Showing papers in "Materials Science and Engineering B-advanced Functional Solid-state Materials in 2013"

Hydrothermal synthesis of carbon nanotube/cubic Fe3O4 nanocomposite for enhanced performance supercapacitor electrode material

Abstract: Carbon nanotube/Fe3O4 (CNT/Fe3O4) nanocomposite with well-dispersed Fe3O4 nano-cubes inlaid on the surfaces of carbon nanotubes, was synthesized through an easy and efficient hydrothermal method. The electrochemical behaviors of the nanocomposite were analyzed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry in 6 M KOH electrolyte. Results demonstrated that CNT as the supporting material could significantly improve the supercapacitor (SC) performance of the CNT/Fe3O4 composite. Comparing with pure Fe3O4, the resulting composite exhibited improved specific capacitances of 117.2 F/g at 10 mA/cm2 (3 times than that of pure Fe3O4), excellent cyclic stability and a maximum energy density of 16.2 Wh/kg. The much improved electrochemical performances could be attributed to the good conductivity of CNTs as well as the anchored Fe3O4 particles on the CNTs.

Magnetite–hematite nanoparticles prepared by green methods for heavy metal ions removal from water

Abstract: Mixed magnetite–hematite nanoparticles were synthesized via different routes such as, coprecipitation in air and N 2 atmosphere, citrate–nitrate, glycine–nitrate and microwave-assisted citrate methods. The prepared samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscope (HRTEM), BET measurements and magnetic hysteresis. XRD data showed the formation of magnetite–hematite mixture with different compositions according to the synthesis method. The particle size was in the range of 4–52 nm for all the prepared samples. From HRTEM micrographs, it was found that, the synthesis method affects the moropholgy of the prepared samples in terms of crystallinity and porosity. The magnetite–hematite mixture was employed as a sorbent material for removal of some heavy metal ions from water such as lead(II), cadmium(II) and chromium(III). The effects of pH value and the contact time on the adsorption process were studied and optimized in order to obtain the highest possible adsorption efficiency of the magnetite–hematite mixture. The effect of the synthesis method of the magnetite–hematite mixture on the adsorption process was also investigated. It was found that samples prepared by the coprecipitation method had better adsorption efficiency than those prepared by other combustion methods.

Fe3O4/carbon composite nanofiber absorber with enhanced microwave absorption performance

Abstract: Fe3O4/carbon composite nanofibers were prepared by electrospinning polyacrylonitrile (PAN)/acetyl acetone iron (AAI)/dimethyl formamide (DMF) solution, followed by stabilization and carbonization. SEM and TEM observations reveal that the fibers are lengthy and uniform, and are loaded with well-distributed Fe3O4 nanoparticles, which are evidenced by XRD. Electrical and magnetic properties of the samples were studied to show the effect of enhancement of electrical conductivity and magnetic hysteresis performance. Finally, the permittivity and permeability parameters were measured by a vector network analyzer, and the reflectivity loss was calculated based on Transmission Line Theory. Results show that Fe3O4/C composite nanofibers exhibit enhanced properties of microwave absorption as compared to those of pure carbon nanofibers by: decreasing reflectivity loss values; widening absorption width and improving performance in low frequency (2–5 GHz) absorption. Absorption properties can be tuned by changing AAI content, carbonization temperature, composite fiber/paraffin ratio and coating thickness. It is shown that with coating thickness of 5 mm and fiber/paraffin ratio of 5 wt.%, the bandwidth for reflection loss under −5 dB can reach a maximum of 12–13 GHz in the range of 2–18 GHz, accompanying with a minimum reflection loss of −40 to −45 dB, and preferred low frequency band absorption can also be obtained. The mechanisms for the enhanced absorption performance were briefly discussed. It is supposed that this kind of composite material is promising for resolving the problems of weak absorption in the low frequency range and narrow bandwidth absorption.

