Kinetics and thermodynamic aspect of the adsorption of Fe(III) on HTTA-imbedded polyurethane foam

The batch kinetics of Fe(III) adsorption on HTTA-loaded polyurethane (PU) foam have been investigated. The rate of controlling the adsorption is found to be intraparticle diffusion. The reaction rate of adsorption and desorption was also evaluated and found to increase and decrease with temperature, respectively. This indicates an endothermic adsorption behavior of Fe(III) on HTTA loaded PU foam. The activation energy of adsorption (80±10 kJ·mol^–1) and of desorption (–45±±2 kJ· mol^–1) indicates the chemical adsorption rather than physical adsorption. The isosteric heat of adsorption (H _ads) was found to be –82.7±5.05 kJ·mol^–1. This shows the formation of new chemical bonds among Fe(III)-HTTA-PU foam. The thermodynamic parameters of G, H and S, and equilibrium constantK _c have been calculated. These functions further support that the process of adsorption of Fe(III) on HTTA-loaded PU foam is endothermic and chemisorption, stabilized through thermodynamic functions.     

Thermodynamics of adsorption of acetone on active carbon supported metal adsorbents

Adsorption of acetone on active carbon and active carbon supported metals (Ni, Cu, Zn and Cd) have been studied as a function of temperature. Thermodynamic parameters such as G ⁰, H ⁰, and S ⁰ are calculated from virial and Langmuir isotherm expressions. It is observed that active carbon supported metals have more adsorption affinity for acetone as compared to active carbon. Results show that the increase in adsorption affinity for active carbon supported metals is not due to configurational factors affecting the entropy of adsorption, but because of enhanced enthalpy of adsorption. XRD spectra show that active carbon supported metals adsorbents are amorphous and metal residues are present on the surface of active carbon in its reduced form. From adsorption data, isosteric heats and molar entropies of adsorption were calculated as a function of coverages and temperature. The values of isosteric heats of adsorption were found to be higher for active carbon supported metals, which may be due to the chemisorption of adsorbate molecules with metal sites present on the surface of active carbon. The extent of coordination of adsorbate molecules with metal sites is discussed on the basis of the acidic character of metal.     

Adsorption of <Emphasis Type="Italic">n</Emphasis>-Butanol from Aqueous Solutions on an Sn-Ga Electrode in the Absence of a Metal-Water Chemisorption Interaction

Data on the dependence of the differential capacitance on potential at the Sn-Ga/H₂O interface in 0.05 M solutions of Na₂SO₄ with various additives of n-butanol are obtained by a bridge method at a frequency of 420 Hz and a temperature of 32°C. In the region of potentials studied, the chemisorption interaction (Sn-Ga)-H₂O is completely absent. The adsorption parameters of n-butanol are obtained by a method of a regression analysis of these data. The data obtained are compared with similar data on various hydrophobic electrodes. Shown is that, on the Sn-Ga and Pb-Ga electrodes, whose “electronic” capacitance is similar, the free energies of adsorption of n-butanol are also similar but differ from the adsorption energy on electrodes of Hg, Bi-Ga, and Tl-Ga. The results that are obtained on an Sn-Ga electrode nicely fit a general correlation dependence between the reciprocal value of the electronic capacitance of various electrodes in the absence of a metal-water chemisorption interaction, (C _m ⁻¹ ), and the free energies of adsorption of molecules of n-butanol on these, ΔG _A ⁰ . The dependence of the free energies of adsorption of molecules of n-butanol in the absence of a metal-water chemisorption interaction on the magnitude of the electronic capacitance of the metal confirms the assumption that we had put forth previously that it is necessary to introduce corrections to criteria of hydrophilicity of metals based on a comparison of quantities ΔG _A ⁰ and potentials of cathodic peak of adsorption-desorption E _des, which are expressed in a rational scale. With the obtained correlation relationships taken into account, criteria of hydrophilicity are suggested, which take into account these correlation relationships.__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 884–892.Original Russian Text Copyright © 2005 by Emets, Damaskin.     

