• Issue front cover thumbnail

      Volume 39, Issue 6

      October 2016,   pages  1371-1618

    • Imine-linked receptors decorated ZnO-based dye-sensitized solar cells

      SATBIR SINGH AMARPAL SINGH NAVNEET KAUR

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      This study reports the synthesis, characterization and photophysical properties of imine-linked receptors decorated ZnO nanoparticles using wet precipitation method. Initially, polymer dye 3 was synthesized usingcondensation reaction between 2-furancarboxaldehyde 1 and polyethylenimine 2. The decoration of imine-linked receptors on ZnO nanoparticles (sample A) was characterized and investigated by X-ray diffraction, scanning electronmicroscope and dynamic light scattering spectroscopic studies. Further, polymer dye 3 was added to ruthenium chloride (RuCl$_3$) to form a polymer–ruthenium-based composite dye-capped ZnO nanoparticles (sample B).The optical properties of sample A were evaluated by fluorescence and UV–Vis spectroscopy. The samples A and B were further processed to dye-sensitized solar cells using wet precipitation method. The results of observationsrevealed that the addition of ruthenium–polymer dye molecules increased the light harvesting capacity of ZnO-based DSSCs. A maximum solar power to electricity conversion efficiency ($\eta$) of 3.83% was recorded for sample B-based DSSCs with ruthenium–metal complex dye as a good photosensitizer. The recorded photovoltaic efficiency of sample B-based DSSCs was enhanced by 1.36% compared to sample A-based DSSCs.

    • Rose bengal-sensitized nanocrystalline ceria photoanode for dye-sensitized solar cell application

      SUHAIL A A R SAYYED NIYAMAT I BEEDRI VISHAL S KADAM HABIB M PATHAN

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      For efficient charge injection and transportation, wide bandgap nanostructured metal oxide semiconductors with dye adsorption surface and higher electron mobility are essential properties for photoanode in dyesensitizedsolar cells (DSSCs). TiO$_2$-based DSSCs are well established and so far have demonstrated maximum power conversion efficiency when sensitized with ruthenium-based dyes. Quest for new materials and/or methods is continuous process in scientific investigation, for getting desired comparative results. The conduction band (CB) position of CeO$_2$ photoanode lies below lowest unoccupied molecular orbital level (LUMO) of rose bengal (RB) dye.Due to this, faster electron transfer from LUMO level of RB dye to CB of CeO$_2$ is facilitated. Recombination rate of electrons is less in CeO$_2$ photoanode than that of TiO$_2$ photoanode. Hence, the lifetime of electrons is more in CeO$_2$ photoanode. Therefore, we have replaced TiO$_2$ by ceria (CeO$_2$) and expensive ruthenium-based dye by a low cost RB dye. In this study, we have synthesized CeO$_2$ nanoparticles. X-ray diffraction (XRD) analysis confirms the formation of CeO$_2$ with particle size $\sim$7 nm by Scherrer formula. The bandgap of 2.93 eV is calculated using UV–visibleabsorption data. The scanning electron microscopy (SEM) images show formation of porous structure of photoanode, which is useful for dye adsorption. The energy dispersive spectroscopy is in confirmation with XRD results,confirming the presence of Ce and O in the ratio of 1:2. UV–visible absorption under diffused reflectance spectra of dye-loaded photoanode confirms the successful dye loading. UV–visible transmission spectrum of CeO2 photoanodeconfirms the transparency of photoanode in visible region. The electrochemical impedance spectroscopy analysis confirms less recombination rate and more electron lifetime in RB-sensitized CeO$_2$ than TiO$_2$ photoanode.We foundthat CeO$_2$ also showed with considerable difference between dark and light DSSCs performance, when loaded with RB dye. The working mechanism of solar cells with fluorine-doped tin oxide (FTO)/CeO$_2$/RB dye/carbon-coatedFTO is discussed. These solar cells show VOC $\sim$360 mV, JSC $\sim$0.25 mA cm$^{−2}$ and fill factor $\sim$63% with efficiency of 0.23%. These results are better as compared to costly ruthenium dye-sensitized CeO$_2$ hotoanode.

