The effect of temperature on toluene sorption by granular activated carbon and its use in permeable reactive barriers in cold regions

Granular activated carbon (GAC) has been used as an adsorbent for hydrocarbons in a range of permeable reactive barriers. This work investigates the influence of temperature on adsorption performance. In particular, the influence of temperature in the range of 20 °C to 4 °C on the sorption equilibrium and kinetics of toluene on GAC surface were investigated. The results show that low temperature leads to decreased toluene sorption by GAC and slower reaction kinetics. Sorption kinetics studies show that diffusion coefficients are also lower at 4 °C (3.65 × 10⁻¹³ m² s⁻¹) than 20 °C (5.112 × 10⁻¹³ m² s⁻¹).     

Catalytic oxidation of carbon monoxide over radiolytically prepared Pt nanoparticles supported on glass

Platinum nanoparticles have been prepared by radiolytic and chemical methods in the presence of stabilizer gelatin and SiO₂ nanoparticles. The formation of Pt nanoparticles was confirmed using UV-vis absorption spectroscopy and transmission electron microscopy (TEM). The prepared particles were coated on the inner walls of the tubular pyrex reactor and tested for their catalytic activity for oxidation of CO. It was observed that Pt nanoparticles prepared in the presence of a stabilizer (gelatin) showed a higher tendency to adhere to the inner walls of the pyrex reactor as compared to that prepared in the presence of silica nanoparticles. The catalyst was found to be active at ≥150 °C giving CO₂. Chemically reduced Pt nanoparticles stabilized on silica nanoparticles gave ∼7% CO conversion per hour. However, radiolytically prepared Pt nanoparticles stabilized by gelatin gave ∼10% conversion per hour. Catalytic activity of radiolytically prepared platinum catalyst, coated on the inner walls of the reactor, was evaluated as a function of CO concentration and reaction temperature. The rate of reaction increased with increase in reaction temperature and the activation energy for the reaction was found to be ∼108.8 kJ mol⁻¹. The rate of CO₂ formation was almost constant (∼1.5 × 10⁻⁴ mol dm⁻³ h⁻¹) at constant O₂ concentration (6.5 × 10⁻³ mol dm⁻³) with increase in CO concentration from 2 × 10⁻⁴ mol dm⁻³ to 3.25 × 10⁻³ mol dm⁻³. The data indicate that catalytic oxidation of CO takes place by Eley-Rideal mechanism.     

Perchlorate removal in Fe0/H2O systems: Impact of oxygen availability and UV radiation

In this study, the removal of perchlorate (0.016 mM ) using Fe⁰-only (325 mesh, 10 g L⁻¹) and Fe⁰ (10 g L⁻¹) with UV (254 nm) reactions were investigated under oxic and anoxic conditions (nitrogen purging). Under anoxic conditions, only 2% and 5.6% of perchlorate was removed in Fe⁰-only and Fe⁰/UV reactions, respectively, in a 12 h period. However, under oxic conditions, perchlorate was removed completely in the Fe⁰-only reaction, and reduced by 40% in the Fe⁰/UV reaction, within 9 h. The pseudo-first-order rate constant (k₁) was 1.63 × 10⁻³ h⁻¹ in Fe⁰-only and 4.94 × 10⁻³ h⁻¹ in Fe⁰/UV reaction under anoxic conditions. Under oxic conditions, k₁ was 776.9 × 10⁻³ h⁻¹ in Fe⁰-only reaction and 35.1 × 10⁻³ h⁻¹ in the Fe⁰/UV reaction, respectively. The chlorine in perchlorate was recovered as chloride ion in Fe⁰-only and Fe⁰/UV reactions, but lower recovery of chloride under oxic conditions might due to the adsorption/co-precipitation of chloride ion with the iron oxides. The removal of perchlorate in Fe⁰/UV reaction under oxic conditions increased in the presence of methanol (73%, 9 h), a radical scavenger, indicating that OH radical can inhibit the removal of perchlorate. The removal of perchlorate by Fe⁰-only reaction under oxic condition was highest at neutral pH. Application of the Langmuir-Hinshelwood model indicated that removal of perchlorate was accelerated by adsorption/co-precipitation reactions onto iron oxides and subsequent removal of perchlorate during further oxidation of Fe⁰. The results imply that oxic conditions are essential for more efficient removal of perchlorate in Fe⁰/H₂O system.     

