Double-layer Approach Research Articles

The double-layer approach to promotion, electrocatalysis, electrochemical promotion, and metal–support interactions

Recent progress in understanding and modeling promotion, electrocatalysis, electrochemical promotion, and metal–support interactions is surveyed. It is shown that via the action of spillover and via the concept of the sacrificial promoter, the phenomena of promotion, electrochemical promotion, and metal–support interactions are functionally identical and only operationally different, as they all correspond to catalysis in presence of a controllable double layer. This is then utilized to derive adsorption isotherms and kinetic expressions which account explicitly for the electrostatic interactions between the double layer and the adsorbed reactants, intermediates, and products. The resulting analytical expressions are shown to be in excellent semiquantitative agreement with experiment and with the recently established promotional rules.

Liquid chromatographic determination of total and β- N-oxalyl- l-α,β-diaminopropionic acid in Lathyrus sativus seeds using both refractive index and bioelectrochemical detection

A further improved chromatographic method for the simultaneous determination of the total amount of ODAP, selectively the amount of its neurotoxic form, β-ODAP, and free l-glutamate in raw Lathyrus sativus (grass pea) seed samples is described using post-column refractive index in combination with bioelectrochemical detection. The biosensor is based on crosslinking horseradish peroxidase (HRP) and an Os-containing mediating polymer with poly(ethyleneglycol)(400) diglycidyl ether (PEGDGE), forming an inner hydrogel layer and then immobilising l-glutamate oxidase (GlOx) as an outer layer on top of a graphite electrode. Addition of polyethylenimine (PEI) to the hydrogel is believed to have sensitivity and stability enhancing effect on the biosensor. The double-layer approach in the biosensor construction avoided direct electrical wiring of GlOx and resulted in a higher sensitivity of 4.6 mA/ M cm 2 with respect to β-ODAP and a wider linear range (1–250 μ M) for both l-glutamate and β-ODAP when compared with a single-layer approach where GlOx, HRP, and Os-polymer are crosslinked together. The limit of detection for the chromatographic–biosensor system was found to be 2 μ M with respect to β-ODAP and 0.7 μ M with respect to l-glutamate. The refractive index detection on-line with the biosensor enabled full control of the chromatographic system for the determination of the total amount of ODAP, selectively the amount of β-ODAP and l-glutamate. Ten grass pea samples have been collected from Lathyrism prone areas of Ethiopia to test the applicability of the presently developed analytical system for real sample analysis. The toxin levels of grass pea collections were determined in an aqueous extracts and ranged from 0.52 to 0.76%, dry mass basis. Comparison of results of an established spectrophotometric assay and that of the present system has shown an extraordinary degree of agreement as revealed by parallel “ t” test (90% confidence limit). The present system has operational stability of more than 50 h. Analysis time per sample is 10 min after extraction for 90 min.

Gas permeability coefficients of ethylene-vinyl acetate copolymer-modified poly(dimethylsiloxane) membranes. Double-column approach for two-phase materials

The Maxwell and the Landauer equations were modified on the basis of the double-layer approach, and that of the double columm approach, for the description of the permeability of a gas through two-phase membranes. The first approach was not found to be useful for the permeability description. With the double-columm approach, the following modified Maxwell and Landauer equations were obtained : the modified Maxwell equation (P-P a )/(P+2P a )=V b (P b -P a )/(P b +2P a ), and the modified Landauer equation (P + 2P b )(P-P a )/(3P) = V b (P b -P a ), where P, P a and P b are the permeability coefficient of the overall system, and of component A and B, respectively, and V b is the volume fraction of component B. The modified equations describe the variation of the measured oxygen and nitrogen permeabilities with the polydimethyl siloxane (PDMS) fraction in ethylene-vinyl acetate copolymer (EVAC)- modified PDMS membranes much better than the original equations. These equations also apply to water vapor with the polyether sulfone (PES) fraction in the PES-phenoxy blends by Swinyard.

Regeneration of periodontal ligament and cementum by BMP-applied tissue engineering.

Previously, we demonstrated that the inductive properties of bone morphogenetic protein (BMP) highly depend on the nature of the carrier material used for implantation. In this paper, we show that administration of BMP incorporated in a fibrous collagen membrane can help to regenerate periodontal ligament and cementum both in cat canines and in monkey molars. The partially purified bovine BMP was combined with one or two layers of a fibrous collagen membrane. Although the single layer approach showed partial regeneration of periodontal defects, it also quite often led to ankylosis. The double layer technique in artificially prepared class III furcation defects in monkey molars gave favorable results. After 12 wk, not only the alveolar process but also the periodontal ligament and cementum had regenerated along the entire treated dentin surface. Collagen fibers were arranged more or less perpendicular to the surface of the new cementum. Ankylosis was not seen. It is concluded that the double-layer approach is superior to the single-layer technique in regenerating cementum.

Surface Structures of 4-Chlorocatechol Adsorbed on Titanium Dioxide

TiO2 has been extensively studied as a photocatalyst for the complete oxidation of a variety of organic pollutants commonly found in groundwater. In this paper, we investigate the surface structures formed between an organic substrate and TiO2 in the context of understanding how these specific surface interactions affect photoreactivity. The surface complexes formed by 4-chlorocatechol (CT) sorbed on TiO2 are investigated as a function of concentration and of pH. Singular-value decomposition of the IR spectra of CT adsorbed on TiO2 indicates that a single bidentate chemisorbed species is present over the pH range of 2−10. The surface-bound species appears to have 40% covalent and 60% ionic bond character. The pH dependence of the adsorption isotherms is modeled using a generalized electric double-layer approach. The data are consistent with the formation of a bidentate binuclear surface group for solution CT concentrations below 50 μM followed by nonspecific multilayer partitioning at concentrations above 100 μM.

An attempt to solve the Geodetic Boundary Value Problem, using a double layer approach for Malkin’s function Stokes’ accuracy accepted

The Boundary Value Problem of Physical Geodesy is usually treated as the problem of finding reliable corrections to be applied to an accepted ellipsoidal model of the Earth in order to get the true values of the gravitational force and the shape of its level surfaces in external space. The accuracy in determining these corrections corresponds, as a rule, to neglecting errors of the order of the flattening of the Earth (3‰, of obtained values). This first approximation identifies the Earth's topography with the so-called Telluroid (see Fig. 1 and below), and uses as only boundary values s.c. true free air anomalies (see not:s). To study the solvability of this problem, integral equations are well suited. For numerical work, they are now-a-days not difficult to handle, because of the availability of powerful high-speed computers. As to my opinion, there is not yet any fully satisfactory solution obtained, which fulfills all boundary conditions. If it should turn out, that no available harmonic models can satisfy the surface-condition and the infinity-conditions (see below) with sufficient accuracy (see above), we have to admit, that we need additional information along the Earth's surface to be able to solve this important problem, by reducing it to the level case of Stokes (see Appendix 1). The paper describes a direct use of a double-layer approach for the s.c. Malkin's function Hy (see below), from which all wanted corrections in space may be deduced. This approach is suggested, because the solvability condition of the resulting singular Fredholm-equation can be used for defining, beforehand, the correct model gravity y . The solution, by definition of the double layer potential, satisfies the weaker infinity condition. DOI: 10.1111/j.2153-3490.1969.tb00465.x