Adsorption properties of aluminum oxide modified with Co and CoO particles

Adsorption properties of γ-Al₂O₃ modified with Co (5 and 10 wt %) and Co (5 wt %) species are investigated by dynamic adsorption. N-hexane, n-heptane, n-octane, benzene, toluene, ethylbenzene, chloroform, and diethyl ether were used as test adsorbates. Adsorption isotherms were measured, and isosteric adsorption heats were calculated for the indicated sorbates. It was shown that the adsorption isotherms of all the adsorbates and at all the temperatures of measurements on γ-Al₂O₃ modified with Co (5 wt %) and CoO (5 wt %) nanoparticles located above that recorded for the initial γ-Al₂O₃ sample. It was established that the surface of modified γ-Al₂O₃ possessed mainly electron-accepting properties. The 5% Со/γ-Al₂O₃ and 5% СоO/γ-Al₂O₃ nanocomposites exhibited the greatest adsorption capacity relative to aromatic hydrocarbons.     

A study of methane adsorption and accumulation on microporous carbon adsorbent in a wide temperature range

This work studies the adsorption properties of microporous activated carbon AU-2 to determine the efficiency of methane accumulation in a wide temperature range, particularly in the low temperature range. Absolute adsorption isotherms of methane are measured in the pressure range of 20 Pa to 25 MPa and temperature range of 178–260 K. It is shown that the adsorbent accumulates up to 130 m³(ntp, CH₄)/m³ at 7 MPa and 298 K. A decrease in the temperature by 55° allows reaching the value of 180 m³(ntp, CH₄)/m³. The experimental data are used to plot methane adsorption isosteres that are well approximated by straight lines in the coordinates of lnp = f(1/T)_a. The values of differential and integral adsorption heats of methane on the adsorbents are calculated on the basis of the experimental isotherms and are used to calculate an increase in the adsorber temperature as a result of adsorption.     

Quantum chemical modeling of the adsorption of chloride ion and water molecule on group 1B metals

Quantum chemical modeling (at DFT-B3LYP level) of the adsorption of Cl^? and H₂O particles on top and into hollow sites of defect-free low index faces of copper, silver, and gold simulated by n-atomic clusters with n = 9 to 17 is carried out. The validity of simulations is confirmed by the comparison to the available literature data on the work function of the metals and the calculated gas-phase adsorption of chlorine. Relative effects of the chemical (metal nature), macrostructural (crystal face), and coordination (adsorption site) factors on the parameters of the chemisorption bond and molecular characteristics of the adsorbate and adsorbent, namely, the E _ads ads adsorption energy at % = 0K, R (Me^? Cl^?) and R(Me-O) adsorption bond lengths, Q effective charges of chlorine atom and water molecule, O-H distance and ∠HOH angle in H₂O molecule, deviation of the H₂O dipole moment vector from normal orientation to the cluster surface, and E _HOMO energies of the highest occupied molecular orbital of Me _n , [Me _n Cl]^?, Me _n H₂O, and [Me _n ClH₂O]^? clusters, are considered. The inner hydration shell of Cl^? is shown to involve six water molecules, the most stable configuration of (H₂O)₆ cluster being prism-like. An electron density shift from chlorine and water molecule to the metal cluster is found to accompany the adsorption and be more pronounced in the case of anion. The character of differences in the hydrophilicity of the group 1B metals and their diverse crystal faces is discussed. The role of hydration effects in the chemisorption of chloride ion on copper, silver, and gold is analyzed in terms of the continuum, molecular, and combined molecular-continuum models.     

Description of methane adsorption on microporous carbon adsorbents on the range of supercritical temperatures on the basis of the Dubinin–Astakhov equation

Temperature dependences of parameters n and E are calculated according to the adsorption equation of Dubinin–Astakhov for methane adsorption on eight active carbons in the range of supercritical temperatures of 170–340 K and pressures of 0–20 MPa. At temperatures above ~240 K, characteristic adsorption energy E of methane grows linearly at an increase in temperature. The temperature coefficients of characteristic energy of methane adsorption on active carbon tend to decrease at an increase in standard characteristic adsorption energy E₀. The average value of parameter <n> for the studied adsorbents tends to grow at an increase in standard characteristic adsorption energy E₀.     