Chemical diffusion coefficient of lithium ion in Li3V2(PO4)3 cathode material

The kinetic properties of monoclinic lithium vanadium phosphate were investigated by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS) method. The PSCA results show that there exists a linear relationship between the current and the square root of the time. The D?_Li values of lithium ion in Li_3-xV₂(PO₄)₃ under various initial potentials of 3.41, 3.67, 3.91 and 4.07 V (vs Li/Li⁺) obtained from PSCA are 1.26 × 10^− 9, 2.38 × 10^− 9, 2.27 × 10^− 9 and 2.22 × 10^− 9 cm²·s^− 1, respectively. Over the measuring temperature range 15-65 °C, the diffusion coefficient increased from 2.67 × 10^− 8 cm²·s^− 1 (at 15 °C) to 1.80 × 10^− 7 cm²·s^− 1 (at 65 °C) as the measuring temperature increased.     

Contribution to carrier densities of the oxygen vacancy in a low-resistivity tin-doped indium oxide film by the hot-cathode plasma sputtering method

In order to clarify the contribution to carrier density by oxygen vacancies in tin-doped indium oxide (ITO) films prepared on glass substrates by the hot-cathode plasma sputtering method, we have investigated the effect of annealing on the electrical properties of an ITO film with a resistivity of 1.0 × 10^− 4 Ω cm. A drastic decrease in carrier density from 2.0 × 10²¹ to 0.88 × 10²¹ cm^− 3 was found with gradual increase in the Hall mobility from 29 to 35 cm² V^− 1 s^− 1 for repeated annealing cycles, when the ITO film was exposed for one hour to 400 °C oxygen gas at atmospheric pressure. The results indicate that the contribution of oxygen vacancies to carrier density was ca. 1.12 × 10²¹ cm^− 3 for the ITO film with an overall carrier density of 2.0 × 10²¹ cm^− 3.     

Deformation and strain rate sensitivity of a Zr-Cu-Fe-Al metallic glass

The deformation behaviour of Zr₆₅Cu₂₀Fe₅Al₁₀ bulk metallic glass has been studied at room temperature under uniaxial compression conditions at the strain rate of 5 × 10⁻⁴ s⁻¹ and performing jump tests for the strain rates (SR) ranging between 5 × 10⁻⁶ s⁻¹ and 5 × 10⁻² s⁻¹. The alloy always shows the formation of shear bands and exhibits serrated flow. In the SR range of 5 × 10⁻⁶ to 5 × 10⁻³ s⁻¹ absence of strain rate sensitivity within the experimental error is observed. However, when the SR changes from 5 × 10⁻³ s⁻¹ to 5 × 10⁻² s⁻¹ the alloy exhibits a negative strain rate sensitivity of −0.0026. The number of shear bands on the side view appears to be correlated with the range of stress softening from the maximum stress to the stress at which the sample fails.     

Transparent conducting Al and Y codoped ZnO thin film deposited by DC sputtering

Transparent conducting Al and Y codoped zinc oxide (AZOY) thin films with high transparency and low resistivity were deposited by DC magnetron sputtering. The effects of substrate temperature on the structural, electrical and optical properties of AZOY thin films deposited on glass substrates have been investigated. X-ray diffraction spectra indicate that no diffraction peak of Al₂O₃ or Y₂O₃ except that of ZnO (0 0 2) is observed. The AZOY thin film prepared at substrate temperature of 250 °C has the optimal crystal quality inferring from FWHM of ZnO (0 0 2) diffraction peak, but the AZOY thin film deposited at 300 °C has the lowest resistivity of 3.6 × 10⁻⁴ Ω-cm, the highest mobility of 30.7 cm² V⁻¹ s⁻¹ and the highest carrier concentration of 5.6 × 10²⁰ cm⁻³. The films obtained have disorderly polyhedral surface morphology indicating possible application in thin film solar cell with good quality and high haze factor without the need of post-deposition etching.     

