Applicability of the film-diffusion model for description of the adsorption kinetics at the solid/solution interfaces

The adsorption kinetics at the solid/solution interfaces has been described by using the kinetic model based on accepting the existence of the concentration gradient in the region of bulk solution close to the solid surface (external film-diffusion model). This model has also been adopted to explain some behaviours observed in the real adsorption systems. Simultaneously, the pseudo-first order (Lagergren) equation can be derived applying this model. The results indicate that the necessary condition to state that the “diffusion across the liquid film” mechanism is involved in controlling the rate of adsorption process is the linearity of the initial parts of kinetic isotherms plotted as the amount adsorbed vs. the time. The two methods have been proposed to distinguish between this mechanism and the classical Langmuir kinetics. The results presented here might be useful in identifying if the concentration gradient in the bulk solution influences the overall adsorption rate.     

A new empirical rate equation for adsorption kinetics at solid/solution interface

It has been shown that most of the previously reported empirical rate equations for kinetics of adsorption at the solid/solution interface show high relative errors at the initial times of adsorption. In the present work we made a modification onto pseudo-first-order and pseudo-second-order models and presented a new empirical rate equation, called the modified pseudo-n-order (MPnO) model. The results of fitting to the experimental data show that the MPnO model has low relative errors in the whole range of adsorption time.     

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.     

Is gold always chemically passive?: Study and comparison of the epoxy-amine/metals interphases

When epoxy-amine liquid mixtures are applied onto metallic substrates (such as Al, Ti, Sn, Zn, Fe, Cr, Cu, Ag, Ni, and Au), concomitant amine chemisorption and metallic surface dissolution occur, leading to organo-metallic complex formation. The interphase formation was studied, using two different amines as hardener (IsoPhoroneDiAmine and DiEthyleneTriAmine). If the complex concentration within the liquid amine or epoxy-amine prepolymer was higher than its solubility limit, the complexes will crystallize. Sharp needle-like crystals were only observed with metal-IPDA organo-metallic complexes. A lot of metals are widely used as reactive substrates with gold as a reference, which is considered chemically inert. It is misleading, since it will be shown in this article that gold reacts with amine, just as the other metals.     

Formation of periodic structures by surface treatments of polyamide fiber: Part II. Low temperature plasma treatment

The processes of low temperature plasma treatment of polyamide fiber were systemically studied. Ripple-like structures in sub-micron size perpendicular to fiber axis were observed under particular treatment parameters. Suggested explanations were given of the mechanisms that produce the structure after the processes of plasma treatment. The fundamental approach used in modelling was considered the temperature profile of the material during the treatment. The morphological study results showed that the stress-field inside the fiber and the degree of crystallinity are essentially important in contributing to structure formation.     

Formation of periodic structures by surface treatments of polyamide fiber: Part I. UV excimer laser irradiation

The processes of UV excimer laser irradiation (both high- and low-fluence) of polyamide fiber were systemically studied, including the surface temperature of the material during the treatment and possible mechanisms for the structure formation. The fluence applied in the high-fluence laser irradiation was above the ablation threshold of the material. The ablation of polymer can be described on the basis of photo-thermal bond breaking within the bulk material. The fluence applied in the low-fluence laser irradiation was far below the ablation threshold of the material. The development of low-fluence laser-induced structures is closely related to the absorption coefficient of the material, the laser fluence used, the polarization of the laser beam, the angle of incidence, and the number of laser pulses applied.     

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.     

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.     

Spectroscopic studies of alumina-supported nickel catalysts precursors: Part I. Catalysts prepared from acidic solutions

Nickel alumina-supported catalysts were prepared from acidic solutions of nickel nitrate by the CIM and DIM methods (classical and double impregnation, respectively). The catalysts exhibited different nickel species due to the existence of various metal-support interaction strengths. As a consequence, the reducibility and other surface properties changed as a function of the preparation method. The aim of this work was to study the interaction between the metal precursor and the alumina surface by means of FT-IR (Fourier transform infrared) and FT-IR/PAS (FT-IR photoacoustic spectroscopy).     