Electrochemical Studies of the Benzoate Adsorption on Au (111) Electrode

Cyclic voltammetry (CV), differential capacity (DC), and charge densitymeasurements have been employed to study the benzoate (BZ) adsorption at the Au(111)electrode surface. Thermodynamic analysis of charge density (_M) data has beenperformed to describe the properties of the adsorbed benzoate ion. The Gibbsexcess , Gibbs energy of adsorption G, and the number of electrons flowingto the interface per adsorbed benzoate ion at a constant potential (electrosorptionvalency) and at a constant bulk concentration of the benzoate (reciprocal of theEsin—Markov coefficient) have been determined. The results demonstrate thatalthough benzoate adsorption starts at negative charge densities, it takes placepredominantly at a positively charged surface. At the most positive potentials,the surface concentration of benzoate attains a limiting value of about 7.3×10^–10mol-cm^–2, which is independent of the bulk benzoate concentration. This valueis consistent with packing density corresponding to a closed-packed monolayerof vertically adsorbed benzoate molecules. At negative charge densities, benzoateassumes a flat (-bonded) surface coordination. The surface coordination ofbenzoate changes, by moving from a negatively to positively charged surface.At the negatively charged surface, the electrosorption bond is quite polar. Thepolarity of the chemisorption bond is significantly reduced due either to a chargetransfer or a screening of the charge on the anion by the charge on the metal.     

Scorpionate‐Type Coordination in MFU‐4l Metal–Organic Frameworks: Small‐Molecule Binding and Activation upon the Thermally Activated Formation of Open Metal Sites

Postsynthetic metal and ligand exchange is a versatile approach towards functionalized MFU‐4l frameworks. Upon thermal treatment of MFU‐4l formates, coordinatively strongly unsaturated metal centers, such as zinc(II) hydride or copper(I) species, are generated selectively. Cu^I‐MFU‐4l prepared in this way was stable under ambient conditions and showed fully reversible chemisorption of small molecules, such as O₂, N₂, and H₂, with corresponding isosteric heats of adsorption of 53, 42, and 32 kJ mol^?1, respectively, as determined by gas‐sorption measurements and confirmed by DFT calculations. Moreover, Cu^I‐MFU‐4l formed stable complexes with C₂H₄ and CO. These complexes were characterized by FTIR spectroscopy. The demonstrated hydride transfer to electrophiles and strong binding of small gas molecules suggests these novel, yet robust, metal–organic frameworks with open metal sites as promising catalytic materials comprising earth‐abundant metal elements.     

Inhibition Effect of N-(Pyridin-2-yl-Carbamothioyl) Benzamide on the Corrosion of C-Steel in Sulfuric Acid Solutions

N-(Pyridin-2-yl-carbamothioyl)benzamide (PCMB) was newly synthesized and tested as a corrosion inhibitor for C-steel in 0.5 M H₂SO₄ using chemical and electrochemical techniques. Polarization measurements showed that the synthesized compound acted as a mixed inhibitor. The inhibition efficiencies obtained from the different methods were in good agreement. The inhibitive action of this compound is discussed in terms of blocking the electrode surface by adsorption of the inhibitor according to the Langmuir isotherm. The effect of temperature on the corrosion behavior in the absence and presence of 2.5 × 10^?5 M of PCMB was studied (283–308 K). The associated activation energies (E _a) and the thermodynamic parameters (ΔH*, ΔS*, K _ads, ΔG°_ads) for the adsorption process were determined. The ΔG°_ads value is ?36.55 kJ/mol, which indicated that the adsorption mechanism of PCMB on C-steel in 0.5 M H₂SO₄ solution was combined between physisorption and chemisorption processes.     

