Interactions of xanthines with activated carbon: II. The adsorption equilibrium

In the present work, we have studied the adsorption of xanthine derivatives by activated carbon sorbents in aqueous solutions. The study comprised both kinetic, equilibrium and thermodynamic aspects. The kinetic results were reported in a previous paper; the equilibrium-related results are discussed here. The two types of carbon used exhibit some differences but the equilibrium isotherms obtained are all of the H-3 type in the classification of Giles. This suggests a high affinity of the sorbents for the sorbates. We also found that the overall adsorption process comprises more than one individual adsorption-desorption process of which one leads to the formation of a “monolayer” and the other to the “precipitation” of the sorbate on the sorbent surface (multilayer adsorption); the amount of sorbate adsorbed in monolayer form was seemingly greater in C-A14.     

Molecular dynamics study of the equilibrium flux of gas molecules to a fractal/rough surface: Effects of gas atom diameter

The frequency of collisions of ideal gas molecules (argon) with a rough surface has been studied. The rough/fractal surface was created using the random deposition technique. By applying various depositions the surface roughness was controlled and, as a measure of irregularity, the fractal dimensions of the surfaces were determined. The surfaces were next immersed in ideal gas and the numbers of collisions with these surfaces were counted. The calculations were carried out using the simplified molecular dynamics simulation technique (only hard core repulsions were assumed). The calculations were performed for various ratios of gas phase atoms diameter to the surface substrate atoms diameter. The results obtained showed that the size of a gas phase atom has crucial influence on the relation between the frequency of collision and the surface fractal dimension     

Enantioseparation on a chiral nanostructured surface: Effect of molecular shape

In this paper we use the Monte Carlo simulation method to study adsorption of chiral molecules on a solid surface with periodic distribution of active sites. Namely, equilibrium adsorption of a racemic mixture of enantiomers represented by homonuclear tetramers is modeled on a square lattice with a chiral pattern of active sites. We consider two possible chiral structures of the tetramers which differ only by chain geometry but have equal adsorption energies. The effect of the chain geometry on the effectiveness of separation is assessed by comparing the corresponding adsorption selectivities obtained from the simulations. We present results of model calculations in which the parameters do not refer to any particular experimental system. These results indicate that the model chiral surface can, in general, adsorb preferentially the complementary enantiomer, regardless of its chain conformation. Specifically, it was shown that changes in the tetramer geometry, from S-shaped to -shaped, lead to marginal changes in the shape of both single component and mixed adsorption isotherms calculated for the enantioselective surface. In this context, the enantiomer separation on the surface proposed in this work was shown to be insensitive to molecular shape of the adsorbing species.     

Interactions of xanthines with activated carbon: I. Kinetics of the adsorption process

Because of their pharmaceutical and industrial applications, we have studied the adsorption of xanthine derivates (caffeine and theophylline) by activated carbon. To this end, we examined kinetic, equilibrium and thermodynamic aspects of the process. This paper reports the kinetics results. The experimental results indicate that the process was first order in C and the overall process was assumed to involve a single, reversible adsorption-desorption process obeying a kinetic law postulated by us.     

Diffusion of particles on a heterogeneous surface: A case of adsorption-induced surface reconstruction

The influence of surface reconstruction on diffusion of particles adsorbed on the surface is investigated in the framework of symmetrical four-position model. The analytical expressions for free energy and diffusion coefficients are obtained assuming the lateral interaction between particles is negligibly small.The critical behavior of the system is described by the Ising spin model. The coverage dependencies of the tracer, jump and chemical diffusion coefficients are calculated for some representative temperatures. The dependencies show clearly strong influence of the surface reconstruction on the thermodynamic and kinetic phenomena: diffusion coefficients become anisotropic on the reconstructed surface. To check the analytical results we have used Monte Carlo simulations of the diffusion on this lattice.     