Electrochemical capacitance performance of titanium nitride nanoarray

Abstract: In this study, titanium nitride (TiN) nanoarrays with a short nanotube and long nanopore structure have been prepared by an anodization process of ultra thin titanium foil in ethylene glycol (EG) solution containing ammonium fluoride, subsequent calcination process in an air atmosphere, and final nitridation process in an ammonia atmosphere. The morphology and microstructure characterization has been conducted using field emission scanning electron microscope and X-ray diffraction. The electrochemical properties have been investigated through cyclic voltammetry and electrochemical impedance spectrum measurements. The electrochemical capacitance performance has been investigated by galvanostatic charge–discharge measurements in the acidic, neural and alkali electrolyte solution. Well-defined TiN nanoarrays contribute a much higher capacitance performance than titania (TiO2) in the supercapacitor application due to the extraordinarily improved electrical conductivity. Such an electrochemical capacitance can be further enhanced by increasing aspect ratio of TiN nanoarray from short nanotubes to long nanopores. A flexible supercapacitor has been constructed using two symmetrical TiN nanoarray electrodes and a polyvinyl alcohol (PVA) gel electrolyte with H2SO4–KCl–H2O–EG. Such a supercapacitor has a highly improved potential window and still keeps good electrochemical energy storage. TiN nanoarray with a high aspect ratio can act well as an ultra thin film electrode material of flexible supercapacitor to contribute a superior capacitance performance.

Three-dimensional graphene/polyaniline composite material for high-performance supercapacitor applications

Abstract: A novel three-dimensional (3D) graphene/polyaniline nanocomposite material which is synthesized using in situ polymerization of aniline monomer on the graphene surface is reported as an electrode for supercapacitors. The morphology and structure of the material are characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD). The electrochemical properties of the resulting materials are systematically studied using cyclic voltammetry (CV) and constant current charge-discharge tests. A high gravimetric capacitance of 463 Fg(-1) at a scan rate of 1 mVs(-1) is obtained by means of CVs with 3 mol L-1 KOH as the electrolyte. In addition, the composite material shows only 9.4% capacity loss after 500 cycles, indicating better cyclic stability for supercapacitor applications. The high specific surface area, large mesopore volume and three-dimensional nanoporous structure of 3D graphene could contribute to the high specific capacitance and good cyclic life. (C) 2012 Elsevier B.V. All rights reserved.

Synthesis and luminescent properties of LaPO4:Eu3+ microspheres

Abstract: LaPO4:Eu3+ microspheres were synthesized, using LaCl3, EuCl3 and (NH4)2HPO4 as starting materials. The morphology, formation mechanism, and luminescent property of samples were systemically studied. X-ray diffraction (XRD) and infrared spectroscopy (IR) show that LaPO4:Eu3+ microspheres have a pure monoclinic phase. Cetyltrimethyl ammonium bromide (CTAB) usually forms spherical micelles above a critical micelle concentration, which plays an important role in the formation of LaPO4:Eu3+ microspheres. The excitation spectrum of LaPO4:Eu3+ microspheres consists of several sharp lines due to the direct excitation of the Eu3+ cations from the ground state to higher levels of the 4f-manifold. The emission intensity of microspheres is higher than irregular particles because of the lowlier surface area. The lifetimes of Eu3+ ions in the LaPO4:Eu3+ microspheres are determined to be 2.41 ms.

Studies on polymer electrolyte poly(vinyl) pyrrolidone (PVP) complexed with ionic liquid: Effect of complexation on thermal stability, conductivity and relaxation behaviour

