner.

    • Resistance-switching properties of Bi-doped SrTiO$_3$ films for non-volatile memory applications with different device structures


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      SrTiO$_3$ and Bi-doped SrTiO$_3$ films were fabricated with different device structures using the sol–gel method for non-volatile memory applications, and their resistance-switching behaviour, endurance and retention characteristics were investigated. SrTiO$_3$ and Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films grown on Si or Pt have the same phase structure, morphologies and grain size; however, the grain size of the Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films grown on Si is slightly larger than those of the SrTiO$_3$ films grown on Si and the Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films grown on Pt. The SrTiO$_3$ or Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films grown on Si or Pt all exhibitbipolar resistive-switching behaviour and follow the same conductive mechanism; however, the Ag/Sr$_{0.92}$Bi$_{0.08}$TiO$_3$/Si device possesses the highest $R_{\rm HRS}/R_{\rm LRS}$ of 10$^5$ and the best endurance and retention characteristics. The doping of Bi is conducive to enhance the $R_{\rm HRS}/R_{\rm LRS}$ of the SrTiO$_3$ films; meanwhile, the Si substrates help improve the endurance and retention characteristics of the Sr$_{0.92}$Bi$_{0.08}$TiO$_3$ films.

    • Thermo-transport properties of Zn-substituted layered Li-nickel oxide, LiNiO$_2$


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      The layered Li-TM-O$_2$ materials have been investigated extensively due to their application as cathodes in Li batteries. The electrical properties of these oxides can be tuned or controlled either by non-stoichiometry or substitution.Hence the thermo-transport properties of Zn-substituted LiNi$_{1−x}$Zn$_x$O$_2$ for $0 \leq x \leq 0.16$ have been investigated in thetemperature range of 300–900 K for potential application as a high-temperature thermoelectric material. For $x$ < 0.08, the compounds were of single phase belonging to the space group R-3mH while for $x$ > 0.08 an additional minority phase, ZnO forms together with the main layered phase.All the compounds exhibit a semiconducting behaviour with electrical resistivity,varying in the range of $\sim$10$^{−4}$ to 10$^{−2}$ $\Omega$m between 300 and 900 K. The electrical resistivity is found to increase with increasing Zn-substitution predominantly due to a decrease in the charge carrier hole mobility. The activation energy remains constant, $\sim$10 meV, with Zn-substitution. The Seebeck coefficient of the compounds is found to decrease with increasingtemperature and increase with increasing Zn-substitution. The Seebeck coefficient decreases from $\sim$95 to 35 $\mu$μV K$^{−1}$ and the corresponding power factor is $\sim$12 $\mu$Wm$^{−1}$ K$^{−2}$ for the $x = 0.16$ compound.

    • Highly enhanced solar conversion efficiency of novel layer-by-layer PbS:Hg and CdS quantum dots-sensitized ZnO thin films prepared by sol–gel spin coating


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      Owing to superior optical properties, ZnO thin films have immense potential in solar cell preparation. ZnO thin films were prepared by sol–gel technology. However, this is prolonged technique and it necessitates a complex precursorsolution. In the present work, ZnO thin films are prepared by sol–gel spin coating with simple precursor, zinc acetate. A very remarkable feature of the method is that polycrystalline, non-abrasive and translucent films were obtained. Additionally, novel PbS:Hg quantum dots (QDs) and CdS QDs are successfully synthesized. Moreover, both types of QDs are deposited layer-by-layer over pure ZnO and Ag:ZnO thin films. The films are characterized by X-ray diffraction, and crystallinity continuation is observed even after the addition of QDs layer. Presence of synthesized QDs over thin films is also confirmed. The films were also characterized by scanning electron microscopy (SEM) and UV–Vis spectroscopy. Uniform, dense and porous surface morphology is clearly revealed. Sensitized thin films show a huge decline in band gap and large enhancement in efficiency. Superior current density (10.87mAcm$^{−2}$) is achieved with PbS:Hg/CdS/Ag:ZnO, which leads to enhancement in overall solar conversion efficiency by 6.34 times.