Preparation of activated carbons previously treated with sulfuric acid: A study of their adsorption capacity in solution

In the present work, cedar wood has been used as raw material for the preparation of activated carbons. The influence of a previous treatment with sulfuric acid on the textural properties of the carbonized and activated samples has been investigated. Finally, the adsorption capacity of para-nitrophenol in aqueous solution has been studied and the corresponding adsorption isotherms have been fitted to Langmuir's equation. The experimental results indicate that the previous dehydration of the raw material with sulfuric acid gives rise to an improvement in the porous texture and adsorption capacity of the activated carbons.     

Ab initio theory of complex electronic ground state of superconductors: II.: Antiadiabatic state—Ground state of superconductors

Based on Q, P-dependent modification of the Born-Oppenheimer approximation (BOA), the ab initio theory of complex electronic ground state of superconductors is presented. As an illustrative example, application of the theory to superconductors of a different character and to the corresponding nonsuperconducting analogues is presented. It is shown that due to electron-phonon (EP) interactions, which drive system from adiabatic into antiadiabatic state, adiabatic translation symmetry is broken and system is stabilized in antiadiabatic state at distorted geometry with respect to adiabatic equilibrium high-symmetry structure. Stabilization effect in the antiadiabatic state is due to strong dependence of the electronic motion on the instantaneous nuclear kinetic energy, i.e. on the effect that is neglected on the adiabatic level within the BOA. At distorted geometry, antiadiabatic ground state is geometrically degenerated with fluxional nuclear configurations in the phonon modes that drive system into this state. It has been shown that until the system remains in antiadiabatic state, nonadiabatic polaron-renormalized phonon interactions are zero in the well-defined k-region of reciprocal lattice. This, along with geometric degeneracy of the antiadiabatic state, enables formation of mobile bipolarons that can move over lattice as supercarriers without dissipation. Moreover, it has been shown that due to EP interactions at transition into antiadiabatic state, k-dependent gap in one-electron spectrum has been opened. Gap opening is associated with shift of the original adiabatic Hartree-Fock orbital energies and with the k-dependent change in density of states of particular band(s) at Fermi level. Corrected one-particle spectrum enables to derive thermodynamic properties in full agreement with corresponding thermodynamic properties of superconductors.Based on the complex ab initio theory, it has been shown that Fröhlich's effective attractive electron-electron interaction term represents correction to electron correlation energy at transition from adiabatic into antiadiabatic state due to EP interactions. It has been shown that increased electron correlation is a consequence of stabilization of the system in superconducting electronic ground state, but not the reason for its formation.     

Demineralisation of a semianthracite char with molten salts/HCl: A study by X-ray diffraction

The effects of chemical heat treatments of a semianthracite char (AC) on the composition of the mineral fraction of the material are investigated. The starting char was first treated with a mixture of LiCl/KCl or LiCl/KCl/CaO at 743, 873 or 1173 K and the products obtained were then washed thoroughly with distilled water. A small fraction of these samples were treated with 10⁻³ M HCl solution. The composition changes were studied by X-ray diffraction. The predominant mineral components initially present in the starting char are quartz, mullite, muscovite and/or kaolinite and oldhamite. The treatments of AC resulted in significant changes in the mineral fraction of the material, in particular when LiCl/KCl/CaO was used. In this case, spurrite, γ-calcium orthosilicate and gehlenite were formed, which were eliminated by treatment with 10⁻³ M HCl solution.     

Stokes integral of economic growth: Calculus and the Solow model

Economic growth depends on capital and labor and two-dimensional calculus has been applied to economic theory. This leads to Riemann and Stokes integrals and to the first and second laws of production and growth. The mathematical structure is the same as in thermodynamics, economic properties may be related to physical terms: capital to energy, production to physical work, GDP per capita to temperature, production function to entropy. This is called econophysics. Production, trade and banking may be compared to motors, heat pumps or refrigerators. The Carnot process of the first law creates two levels in each system: cold and hot in physics; buyer and seller, investor and saver, rich and poor in economics. The efficiency rises with the income difference of rich and poor. The results of econophysics are compared to neoclassical theory.     