    • Dye-sensitized solar cell and photocatalytic performance of nanocomposite photocatalyst prepared by electrochemical anodization

      MOHAMAD MOHSEN MOMENI

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      This study compares different Fe-doped TiO$_2$ nanostructures in terms of their photocatalytic performance. Iron-doped TiO$_2$ nanostructures (FeTNs) were prepared by in situ anodizing of titanium in a single-stepprocess in the presence of 3, 9, 15 and 21 mM K$_3$Fe(CN)$_6$. Potassium ferricyanide was used as the iron source. Prepared films are amorphous, so these layers were thermally annealed. The effect of iron doping on the photoelectrochemical properties (including dye-sensitized solar cells) and photocatalysis properties (decomposition of methomyl) was investigated. In all investigated cases, the sample C, which was formed by anodizing in a ethylene glycol electrolyte containing 9 mM K$_3$Fe(CN)$_6$, exhibited better performance than the bare TiO$_2$ and FeNTs fabricated using other iron concentrations. This study demonstrated a feasible and simple anodizing method to fabricate an effective, reproducible and inexpensive photocatalyst for various applications.

    • Dye-sensitized solar cells based on composite TiO$_2$ nanoparticle–nanorod single and bi-layer photoelectrodes

      F REZVANI E PARVAZIAN S A HOSSEINI

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      TiO$_2$ nanoparticle (NP), composite TiO$_2$ nanoparticle–nanorod (NP–NR) and bi-layer TiO2 nanoparticle/ nanorod (NP/NR) with the optimized diameter of NRs had been prepared as anode layer in dye-sensitized solarcells (DSSCs). Morphology and thickness of anode layers were provided by field emission scanning electron microscope (FE-SEM) and scanning electron microscopy (SEM) devices. Current density–voltage diagrams were preparedby potentiostat and solar simulator devices at air mass (AM) 1.5. It is determined that DSSCs based on composite NP–NR photoelectrode had the best conversion efficiency of 5.07%. Also, the results of the electrochemical modelling of these DSSCs indicated that solar cells based on NP–NR electrode had the highest electron transport time ($\tau_d$) of 312.87 ms, electrons’ recombination lifetime ($\tau_n$) of 130.4 ms and the lowest transfer resistance ($R_{ct}$) as wellas transport resistance ($R_t$) of 22.46 and 9.4 $\Omega$, respectively.

    • Fabrication of dye-sensitized solar cells with multilayer photoanodes of hydrothermally grown TiO$_2$ nanocrystals and P25 TiO$_2$ nanoparticles

      MAZIAR MARANDI MAHBOUBEH NAEIMI SANI SABET FARZANEH AHMADLOO

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      TiO$_2$ nanocrystals (NCs) with sizes around 20 nm were synthesized by hydrothermal method in acidic autoclaving pH. The hydrothermally grown TiO$_2$ NCs and P25 TiO$_2$ nanoparticles (NPs) were used in the preparationof two different pastes using different procedures. These pastes with different characteristics were separately deposited on FTO glass plates to form multilayer photoanodes of the dye-sensitized solar cells. The aim of this study was to search how a thin sub-layer of the hydrothermally grown TiO2 NCs in the photoanodes could improve the efficiency of TiO$_2$ P25-based solar cells. The highest efficiency of 6.5% was achieved for a cell with a photoanodecomposed of one transparent sub-layer of hydrothermally grown TiO$_2$ NCs and two over-layers of P25 NPs. Higher energy conversion efficiencies were also attainable using two transparent sub-layers of hydrothermally grown TiO$_2$ NCs. In this case, an efficiency of 7.2% was achieved for a cell with a photoelectrode made of one over-layer of P25 TiO$_2$ NPs. This could show an increase of about 30% in the efficiency compared to the similar cell with a photoanode made of two layers of hydrothermally grown TiO2 NCs.

    • Ideal shear strength and deformation behaviours of L1$_0$ TiAl from first-principles calculations

      PING-YING TANG GUO-HUA HUANG QING-LIAN XIE JIAN-YING LI

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      The stress–strain relationships for four different shear processes of L1$_0$ TiAl have been investigated from first-principles calculations, and the peak shear stresses in these slip systems were obtained. By analysing the structural unit cell, bond length and charge density, the deformation modes under shear were elaborately discussed. Both of the peak shear stresses and the charge density indicate that the ideal shear strength of L10 TiAl occurs in the $\langle 11\bar{2}]${111} direction. It is shown that some bonds are enormously stretched accompanying with depletion of charge density as the strain increase. The density of states was studied in detail. It is indicated that strong hybridizationexists between Ti 3$d$ and Al 2$p$, and the structural stability would be lowered with increase of the strain.