Abstract: Polymer electrolyte films of PVP + x wt% ionic liquid (IL) (1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF 4 ]) for x = 0, 5, 10, 15, 20, 25 wt% have been prepared using solution cast technique. These films were characterized by TGA, DSC, FT-IR and ac impedance spectroscopy techniques. From XRD studies it is found that the inclusion of IL increases the amorphocity of polymeric membranes. DSC thermograms show that the glass transition ( T g ) and melting temperatures ( T m ) of PVP shift upon complexation with IL. FT-IR analysis shows the complexation of PVP with IL. Thermogravimetric studies show that PVP decomposes in a single step while PVP/IL membranes exhibit two step decomposition; lower value of decomposition temperature corresponds to the decomposition of PVP/IL complex while the higher decomposition temperature has been attributed to the decomposition of PVP. The decomposition temperature of PVP/IL complex decreases with the increasing amount of IL in the PVP membrane. Temperature dependence of conductivity and dielectric relaxation frequencies have also been studied for PVP and PVP/IL membranes. Both show thermally activated Arrhenius behaviour.

Synthesis, characterization and photocatalytic activity of ZnO-SnO2 nanocomposites

Abstract: Nanocomposites of coupled ZnO-SnO2 photocatalysts were synthesized by the coprecipitation method and were characterized by X-ray diffraction, UV–vis diffuse reflectance spectroscopy, surface area analyzer and scanning electron microscopy. Their photocatalytic activity was investigated under UV, visible and solar light and evaluated using methylene blue (MB) as a model pollutant. The performance of the coupled ZnO-SnO2 photocatalysts was found to be related to the Zn/Sn molar ratio and to the calcination conditions. The photocatalyst with a Zn/Sn molar ratio of 1:0.05 calcined at 600 °C for 2 h showed the maximum degradation rate of MB under different lights used. Its photocatalytic activity was found to be about two times that of ZnO and about 10 times that of SnO2 which can be explained by the heterojunction effect. Charge separation mechanism has been studied.

Photoreduction of Cr(VI) in water using Bi2O3–ZrO2 nanocomposite under visible light irradiation

Abstract: Chromium(VI) is a common heavy metal pollutant and extensively used in variety of industrial processes. In the present study, bismuth oxide–zirconium oxide nanocomposite (Bi 2 O 3 –ZrO 2 ) was synthesized to improve photoreduction of Cr(VI) under visible light irradiation. The synthesized photocatalyst was characterized by UV-visible-diffuse reflectance spectroscopy (UV-vis-DRS), X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), Brunauer–Emmett–Teller (B.E.T) surface area analysis and photoluminescence spectroscopy (PL). Bi 2 O 3 –ZrO 2 was found to be more photoactive than Bi 2 O 3 , ZrO 2 , TiO 2 and ZnO for the reduction of Cr (VI). The influences of various reaction parameters like the effect of catalyst concentration, initial Cr(VI) concentration and addition of inorganic salts on the photocatalytic activity have been investigated in detail. Meanwhile, the stability of Bi 2 O 3 –ZrO 2 was investigated by repeatedly performing Cr(VI) photoreducing experiments.

Poly(vinyl alcohol)/poly(acrylic acid)/TiO2/graphene oxide nanocomposite hydrogels for pH-sensitive photocatalytic degradation of organic pollutants

Abstract: Poly(vinyl alcohol)/poly(acrylic acid)/TiO 2 /graphene oxide nanocomposite hydrogels were prepared using radical polymerization and condensation reaction for the photocatalytic treatment of waste water. Graphene oxide was used as an additive to improve the photocatalytic activity of poly(vinyl alcohol)/poly(acrylic acid)/TiO 2 nanocomposite hydrogels. Both TiO 2 and graphene oxide were immobilized in poly(vinyl alcohol)/poly(acrylic acid) hydrogel matrix for an easier recovery after the waste water treatment. The photocatalytic activity of poly(vinyl alcohol)/poly(acrylic acid)/TiO 2 /graphene oxide nanocomposite hydrogels was evaluated on the base of the degradation of pollutants by using UV spectrometer. The improved removal of pollutants was due to the two-step mechanism based on the adsorption of pollutants by nanocomposite hydrogel and the effective decomposition of pollutants by TiO 2 and graphene oxide. The highest swelling of nanocomposite hydrogel was observed at pH 10 indicating that poly(vinyl alcohol)/poly(acrylic acid)/TiO 2 /graphene oxide nanocomposite hydrogels were suitable as a promising system for the treatment of basic waste water.