A molecular orbital approach to chemisorption: I. Atomic hydrogen on graphite

We examine the use of Extended Hückel Theory, a semi-empirical molecular orbital approach, in treating chemisorption. The calculations include all valence electrons and overlap integrals. Adsorbate energy levels are self consistently determined. The substrate is represented by a relatively small number of atoms which is shown to be adequate for obtaining semi-quantitative results. The small representation permits investigation of adsorbate interactions with both ideal and imperfect surfaces. The binding energy, binding sites, and barrier to surface mobility exhibited by atomic hydrogen on a graphite basal surface are obtained. The experimentally observed formation of CH₄ on adsorption of hydrogen is also considered. Calculations on electrophilic adsorbates reveal the necessity for a more completely self consistent treatment in which all energy levels are adjusted.     

Cross-impact balances: Applying pair interaction systems and multi-value Kauffman nets to multidisciplinary systems analysis

Cross-impact analysis is the name for a familiar method for multidisciplinary systems analysis in social sciences and management sciences, especially in technology foresight, technology assessment and scenario planning. A recently proposed form of cross-impact analysis, CIB, may be of interest for physicists, sociophysicists and complex network researchers because the CIB concept reveals considerable relations to some concepts of these research fields.This article describes the basics of CIB analysis framework, its applications in the social sciences, and its relations to the equilibrium points of pair interaction systems, random graphs, and generalized Kauffman nets.Therefore CIB can be seen as a merger of concepts originating in utterly different scientific fields. This may prove to be fruitful for both sides: For sociophysicists as an example of the application of complex network concepts in the social sciences and for cross-impact practitioners as a source of theoretical insights in the background of their tool.     

Noise generation by vacuum cleaner suction units: Part II. Effect of vaned diffuser on noise characteristics

Noise emitted by a vacuum cleaner suction unit has aerodynamic, mechanical and electromagnetic noise origins. The aerodynamically generated noise within the blower mostly prevails in the total emitted noise at design and off-design operations. The vaned diffuser built into the blower has an important effect on the aerodynamically generated noise and its spectra. Therefore, in this part of the paper, the effects of the vaned diffuser on the performance and noise characteristics have been measured and analysed at the design and off-design operation. Analysis of measurement results have shown that the built-in vaned diffuser has numerous disadvantages, including: increase in the rotational noise, increase in the non-rotational turbulent noise, especially at off-design operation, increase in production costs and reduction of the flow rate. Therefore, and due to variable operating conditions of the suction units built into a vacuum cleaner, it could be omitted or replaced by a vaneless one.     

Microwave enhanced synthesis of N-propargyl derivatives of imidazole: A green approach for the preparation of fungicidal compounds

N-Propargyl imidazole has been synthesized by Knoevenagel condensation of benzaldehyde with propargyl bromide, assisted by microwave irradiation. Two alkaline-promoted clays (Li⁺- and Cs⁺-exchanged saponites) have been used as catalysts. The influence of several factors, such as irradiation power, irradiation time and alkaline promoter has been studied. The catalysts were characterized by XRD and chemical analysis. The basicity enhancement is directly connected to the presence of alkaline metal promoters in the saponite structure. In addition, a significant increase in the conversion values has been found when the reaction is activated by microwave irradiation, as compared with thermal activation. The yield to the N-propargyl imidazole shows a maximum for the Cs⁺-saponite at 750 W in only 5 min of microwave irradiation. This green and solvent-free procedure can be extended to the preparation of other N-substituted heterocycles, which could serve as precursors in the primary route to pharmaceutical compounds of interest.     

Demineralisation of semi-anthracite char with molten salts/HCl: Effects on the porous texture and reactivity in air

The effects of chemical heat treatments of a semi-anthracite char (AC) on textural properties and reactivity in air of the material are investigated. The starting char was first treated with a mixture of LiCl/KCl or LiCl/KCl/CaO at 743, 873 or 1173 K and the products obtained were then washed thoroughly with distilled water. A small fraction of these samples were treated with 10⁻³ M HCl solution. Valuable information on textural modifications produced in the material was derived from the adsorption isotherms for CO₂ at 273 K. The reactivity tests were carried out at 808, 823 and 823 K. The microporosity developed and the reactivity in air increased in the partially demineralised products. The former effect was stronger for the LiCl/KCl/CaO-treated samples and the latter for a larger number of the LiCl/KCl-treated samples.     