Improved microstructure and ohmic contact of Nb electrode on n-type 4H-SiC

Niobium was deposited as an electrode material on an n-type SiC wafer for power device application. The reaction microstructure and electrical contact property were investigated after annealing at 700 to 1000 °C and compared with the results for an Ni electrode. Microstructure-related problems of the Ni electrode could be resolved without sacrificing ohmic contact behavior with a low contact resistivity of 1.53 × 10^− 4 Ω cm². Carbon precipitation was completely eliminated with Nb by the formation of carbides, leading to good adhesion upon wire bonding process. At the reaction interface, Nb₅Si₃ was formed in an epitaxial relationship with SiC, leading to a good interface contact property as well as good interface adhesion.     

Study of SHI induced recrystallization effects in SOI structures synthesized by nitrogen and oxygen ion implantation in silicon

Silicon oxynitride (Si_xO_yN_z) buried insulating layers were synthesized by implantation of nitrogen (¹⁴N⁺) and oxygen (¹⁶O⁺) ions sequentially in the ratio 1:1 at 150 keV to ion-fluences ranging from 1 × 10¹⁷ to 5 × 10¹⁷ cm⁻² to prepare silicon on insulator (SOI) structures. The as implanted samples were held at 270 °C and irradiated to total fluence of 1 × 10¹⁴ cm⁻² by 60 MeV Ni⁺⁵ to study the structural changes/recrystallization of SOI structures induced by swift heavy ion (SHI) irradiation. Fourier transform infrared (FTIR) measurements on the as implanted samples (≤1 × 10¹⁸ cm⁻²) show a single absorption band in the wavenumber range 1300-750 cm⁻¹ attributed to the formation of silicon oxynitride (Si-O-N) bonds in the implanted silicon. It is observed that a nitrogen rich silicon oxynitride structure is formed after SHI irradiation. The study of X-ray rocking curves on the samples show the formation of small silicon crystallites due to swift heavy ion irradiation.     

Optimization in fabricating bismuth telluride thin films by ion beam sputtering deposition

N-type bismuth telluride (Bi₂Te₃) thermoelectric thin films were deposited on BK7 glass substrates by ion beam sputtering method. Various substrate temperatures were tried to obtain optimal thermoelectric performance. The influence of deposition temperature on microstructure, surface morphology and thermoelectric properties was investigated. X-ray diffraction shows that the films are rhombohedral with c-axis as the preferred crystal orientation when the deposition temperature is above 250 °C. All the films with single Bi₂Te₃ phase are obtained by comparing X-ray diffraction and Raman spectroscopy. Scanning electron microscopy result reveals that the average grain size of the film is larger than 500 nm when the deposition temperature is above 300 °C. Thermoelectric properties including Seebeck coefficient and electrical conductivities were measured at room temperature, respectively. It is found that Seebeck coefficients increase from − 28 μV k^− 1 to − 146 μV k^− 1 and the electrical conductivities increase from 1.87 × 10³ S cm^− 1 to 3.94 × 10³ S cm^− 1 when the deposition temperature rose to 250 °C and 300 °C, respectively. An optimal power factor of 6.45 × 10^− 3 Wm^− 1 K^− 2 is gained when the deposition temperature is 300 °C. The thermoelectric properties of bismuth telluride thin films have been found to be strongly enhanced by increasing the deposition temperature.     