    • First-principles study of the double perovskites Sr$_2$XOsO$_6$ (X = Li, Na, Ca) for spintronics applications

      M FAIZAN G MURTAZA S H KHAN A KHAN ASIF MEHMOOD R KHENATA S HUSSAIN

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      We investigated double perovskite compounds of the form Sr$_2$XOsO$_6$ (X = Li, Na, Ca) using the fullpotential linearized augmented plane wave (FP-LAPW) method. For the exchange-correlation energy, Wu andCohen generalized gradient approximation (WC-GGA), Perdew, Burke and Ernzerhof GGA (PBE-GGA), Engel and Vosko GGA (EV-GGA), and GGA plus Hubbard U-parameter (GGA $+$ U) were used. The calculated structuralparameters are in good agreement with the existing experimental results. Calculation of different elastic constants and elastic moduli reveals that these compounds are elastically stable and possess ductile nature. The GGA $+$ Uapproach yields quite accurate results of the bandgap as compared with the simple GGA schemes. The density of states plot shows that Sr-4d, Os-5d and O-2p states predominantly contribute to the conduction and valence bands.Further, our results regarding to the magnetic properties of these compounds reveal their ferromagnetic nature. In addition, these compounds seem to possess half-metallic properties, making them useful candidates for applicationsin spintronics devices.

    • Effect of spin polarization on the structural properties and bond hardness of Fe$_x$B ($x = 1, 2, 3$) compounds first-principles study

      AHMED GUEDDOUH BACHIR BENTRIA IBN KHALDOUN LEFKAIER YAHIA BOUROUROU

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      In this paper, spin and non-spin polarization (SP, NSP) are performed to study structural properties and bond hardness of Fe$_x$B ($x = 1, 2, 3$) compounds using density functional theory (DFT) within generalized gradientapproximation (GGA) to evaluate the effect of spin polarization on these properties. The non-spin-polarization results show that the non-magnetic state (NM) is less stable thermodynamically for Fe$_x$B compounds than spinpolarization by the calculated cohesive energy and formation enthalpy. Spin-polarization calculations show that ferromagnetic state (FM) is stable for FexB structures and carry magnetic moment of 1.12, 1.83 and 2.03 $\mu$B inFeB, Fe$_2$B and Fe$_3$B, respectively. The calculated lattice parameters, bulk modulus and magnetic moments agree well with experimental and other theoretical results. Significant differences in volume and in bulk modulus werefound between the ferromagnetic and non-magnetic cases, i.e., 6.8, 32.8, respectively.We predict the critical pressure between ferromagnetic and non-magnetic phases. The model for hardness calculation using Mulliken population coupled to semi-empirical hardness theory proved effective in hardness prediction for the metal borides which agree well with the experimental values. These results would help to gain insight into the spin-polarized effect on the structural and bond hardness.

    • Effect of ‘Al’ concentration on spin-dependent resonant tunnelling in InAs/Ga$_{1−y}$Al$_y$As symmetrical double-barrier heterostructures

      L BRUNO CHANDRASEKAR K GNANASEKAR M KARUNAKARAN R CHANDRAMOHAN

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      The effect of ‘Al’ concentration on spin-dependent tunnelling in strained non-magnetic symmetric double-barrier semiconductor has been theoretically investigated. The separation between spin-up and spin-down components, barrier transparency, polarization efficiency and tunnelling lifetime were calculated using the transfer matrix approach. The separation between spin-up and spin-down resonances and tunnelling lifetime were reportedfor the first time in the case of InAs/Ga$_{1−y}$Al$_y$As heterostructures for various ‘Al’ concentrations and for various barrier widths. Cent percentage polarization can be obtained in this strained non-magnetic double-barriersemiconductor even without any external field.

    • Bandgap engineered graphene and hexagonal boron nitride for resonant tunnelling diode

      PENCHALAIAH PALLA GOPI RAJA UPPU ANITA S ETHIRAJ J P RAINA

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      In this article a double-barrier resonant tunnelling diode (DBRTD) has been modelled by taking advantage of single-layer hexagonal lattice of graphene and hexagonal boron nitride (h-BN). The DBRTD performance and operation are explored by means of a self-consistent solution inside the non-equilibrium Green’s function formalism on an effective mass-Hamiltonian. Both p- and n-type DBRTDs exhibit a negative differential resistance effect, which entails the resonant tunnelling through the hole and electron bound states in the graphene quantum well, respectively. The peak-to-valley ratio of approximately 8 (3) for p-type (n-type) DBRTD with quantum well of 5.1 nm (4.3 nm) at a barrier width of 1.3 nm was achieved for zero bandgap graphene at room temperature.