Studies on the structure and gas sensing properties of nickel-cobalt ferrite thin films prepared by spin coating

Abstract: The influence of Co2+ ions content on structure and sensing properties of Ni1−xCoxFe2O4 (x = 0.25, 0.5, 0.75) thin films deposited on glass substrates by spin coating is presented. Structural characterization evidenced thin films with cubic spinel structures and morphologies dependent on cobalt content. Repartition of cations in spinel tetrahedral and octahedral sites was determined and was found that the presence of Co2+ ions in octahedral sites favor the formation of Fe2+ species. The sensitivity to some reducing vapor gases (acetone, liquefied petroleum gas LPG, ethyl alcohol and methyl alcohol) was investigated and was found that thin films with x = 0.75 exhibit high sensitivity to ethyl alcohol and thin films with x = 0.25 have high sensitivity to acetone. This sensitivity largely depends on the temperature and test gas concentration and was related to the Fe2+ species formed in octahedral sites.

Effects of ZnNb2O6 addition on BaTiO3 ceramics for energy storage

Abstract: a b s t r a c t BaTiO3 ceramics were prepared using solid state reaction with addition of ZnNb2O6, to investigate the effects of ZnNb2O6 addition on structure and properties. The results show that the ZnNb2O6 addition lowers sintering temperature, decreases grain size, while introduces second phase (Ba2Ti5O12) for x ≥ 7.26 wt%. The dielectric breakdown strength is enhanced with the increasing doping level of ZnNb2O6 and reaches a maximum value at x = 7.26 wt%, exhibiting a maximum energy storage capability.

Hydrogen in porous silicon — A review

Abstract: a b s t r a c t This review is devoted to summarising the hydrogen-assisted properties and applications of porous silicon (PS) The role of hydrogen as an intermediate product in silicon porosification technology is accentuated The regularities of hydrogen bonding in PS and its applications for hydrogen storage are listed The models of hydrogen influence on luminescence and electrical properties of PS are analysed The corresponding applications of PS for H2 gas sensors and pH metres are illustrated Hydrogen-assisted explosion and grafting of PS are discussed Such a review can be useful for the tailoring of PS properties

Structural, morphological and electrical properties of Cr2O3 nanoparticles

Abstract: Chromium oxide (Cr 2 O 3 ) nanoparticles have been prepared by chemical precipitation followed by calcination at high temperatures. The influence of calcination temperature on the particle size, microstructure, surface area and morphology was examined by X-ray diffraction, Fourier transform infrared, N 2 adsorption–desorption isotherms, transmission electron microscopy and thermal analysis techniques. The results indicate the formation of a nanosized single Cr 2 O 3 phase. The particles possess high specific surface area and mesoporous structure, and their sizes increase with increasing the calcinations temperature. DC conductivity was measured in the temperatures range of 170–475 K. For the high temperature region, the conduction was found to be due to small polaron hopping of holes. While for the low temperatures region, the conduction was attributed to variable range hopping mechanism of holes. The temperature dependence of the AC conductivity and dielectric constant was investigated in the same temperature range at four test frequencies. In addition, the impedance spectra of these nanoparticles were investigated only at temperatures above 350 K.

Effect of ball milling and moderate surface oxidization on the microwave absorption properties of FeSiAl composites

Abstract: Commercially available irregular FeSiAl alloys were used as raw materials. The microwave absorption properties of FeSiAl/paraffin composites were improved by ball milling the alloys and moderately oxidizing their surfaces. Permittivity and permeability of the as-milled composites distinctly increased compared with those before milling. Moderate surface oxidization significantly reduced permittivity whereas permeability almost maintained its initial value compared with those of as-milled composites. Consequently, the microwave absorption properties were significantly improved. The minimum reflection loss (RL) of the absorber with 35 vol% surface-oxidated flake reached −39.67 dB at 1.40 GHz at a thickness of 4 mm. Effective microwave absorption (RL