Growth and electrical properties of mercury indium telluride single crystals

A novel photoelectronic single crystal, mercury indium telluride (MIT), has been successfully grown by using vertical Bridgman method (VB). The crystallinity, thermal and electrical properties of the MIT crystal were investigated. The results of X-ray rocking curve show that the as-grown MIT crystal has good crystal quality with the FWHM on (3 1 1) face of about 173 in. DSC measurement reveals that the Hg element is easy to solely evaporate from the compound when the temperature is higher than 387.9 °C in the open system. Hall measurements at room temperature show that the resistivity, carrier density and mobility of the MIT crystal were 4.79 × 10² Ω cm, 2.83 × 10¹³ cm⁻³ and 4.60 × 10² cm² V⁻¹ s⁻¹, respectively. The reduction of carrier mobility and the increase of the resistivity are related to the adding of In₂Te₃ into HgTe, which changes the energy band structure of the crystal.     

A study on the interface and bulk charge density of AlN films with sputtering pressure

An attempt to correlate deposition-induced effects and the morphological properties with the electrical properties of the aluminum nitride (AlN) films have been made. The AlN film was sputter deposited on silicon while increasing the pressure in steps from 2×10⁻³ to 8×10⁻³ mbar. An X-ray diffractogram revealed that the intensity of (0 0 2) orientation increased till 6×10⁻³ mbar pressure, but it changed to (1 0 0) orientation of the AlN film at 8×10⁻³ mbar. The FTIR spectra of the absorption band of the films were observed around 682 cm⁻¹ and became prominent at 6×10⁻³ mbar. A decrease in the grain size was seen by SEM images at 8×10⁻³ mbar. The AFM measurements revealed that the surface roughness varied from 1.56 to 3.24 nm with pressure. It was found that the insulator charge density (Q_in) increased from 1.4×10¹¹ cm⁻² to 1.3×10¹² cm⁻² with increase in pressure. On the other hand, the interface state density (D_it) was found minimum (7.3×10¹¹ eV⁻¹ cm⁻²) at 6×10⁻³ mbar. It is found that presence of the Q_in and D_it are primarily governed by the sputtering pressure of the AlN film.     

Nitrate removal from groundwater by cooperating heterotrophic with autotrophic denitrification in a biofilm-electrode reactor

An intensified biofilm-electrode reactor (IBER) combining heterotrophic and autotrophic denitrification was developed for treatment of nitrate contaminated groundwater. The reactor was evaluated with synthetic groundwater (NO₃⁻-N50 mg L⁻¹) under different hydraulic retention times (HRTs), carbon to nitrogen ratios (C/N) and electric currents (I). The experimental results demonstrate that high nitrate and nitrite removal efficiency (100%) were achieved at C/N = 1, HRT = 8 h, and I = 10 mA. C/N ratios were reduced from 1 to 0.5 and the applied electric current was changed from 10 to 100 mA, showing that the optimum running condition was C/N = 0.75 and I = 40 mA, under which over 97% of NO₃⁻-N was removed and organic carbon (methanol) was completely consumed in treated water. Simultaneously, the denitrification mechanism in this system was analyzed through pH variation in effluent. The CO₂ produced from the anode acted as a good pH buffer, automatically controlling pH in the reaction zone. The intensified biofilm-electrode reactor developed in the study was effective for the treatment of groundwater polluted by nitrate.     

Physical properties of electrically conductive Sb-doped SnO2 transparent electrodes by thermal annealing dependent structural changes for photovoltaic applications

We have investigated the optical and electrical characteristics of antimony (Sb)-doped tin oxide (SnO₂) films with modified structures by thermal annealing as a transparent conductive electrode. The structural properties were analyzed from the relative void % by spectroscopic ellipsometry as well as the scanning electron microscopy images and X-ray diffraction patterns. As the annealing temperature was raised, Sb-doped SnO₂ films exhibited a slightly enhanced crystallinity with the increase of the grain size from 17.1 nm at 500 °C to 34.3 nm at 700 °C. Furthermore, the refractive index and extinction coefficient gradually decreased due to the increase in the relative void % within the film during the annealing. The resistivity decreased to 8.2 × 10⁻³ Ω cm at 500 °C, but it increased rapidly at 700 °C. After thermal annealing, the optical transmittance was significantly increased. For photovoltaic applications, the photonic flux density and the figure of merit over the entire solar spectrum were obtained, indicating the highest values of 5.4 × 10¹⁴ cm⁻² s⁻¹ nm⁻¹ at 1.85 eV after annealing at 700 °C and 340.1 μA cm⁻² Ω⁻¹ at 500 °C, respectively.     