    • Growth and properties of lead iodide thin films by spin coating

      D ACUÑA B KRISHNAN S SHAJI S SEPÚLVEDA J L MENCHACA

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      In this study, lead iodide (PbI$_2$) thin films were deposited on glass substrates by spin coating a solution of 0.2 M PbI$_2$ dissolved in dimethylformamide, varying the deposition time and the spin speed. The thickness of the thin films decreased with increase in spin speed and deposition time, as examined by profilometry measurements.The structure,morphology, optical and electrical properties of the thin films were analysed using various techniques. X-ray diffraction patterns revealed that the thin films possessed hexagonal structures. The thin films were grown highly oriented to [001] direction of the hexagonal lattice. Raman peaks detected at 96 and 136 cm$^{-1}$ were corresponding to the characteristic vibration modes of PbI$_2$. The X-ray photoelectron spectroscopy detected the presence of Pb and I with core level binding energies corresponding to that in PbI2. Atomic force microscopy showed smooth and compact morphology of the thin films. From UV–Vis transmittance and reflectance spectral analysis, the bandgap of the thin films $\sim$2.3 eV was evaluated. The dark conductivity of the thin films was computed and the value decreased as the deposition time and spin speed increased.

    • Graphene/TiO$_2$ hydrogel: a potential catalyst to hydrogen evolution reaction

      VIRGIL CHRISTIAN CASTILLO JULIET Q DALAGAN

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      In this study, graphene was synthesized from graphite. Graphite was oxidized via modified Hummer’s method and sonicated to form graphene oxide (GO). Infrared spectroscopy revealed the successful oxidation of graphite by the emergence of oxygen functionalities. The spectrum of GO showed peaks at 3270, 1629, 1227 and 1096 cm$^{−1}$, indicating O–H, C=O, C–OH and C–O–C functional groups, respectively. Graphene hydrogels were prepared by the addition of L-ascorbic acid to GO suspensions and subsequent heating at 90$^{\circ}$C. Composite hydrogels of graphene and titanium (IV) oxide (TiO$_2$) were synthesized with various TiO$_2$ to GO mass ratios. Composites were applied to photocatalytic hydrogen evolution reaction (HER) and the hydrogen gas produced was analysed by gas chromatography with thermal conductivity detector. Highest HER yield was 66.00% H$_2$.

    • Experimental investigation on tribological behaviours of PA6, PA6-reinforced Al$_2$O$_3$ and PA6-reinforced graphite polymer composites

      S SATHEESKUMAR G KANAGARAJ

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      This article reports on the preparation, characterization and experimental investigation of polyamide 6 (PA6) reinforced with alumina oxide (Al$_2$O$_3$) and graphite composites. The test specimens were prepared in an injection-moulding machine by varying the weight proportions of Al$_2$O$_3$ and graphite particles blended with PA6. The tribological properties of the composites were observed by using pin-on-disc wear test rig under dry slidingconditions. The worn surfaces of the composites were examined using scanning electron microscope. The addition of Al$_2$O$_3$ and graphite significantly enhanced the tribological properties of PA6. The PA6 containing 30 wt% Al$_2$O$_3$ and 20 wt% graphite revealed the best tribological behaviours due to the stronger interfacial bonding characteristics with improved wear resistance. Further, the thermal stability of Al$_2$O$_3$ and graphite particles was studiedthrough thermogravimetric analysis test. It was also found that further addition of Al$_2$O$_3$ and graphite in PA6 had no significant improvement in wear resistance, the co-efficient of friction and heat generation.

    • Metal oxide blended ZSM-5 nanocomposites as ethanol sensors

      MADHURI LAKHANE RAJENDRA KHAIRNAR MEGHA MAHABOLE

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      Nano-ZSM-5 is synthesized without organic template via microwave-assisted hydrothermal technique. The synthesized nano-ZSM-5 zeolite is blended with metal oxides (ZnO and TiO$_2$) to have novel composites as ethanol sensors. The composites are characterized by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) techniques. A study on ethanol sensing behaviour of metal oxide blended composite screen-printed thick films is carried out and the effect of metal oxide concentration on various ethanol sensing features, specifically operating temperature, response/recovery time and active region of the sensor, are investigated. XRD and FTIR confirm the blending of metal oxides in ZSM-5 matrix. Both, ZnO and TiO$_2$ blended, composite films are sensitive to ethanol. It can be concluded that metal oxide blending improves the preformance of sensor for ethanol detection. The response/recovery time and active sensing regions depend upon the concentration of metal oxide in host zeolite. The ZnO/ZSM-5 and TiO$_2$/ZSM-5 composite films are the excellent ethanol sensors.