Surface characterization and thermodynamics of adsorption of Sr2+, Ce3+, Sm3+, Gd3+, Th4+, UO 2 2+ on activated charcoal from aqueous solution

Surface parameters of the activated charcoal were measured using precise instrumental techniques for dehydration, carbon content, trace metals impurities, anions, bulk, tap and true densities, surface area, pore volume, porosity and average particle diameter. The adsorption of Sr²⁺, Ce³⁺, Sm³⁺, Gd³⁺, Th⁴⁺ and UO ₂ ²⁺ ions on activated charcoal from aqueous solution was studied as a function of temperature. Thermodynamic parameters such as HH ⁰ and S ⁰ were calculated from the slopes and intercepts of the linear variation of lnK ₁ vs. 1/T, whereK ₃ is obtained from Langmuir equation. The results show endothermic heats of adsorption, but negative free energy values indicate that the adsorption process of metal ions on activated charcoal is favored at high temperature. The value of isosteric heat of adsorption, calculated from the Clausius-Clapeyron equation, shows that the surface of the activated charcoal is heterogeneous with respect to activity. A wavelength dispersive x-ray fluorescence spectrometer was used for measuring the concentration of metal ions.     

Surface acid sites of H<Subscript>3</Subscript>PW<Subscript>12</Subscript>O<Subscript>40</Subscript> as studied by the adsorption of stable nitroxyl radicals

The surface acidity of H₃PW₁₂O₄₀ and Na_xH_3-xPW₁₂O₄₀(x = 1-3) was studied using the adsorption of 2,2,6,6-tetramethyl-4-oxopiperidine-1-oxyl (TEMPON) and 2,2,6,6-tetramethyl-4-hydroxypiperidine-1-oxyl (TEMPOL) radicals. It was found that the amount of surface proton sites determined from the adsorption of TEMPON decreased with the degree of substitution of Na⁺ cations for protons. A correlation between amount of strong surface proton sites and catalytic activity of Na_xH_3-xPW₁₂O₄₀(x = 0-3) in the dealkylation reaction of 2,6-di-tert-butyl-4-methylphenol was found.Translated from Kinetika i Kataliz, Vol. 46, No. 1, 2005, pp. 131–136.Original Russian Text Copyright © 2005 by Timofeeva, Ayupov, Volodin, Pak, Volkova, Echevskii.     

二维TiC 层表面H2的化学吸附与物理吸附

第一性原理计算研究发现由于二维TiC 单原子层具有高的比表面积与大量的暴露在表面的Ti 原子,其是一种非常有潜力的储氢材料. 计算结果显示H₂可以在二维TiC 单原子层表面进行物理吸附与化学吸附. 其中化学吸附能为每个氢分子0.36 eV,物理吸附能是每个氢分子0.09 eV. 覆盖度为1和1/4层（ML）时,H₂分子在二维TiC 单原子层表面的离解势垒分别为1.12 和0.33 eV. 因此,除了物理吸附与化学吸附,TiC 表面还存在H单原子吸附. 最大的H₂储存率可以达到7.69%（质量分数）. 其中,离解的H原子、化学吸附的H₂、物理吸附的H₂的储存率分别为1.54%、3.07%、3.07%. 符合Kubas吸附特征的储存率为3.07%. 化学吸附能随覆盖度的变化非常小,这有利于H₂分子的吸附与释放.     

π-Complex of Cu(I) Chloride with 1-Allyloxybenzotriazole CuCl · C<Subscript>6</Subscript>H<Subscript>4</Subscript>N<Subscript>3</Subscript>(OC<Subscript>3</Subscript>H<Subscript>5</Subscript>)

Single crystals of CuCl · C₆H₄N₃(OC₃H₅)(I) are synthesized by ac electrochemical method from Cu(II) chloride and 1-allyloxybenzotriazole in ethanol solution and their unit cell parameters are determined: space group P2₁/a a=11.583(4) , b=11.443(7) , c=8.620(4) , =108.77(3)°, V=1082(2) ³, R(F)=0.0366, R _w (F)=0.0396 for 1095 reflections. In the structure of -complex I, inorganic fragment Cu₂Cl₂ forms centrocymmetric parallelogram. A molecule of 1-allyloxybenzotriazole acts as a bridge, which is bonded to the Cu atoms of two inorganic dimers through the C=C bond of the allyl group and to the N atom of a triazole ring. Owing to this bridging function, the ligand molecules form zigzag organometallic layers. The trigonal-pyramidal coordination sphere of a metal atom includes two Cl atoms and the C=C group. The structural motif of complex I significantly differs from that of the previously studied 2CuCl · C₆H₄N₃(OC₃H₅) and resembles the motif of a bromide analog Cu₂Br₂ · [C₆H₄N₃(OC₃H₅)]₂.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 5, 2005, pp. 364–369.Original Russian Text Copyright © 2005 by Goreshnik, Myskiv.     