Ce–Nd codoping effect on the structural and optical properties of TiO2 nanoparticles

Abstract: We report the changes in the structural and optical property of TiO 2 nanoparticles on codoping Ce–Nd ions. X-ray diffraction clearly demonstrates the structural changes occurring in the codoped TiO 2 nanoparticle. Oxygen defects disturb the Ti O bonds in the TiO 6 octahedra and result in the shifting and broadening of the Raman E g peak. Pure TiO 2 nanoparticles show absorption peak in the UV region. However, codoped TiO 2 nanoparticles exhibit absorption peaks in the visible region corresponding to the f–d and f–f electronic transition of Ce 3+ and Nd 3+ in the crystalline environment of TiO 2 . The visible emission peaks of pure and codoped TiO 2 nanoparticles are mainly associated with oxygen vacancies. Incorporation of cerium intensifies the visible emission peaks of TiO 2 nanoparticles. On the other hand, codoping of Nd forms some non radiative recombination centres and increases the possibility of emission energy transfer among dopants, defects, thereby quenching the intensity of the visible emission peaks.

Photoluminescence and thermoluminescence studies of Tb3+ doped ZnO nanorods

Abstract: Here in, the synthesis of the terbium doped zinc oxide (ZnO:Tb3+) nanorods via room temperature chemical co-precipitation was explored and their structural, photoluminescence (PL) and thermoluminescence (TL) studies were investigated in detail. The present samples were found to have pure hexagonal wurtzite crystal structure. The as obtained samples were broadly composed of nanoflakes while the highly crystalline nanorods have been formed due to low temperature annealing of the as synthesized samples. The diameters of the nanoflakes are found to be in the range 50–60 nm whereas the nanorods have diameter 60–90 nm and length 700–900 nm. FTIR study shows Zn O stretching band at 475 cm−1 showing improved crystal quality with annealing. The bands at 1545 and 1431 cm−1 are attributed to asymmetric and symmetric C O stretching vibration modes. The diffuse reflectance spectra show band edge emission near 390 nm and a blue shift of the absorption edge with higher concentration of Tb doping. The PL spectra of the Tb3+-doped sample exhibited bright bluish green and green emissions at 490 nm (5D4 → 7F6) and 544 nm (5D4 → 7F5) respectively which is much more intense then the blue (450 nm), bluish green (472 nm) and broad green emission (532 nm) for the undoped sample. An efficient energy transfer process from ZnO host to Tb3+ is observed in PL emission and excitation spectra of Tb3+-doped ZnO ions. The doped sample exhibits a strong TL glow peak at 255 °C compared to the prominent glow peak at 190 °C for the undoped sample. The higher temperature peaks are found to obey first order kinetics whereas the lower temperature peaks obey 2nd order kinetics. The glow peak at 255 °C for the Tb3+ doped sample has an activation energy 0.98 eV and frequency factor 2.77 × 108 s−1.

Structural, optical and ferromagnetic properties of Cr doped TiO2 nanoparticles

Abstract: Cr doped TiO 2 nanoparticles are prepared with three different concentrations of chromium, 1.5%, 3.0% and 4.5 mol% respectively. Doping decreases the crystallinity and increases the width of the X-ray diffraction peak. The Raman active E g peak of TiO 2 nanoparticles become asymmetric and shifted to higher energy on doping of 4.5% chromium. Electron paramagnetic resonance spectra reveal the presence of Cr 3+ in the host TiO 2 matrix. The absorption spectra of Cr doped TiO 2 nanoparticles contain absorption peaks corresponding to d – d transition of Cr 3+ in octahedral coordination. Most of the visible emission peaks are due to the electrons trapped in the oxygen vacancy centers. Undoped TiO 2 nanoparticles show diamagnetism at room temperature while all chromium doped samples show ferromagnetism. The magnetization of the doped samples increases at 1.5% and 3.0% and decreases at 4.5%. The ferromagnetism arises owing to the interaction of the neighboring Cr 3+ ions via oxygen vacancies. The decrease of magnetization at the highest doping is possibly due to the antiferromagnetic interactions of Cr 3+ pairs or due to Cr 3+ O 2− Cr 3+ superexchange interaction in the lattice.