    • Smart dendrimer-based nanogel for enhancing 5-fluorouracil loading efficiency against MCF7 cancer cell growth

      PHUNG NGAN LE NGOC HOA NGUYEN CUU KHOA NGUYEN NGOC QUYEN TRAN

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      Nano-carriers are not only evaluated as a novel kind of drug delivery, but also expected to bypass the critical bottleneck of conventional cancer chemotherapeutics. Among them, thermo-sensitive nanogel draws muchattention due to its efficacy in the loading and release of hydrophobic drugs. In the study, we developed a promising thermosensitive polymer-grafted dendrimer to enhance drug-loading efficiency, which was prepared from conjugationof thermo-sensitive carboxylic-terminated poly(N-isopropylacrylamide) polymer (PNIPAM) with polyamidoamine (PAMAM) dendrimer (G3.0). The obtained copolymer structure and molecular weight were confirmed by proton nuclear magnetic resonance (${}^!$H NMR) and gel permeation chromatography (GPC), respectively. Morphology of the nanocarrier was observed around 120–150 nm by transmission electron microscopy (TEM) and 200 nm by dynamic light scattering (DLS). The nanocarrier exhibited the higher drug loading (DL = 7.79%) and entrapment efficiency (EE = 42.25%) of 5-FU compared to PAMAM dendrimer G3.0 (DL = 2.25% and EE = 11.52%). In-vitro test, the 5-FU-loaded in PAMAM G3.0–PNIPAM could release approximately 40% of the encapsulated drug at pH = 7.4 after 5 days tracking, while the cumulative anticancer drugs achieved nearly two-fold increase (around 75%)at pH 5.5 during the same time.Moreover, the cytotoxicity assay results also indicated that the drug-loaded nanocarrier exhibited a significant growth inhibition of the MCF-7 cancer cell. The obtained resulted possibly offered agreat potential of the nanocarrier which may be utilized in delivering other anticancer drugs or dual drugs for chemotherapy in future.

    • Co$_9$S$_8$ nanotubes: facile synthesis and application in the catalytic reduction of 4-nitrophenol

      TAO GENG YONGHONG NI HONGYAN WANG XIA ZHOU

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      Co$_9$S$_8$ nanotubes have been successfully synthesized via a facile two-step solvothermal method without the assistance of any template or surfactant, using cobalt sulphate (CoSO$_4$·7H$_2$O), urea and sodium sulphide (Na$_2$S·9H$_2$O) as starting reactants, and deionized water and glycol as the reactive medium. The phase and the morphologyof the as-obtained product were characterized by means of powder X-ray diffraction, energy dispersive spectrometry and scanning electron microscopy. The result displays that the Co9S8 nanotubes have hexagonal crosssections,the diameter of the nanotubes is about 200 nm and the wall thickness is of 50 nm. The experiments showed that the Co$_9$S$_8$ nanotubes could be used as new-type catalysts for the reduction of 4-nitrophenol. It was found thatthe as-obtained Co$_9$S$_8$ nanotubes contributed to the best catalytic activity.

    • Photocatalytic degradation of methylene blue by C$_3$N$_4$/ZnO: the effect of the melamine/ZnO ratios

      PONGSATON AMORNPITOKSUK SUMETHA SUWANBOON URAIWAN SIRIMAHACHAI CHAMNAN RANDORN KASIDID YAEMSUNTHORN

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      The C$_3$N$_4$/ZnO composite photocatalysts were synthesized by mechanical milling combined with a calcination process. Various ratios of melamine and ZnO powders were milled by a planetary ball mill for 10 h. Afterheating at 540$^{\circ}$C for 3 h in air, melamine was converted to C3N4 but the formation of C$_3$N$_4$ depended on the ratios of the melamine and ZnO (M/Z) powders. From the experimental results, the conversion of melamine to C$_3$N$_4$ could be inhibited by ZnO particles; as there was no detectable C$_3$N$_4$ in the sample at low M/Z values or high ZnO contents. The photocatalytic activities of prepared samples were investigated under the illumination of blacklight and fluorescent lamps as the low wattage light source. The C$_3$N$_4$/ZnO showed a better photocatalytic activity than ZnO to degrade a methylene blue (MB) dye solution using blacklight lamps, but there is no significant difference in photocatalytic activities between ZnO and prepared C$_3$N$_4$/ZnO under visible light by the fluorescent lamps. However, the prepared C$_3$N$_4$/ZnO can well function under illumination by Xe lamp as the high power light source. Ecotoxicities of MB solutions before and after photocatalytic process were also studied through growth inhibition of the alga Chlorella vulgaris.