Structural and optical properties of γ-alumina thin films prepared by pulsed laser deposition

Preparation of γ-alumina thin films by pulsed laser deposition from a sintered α-alumina target is investigated. The films were deposited on (100) silicon substrates at 973 K with varying oxygen partial pressures in the range 2.0 × 10⁻⁵-3.5 × 10^− 1 mbar. X-ray diffraction results indicated that the films were polycrystalline γ-Al₂O₃ with cubic structure. The films prepared in the oxygen partial pressure range 2.0 × 10^− 5-3.5 × 10^− 2 mbar contained nanocrystals of sizes in the range 10-16 nm, and became amorphous at pressures > 3.5 × 10^− 1 mbar. Topography of the films was examined by atomic force microscopy using contact mode and it showed the formation of nanostructures. The root-mean square surface roughness of the film prepared at 2.0 × 10^− 5 mbar and 3.5 × 10^− 1 mbar were 1.4 nm and 3.5 nm, respectively. The thickness and optical properties were studied using ellipsometry in the energy range 1.5-5.5 eV for three different angles of incidence. The refractive index was found to decrease from 1.81 to 1.73 with the increase of oxygen partial pressures from 2.0 × 10^− 5 to 3.5 × 10^− 2 mbar. The variation in the refractive index has been found to be influenced by the microstructure of the films obtained as a function of oxygen partial pressure.     

Construction of new iodide selective electrodes based on bis(trans-cinnamaldehyde)1,3-propanediimine(L) zinc(II) chloride [ZnLCl2] and bis(trans-cinnamaldehyde) 1,3-propanediimine(L) cadmium(II) chloride [CdLCl2]

New plasticized PVC membranes iodide selective electrodes have been prepared by incorporating bis(trans-cinnamaldehyde)1,3-propanediimine zinc(II) chloride [ZnLCl2] and bis(trans-cinnamaldehyde) 1,3-propandiimine cadmium(II) chloride [CdLCl2] on the surface of graphite disk electrodes. At optimum value of variables the proposed electrodes have selective response to iodide with respect to a number of inorganic and organic anions with near-Nernstian slopes of − 60 ± 1.9 and − 58.5 ± 1.9 mV/decade of iodide concentration over the range 1.0 × 10^− 6-1.0 × 10^− 1 M with detection limits of 4.0 × 10^− 7 and 3.0 × 10^− 7 M for the electrodes based on [ZnLCl₂] and [CdLCl₂], respectively. The electrodes based on both ionophores have response times of about (6 s), with stable reproducible response during 2 months, while their responses is independent of pH over the range 2.5-10.5. The proposed electrodes successfully have been applied for evaluation of iodide ion content in real samples with complicated matrices including water and pharmaceutical samples.     

Photocatalytic degradation of paraoxon-ethyl in aqueous solution using titania nanoparticulate film

Photocatalytic degradation of paraoxon-ethyl (o,o-diethyl o-(4-nitrophenyl) phosphate), a well known surrogate of chemical warfare agents, in aqueous solution was studied by using titania nanoparticulate film. Reaction followed pseudo first order behaviour. Photolytic degradation reaction of paraoxon-ethyl demonstrated relatively low rate with a value of rate constant of 2.5 × 10^− 3 min^− 1. Whereas, degradation reaction in the presence of titania nanoparticulate film and UV light displayed enhanced rate with a value of rate constant of 6.9 × 10^− 3 min^− 1 due to photocatalysis. Gas chromatography-mass spectrometry analysis showed the formation of p-nitrophenol, o,o-diethyl phosphonic acid, o-ethyl, diphosphonic acid, phosphoric acid, dimerized product of o,o-diethyl phosphonic acid, acetaldehyde, and carbon dioxide due to photocatalytic degradation of paraoxon-ethyl. It indicates that, photocatalytic degradation reaction begins with destruction of P-O-C bonds. Subsequently, P, C atoms were found to be oxidized gradually, and contributed to its photocatalytic degradation.     

