Synthesis and characterization of catalysts produced from paper mill sludge. I. Determination Of NOx removal capability

Characteristics and catalytic properties of a series of carbon-based catalysts (CBCs) produced from paper mill sludge were evaluated. The major processes involved in the production of the catalysts were chemical activation, impregnation, pyrolysis, and post pyrolysis rinsing. The porous structure, catalytic activity and thermostability of the catalysts were tailored during the production stage by introducing hetero-atoms (zinc chloride, and ferric nitrate) in the carbon structure. Characterization of the produced CBCs included determination of the surface area, pore size, and pore size distribution (PSD) from standard N₂-adsorption isotherm data. The extent of graphitization and the presence of metal crystals were identified from X-ray diffraction (XRD). The limit of the catalyst gasification was estimated from thermogravimetric analysis (TGA) conducted in an oxidized environment. The NO_x reduction capability of the produced catalysts was evaluated in the presence of carbon monoxide using a fixed bed reactor. The reaction temperature ranged from 300 to 500°C. It was shown that paper mill sludge is an excellent precursor for the production of CBCs with NO_x removal capability of 66–94%. The catalytic capability of the produced CBCs varied according to the method of production, catalyst surface properties (surface area, pore structure, PSD), metal composition and reaction temperature. The highest NO_x removal capacity was observed for the catalytic reactions carried out at 400°C. The mesoporous catalyst produced with a Zn:Fe molar ratio of 1:0.5 exhibited the maximum NO_x removal catalytic activity of 94%.     

Spatial regression analysis of NOx and O3 concentrations in Madrid urban area using Radial Basis Function networks

This paper discusses the performance of Radial Basis Function networks (RBF) in a problem of spatial regression of pollutants in Madrid. Specifically, the spatial regression of NO_x and O₃ is considered, in such a way that, starting from a set of measuring points provided by the air quality monitoring network of Madrid, the complete surface of the pollutants in the city is obtained. This pollutant surface can be used as an initial step for modeling intra-urban pollution using land-use regression techniques for example. Also, different works has used a pollutant surface to study the patterns of pollution in different cities in the world and also to establish their air monitoring networks under mathematical criteria. The paper is focussed in analyzing the performance of RBF networks to obtain this first pollutant surface, so different RBF training algorithms are tested in this paper. Specifically, evolutionary-based RBF training algorithms are described, and compared with classical training algorithms for RBF networks with Gaussian kernels. The inclusion of meteorological variables in the RBF networks are also discussed in the paper. The experimental part of the article studies real results of the application of RBF networks to obtain a first pollutant surface of NO_x and O₃, using the data of the air pollution monitoring network of Madrid and the meteorological network of the city.     

Cyanide removal from cassava mill wastewater using Azotobactor vinelandii TISTR 1094 with mixed microorganisms in activated sludge treatment system

Cassava mill wastewater has a high organic and cyanide content and is an important economic product of traditional and rural low technology agro-industry in many parts of the world. However, the wastewater is toxic and can pose serious threat to the environment and aquatic life in the receiving waters. The ability of Azotobactor vinelandii TISTR 1094, a N₂-fixing bacterium, to grow and remove cyanide in cassava wastewater was evaluated. Results revealed that the cells in the exponential phase reduce the level of cyanide more rapidly than when the cells are at their stationary growth phase. The rate of cyanide removal by A. vinelandii depends on the initial cyanide concentration. As the initial cyanide concentration increased, removal rate increased and cyanide removal of up to 65.3% was achieved. In the subsequent pilot scale trial involving an activated sludge system, the introduction of A. vinelandii into the system resulted in cyanide removals of up to 90%. This represented an improvement of 20% when compared to the activated sludge system which did not incorporate the strain.     

Structural and mechanical characterization of BCxNy thin films deposited by pulsed reactive magnetron sputtering

BC_xN_y thin films deposited at 250 °C by pulsed reactive magnetron sputtering of a B₄C target in an Ar/N₂ plasma were studied by elastic recoil detection analysis, Fourier transform infrared, Raman, and photoelectron spectroscopy, electron microscopy, and nanoindentation. In the concentration range of 6% to 100% N₂ in the sputter plasma the segregation into nanocrystalline hexagonal boron nitride and amorphous sp² carbon is the dominant process during the film growth. The stoichiometric ratio and structural details of the major phases depend on the N₂ concentration in the plasma and have significant influence on the Young′s modulus and the elastic recovery of the BC_xN_y thin films.     