Adsorption of hexane and benzene on fluorinated silicas: The effect of the perfluoralkyl chain length

By means of the gas chromatography and a static adsorption method, the extent of fluorination of the carrier surface, determined by the length of the grafted radical chain, affects the adsorption properties of silicas with perfluorohexyl, perfluoropropyl, and trifluoromethyl coatings. The analysis of data on the original carrier and chemically hydrophobized silicas, including a sample with grafted octyl groups used as the reference, shows that modification leads to the decrease in both the adsorption (a at 298 K and the Henry constants (K _H ) in a wide temperature range for hexane and benzene. However, in contrast to silicas with perfluoropropyl or perfluorohexyl coatings, the a and K _H values on trifluorometylsilica became equal (n-alkanes) or even somewhat lower (aromatic hydrocarbons) than those observed on the non-polar octylsilica surface. Irrespective of the degree of fluorination of the silica surface, the substitution and screening of silanol groups in silica lead to weakening the polarity of polyfluoroalkylsilicas as compared with the original carrier.     

Adsorption of Ni(II), Cu(II), and Zn(II) ions by natural alumosilicate modified with <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>'-<Emphasis Type="Italic">bis</Emphasis>(3-triethoxysilylpropyl)thiocarbamide

Immobilization of N,N'-bis(3-triethoxysilylpropyl)thiocarbamide on the surface of natural alumosilicates from Eastern Transbaikal has been carried out. Adsorption isotherms of Ni(II), Cu(II), and Zn(II) ions on modified adsorbents have been plotted. The experimental data have been treated using the Langmuir, Freundlich, BET, and Dubinin–Radushkevich models. The constants of these equations have been determined. It has been shown that adsorption on alumosilicates modified with N,N'-bis(3-triethoxysilylpropyl)thiocarbamide is described in the best way by the Freundlich and Langmuir adsorption models. The Dubinin–Radushkevich model has been employed for the calculation of free energy of adsorption. For all the specimens under study, the free energy of adsorption indicates the presence of an ion-exchange mechanism, while the adsorption of heavy-metal ions has a chemical nature.     

Sorption of copper,nickel and cadmium on bone char

The sorption capacity of bone char was tested on the removal of copper, nickel and cadmium ions, from aqueous solutions. The Freundlich and Langmuir models were applied to the adsorption isotherms. The equilibrium data fitted well with the Langmuir model and the maximum loading capacities showed the following affinity order: Cu²⁺ (1.093 mmol g^–1 at pH _i 3, and 0.884 mmol g^–1 at pH _i 4) > Cd²⁺ (0.760 mmol g^–1 at pH _i 3, and 0.690 mmol g^–1 at pH _i 4) > Ni²⁺ (0.453 mmol g^–1 at pH _i 3, and 0.225 mmol g^–1 at pH _i 4). The kinetic data follow a diffusion model in the film and inside particles. A sorption mechanism based on ion exchange, attack by protons of the carbonate and hydroxide positions in the apatite lattice, and also on the adsorption of protons on the basic active sites of carbon, is proposed to explain the heavy metals removal and the pH decreasing in solution.     

The Effect of a Nanosize TiO<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript> Layer on the Performance of an Organic Solar Cell

This work studies the role of a cathodic TiO_x buffer layer in operation of a photovoltaic organic solar cell (OSC) based on a photoactive layer with a bulk heterojunction. Using a liquid solution to obtain a TiO_x layer is of current interest for simplification of process technologies of successive formation of OSC layers. It is found that the optimum thickness of the TiO_x layer is 10 nm; at this thickness, the efficiency of the OSC reaches the value of 4.36%. The effect of air oxygen on the OSC samples is studied and it is found that samples with a TiO_x buffer layer undergo degradation to a lesser extent as compared to the samples with no such layer. The effect of oxygen on operation of the photovoltaic device is discussed.     

Interaction of stilbenes with TiO<Subscript>2</Subscript> studied by Fourier IR spectroscopy

Adsorption interactions of stilbene (1,2-diphenylethylene) and its hydroxy- and methoxyderivatives with nanodispersed TiO₂ aerogel surface were studied by means of Fourier IR radiosity spectroscopy. Stilbene trans- and cis-isomers were shown to be weakly adsorbed on TiO₂ surface forming hydrogen bonds. UV irradiation (wavelength 285–305 nm) of adsorbed compounds results in their partial destruction, yielding aldehydes, ketones, and carboxylates. The products of stilbene photolysis are strongly bound to TiO₂ surface. Modification of TiO₂ surface with trans-hydroxystilbenes is characterized by the formation of various hydrogen bonds and surface colored quinoid compounds. The interaction of TiO₂ with trans-methoxystilbenes changes the state of surface hydroxyl groups and yields stable carboxylate compounds. UV irradiation results in the partial destruction of adsorbed stilbenoids, yielding aldehyde, ketone, and carboxylate surface compounds.     