Silsesquioxane-based hybrid nanocomposites with methacrylate units containing titania and/or silver nanoparticles as antibacterial/antifungal coatings for monumental stones

Abstract: The present paper reports on the evaluation of two silsesquioxane-based hybrid nanocomposites with methacrylate units containing titania and/or silver nanoparticles aimed as antibacterial coatings for monumental stones. Sol–gel reaction of titanium isopropoxide and/or 3-(trimethoxysilyl)propyl methacrylate, in the presence of silver nitrate and a primary amine surfactant, yielded new types of hybrid nanocomposites with high antibacterial/antifungal efficacy. Different polymer behaviours regarding a frequently used monumental stone originating from Romania were evidenced through Fourier-transform infrared (FTIR) spectroscopy and powder X-ray diffraction (PXRD) technique. Conclusions regarding the stones acid-resistant character and lower influence of salt weathering on its durability, as well as a better protective coating containing titania units were revealed.

Electrical and luminescence properties of Er-doped Bi0.5Na0.5TiO3 ceramics

Abstract: The influences of Er content on the dielectric and photoluminescence performances of Bi0.5Na0.5TiO3-xEr (x = 0, 0.005, 0.01, 0.015, 0.02, 0.03) ceramics have been investigated. The results show that Bi0.5Na0.5TiO3-xEr ceramics with x = 0.01 Er have maximum values of photoluminescence and piezoelectric properties. A bright green emission at 550 nm and enhanced piezoelectric response are achieved in the ceramic Bi0.5Na0.5TiO3-0.01Er at room temperature. Furthermore, the photoluminescence performance of the ceramics is significantly enhanced by electric poling.

Silicon heterojunction solar cells: Optimization of emitter and contact properties from analytical calculation and numerical simulation

Abstract: The key constituent of silicon heterojunction solar cells, the amorphous silicon/crystalline silicon heterojunction (a-Si:H/c-Si), offers a high open-circuit voltage (Voc) potential providing that both the interface defect passivation and the band bending in the c-Si absorber are sufficient. We detail here analytical calculations of the equilibrium band bending in c-Si (ψc-Si) in Transparent Conductive Oxide (TCO)/a-Si:H emitter/c-Si absorber structures. We studied the variation of some electronic parameters (density of states, work function) according to relevant experimental values. This study introduces a discussion on the optimization of the doped emitter layer in relation with the work function of the TCO. In particular, we argue on the advantage of having a highly defective (p)a-Si:H emitter layer that maximizes ψc-Si and reduces the influence of the TCO on Voc.

Magnetic and dielectric properties of Co–Zn ferrite

Abstract: Nanocrystalline powders of Co substituted Zn ferrite with the chemical formula CoxZn1−xFe2O4 (x = 0, 0.2, 0.4, 0.6, 0.8, 1) were synthesized by sol–gel autocombustion method using tartaric acid as fuel agent. The samples were sintered in static air atmosphere for 7 h at 773 K, 7 h at 973 K and 10 h at 1173 K. The organic phase extinction and the spinel phase formation were monitored by means of Fourier transform infrared spectroscopy. The X-ray diffraction patterns analysis confirmed the spinel single phase accomplishment. Crystallite size, average grains size, lattice parameter and cation distribution were estimated. Magnetic behavior of the as-obtained samples by means of M-H hysteresis measurements was studied at room temperature. Permeability and dielectric permittivity at room temperature versus frequency was the subject of a comparative study for the CoxZn1−xFe2O4 series. In agreement with the proposed cation distribution the sample with Co0.8Zn0.2Fe2O4 formula exhibits the optimal magnetic and dielectric properties.