    • Sn-adopted fullerene (C$_{60}$) nanocage as acceptable catalyst for silicon monoxide oxidation


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      In recent years, the discovery of metal catalysts for the oxidation of silicon monoxide (SiO) has become extremely important. In first step, the Sn adoption of fullerene (C$_{60}$) was investigated and then activation of surface ofSn-C$_{60}$ via O$_2$ molecule was examined. In second step, the SiO oxidation on surface of Sn-C$_{60}$ via Langmuir Hinshelwood (LH) and Eley Rideal (ER) mechanisms was investigated. Results show that O$_2$-Sn-C$_{60}$ can oxidize the SiO molecule via Sn-C$_{60}$-O-O$^∗$ $+$ SiO $\to$ Sn-C$_{60}$-O-O$^∗$-SiO $\to$ Sn-C$_{60}$-O$^∗$ $+$ SiO$_2$ and Sn-C$_{60}$-O$^∗$ $+$ SiO $\to$ Sn-C$_{60}$ $+$ SiO$_2$ reactions.Results show that SiO oxidation via the LH mechanism has lower energy barrier than ER mechanism. Finally, Sn-C$_{60}$ is an acceptable catalyst with high performance for SiO oxidation in normal temperature.

    • Effects of conjugation on the properties of alkynylcarbazole compounds: experimental and theoretical study


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      Four novel dyes containing alkynylcarbazole, namely, 2-((9$H$-carbazol-3-yl)ethynyl)-9-ethyl-9$H$-carbazole, 3,6-bis((9-ethyl-9$H$-carbazol-2-yl)ethynyl)-9$H$-carbazole, 3-(phenylethynyl)-9$H$-carbazole and 3,6-bis(phenylethynyl)-9$H$-carbazole, were synthesized on the basis of single and double substitutes by following the Sonogashira coupling method.The synthesized dyeswere then assessed as novel photosensitizers in visible-light photopolymerization to evaluate the effects of conjugation on the properties of aromatic compounds. A comparison between UV–vis and TD/DFT electron transition spectra shows that λmax in theoretical ultraviolet spectra matched well with the experimental spectra; every conjugated alkynylcarbazole dye exhibits a wide absorption band in the range of 300–400 mm. Moreover, conjugation enhancement by switching carbazoleacetylene moieties caused a red shift in the absorption bands. The theoretical study showed that the maxima $\gamma$ of these molecules ranged from $\sim$330 to 370 mm, corresponding to $\pi\to \pi^∗$ and $n\to \pi^∗$ electron transitions. Fluorescence spectroscopic data show that the strongest emission peaks exhibit a red shift because of the addition of conjugated acetylene groups. A combination of alkynyl dyes and iodonium under a halogen lamp atmosphere by visible-light photopolymerizationdisplayed a positive response to the cationic polymerization of bisphenol-A epoxy resin A and free-radical of tripropylene glycol diacrylate.

    • A review of the biological synthesis of gold nanoparticles using fruit extracts: scientific potential and application


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      Gold nanoparticles (GNPs) arewell-known nanomaterials that can be used for multiple biomedical applications. There are various methods for synthesis of GNPs using microorganisms and plants, particularly through the use of fruitextracts. Their use is due to the fact that fruit extracts are the natural concentrate of substances that possesses therapeutic properties. In this review, we aim to compare the recent studies concerning the methods for synthesis of GNPs from fruit extracts, the methods used to characterize the properties of GNPs and capping biomaterial and the potential applications of GNPs. The most frequently used methods to characterize GNPs and capping biomaterial are UV–visible spectroscopy, transmission or scanning electron microscopy, dynamic light scattering and Fourier transformation infrared spectroscopy techniques. Because of GNPs’ optoelectronic properties, biocompatibility, stability and oxidation resistance, they can be used in areas such as electronics, chemical and biological sensing, tumour imaging, drug delivery and phototherapy.