Noise generation by vacuum cleaner suction units: Part I. Noise generating mechanisms - An overview

Among all household appliances, the vacuum cleaner is the most powerful source of noise. The built-in suction unit, consisting of an electric motor and a centrifugal blower, represents the main source of noise; this is partially aerodynamic, mechanical and electromagnetic in origin. The contribution of the particular origin of noise generation to the total noise level depends on the geometry of the suction unit and operating conditions. The operating point of a suction unit built into a vacuum cleaner depends on the amount of dust particles in the dust bag and is constantly changing during operation until it reaches a zero flow rate. There are differences in noise generation at different operating conditions as well as between the suction units having a blower without and with a vaned diffuser. In this part of the paper, an overview of aerodynamic, mechanical and electromagnetic noise origins at different operating conditions is given.     

Electrodeposition of CoWP film: V. Structural and morphological characterisations

CoWP films were electrochemically deposited on copper-coated silicon wafers from citrate electrolytes containing cobalt sulphate, sodium tungstate and sodium hypophosphite under various deposition conditions and characterisations of the films were carried out using various instrumental techniques. Composition analyses using XPS showed that the surfaces of the films contained large amounts of oxides and hydroxide of tungsten and cobalt, respectively. An AES depth-profile, however, revealed that the bulk of the films predominantly consisted of cobalt, tungsten and phosphorus. Microstructural analyses using XRD showed that, depending on the composition and/or deposition conditions, CoWP films could be amorphous, polycrystalline and crystalline with a strong preferred orientation. Amorphous films were obtained when deposited at higher applied potential and current density or the films contained high amount of phosphorus and/or tungsten, while films deposited by very low applied potential and current density were crystalline with a preferred orientation of [0 0 2] of hexagonal cobalt. SEM images showed that the films deposited from neutral or acidic baths at room temperature had typical spherical nodular structures, while the films deposited from basic solution or at elevated temperature had needle-like crystallites. The crystalline films were much rougher than the amorphous films.     

Surface modification by oil jet peening in Al alloys, AA6063-T6 and AA6061-T4: Part 2: Surface morphology, erosion, and mass loss

Oil jet peening is a new surface treatment technique that can be potentially applied to impart compressive residual stresses in metal parts. The effect of oil jet pressure on the surface integrity and texture of metals are discussed. The surface morphology, mass loss rate, indentation, and erosion are reported. With increasing stand-off distance, the size of indents significantly decreases and reduces the average roughness in the both specimens. Results are also compared with other mechanical surface treatment process such as shot peening, laser shock peening, and water jet peening.     

CO2 sorption on substituted carbon materials: Computational chemistry studies

Theoretical study of sorption of CO₂ on the 4-ring graphene (“unmodified” or N-, O-, and OH-substituted) structures possessing one completely unsaturated edge zigzag site is reported using the DFT (B3LYP/6-31G(d,p)) method. Lactone and heterocyclic complexes (due to thermodynamic favourability) are taken into account. The analysis of theoretical results shows that the enthalpy of reaction strongly depends on the chemical nature, i.e. the position of the doping of atom(s) is crucial. All substitutions do not change or decrease the enthalpy in comparison with the “unmodified” graphene sheet. The well-known theoretical reactivity indices (ionization potential, electron affinity, global softness, and HOMO-LUMO gaps) are calculated for the studied adsorbents in order to explain the above-mentioned tendencies. Finally, the effect of the presence of heteroatoms on the enthalpy of reaction (ΔH²⁹⁸) for all CO₂-heteroatom-doping adsorbent complexes is shown. Thus, carbon dioxide molecules adsorb on the edge plane surface of N-, O-, OH-containing carbon surfaces similarly or much less favourably in comparison with the “unmodified” adsorbents. This confirms some experimental observations.