Synthesis, characterization and photoresponse study of undoped and transition metal (Co, Ni, Mn) doped ZnO thin films

Abstract: The synthesis, characterization and photoresponse studies of undoped and transition metal doped zinc oxide thin films are carried out in this work, in prospect of visible light photo detection and sensor applications. The undoped and transition metal ions such as, Co, Ni and Mn doped ZnO films in this study were synthesized by chemical solution deposition, involving spin-coating. We have characterized the deposited films using X-ray diffraction, scanning electron microscopy, photoluminescence and UV–vis spectroscopy studies. The devices of the films for photoresponse study were fabricated by top Ag contacts on the film surface in metal–semiconductor–metal configuration. The current–voltage characteristics and switching measurements of these devices were studied under the illumination of an incandescent lamp. We found a high ON/OFF ratio of 8 and highest photocurrent density of 0.7 mA/cm 2 for Ni doped ZnO film.

Synthesis and characterization of Ag/TiO2-B nanosquares with high photocatalytic activity under visible light irradiation

Abstract: Square-like B doped TiO2 nanocrystals were first synthesized by a mild solvothermal method with H3BO4 and titanium isopropoxide as the precursors, and isopropyl alcohol as reaction medium. Then, Ag nanoparticles were deposited on TiO2-B nanosquares by photo-deposition. The as-synthesized products have been investigated by photocatalytic reaction test and characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV–vis diffuse reflectance spectra (DRS). The results showed that boron was successfully doped into TiO2 nanosquares under solvothermal condition. The obtained Ag/TiO2-B composite showed high efficiency in degradation of acid orange II under visible light irradiation. The high photocatalytic performance could be attributed to the synergistic effect of B doping and the plasmon photocatalysis role of the deposited silver nanoparticles over TiO2.

Enhanced photodegradation activity of Rhodamine B by Co3O4/Ag3VO4 under visible light irriadiation

Abstract: Co 3 O 4 /Ag 3 VO 4 composite photocatalysts were synthesized by the wetness impregnation method and characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance spectroscopy (DRS). The photoactivity testing result shows that the Co 3 O 4 /Ag 3 VO 4 composite exhibits enhanced photodegradation activity for Rhodamine B (RhB) under visible-light irradiation. The Co 3 O 4 content and calcination temperature have a significant impact on the photocatalytic activities of the samples. The highest efficiency was observed on the 1.0 wt.% Co 3 O 4 /Ag 3 VO 4 sample calcined at 653 K. Moreover, the photoelectrochemical performance with the method of transient photocurrent–time was investigated. Based on the results of the characterizations, the mechanism of enhanced photocatalytic activity is discussed.

Luminescent and scintillation properties of orthotantalates with common formulae RETaO4 (RE = Y, Sc, La, Lu and Gd)

Abstract: Samples of undoped and Ce-, Eu- and Pr-doped orthotantalates with common formulae RETaO 4 (RE = Y, Sc, La, Lu and Gd) have been obtained by solid-state reaction. Optical and luminescent characteristics in visible and UV bands have been explored. The most intense light output is determined for GdTaO 4 , YTaO 4 , and LuTaO 4 (for GdTaO 4 it is 111% compared to BGO). Among lanthanide-doped samples, the highest light output is achieved with Eu-doped YTaO 4 , GdTaO 4 and LuTaO 4 (up to 136% compared to BGO). Undoped rare-earth tantalates may be considered as promising materials for high energy physics due to extremely high density, substantial light output, and fast decay. Eu 3+ -doped orthotantalates are the brightest among the studied samples for X-ray radiography, or other application where slow decay is acceptable.