    • Preparation and properties of Pr$_{3+}$/Ce$_{3+}$:YAG phosphors using triethanolamine as dispersant and pH regulator

      SHIHONG TONG JUNYAN ZHAO XIU WEN

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      Pr$_{3+}$/Ce$_{3+}$:YAG precursors were co-precipitated using triethanolamine as dispersant and pH regulator. The different dosages of triethanolamine (D) vs. the properties of Pr$_{3+}$/Ce$_{3+}$:YAG phosphors were discussed. When $D = 0.5$ vol%, the pH of titration process was controlled in the range of $\sim$7.94–8.16 to guarantee the uniform distribution of Al, Y, Ce and Pr in the precursors. The relatively higher pH could decrease the loss of Ce and Pr in the precursors and increase the particle size of the obtained powders, which was beneficial to the enhancement of luminescent intensity. Therefore, the precursors directly converted to pure-phase YAG at 900$^{\circ}$C, and the phosphors calcined at 1000$^{\circ}$C showed the best dispersity due to the dispersion effect of triethanolamine and the most excellent luminescent property. When $D ≥ 2$ vol%, although pure-phase YAG was detected, the emission intensity of the phosphors decreased due to the decrease of dispersity and purity. Moreover, the co-doped Pr$^{3+}$ enhanced the red emission of Pr$^{3+}$/Ce$^{3+}$:YAG phosphors.

    • Photocurrent analysis of AgIn$_5$S$_8$ crystal

      MAHMUT BUCURGAT SELAHATTIN OZDEMIR TEZER FIRAT

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      The photocurrent (PC) spectrum of AgIn$_5$S$_8$ crystal consists of a single peak, which provides to determine the bandgap energy by applying the Moss rule. The temperature dependence of the bandgap energy was alsocalculated. The PC dramatically increased by pre-illumination with light having wavelength corresponding to the bandgap of AgIn$_5$S$_8$. The temperature-dependent PC of the sample was measured at different temperatures from80 to 300 K and the PC spectrum consisted a single broad peak. Thermal quenching of the PC was observed to start at $\sim$105 K and the PC completely quenched at $\sim$180 K. The quenching mechanism was discussed in terms of the two-centre model. The height of the PC peak rised linearly with applied voltage up to 5.0 V under constant intensity of light. Similarly, the dark current–voltage characteristics consisted of a single region dominating an ohmicbehaviour, and no space charge limited region was apparent at various temperatures up to 20 V.

    • Cavity cutting efficiency of a Bioglass$^{\rm TM}$ and alumina powder combination utilized in an air abrasion system

      IMRAN FAROOQ IMRAN ALAM MOHEET EMAD ALSHWAIMI

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      This study investigated the attempt to replace alumina in the air abrasion system with an alternative material that is effective at cutting and also has remineralization potential. The powder samples were randomized into three groups: group 1—alumina (composed of aluminium and oxygen), group 2—45S5 (composed of 45% silica, 24.5% calcium oxide, 24.5% sodium oxide and 6% phosphorus pentoxide in weight percentage) and group 3—alumina + 45S5. Thirty human enamel blocks and microscope glass slides of 0.5mm thickness were randomly divided into these three groups. The time taken to cut a hole through the glass slide and for the cutting of human enamel blocks was recorded, the cutting time was fixed at 15 s. The depths of the cavities were measured using a periodontal probe and the enamel blocks were then analysed by scanning electronmicroscope (SEM). The mean time taken to cut a hole through the microscope glass slide was 2.96, 23.01 and 3.02 s for groups 1, 2 and 3, respectively. After cutting the human enamel blocks, the mean cavity depths produced were measured to be 2.5, 1.0 and 2.0 mm for groups 1, 2 and 3, respectively. The SEM micrographs revealed that the cavities formed by 45S5 were more conical in shape, whereas cavities produced by alumina and alumina + 45S5 were more cylindrical. The combined use of alumina and 45S5 has demonstrated a promising cutting efficiency and it has the potential to achieve effective cutting with the possibility of the remineralization.

    • Galvanostatic response of AA2024 aluminium alloy in 3.5% NaCl solution

      U DONATUS G E THOMPSON

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      Galvanostatic responses of AA2024T3 alloy in de-aerated and naturally aerated 3.5% NaCl solution have been investigated. In the de-aerated condition, two distinct stages of polarization were revealed. From the first stage, the relationships between the pitting incubation time, pitting potential and applied current density for AA2024T3 alloy in the de-aerated condition were established. The curves in the aerated condition showed no particular incubation time-applied current density relationship.