Synthesis and characterization of nano-sized BaxSr1?xSO4 (0 ≤ x ≤ 1) solid solution by a simple surfactant-free aqueous solution route

A facile aqueous solution route has been employed to synthesize Ba _x Sr_1−x SO₄ (0 ≤ x ≤ 1) solid solution nanocrystals at room temperature without using any surfactants or templates. The as-synthesized products were characterized by means of X-ray diffraction (XRD), X-ray fluorescence spectrometer (XRF), scanning electron microscopy (SEM), and differential scanning calorimetry-thermogravimetry (DSC-TG). The Ba _x Sr_1−x SO₄ solid solution nanocrystals exhibit an orthorhombic structure and an ellipsoidal-shaped morphology with an average size of 80–100 nm. The lattice parameters of Ba _x Sr_1−x SO₄ solid solution crystals increase with increasing x value. However, they are not strictly coincident with the Vegard’s law, which indicates that the as-obtained products are non-ideal solid solutions. The Ba _x Sr_1−x SO₄ solid solution nanocrystals have an excellent thermal stability from ambient temperature to 1300°C with a structural transition from orthorhombic to cubic phase at about 1111°C.     

Correlation of magnetic properties to oxygen and potassium stoichiometry in single-crystal Ba1?xKxBiO3?y

Recent theoretical calculations have suggested the coupling of electrons to high-energy oxygen phonons as an explanation of superconductivity in the Ba_1–x K _x BiO_3–y system. We have synthesized high-quality single crystals of the material and have examined the behaviors of critical field and critical current parameters as a function of changes in the oxygen content and in the Ba/K ratio. We have determined, via positron lifetime spectroscopy and singlecrystal X-ray measurements, that the oxygen stoichiometry in this system can be varied without significant impact on the metal atom sublattice. These results facilitate an investigation of the dependence of critical parameters on dopant and defect levels in this system.     

Superconductivity and Ferromagnetism of the Ru-1232 Compounds in the (Ru1?xNbx)Sr2(GdCe1.8Sr0.2)Cu2Oz System

The Ru-1232 compounds have been synthesized in the (Ru_1–xNb _x )Sr₂(GdCe_1.8Sr_0.2)Cu₂O _z system, and effects of Nb substitution for Ru on superconductivity and ferromagnetism of the Ru-1232 compounds have been investigated. First, X-ray powder diffraction study shows that nearly the single 1232 phase samples can be obtained in the x composition range from 0.0 to 0.3. Then, from the electrical resistivity study, it is found that each of the samples shows resistivity dropping phenomenon at two temperatures of T _c ^l and T _c ^h, which originates from superconductivity of the Ru-1232 phase and the Ru-1222 one, respectively. Both of the starting temperatures are lowering with increasing Nb content x. Lastly, from the magnetic susceptibility study, it is found that superconducting transition temperature T _c is 20 K for the Ru-1232 sample with x = 0.0 and the ferromagnetic transition temperature T _m is about 90 K. This study also shows that both of the values of T _c and T _m become low with increasing x from 0.0 to 0.3.     

SO2 and NOx removal by electron beam and electrical discharge induced non-thermal plasmas

An installation containing a DC negative corona discharge reactor, a pulse corona discharge reactor and a combined electron beam and microwave induced plasma reactor is presented. SO₂ is removed up to 42% through spontaneous reaction with ammonia without electron beam or microwave irradiation at the temperature below 70 °C. For the same removal efficiency of 98% for SO₂ and 80% for NO_x at separate EB irradiation of 40 kGy, the required absorbed dose is about two times smaller for simultaneous electron beam and microwave irradiation. The SO₂ removal efficiency of simultaneous DC or positive discharge and microwave discharge is higher than separate DC, pulse and MW discharge. Also, the applied voltage level at which the removal efficiency reaches the maximum value is less than for the separate application of DC or pulse discharge. The NO_x removal efficiency of DC or pulse discharge suffers little change by additional use of the microwave energy.     

Salt-assistant combustion synthesis of nanocrystalline Nd2(Zr1 − xSnx)2O7 (0 ≤ x ≤ 1) solid solutions

Nanocrystalline Nd₂(Zr_{1 − x}Sn_x)₂O₇ series solid solutions were prepared by a convenient salt-assisted combustion process using glycine as fuel. The samples were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, transmission electron microscopy and high-resolution transmission electron microscopy. The results showed the Zr ion can be partially replaced by Sn ion. The partial substituted products were still single-phase solid solutions and the crystal form remained unchanged. TEM images reveal that the products are composed of well-dispersed square-shaped nanocrystals. The method provides a convenient and low-cost route for the synthesis of nanostructures of oxide materials.     