The chemisorption of hydrogen on Cu(111): A dynamical study

Ab initio band-structure calculations within a density functional formalism were performed to compute the binding energy curves of atomic hydrogen with the high-symmetry adsorption sites of the (111) surface of copper. For a two-layer slab of Cu atoms and H coverage equal to 0.25, the binding energies are 2.25, 3.12, and 3.24 eV, for on-top, bridge, and threefold sites, so that the chemisorption of H₂ on Cu(111) is exothermic for threefold and bridge sites, but endothermic for on-top sites. Starting from these results, an LEPS potential for the interaction of H₂ with the Cu(111) surface was built. In this model potential, the most favored approaches correspond to a H₂ molecule parallel to the Cu surface, and for them, the activation barrier is located at the corner between the entrance and the exit channels of the reaction, and its lowest value is 0.6 eV. The LEPS potential was used in quasi-classical trajectories calculations to simulate the adsorption of a beam of H₂ molecules on Cu(111). The results show that (a) when H₂ is in the ground vibrational state the dissociative adsorption probability P_a increases from 0 to .90 along a roughly sigmoidal curve by increasing the collision kinetic energy from 0.4 to 1.3 eV, and (b) the vibrational energy can be as effective as the translational one in promoting dissociative chemisorption, in agreement with the experimental results. © 1994 John Wiley & Sons, Inc.     

Peculiarities of the crystal structure and packing of the host and guest molecules in the [M(4-McPy)4(NCS)2]·0.67(4-McPy)·0.33 H2O Clathrates (M = Cu(II), Mn(II); 4-MePy = 4-Methylpyridine)

The crystal structures of the two clathrates with the composition [M(4-MePy)₄(NCS)₂]·0.67(4-McPy)·0.33 H₂O (M=Cu(II), Mn(II); 4-MePy=4-methylpyridine) have been determined. These compounds are trigonal, with the [M(4-MePy)₄(NCS)₂] host molecules being centrosymmetric. The parameters of the unit cells area = 27.365(7) and 27.738(6),c = 11.303(9) and 11.250(8) Å,V = 7325(2) and 7493(2) ų, space group R , R = 0.053 and 0.109 for M = Cu(II) and Mn(II), respectively. ForZ = 9d _calcd is equal to 1.271 and 1.225 g/cm³, andd _measd is equal to 1.252(2) and 1.213(2) g/cm³ for the Cu and Mn clathrates, respectively. The coordination environment of the metal atoms in these compounds is an irregular octahedron, while in the Mn compound these distortions are rather small (Mn-N_MePy 2.30, 2.34 Å, Mn-N_NCS 2.18 Å, and Cu-N_MePy 2.06 Å, Cu-N_NCS 1.98 Å and Cu-N_MePy 2.50 Å).The molecular packing in the structures is such that the channels of variable diameter are formed along the short cell dimension (the maximum diameter is 10 Å, the minimum being 6 Å) where the guest 4-MePy and H₂O molecules are placed.     

Thermodynamics of adsorption (as a function of temperature and pressure) of N2, C02, Ar,CH4 and C2H4 on charcoals

Summary A quantitative treatment pertaining to the evaluation of the Gibbs function for the adsorption study of Ar, N₂, CO₂, CH₄ and C₂H₄ on wood-charcoal and charcoal is given. The specific surface areas were determined from the Langmuir adsorption equation; Gibbs function,, was estimated from the areas under them-lnP curves (from data from literature). Related thermodynamic functions are calculated in order to validate a correlation between the quantitatively deduced results with the known qualitative surface aspects in relation to a transition from mobile to a partly localized state for N₂ arid CH₄.