    • Adsorption of strontium (II) metal ions using phosphonate-functionalized polymer

      S M BHOSLE S PONRATHNAM S S TAMBE N N CHAVAN

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      Diethyl[3-(methoxydimethylsilyl)propyl]phosphonate (DMPP) polymer was synthesized for the strontium (II) metal ion recovery using diethylallylphosphonate as staring material. Diethylallylphosphonate was reactedwith poly(methylhydro)siloxane (MW 1900–2000 g mol$^{−1}$) in the presence of Speier’s catalyst. The synthesized monomer was characterized by IR, ${}^1$H NMR, ${}^{13}$C NMR and FT-IR spectroscopy techniques, and the synthesizedpolymers were characterized by IR and NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis and solubility. The synthesized polymer was used for sequestering strontium metal from the aqueous solution. The metal binding was examined by the energy dispersive spectroscopy and scanning electron microscopy for the adsorbed Sr(II). Batch adsorption studies were performed by varying three parameters, namely initial pH, adsorbentdose and the contact time. The reaction kinetics was determined by the Langmuir, Freundlich, and pseudo-firstand second-order models. Results of this study indicate that the synthesized polymer DMPP has been effective inremoving Sr(II) from the aqueous solution.

    • Synthesis, characterization and gas sensing performance of aluminosilicate azide cancrinite

      A V BORHADE T A KSHIRSAGAR S G WAKCHAURE A G DHOLI

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      The present investigation deals with synthesis and gas sensing performance of Na$_8$[AlSiO$_4$]$_6$(N$_3$)$_{2.4}$(H$_2$O)$_{4.6}$ cancrinite-based thick film. The product obtained was characterized by Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscope, thermogravimetric analysis and magic-angle spin nuclear magneticresonance (MAS NMR). The crystal structure of the product was determined from X-ray powder diffraction data by applying Rietveld refinement. Refinement showed that azide cancrinite crystallize in the space group P6$_3$. Alternate arrangement of Si and Al atoms was confirmed by single intense peak of MAS NMR analysis. For the first time, this study reports the gas sensing performance of aluminosilicate azide cancrinite. The effect of annealing andoperating temperature on gas sensing characteristic of azide cancrinite thick film is investigated systematically for various gases at different operating temperatures. This sensor was observed to be highly sensitive and selective toammonia gas.

    • Synthesis and characterization of multicolour fluorescent nanoparticles for latent fingerprint detection

      G A SOBRAL Jr M A GOMES Z S MACEDO M A R C ALENCAR S M V NOVAIS

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      In this study, we successfully developed Y$_2$O$_3$ nanoparticles doped with Tb$^{3+}$ and Eu$^{3+}$ ions to generate fluorescent images of latent fingerprints. The optical and structural characterization of the nanoparticles was carried out and the fluorescence mechanisms are discussed. In our studies, the developed nanoparticles were effective in producing fluorescent images of latent fingerprints in shades of green, red and yellow with high-contrast colour under ultraviolet lighting.

    • Synthesis, structure and spectroscopic characteristics of Ti(O,C)$_2$/carbon nanostructured globules with visible light photocatalytic activity

      V N KRASIL’NIKOV E V SHALAEVA I V BAKLANOVA M A MELKOZEROVA M V KUZNETSOV E V ZABOLOTSKAYA O I GYRDASOVA L YU BULDAKOVA A M MURZAKAEV

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      A morphology-controlled facile synthesis of titanium-glycolate precursors with subsequent annealing in He and air atmospheres has been exploited for the production of nanostructured composite globules, whiskers and plates of C-modified titanium dioxide. Characterisation tests proved the as-obtained globule composites to exclusively exhibit high-specific surface area (up to 150–170 m$^2$ g$^{−1}$), thus being useful for photocatalytic applications inthe visible-light region. The combination of the electron paramagnetic resonance, X-ray photoelectron spectroscopy, absorption spectroscopy and transmission electron microscopy revealed the presence of three kinds of carbon in the globules: a small bandgap (with measured width of 0.8 eV) amorphous carbon surrounding the anatase nanocrystallites,C-containing radicals including carbonates on the surface of TiO$_2$ and interstitial carbon in the oxygen position of the TiO$_2$ lattice. It was found that the maximum visible-light photocatalytic activity of the globules is determinedby the optimal surface concentration of amorphous carbon of about 0.002 wt.% m$^{−2}$. Under these conditions, the highest synergic photosensitising effect on TiO$_2$ nanocrystallites of all three kinds of carbon is expected.

    • Structural, elastic, electronic and optical properties of bi-alkali antimonides

      G MURTAZA MAZHAR ULLAH NAEEM ULLAH MALIKA RANI M MUZAMMIL R KHENATA SHAHID M RAMAY UMAIR KHAN

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      The structural parameters, elastic constants, electronic and optical properties of the bi-alkali antimonides (Na$_2$KSb, Na$_2$RbSb, Na$_2$CsSb, K$_2$RbSb, K$_2$CsSb and Rb$_2$CsSb) were calculated using state-of-the-art density functional theory. Different exchange-correlation potentials were adopted to predict the physical properties of these compounds. The calculated structural parameters are found in good agreement with the available experimental and theoretical results. All the compounds are mechanically stable. The compounds Na$_2$KSb, K$_2$RbSb, K$_2$CsSb and Rb$_2$CsSb have direct bandgaps, in which chemical bonding among the cations and anions is mainly ionic. Furthermore, the optical properties of these compounds are described in detail in terms of the dielectric function, refractive index, reflectivity, optical conductivity and absorption coefficient.