    • Distribution of relaxation times investigation of Co$^{3+}$ doping lithium-rich cathode material Li[Li$_{0.2}$Ni$_{0.1}$Mn$_{0.5}$Co$_{0.2}$]O$_2$


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      The element Co$^{3+}$ was introduced into lithium-rich material 0.5Li$_2$MnO$_3$ $\cdot$ 0.5LiNi$_{0.5}$Mn$_{0.5}$O$_2$ by apolyacrylamide-assisted sol–gel method to form Li[Li$_{0.2}$Ni$_{0.1}$Mn$_{0.5}$Co$_{0.2}$]O$_2$ and better electro-chemical performances were observed. Electrochemical impedance spectroscopy spectra were measured on 11 specific open circuit voltage levels on the initial charge profile. Then they were converted to the distribution of relaxation times (DRTs) $g(\tau)$ by self-consistent Tikhonov regularization method. The obtained DRTs offered a higher resolution in the frequency domain and providedthe number and the physical origins of loss processes clearly. Through the analysis of DRTs, the rapid augmentation of resistance to electronic conduction and charge transfer within the voltage range 4.46–4.7 V where the removal of Li$_2$O from Li$_2$MnO$_3$ component took place was the most remarkable phenomenon and the Co$^{3+}$ doping greatly reduced the resistanceto electronic conduction Re. This gave us more evidence about the complicated ‘structurally integrated’ composite character of the material.

    • Experimental investigations into viscosity, pH and electrical conductivity of nanofluid prepared from palm kernel fibre and a mixture of water and ethylene glycol


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      Extensive research has been carried out on the synthesis and applications of nanofluid produced from metals, nonmetals and their oxides. However, little or no attention has been paid to bio-based nanoparticles. The need for the use ofbio-based nanoparticles and bio-based nanofluids is imperative to mitigate over-dependence on toxic synthetic nanoparticles. This idea is also in line with renewable and sustainable developmental goals.Moreover, bio-based materials like palm kernel fibre (PKF) constitute environmental waste in some quarters and its conversion to useful products for engineering application will take a long time in solving environmental issues and health hazards. In this study, the top-down approach was used to synthesize nanoparticles from PKF using a ball-milling machine. The PKF nanoparticles with an average size of $\sim$40 nmwere dispersed in an ethylene glycol (EG)/water (50:50) base fluid up to 0.5% of the volume fraction. The viscosity, pH and electrical conductivity of PKF–water and EG (50:50) were studied for temperature ranging from 10 to 60$^{\circ}$C. The results showed that the viscosity of the PKF-based nanofluid increases with an increase in volume fraction and decreases exponentially with an increase in the working temperature of the nanofluid. The pH and the electrical conductivity increased as the volume fraction of the PKF nanoparticle was increased from 0.1 to 0.5%. However, the pH decreased with an increase in the temperature while the electrical conductivity increased with an increase in the volume fraction. Since the notable theoretical models in the literature were unable to estimate the viscosity of the PKF–EG/water nanofluid, in the present case an empirical correlation based on dimensional analysis was proposed to estimate the viscosity of the PKF–EG/water nanofluids.

    • Effects of sintering conditions on the microstructure and mechanical properties of SiC prepared using powders recovered from kerf loss sludge


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      The effects of sintering conditions on the microstructure and mechanical properties of the sintered SiC prepared using the SiC powder recovered from the kerf loss sludge were investigated. The recovered SiC powders were consolidated by spark plasma sintering (SPS) and conventional sintering methods. The effects of sintering temperature, time and methods(SPS and conventional sintering) on the phase, grain size and density of SiC were systematically studied. The Vickers hardness of spark plasma-sintered (SPSed) samples was higher than that of conventional sintered samples due to small grain size. When holding time was increased from 10 to 30 min, the grain size and relative density of SPSed samples were also increased, which lead to the almost constant Vickers hardness by competing effects of grain size and relative density.When holding time was over 30 min, no appreciable change of the relative density and grain size were observed, which can lead to similar values of Vickers hardness. SPS process can be used to make SiC with high density and hardness at relatively low temperature compared with the conventional sintering process.