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Zusammenfassung Es wird eine quantitative Ermittlung der Gibbsschen Funktion für die Adsorption von Ar, N₂, CO₂, CH₄ und C₂H₄ an Holzkohle und Kohle gegeben. Die spezifischen Oberflächen wurden aus der Langmuir-Adsorptionsgleichung ermittelt, und die Gibbssche Funktion wurde aus den Flächen unter denm-InP Kurven entnommen (nach Literaturdaten). Um Zusammenhänge zwischen den quantitativ abgeleiteten Ergebnissen und Oberflächenaspekten in Bezug auf einen Übergang von einem mobilen in einen weniger mobilen Zustand von adsorbiertem Stickstoff und Methan zu erlangen, wurden weitere thermodynamische Funktionen berechnet.

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With 11 figures and 6 tables     

Adsorption of n-Butanol from Aqueous Solutions on a Bi–Ga Electrode

Curves of the differential capacitance at the Bi–Ga/H₂O interface in 0.05 M Na₂SO₄ solutions with different concentrations of n-C₄H₉OH are obtained by a bridge method at 420 Hz and 32°C. Adsorption parameters of n-C₄H₉OH, determined by a regression analysis of these curves, are compared with relevant data for mercury and partially fused polycrystalline bismuth (pBi). That the adsorption behavior of organic molecules at Hg differs from that at pBi and Bi–Ga is due not to their different hydrophilicity but to a different physical interaction water–electrode. The reason for this phenomenon can be an unequal spread of electron density beyond the ionic cores of Hg and Bi. These notions are corroborated by the fact that the Bi–Ga data fit overall correlation dependence between the electronic capacitance of different electrodes in the absence of a chemisorption interaction metal–water and the adsorbability of the n-C₄H₉OH molecules on them.     

The molecular mechanism of low-temperature decomposition of hydrogen sulfide under conjugated chemisorption-catalysis conditions

The molecular mechanism of interaction of two hydrogen sulfide molecules with the (Co^III-H_o)₂S₂(SH₂)₄ model active center containing occluded hydrogen was studied by the density functional theory method with the B3P86 hybrid exchange-correlation functional. The reaction was found to occur in the following elementary steps: molecular adsorption of hydrogen sulfide ? dissociative chemisorption ? S-S bond formation in the surface intermediate {2Co^III ? (μ-S₂) + 2H(ads)} with the release of the first hydrogen molecule into the gas phase H₂(g) ? the release of the second hydrogen molecule into the gas phase H₂(g) ? the formation of cyclooctasulfur in the reaction 4S₂(ads) → S₈(ads). The first three steps occur spontaneously at room temperature, the thermodynamic driving force of the process being the stoichiometric reaction of S-S bond formation at the stage of conjugated chemisorption of two hydrogen sulfide molecules on two adjacent metal ions with the release of the first hydrogen molecule into the gas phase. The catalytic cycle is terminated by the recombination of molecular sulfur S₂ into cyclooctasulfur S₈ in the adsorption layer and the release of the second hydrogen molecule into the gas phase.     

ESR signals from gases adsorbed on reduced rutile at low temperatures

ESR spectra are reported for O₂, H₂SO₂, and N₂O adsorbed at low temperatures on n-type rutile after reduction with hydrogen at 700–1000C (<1% reduction). The gases alter the conductivity and produce ESR signals at liquid-nitrogen temperature (i. e., are chemisorbed), but the binding is very weak, being reversible for O₂, H₂, and He at that temperature. It is considered that the high polarizability of the lattices causes very shallow surface acceptor levels to arise by physical adsorption; these localize the conduction electrons at lattice ions adjacent to the adsorbed molecules.     