Preparation of YBa2Cu3O7–x high-Tcceramic superconductors from melt

Fabrication of high-T _c ceramic superconductor in the system Y₂O₃-BaO-CuO by melting a mixture of component oxides has been investigated. The compositions of the resulting specimens and the effects of heat treatment have been investigated. It was determined that molten material was composed of phases including BaCuO₂, CuO, Y₂O₃, and Y₂BaCuO₅. A subsequent heat treatment in air produced a nominal amount of the high-T _c phase, while heat treatment in an O₂ atmosphere resulted in a significantly large percentage of the superconducting phase.     

Doping-induced microstructural, textural and optical properties of In2Ti1−xVxO5+δ semiconductors and their role in the photocatalytic splitting of water

The physicochemical properties of V-doped indium titanates (In₂Ti_1−xV_xO_5+δ, 0.0 ≤ x ≤ 0.2) were investigated by using XPS, powder XRD, UV–vis, SEM and luminescence spectroscopy techniques. The Rietveld refinement of XRD data revealed that even though the V-containing samples were isostructural with In₂TiO₅ (orthorhombic space group Pnma), a systematic x-dependent variation was noticeable in the Ti–O bond lengths in [TiO₆] octahedral units, cell parameters and in the value of δ. XPS results confirmed the coexistence of V⁵⁺ and V⁴⁺ states, leading thereby to an enhancement in oxygen non-stoichiometry in the doped samples. A loading-dependent progressive shift from 400 to 750 nm was also observed in the onset of the absorption edge, indicating a significant narrowing of the band gap. Furthermore, the samples with higher V-content were comprised of the grain clusters having larger size and an irregular shape. The UV–vis, photoluminescence and thermoluminescence studies indicate that the doping-induced lattice defects may give rise to certain closely spaced acceptor/donor energy levels in between the band gap of host matrix. The indium titanates are found to serve as stable photocatalysts for water splitting under visible light, where oxygen was the major reaction product. The role of microstructural and morphological properties in the photocatalytic activity is discussed.     

Superconductivity of Ba1 ? xKxBiO3 (0.35 < x < 1) Synthesized by the High Pressure and High Temperature Technique

Ba_{1 – x} K _x BiO₃ (BKBO) samples with 0.35 < x < 1 were synthesized by the high pressure and high temperature technique. XRD analysis showed that the BKBO samples were single phase for the whole range of the potassium doping concentration. The change of superconducting transition temperature, T _c, as well as lattice parameters have been investigated upon doping concentration. As the K doping concentration (x) increases from x = 0.37, T _c decreases from 30.4 K to almost zero at x = 0.74. However, in some BKBO samples without including any barium in the starting composition (x = 1), which is denoted as KBO samples, superconductivity is observed with T _c as high as 9 K with partial substitutions of Bi at the K site. Depending on the synthesis condition of the KBO samples, T _c and lattice parameters were different from sample to sample. Compared with other superconducting bismuthates, the evolution of T _c by potassium doping in the cubic BKBO system is discussed in terms of its electronic band structure.     

Low-field magnetic properties of high-TcGdxY1?xBa2Cu3Oy superconductor

The magnetization of Gd_0.85Y_0.15Ba₂Cu₃O _y high-T _c superconductor was measured at low fields (<100 Oe) and at a constant temperature of 77 K. The magnetization curves deviate from linearity at 25 Oe, causing the destruction of the weak couplings of the superconducting grains. The hysteresis due to granular superconductivity was also observed.     

Structure and properties of Ta/TaOx barrier films deposited by direct current magnetron sputtering

Double-layer Ta/TaO_x films were deposited on glass substrates by direct current magnetron sputtering. The impact of the underlying TaO_x on the structure and properties was also investigated using X-ray diffraction analysis, Auger electron microscopy, scanning electron microscopy and atomic force microscopy. This study finds that the structure and properties of Ta/TaO_x films depends on the O₂ flow during the under-layer TaO_x deposition. As the O₂ gas flow ratio increases from 3 to 7%, more and more oxidized amorphous TaO_x films in the under-layer were formed, which caused the preferred growth orientation of upper Ta films to change from (200) to (221) systematically. Increasing the oxygen flow ratio of under-layer TaO_x films also makes the average grain size of upper Ta films decrease from 10.7 to 2.2 nm.     