    • Spin-orbit coupling in graphene, silicene and germanene: dependence on the configuration of full hydrogenation and fluorination


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      We investigate the effect of full hydrogenation and fluorination on the spin-orbit coupling (SOC) in graphene, silicene and germanene. In chair conformation, the fluorination of graphene increases the spin-orbit splitting ($E_{\rm so}$), while the hydrogenation and fluorination of other structures reduce the $E_{\rm so}$ at the $\Gamma$-point. In case of boat conformation, the hydrogenation and fluorination reduce the symmetry of honeycomb structure, which in turn remove the degeneracy of valence band maximum at the $\Gamma$-point. The change in band gaps due to SOC is very small in boat conformation structuresas compared to that in the corresponding chair conformation structures.

    • Effect of annealing temperature and CdCl$_2$ treatment on the photo-conversion efficiency of CdTe/Zn$_{0.1}$Cd$_{0.9}$S thin film solar cells


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      We report the effects of annealing in conjunction with CdCl$_2$ treatment on the photovoltaic properties of CdTe/Zn$_{0.1}$Cd$_{0.9}$S thin film solar cells. CdTe layer is subjected to dry CdCl$_2$ treatment by thermal evaporation method and subsequently, heat treated in air using a tube furnace from 400 to 500$^{\circ}$C. AFM and XRD results show improved grain size and crystallographic properties of the CdTe film with dry CdCl$_2$ treatment. This recrystallization and grain growth of the CdTe layer upon CdCl$_2$ treatment translates into improved photo-conversion efficiencies of CdTe/Zn$_{0.1}$Cd$_{0.9}$S cell. The results of dry CdCl$_2$ treatment were compared with conventional wet CdCl$_2$ treatment. Photo-conversion efficiency of 5.2% is achieved for dry CdCl$_2$-treated cells in comparison with 2.4% of wet-treated cell at heat treatment temperature of 425$^{\circ}$C.

    • Study of optical properties of potassium permanganate (KMnO$_4$) doped poly(methylmethacrylate) (PMMA) composite films


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      We have developed films of pure polymethylmethacrylate (PMMA) (0.5, 1, 2 and 5%) and potassium permanganate (KMnO$_4$)-doped PMMA composite films of thickness ($\sim$100 $\mu$m) using the solution-cast technique. To identify the possible change that happen to the PMMA films due to doping, the optical properties were investigated for different concentrations of KMnO$_4$ by recording the absorbance ($A$) and transmittance ($T$%) spectra of these films using UV–Vis spectrophotometer in the wavelength range of 300–1100 nm. From the data obtained from the optical parameters viz. absorption coefficient ($\alpha$), extinction coefficient ($\kappa$), finesse coefficient ($F$), refractive index ($\eta$), real and imaginary parts of dielectric constant ($\epsilon_r$ and $\eplsilon_i$) and optical conductivity ($\sigma$) were calculated for the prepared films. The indirect optical band gap for the pure and the doped-PMMA films were also estimated.

    • Microwave-hydrothermal synthesis of mesoporous $\gamma$-Al$_2$O$_3$ and its impregnation with AgNPs for excellent catalytic oxidation of CO


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      Mesoporous $\gamma$-alumina was synthesized by the microwave-hydrothermal process with a shorter duration time at 150$^{\circ}$C/2 h followed by calcination at 550$^{\circ}$C/1 h. Ag nanoparticles (AgNPs) were impregnated into $\gamma$-alumina under a reducing atmosphere at 450$^{\circ}$C. The synthesized product was characterized by X-ray diffraction (XRD), thermogravimetric (TG)/differential thermal analysis (DTA), X-ray photoelectron spectroscopy (XPS), N$_2$ adsorption–desorption study, fieldemissionscanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The BET surface area values of $\gamma$-alumina and Ag-impregnated $\gamma$-alumina were found to be 258 and 230 m$^2$ g$^{−1}$, respectively. FESEM images showed the formation of grain-like particles of 50–70 nm in size with a flake-like microstructure. The XRD, XPS and TEM studies confirmed the presence of Ag in the synthesized product. Catalytic properties of the product for CO oxidation was studied with the $T_{50}$ (50% conversion) and $T_{100}$ (100% conversion) values of 118 and 135$^{\circ}$C, respectively; the enhancedvalues were compared with the literature reported values.