Magnetic properties of <Emphasis Type="Italic">R</Emphasis>Co<Subscript>2</Subscript> compounds in the exchange-striction model of ferrimagnets

The original version of the exchange-striction model of a ferrimagnet has been employed for calculating a number of magnetic properties of RCo₂ ferrimagnets, where R = Er, Ho, Dy, Tb, and Gd are rareearth ions. The following magnetic properties are calculated: pressure dependence of the Curie temperature (Т _С), temperature dependences of magnetization in sublattices of cobalt and rare-earth atoms, and isotherms of magnetization of these lattices at Т > Т _С. For an ErСо₂ sample, the Н–Т phase diagram has been constructed and the magnetization in the magnetic fields Н = 0–70 Т has been calculated. The calculated and experimental results have been compared. Based on the exchange-striction model, the qualitative explanation of the difference in the type of the magnetic phase transformation in the intermetallic compounds with R = Tb and Gd and R = Er, Ho, and Dy is given.     

Adsorption of stilbenoids on silica

TLC, HPLC, and statistical methods are used to study the adsorption of stilbenoids from organic solvents on SiO₂ in a wide range of concentrations. The dependence of adsorption of trans-stilbene hydroxy and methoxy derivatives on the nature of functional groups, their amount and position in the molecular structure, and also on the concentration and proton-acceptor properties of the polar component of the binary organic solvent is found. It is shown that experimental isotherms of stilbenoid adsorption on aerosil from the mixture of n-hexane and ethyl acetate are well approximated by the Freundlich equation. The adsorption of stilbenoids and phenols on SiO₂ is compared. It is found that adsorption properties of phenols and hydroxystilbenes with a similar number of OH groups are practically similar.     

Photoelectron spectroscopy and diffraction of NbO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Nb(110) surface

Methods of X-ray photoelectron spectroscopy and diffraction were used to investigate the oxygen-induced surface structures on the Nb(110) face which were formed as a result of oxygen segregation from the volume of the crystal upon thermal annealing at 2000 K in a vacuum and/or oxygen adsorption in situ at temperatures higher than 1100 K. The niobium atoms on the crystal surface form quasi-ordered structures in the form of monatomic Nb chains surrounded by oxygen atoms and from the viewpoint of the nearest surroundings and chemical bonding they are close to the states of the metal in NbO _x . The thickness of such NbO _x -like structure is estimated as 0.5 nm at the degree of coverage of the surface of 50%. Two chemically nonequivalent states of oxygen at Nb(110) have been distinguished, supposedly, (1) atomic chemisorbed oxygen on the surface of Nb metal and (2) oxygen in the composition of NbO _x -like clusters on the Nb(110) plane. The NbO _x /Nb(110) model of the surface allows for the distortion of the structure of NbO _x clusters, i.e., periodic atomic displacements of metal atoms in Nb chains by height and changes in the Nb-O bond angles.     

Study on Microstructures and Mechanical Properties of Foam Titanium Carbide Ceramics Fabricated by Reaction Sintering Process

Foam titanium carbide (TiC) ceramics with a three-dimensional network structure were fabricated by the reaction sintering process, in which polyurethane foam was taken as the template, and TiO₂ and phenolic resin were used as the reactants. Phase, microstructures and fracture morphologies of foam TiC ceramics were characterized by x-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results show that when the mass ratios of phenolic resin and TiO₂ (F/T) are (0.8-1.2): 1, foam TiC ceramics with pure TiC phase can be formed. As the F/T ratios increase, crystal lattice parameters of fabricated foam TiC ceramics become bigger. When the value of F/T decreases from 1.2 to 0.8, grain size of TiC grows larger and microstructures get denser; meanwhile, the compressive strength increases from 0.10 to 1.05 MPa. Additionally, either raising the sintering temperatures or extending holding time can facilitate the completion of the reaction process and increase the compressive strength.     