    • Electromagnetic properties of nanocrystalline Al$^{3+}$ substituted MgCuMn ferrites synthesized by microwave hydrothermal method

      T RAMESH S R MURTHY

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      The effect of Al$^{3+}$ substitution on electromagnetic properties has been studied for nanocrystalline Mg$_{0.8}$Cu$_{0.2}Mn$_{0.05}$Al$_x$Fe$_{1.95−x}$O$_4$ ferrites, wherein $x$ varies from 0 to 0.4 in steps of 0.1. These ferrites were synthesizedby using microwave hydrothermal method and then characterized using X-ray diffractometer (XRD), Fourier transform infrared and transmission electron microscopy. The synthesized powders were densified using microwavesintering method at 950◦C/50 min. Structural and surface morphology of sintered samples were characterized using XRD and atomic force microscopy, respectively. The complex permittivity and permeability properties were measuredover a frequency range 100 Hz–1.8 GHz. The temperature variation of magnetic properties were measured in the temperature range of 300–650 K. The electrical and magnetization studies inferred that the values of d.c. resistivity increases by 27%, whereas saturation magnetization decreases linearly from 38.6 to 23.0 emu g$^{−1}$ and Curie temperature was found to be decreased from 628 to 513 K with an increase of Al$^{3+}$ ions. The low dielectric, magnetic losses, moderate saturation magnetization and high-temperature stability properties exhibited by Al$^{3+}$ substituted MgCuMn ferrites make them find applications in microwave devices, such as circulators and isolators etc. The applicability of present samples formicrowave devices has been tested by the measurement of ferromagnetic resonance linewidth at K$_a$ band.

    • Electrochemical properties of dip-coated vanadium pentaoxide thin films

      R S INGOLE B J LOKHANDE

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      Vanadium oxide (V$_2$O$_5$) thin films have been deposited on to the stainless-steel substrates by simple dip-coating technique using vanadium pentaoxide as an initial ingredient. Deposited samples were annealed at773 K for 3 h in air. X-ray diffraction analysis of the sample shows crystalline with orthorhombic crystal structure. Scanning electron microscopy study depicts the homogeneous and dense surface morphology. Optical study provesthe direct bandgap transition with energy $\sim$2.25 eV. Electrochemical performance of the deposited electrode was studied in 1 M NaNO$_3$ electrolyte using cyclic voltammetery, electrochemical impedance spectroscopy and galvanostatic charge–discharge tests. Prepared V$_2$O$_5$ electrode shows 207.50 F g$^{−1}$ specific capacitance at the scan rate 5 mV s$^{−1}$, specific energy, specific power and efficiency are 41.33 Whkg$^{−1}$, 21 kW kg$^{−1}$ and 96.72%, respectively. The internal resistance observed from impedance spectroscopy is $\sim$8.77 ohm. Electrode exhibits excellent chemicalstability up to 1000 cycles.

    • Morphology, thermal stability and thermal degradation kinetics of cellulose-modified urea–formaldehyde resin

      M A ARSHAD A MAAROUFI G PINTO S EL-BARKANY A ELIDRISSI

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      This article reports a study on the structural characterization and evaluation of thermal degradation kinetics of urea–formaldehyde resin modified with cellulose, known as UFC resin. Structural characterization of UFC undertaken by scanning electron microscopy, Fourier transform infrared and X-ray diffractionanalyses reveals that the resin is fairly homogenous, and it constitutes of partly crystalline structure including urea–formaldehyde/cellulose interface morphology different from UFC precursors. Measurement of inherent thermal stability, probing reaction complexity and the thermal degradation kinetic analysis of UFC have been carried out by thermogravimetric/differential thermal analyses (TGA/DTA) under non-isothermal conditions. The integral proceduredecomposition temperature elucidates significant thermal stability of UFC. TGA/DTA analyses suggest highly complicated reaction profile for thermal degradation of UFC, comprising various parallel/consecutive reactions.Different differential and integral isoconversional methods have been employed to determine the thermal degradation activation energy of UFC. Substantial variation in activation energy with the advancement of reaction verifiesmulti-step reaction pathway of UFC. A plausible interpretation of the obtained kinetic parameters of UFC thermal degradation with regard to their physical meanings is given and discussed in this study.

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