Producing CuO and ZnO composite thin films using the spin coating method on microscope glasses

Abstract: In this work, we have presented a new route to produce pure ZnO and composite ZnO-CuO thin films. In the process we have started with pure ZnO thin films and ended up with CuO by doping Cu in various percentages, ranging from 0% to 100%. We have managed to attain crystal phases in all doping concentrations. All the produced thin films have been crystallized at the annealing temperatures of 600 and 700 °C for 6 h. The X-ray diffraction (XRD) spectra have been performed to see the formation of crystal phases of all pure ZnO and composite ZnO-CuO thin films. These give insight that the two crystal phases related to ZnO and CuO stayed together within the thin film matrices, which were produced in different doping concentrations, i.e. n ZnO + m CuO (0 ≤ n , m ≤ 100%). The scanning electron microscopy (SEM) micrographs and UV–vis absorption spectra have also been taken to elucidate the structure and composition of the all films.

Band bending at free Pb(Zr,Ti)O3 surfaces analyzed by X-ray photoelectron spectroscopy

Abstract: This paper analyses in detail the core levels evolution of Pb(Zr,Ti)O 3 , i.e. Pb 4f, Zr 3d, Ti 2p, O 1s in various conditions: absolutely freshly prepared sample, sample stored under air, and the effects of in vacuum annealing. The aim of the study is to quantify separately the chemical reactivity at the surface and the band bending effects due to the ferroelectric polarization. It is found that freshly prepared samples present mostly inwards (↓) polarization. This phenomenon is mostly revealed by the Ti 2p and O 1s spectra, manifested as a distinct component with 1.8 eV lower binding energy in the O 1s binding energy and by 1.1 eV in the Ti 2p binding energy. Sample aging under air suppresses the inwards polarization, and most signal comes from surfaces not presenting ferroelectric permanent polarization perpendicular to the sample surface. This process conducts also to the formation of Pb(CO 3 ) 2 on the surface. Annealing to temperatures up to 400 °C stabilizes a surface composed by a main part of surface without polarization perpendicular to the surface, and with some areas presenting outwards (↑) polarization. These areas have, most probably, different terminations, the polarized area being (Ti,Zr)O 2 terminated.

Structural, thermal and dielectric studies of polypyrrole nanotubes synthesized by reactive self degrade template method

Abstract: In this work we investigate the structural, thermal and dielectric properties of polypyrrole nanotubes synthesized by in situ chemical oxidative polymerization method. Cetyl trimethylammonium bromide (CTAB) modified Methyl Orange (MO)-FeCl 3 reactive self degrade template is used to support the growth of PPy nanotubes. The diameter of the tubes decreased with increase in CTAB concentration and found to be 140–52 nm. The synthesized polypyrrole nanotubes are investigated by high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), FTIR, UV–vis, conductivity measurements, TGA and impedance analysis. TGA analysis shows decrease in decomposition rate with decrease in tube diameter. The response of the charge carriers to the ac field is also carried out in the frequency range of 42 Hz–5 MHz. The shifting of peak towards higher frequency in imaginary modulus formalism with decrease in CTAB concentration suggests faster relaxation.

PPy/graphene nanosheets/rare earth ions: A new composite electrode material for supercapacitor

Abstract: Highly conductive PPy/graphene nanosheets/rare earth ions (PPy/GNS/RE3+) composites were prepared via in situ polymerization with p-toluenesulfonic acid as a dopant and FeCl3 as an oxidant. The effects of GNS and RE3+ on the electrical conductivity of the composites were investigated. The results showed that the GNS as a filler had effect on the conductivity of PPy/GNS/RE3+ composites, which played an important role in forming a conducting network in PPy matrix. The microstructures of GNS and PPy/GNS/RE3+ were characterized by the SEM and TEM examinations. It was found that GNS and PPy nanospheres formed a uniform composite with the PPy nanospheres absorbed on the GNS surface and/or filled between the GNS. Such uniform structure together with the observed high conductivities afforded high specific capacitance when used as supercapacitor electrodes. A specific capacitance of as high as 238 F/g at a current density of 1 A/g was achieved over the PPy/GNS/Eu3+ composite.