    • Recovering value from waste: biomaterials production from marine shell waste


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      Marine shell waste is rich in calcium carbonate (CaCO$_3$), which can be a good source for the synthesis of hydroxyapatite (HAP). HAP is a potential component in bone tissue engineering as it possesses similar elements tobone structure. In this study, three different species of marine shells that are normally found in Malaysia, namely shortnecked clam (Paphia undulate), blood cockle (Anadara granosa) and hard clam (Meretrix lyrata) were used to produce CaCO$_3$ and HAP. The characterization results indicate that the produced CaCO$_3$ consists of mainly aragonite polymorph. Subsequently, the produced CaCO$_3$ was used as the calcium source for the formation of HAP through the wet slurry precipitation method. The results from the analyses on crystallinity, functional group, surface morphology and elemental analysis of the synthesized HAP powders that were obtained through X-ray diffraction (XRD), Fourier-transform infrared (FTIR), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) have confirmed that HAP is comparable with other studies. Overall, the results obtained through this study indicate that it is possible to produceCaCO$_3$ and HAP from various marine-based shell waste through greener synthesis routes with less chemicals and reaction time.

    • Exfoliated WS$_2$ nanosheets: optical, photocatalytic and nitrogen-adsorption/desorption characteristics


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      In this work, we report on structural, optical, photocatalytic and nitrogen adsorption–desorption characteristics of WS$_2$ nanosheets developed via a hydrothermal route. X-ray diffraction (XRD) studies have revealed a hexagonal crystal structure, whereas nanodimensional sheets are apparently observed in scanning and transmission electron microscopy (SEM and TEM) micrographs. As compared to the bulk counterpart, the WS$_2$ nanosheets exhibited a clear blue shift. Through Brunauer–Emmett–Teller (BET) surface area analysis, average surface area, pore volume and pore size of the NSs were calculated as 211.5 m$^2$ g$^{−1}$, 0.433 cc g$^{−1}$ and 3.8 nm, respectively. The photocatalytic activity of the WS$_2$ nanosheets was also examined with malachite green (MG) as the target dye under both UV and day light (visible) illumination conditions.Accordingly, a degradation efficiency as high as 67.4 and 86.6% were witnessed for an irradiation time duration of 60 min. The nano-WS$_2$ systems have immense potential in optoelectronics, solid-lubrication and other next generation elements.

    • Investigation of the influence of Br- and As-doped silica single-wall nanotubes: Hartree–Fock method


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      Synthesis of silica single-wall nanotubes was reported based on single-membered ring (single unit cell) with the element As. These results are supported by performing the Hartree–Fock/6-311G method. The electronic structure, opticalband gaps, hardness ($\eta$) and softness ($S$) are discussed. No difference in the computed bond length and angle of doped silica was found. Doping of As and Br atoms leads to a decrease in the energy gap of pure silica. This will make the silica doped with Br and As molecules not require more energy to be excited.

    • Optimization of the liquid–liquid interfacial precipitation method for the synthesis of C$_{60}$ nanotubes


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      Tubular fullerene nanowhiskers called ‘fullerene nanotubes’ are composed ofC60 fullerene molecules (C$_{60}$ NTs) are synthesized at room temperature using the liquid–liquid interfacial precipitation method in the pyridine and isopropyl alcohol (IPA) system.The growth control of fullerene nanotubes is important for their chemical and physical properties as well as for their future applications. In the present study, we investigated the effect of light, water, solvent ratio and temperature on the synthesis of C60 nanotubes. A marked development in the yield of C$_{60}$ NTs was achieved using dehydrated solvents, a solution with a volume ratio of 1:9 for pyridine: IPA, a growth temperature equal to 5$^{\circ}$C and by illuminating the C$_{60}$-pyridinesolution with ultraviolet light (wavelength 302 nm) for 102 h. The synthesized fullerene nanotubes were characterized by different analytical techniques including Raman and Fourier transform infrared spectroscopy, optical microscopy, focussed ion beam scanning electron microscopy and transmission electron microscopy.

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