X-Ray and neutron scattering studies of YBa2Cu3O6+x compounds: Oxygen insertion and spin dynamics

In the first part of this paper the results of X-ray and neutron diffraction studies of the structural aspects related to oxygen insertion in the CuO _x planes of YBa₂Cu₃O_6+x compounds are presented. The second part is devoted to the inelastic neutron scattering study of the spin dynamics in the three regimes (weakly doped, heavily doped, and overdoped) of the metallic phases of YBa₂Cu₃O_6+x .     

Microstructures and thermoelectric properties of p-type pseudo-binary AgxBi0.5Sb1.5−xTe3 (x = 0.05–0.4) alloys prepared by cold pressing

The p-type pseudo-binary Ag_xBi_0.5Sb_1.5−xTe₃ (x = 0.05–0.4) alloys were prepared by cold pressing. The thermal conductivities (κ) were calculated from the values of heat capacities, densities and thermal diffusivities measured, and range approximately from 0.66 to 0.56 (W K^− 1 m^− 1) for the Ag_xBi_0.5Sb_1.5−xTe₃ alloy with molar fraction x being 0.4. Combining with the electrical properties obtained in the previous study, the maximum dimensionless figure of merit ZT of 1.1 was obtained at the temperature of 558 K.     

Evaluation of superconducting ceramic thick films produced from a large bulk specimen of YBa2Cu3Ox

This experimental study concerns the production and evaluation of YBa₂Cu₃O _x superconducting thick films produced by slicing these films from a large bulk specimen. The resistivity/temperature behavior of these films was found to be equivalent to, or better than, the resistivity/temperature behavior of identically prepared bulk specimens made from the same material. Practical applications involving the use of this technique are probably most likely in hybrid microelectronic devices. Applications involving larger-scale electronic circuits and other superconducting devices are also possible.     

Direct Peritectic Growth of c-Axis Textured YBa2Cu3Ox on a Flexible Metallic Substrate

Previous work in the development of YBa₂Cu₃O _x (YBCO) superconducting wires and tapes has been focused on the deposition of YBCO on buffered metallic substrates. Although such an approach has proved successful in terms of achieving grain texturing and high transport current density, critical issues involving continuous processing of long-length conductors and stabilization of the superconductor have not yet been entirely settled. We have developed a novel process, the so-called direct peritectic growth (DPG), in which textured YBCO thick films have been successfully deposited directly onto a silver alloy substrate. No buffer layer is employed in the film deposition process. The textured YBCO grains have been obtained through peritectic solidification over a wide range of temperatures and times. The substrate materials have not demonstrated any observable reaction with the YBCO melt at the maximum processing temperature near 1010°C. The transport J _c has reached a respectable value of 10⁴ A/cm² at 77 K and zero magnetic field. Based on the experimental results in this work, we show that the DPG method offers an effective alternative for the fabrication of long-length YBCO conductors. Also reported is a physical explanation of the texturing mechanism on the metal substrate.     

Chemical vapor deposition of the superconductor YBa2Cu3O7?x(s) from the gas phase

The deposition of the condensed phase YBa₂Cu₃O_7–x from a gas mixture composed of YCl₃, BaCl₂, Cu₃Cl₃, and Ar reacting with another consisting of O₂ and Ar in a flow system at elevated temperatures was investigated by means of the virtual equilibrium model, and the deposition rates were computed as a function of input gas stream compositions. The optimum growth conditions were identified.     

A scheme for solving strongly coupled chemical reaction equations appearing in the removal of SO2 and NOx from flue gases

The removal of NO_x from mixtures of NO-NO₂-N₂ and NO-NO₂-O₂-H₂O is discussed theoretically in this study, and the removal of ₂SO and xNO is further discussed when a gas system of NO_x-N₂-O₂-H₂O contains CO₂ and SO₂. The involved chemical reaction rate equations in the process of SO₂/NO_x removal are solved numerically using Treanor's method, in which a scheme separating chemical reactions into fast and slow groups has been proposed for improving the numerical stability. Numerical results show that the contribution of ion reactions to xNO removal is negligible, and that high temperature is not beneficial for the NO oxidation. However, high concentration of O₂ is conducive to the NO oxidation. Addition of water facilitates the NO_x removal, and increasing water vapor concentration enhances the NO_x removal efficiency; inclusion of CO₂ and SO₂ into the system favors the NO removal.