Preparation and properties of negative thermal expansion Zr2WP2O12 ceramics

Using solid-state reaction method, Zr₂WP₂O₁₂ powder was synthesized for this study. The optimum heating condition was 1200 °C for 4 h. The obtained powder was compacted and sintered. The relative density of the Zr₂WP₂O₁₂ ceramics with no sintering additive was 60%. That of samples sintered with more than 0.5 mass% MgO was about 97%. The average grain size (D₅₀), as estimated from the polished surface of a sample sintered at 1200 °C for 4 h was about 1 μm. The obtained ceramics showed a negative thermal expansion coefficient of about −3.4 × 10⁻⁶ °C⁻¹. Young's modulus, Poisson's ratio, three-point bending strength, Vickers microhardness, and fracture toughness of the obtained ceramics were, respectively, 74 GPa, 0.25, 113 ± 13 MPa, 4.4 GPa and 2.3 MPa m^1/2.     

An aqueous sol-gel synthesis of chromium(III) doped mesoporous titanium dioxide for visible light photocatalysis

Nanoparticles of titanium dioxide doped with Cr³⁺ ions have been prepared through an aqueous sol-gel method. The mesoporous nature of both pure and Cr³⁺ doped TiO₂ powders, with specific surface area of 7.4 and 6.6 m² g⁻¹, respectively, is maintained even at calcination temperature of 800 °C. The transformation of TiO₂ from the anatase to rutile phase is suppressed up to 800 °C by Cr³⁺ ion doping. Even though surface area values are decreased, the doped materials show improved photocatalytic activity, which may be due to increased crystallinity of the anatase phase without the formation of rutile. Doped materials have a red-shift in the band gap energy and hence, photoactivity under visible light. The rate of photodegradation of methylene blue dye for both pure and doped TiO₂ under visible light has been monitored in this study. The 0.25 mol% Cr(III) doped photocatalyst, calcined at 800 °C, shows the highest photocatalytic activity under visible light with a rate constant of ∼15.8 × 10⁻³ min⁻¹, which is nearly three times higher than that of commercially available Degussa P25 titania (5.8 × 10⁻³ min⁻¹).     

Sol-gel synthesis of nickel oxide thin films and their characterization

Sol-gel method has been employed for the synthesis of nanocrystalline nickel oxide (NiO). The NiO powders were sintered at 400-700 °C for 1 h in an air. Thin films of sintered powders were prepared on glass substrate using spin coating technique and changes in the structural, morphological, electrical and optical properties were studied. The structural and microstructural properties of nickel oxide films were studied by means of X-ray diffraction and field emission scanning electron microscopy. Structural analysis shows that all the films are crystallized in the cubic phase and present a random orientation. Surface morphology of the nickel oxide film consists of nanocrystalline grains with uniform coverage of the substrate surface with randomly oriented morphology. The electrical conductivity showed the semiconducting nature with room temperature electrical conductivity increased from 10^− 4 to 10^− 2 (Ω cm) ^− 1 after sintering. The electron carrier concentration (n) and mobility (μ) of NiO films annealed at 400-700 °C were estimated to be of the order of 1.30 to 3.75 × 10¹⁹ cm^− 3 and 1.98 to 4.20 × 10^− 5 cm² V^− 1 s^− 1.The decrease in the band gap energy from 3.86 to 3.47 eV was observed for NiO sintered between 400 and 700 °C. These mean that the optical quality of NiO films is improved by sintering.