Studies on the Effects of Additional Components on Micellization of CTAB via Surface Tension Measurements

The effects of Tris-HCl buffer solution on the cmc of cetyltrimethylammonium bromide (CTAB) were studied by surface tension measurement. The result shows that the effect of the buffer solution depends on the interaction between CTAB and NaCl and the structure accelerants of water, Tris. A series of parameters, including the critical micelle concentration (cmc), the surface tension at cmc (γ_cmc), the adsorption efficiency (pC₂₀), and the effectiveness of surface tension reduction (∏_cmc) were obtained from the surface tension measurements in the presence of glycine with different concentration in the Tris-HCl buffer solution at 27°C. In addition, maximum surface excess concentration (Γ _max) and minimum surface area per molecule (A_min) at the air-water interface were estimated according to the Gibbs adsorption isotherm. The thermodynamic parameters (Δ C _p,m , Δ H _m,tr , Δ C _p,m,tr ) of micellization for CTAB in the absence and presence of glycine at different temperature were also been obtained.     

X-ray diffraction study of acid anilinium dodecatungstenphosphate

Acid anilinium dodecatungstenphosphate of composition (C₆H₅NH₃)₂H[PW₁₂O₄₀] 2H₂O is synthesized and characterized by X-ray diffraction analysis, IR spectroscopy, and thermogravimetry. The crystals are monoclinic: space group P2₁/m, a = 9.940(2) , b = 15.412(3) , c = 16.201(3) , = 100.42(3)°, Z = 2, _calcd = 4.221 g/cm³. The structure contains heteropolyanions [PW₁₂O₄₀]^3–, cations [C₆H₅NH₃]⁺ and H⁺, and molecules of water of crystallization. The heteropolyanions and anilinium cations in crystal are linked by the electrostatic interaction and hydrogen bonds.__________Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 4, 2005, pp. 273–279.Original Russian Text Copyright © 2005 by Kaziev, Dutov, Quinones, Koroteev, Belskii, Stash, Kuznetsova.     

Reactivity of positively charged cobalt cluster ions with CH4, N2, H2, C2H4, and C2H2

Reactivity of positively charged cobalt cluster ions (Co _n ⁺ ,n=2?22), produce by laser vaporization, with various gas samples (CH₄, N₂, H₂, C₂H₄, and C₂H₂) were systematically investigated by using a fast-flow reactor. The reactivity of Co _n ⁺ with the various gas samples is qualitatively consistent with the adsorption rate of the gas to cobalt metal surfaces. Co _n ⁺ highly reacts with C₂H₂ as characterized by the adsorption rate to metal surfaces, and it indicates no size dependence. In contrast, the reactions of Co _n ⁺ with the other gas samples indicate a similar cluster size dependence; atn=4, 5, and 10?15, Co _n ⁺ highly reacts. The difference can be explained by the amount of the activation energy for chemisorption reaction. Compared with neutral cobalt clusters, the size dependence is almost similar except for Co ₄ ⁺ and Co ₅ ⁺ . The reactivity enhancement of Co ₄ ⁺ and Co ₅ ⁺ indicates that the cobalt cluster ions are presumed to have an active site for chemisorption atn=4 and 5, induced by the influence of positive charge.     

O2, CO2, and H2O Chemisorption on UN(001) Surface: Density Functional Theory Study

We performed density functional theory calculations of O₂, CO₂, and H₂O chemisorption on the UN(001) surface using the generalized gradient approximation and PW91 exchange-correlation functional at non-spin polarized level with the periodic slab model. Chemisorp-tion energies vs. molecular distance from UN(001) surface were optimized for four sym-metrical chemisorption sites. The results showed that the bridge parallel, hollow parallel and bridge hydrogen-up adsorption sites were the most stable site for O₂, CO₂, and H₂O molecular with chemisorption energies of 14.48, 4.492, and 5.85 kJ/mol, respectively. From the point of adsorbent (the UN(001) surface), interaction of O₂ with the UN(001) surface was of the maximum magnitude, then CO₂ and H₂O, indicating that these interactions were associated with structures of the adsorbate. O2 chemisorption caused N atoms on the surface to migrate into the bulk, however CO₂ and H₂O had a moderate and negligible effect on the surface, respectively. Calculated electronic density of states demonstrated the electronic charge transfer between s, p orbital in chemisorption molecular and U6d, U5f orbital.