Characterization of Microstructure and Wear Resistance of PEO Coatings Containing Various Microparticles on Ti6Al4V Alloy

Titania-based composite coatings were prepared by plasma electrolytic oxidation (PEO) treatment of Ti6Al4V alloy in electrolyte with α-Al₂O₃, Cr₂O₃ or h-BN microparticles in suspension. The microstructure, composition of PEO composite coatings were analyzed by SEM, EDS and XRD. The wear resistance of composite ceramic coatings was studied by ball-on-disk wear test at ambient temperature and 300 °C. The results showed that the addition of microparticles accelerated the growth rate of PEO coating and changed the microstructure and composition of PEO coating. PEO coating was porous and mainly composed of rutile-TiO₂, anatase-TiO₂ and Al₂TiO₅. PEO/α-Al₂O₃ (Cr₂O₃ or h-BN) composite coating only had small micropores and appeared some α-Al₂O₃ (Cr₂O₃ or h-BN) phase. Besides, the addition of α-Al₂O₃ (Cr₂O₃ or h-BN) microparticles greatly improved the wear resistance of PEO coating. At ambient temperature, abrasive wear dominated the wear behavior of PEO coating, but abrasive wear and adhesive peel simultaneously happened at 300 °C. Whether at ambient temperature or 300 °C, PEO composite coating had better wear resistance than PEO coating. Besides, PEO/h-BN composite coating outperformed other composite coatings regardless of the temperature.     

Short-range atomic order in Fe<Subscript>2</Subscript>B powders

The possibility of application of a local atomic displacement (LAD) model for describing the mechanism of formation of a low-field part (H _hf ≤ 23.6 T) of a hyperfine-field distribution P(H) in a Fe₂B alloy at early stages of grain refinement has been investigated. It has been found that the appearance of Mössbauer contributions, which are not typical of the tetragonal C16 structure, in the P(H) function of the Fe₂B alloy is induced by a decrease in the relative interatomic distances Δr _Fe-B/r _Fe-B to ≤0.18 for some configurations of iron and boron atoms in the unit cell.     

Experimental Investigation of Newly Synthesized Gemini Cationic Surfactants as Corrosion Inhibitors of Mild Steel in 1.0 M HCl

Three Gemini cationic surfactants named N¹,N¹,N³,N³-tetramethyl-N¹,N³-bis(3-octanamidopropyl) propane-1,3-diaminium bromide (C8-S3-C8), N¹,N¹,N³,N³-tetramethyl-N¹,N³-bis(3-dodecanamidopropyl) propane-1,3-diaminium bromide (C12-S3-C12) and N¹,N¹,N³,N³-tetramethyl-N¹,N³-bis(3-hexadecanamidopropyl) propane-1,3-diaminium bromide (C16-S3-C16) were evaluated as corrosion inhibitors for mild steel in 1.0 M HCl. The corrosion rate of mild steel in 1.0 M HCl at three different temperatures 25, 45 and 60oC was investigated gravimetrically. The corrosion rate of mild steel was confirmed electrically at 25oC. The corrosion inhibition efficiency directly proportionally with the hydrophobic chain length of inhibitors. The inhibition efficiency exhibit a positive trend with raising the solution temperatures. The potentiostatic polarization study revealed that the tested gemini cationic surfactants act as mixed type inhibitors with predominant control of cathodic reaction. The Villamil isotherm provide the best describing of the adsorption process on the selected steel in 1.0 M HCl. The adsorption of the tested inhibitors on the steel surface is a mixture of chemical and physical adsorption.     

Nanoporous materials and their adsorption properties

Principal regularities of forming microporous adsorbents with different surface composition, in particular, active coals, zeolites, silica gels, alumina gels, fullerenes, and carbon nanotubes are considered. The data on the structure-energetecal characteristics of the adsorbents and systems are correlated. Principal characteristic features of the microporous adsorbents deformation during CO₂,CH₄, Ar, N₂, and Xe adsorption in a 177.65–393 K temperature range at the pressures of up to 7.0 MPa are studied by example of the AUK microporous carbonaceous adsorbent and the NaX zeolite. An analysis of the adsorption deformation of the microporous adsorbents as a function of the adsorption amount, temperature, and physicochemical properties of adsorbed gas is presented. Based on the analysis of benzene adsorption isotherms for the C60 and C70 fullerenes, a suggestion is advanced on the formation of fullerene-benzene adsorption complexes comprising on average three fullerene and two benzene molecules; their characteristic energy comes to E _o ～ 25 kJ/mol. It is shown, by using the adsorption and SEM data that the cuminol adsorption at the nanotubes yields supramolecular complexes in which the cumene molecules act as coordinating ones. By using the micropore bulk filling theory, the hydrogen adsorption is calculated for model supramolecular systems in which the carbon nanotubes are bundled up, with leaving gaps between the bundles.     