Self-diffusion coefficients and orientational correlation times in aqueous NaCl solutions: Complementarity with structural investigations

The dynamical properties of pure water and aqueous NaCl solutions over a wide range of salt concentrations (0-6 m) at ambient conditions are characterized by molecular dynamics (MD) simulations. MD simulations are performed with a flexible SPC water model as a solvent, while the ions are treated as charged Lennard-Jones particles. In this paper, attention has been focused on the self-diffusion coefficients (D_i) of ions and water molecules and on orientational correlation time of water molecules. It is found that the self-diffusion coefficients decrease with ion concentration. Moreover, the self diffusion coefficients of sodium and chloride at higher salt concentrations are very comparable which may be due to the formation of clusters of these ions. The deduced rotational dynamics speeds up as the salt concentration increases. Some complementarities between dynamical properties and structural ones, recently obtained, are carried out.     

Competition between surface reaction and diffusion of gold deposited onto ZrTe3

Surface reaction and diffusion of gold, deposited onto the (0 0 1) ZrTe₃ van der Waals (vdW) surface, is studied by transmission electron and scanning tunneling microscopy. It is shown that both processes compete at temperatures as low as room temperature. In case of diffusion the deposited gold mostly disappears from the surface and intercalates into the vdW gaps of the substrate. Residual unreacted gold agglomerates are rather mobile and are often displaced by the scanning tip along the [1 0 0] direction of the substrate. In case of reaction, which usually takes place at somewhat higher substrate temperatures, grains of Zr₃Te₂, AuTe₂ and/or Au₂Te₃ are formed. Contrary to unreacted gold, the reaction products are not mobile.     

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.     

Polarization transfer in the 2H(d,n)3He reaction at θ = 0°

The vector polarization transfer coefficient K_y^y′ and the tensor analyzing power A_zz have been measured for the ²H($\text{d}$$\text{n}$)³He reaction at θ = 0° over an incident deuteron energy range from 1 to 15 MeV in 0.5 MeV steps. The results agree with the previous ²H($\text{d}$$\text{n}$)³He measurements of Simmons et al. and are nearly identical to the ²H($\text{d}$$\text{n}$)³H measurements of Clegg et al. in the region of overlap. The present results provide an accurate and complete set of the observables necessary to use the ²H($\text{d}$,$\text{n}$)³He reaction as a source of polarized neutrons.     

Combinatorial materials research applied to the development of new surface coatings: VIII: Overview of the high-throughput measurement systems developed for a marine coating workflow

A combinatorial workflow has been produced for the development of novel, environmental-friendly marine coatings. A particularly challenging aspect of the workflow development was the selection and development of high-throughput screening methods that allow for some degree of prediction of coating performance in the aquatic environment of interest. The high-throughput screening methods currently in place include measurements of surface energy, viscoelastic properties, pseudobarnacle adhesion, and a suite of biological assays based on various marine organisms. An experiment involving a series of fouling-release coatings was used to correlate high-throughput screening data to data obtained from ocean site immersion testing. The results of the experiment showed that both bacterial biofilm surface coverage and storage modulus at 30 °C showed a good correlation with barnacle adhesion strength and a fair correlation with fouling rating, but surface energy and pseudobarnacle adhesion did not correlate with the results from ocean site testing.     

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.     

Stratified dust grains in the interstellar medium. III: Infrared cross-sections

We construct a model of interstellar dust in which H-rich amorphous carbon is deposited on silicate substrates in the interstellar medium, and is annealed to form H-poor amorphous carbon. The model grains are stratified spheres composed of hollow silicate cores coated with two carbonaceous layers, the inner layer of sp² carbon and the outer layer of sp³ carbon. Using an accurate method of computing the optical properties of such layered grains, we explore the consequences of varying the core-grain size distribution and the thicknesses of the carbonaceous layers on the resulting infrared extinction. We find a wide dispersion in the curve morphology that reflects the grain size distributions and the chemical composition of dust materials.     

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.     

The brute-force polarization of 23Na and the 23Na(n, γ)24Na reaction

A Na target has been polarized by brute force to 22% and the γ-radiation produced by polarized thermal neutron capture has been investigated. The J^π = 2⁺ channel spin contribution has been determined model-independently and unambiguously for 22 primary transitions. The average J^π = 2⁺ channel contribution is 5.8(5)%. The data resulted in one spin assignment and two spin restrictions. The energies and lifetimes of positive-parity levels as well as branching ratios and the magnetic moment of the ground state are in agreement with a shell-model calculation in the complete sd shell.