Experimental Determination of the Phase Equilibria of the La-Zn-Si System at 600 °C

The isothermal section at 600 °C of the La-Zn-Si system was established by using equilibrated alloys and the diffusion couple technique. Microstructural observation and phase identification were performed using optical microscopy, scanning electron microscopy with energy dispersive x-ray spectroscopy and a wave dispersive x-ray spectrometer, and x-ray powder diffraction. Seven ternary compounds were identified in this ternary system, and temporally designated as τ ₁, τ ₂, τ ₃, τ ₄, τ ₅, τ ₆ and τ ₇. Two previously reported ternary compounds, viz. τ ₁ and τ ₂, were found to exist at 600 °C. EDS analysis revealed that the τ ₁ phase contained Si from 2.4 to 6.1 at.% and La from 22.3 to 23.3 at.%. The compositional region of the τ ₂ single-phase ranged from 28.3 to 40.7 at.% for Si and from 31.5 to 33.1 at.% for La. Two new ternary phases, τ ₅ and τ ₆, were identified. The τ ₅ phase with the CeNiSi₂-type was determined to have a composition range of 36.9-39.2 at.% Si for about 24 at.% La. The τ ₆ phase with the ThCr₂Si₂-type was found to have a composition range of 18.9-19.7 at.% La and 27.4-30.6 at.% Si. The crystal structures of τ ₃, τ ₄, and τ ₇ were not determined. The solubility of Si in LaZn₁₃, LaZn₁₁, La₂Zn₁₇, La₃Zn₂₂, and LaZn₅ was negligible, and that of Si in LaZn₄, LaZn₂ and Zn in LaSi₂, La₃Si₂ was determined as 5.1, 2.3, 16.2 and 3.8 at.%, respectively.     

Influences of carbon and silicon on blister formation in scale surface during high temperature oxidation of carbon steels

The in-situ blistering phenomena of the scale ‘surface’ was investigated on three carbon steels with respect to carbon and silicon concentrations, such as 0.05 wt%C, 0.2 wt%C, and 0.2 wt%C-0.2 wt%Si. The oxidation and blistering kinetics and blister area fraction during high temperature oxidation were analyzed. The average thickness of the surface scale by oxidation during isothermal holding from 800 to 1200 °C in dry air was observed to decrease when the amount of carbon increased and/or when Si was inserted additionally. Thus, the blistering behavior depended primarily on a change in oxidation temperature (T _ox ) as well as amounts of carbon and silicon in the matrix. It is also revealed that such blister formation would be triggered by growth of internal stress and active generations of CO and/or CO₂ gases at the interface between the scale and matrix since carbon would result in an increase in the blister formation by generating CO and/or CO₂ gas. In addition, silicon might play an important role in preventing the blister formation at T _ox below 900 °C by reducing the thickness of the surface scale whilst silicon might enhance the blister formation by means of the appreciable micro-void formation in the scale layer at T _ox higher 900 °C.     

Experimental Investigation of the Binary Mn-Sb Phase Diagram

The binary manganese-antimony (Mn-Sb) phase diagram was reinvestigated in the whole composition range using powder-XRD, DTA and SEM-EDX. The phase boundaries and melting temperatures of the ferromagnetic phases MnSb and Mn₂Sb were modified by taking into account the new experimental data. Most of the reaction temperatures could be verified within a range of ±10 °C. Nevertheless, a few temperatures had to be revised, such as the eutectic reaction L → β-Mn + Mn ₂ Sb at 893 °C and the eutectoid reaction β-Mn → α-Mn + Mn ₂ Sb at 718 °C. The previously reported peritectic melting behavior of MnSb could be confirmed. The variation of the lattice parameters of the NiAs-(B8 ₁ ) type MnSb phase with composition was determined. A revised version of the of the Mn-Sb phase diagram is presented.