György Fóti

Oxidation of organics by intermediates of water discharge on IrO2 and synthetic diamond anodes

IrO2 and boron-doped diamond electrodes were tested by preparative electrolysis of simple model compds. in acid medium. In oxidn. reactions of more complex mechanism than simple electron transfer, these electrodes are active only at potentials of simultaneous oxygen evolution. At IrO2 electrodes, the reaction is mediated by chemisorbed oxygen, probably forming IrO3-type active sites, and yield highly selective oxidn. products at low overpotentials and with moderate current efficiency. At diamond electrodes, mediation at high overpotentials is due to physisorbed OH radicals leading to complete combustion of the org. compd. with high current efficiency. [on SciFinder (R)]

Basic principles of the electrochemical mineralization of organic pollutants for wastewater treatment

The electrochemical mineralization of organic pollutants is a new technology for treatment of dilute wastewater (COD < 5 g∕L). In this method, utilizing the electrical energy, a complete oxidation of pollutants can be achieved on high oxidation power anodes. An ideal anode for this type of treatment is a boron-doped diamond electrode (BDD) characterized by a high reactivity toward organics oxidation. In the present work, both thermodynamic and kinetic aspects of organics mineralization are discussed. The proposed theoretical kinetic model of organics mineralization on BDD anodes is in excellent agreement with the experimental results. In addition, the economical aspect of electrochemical organics mineralization is reported.

Role of unreacted silanols in the adsorption properties of derivatized silica

Abstract The adsorbents studied were samples of a precipitated silica, covered with a dense layer of (3,3-dimethylbutyl)dimethylsiloxy-, (5-cyano-3,3-dimethylpentyl)-dimethylsiloxy-and tetradecyldimethylsiloxy-substituents. Deuteration of unreacted silanols across the graft was investigated, using dilute solutions of hydroxy-deuterated water, methanol and ethanol in acetonitrile. Excess adsorption isotherms of the solutes were also determined. The results suggest that access to all silanols is sterically hindered by the surface substituents but to different extends. They are accessible in a time average through occasional holes in the graft, formed by the lateral vibrational motion of the substituents.

Electrochemical Oxidation of Organics on Iridium Oxide and Synthetic Diamond Based Electrodes

Oxidative electrochemical processes promising versatility, environmental compatibility and cost effectiveness have a continuously growing importance both in selective organic synthesis and in the electrochemical incineration (ECI) of organic pollutants in aqueous media. In the case of organic electrosynthesis selectivity is to be enhanced and in the ECI process the aim is the mineralization of the toxic and non-biocompatible pollutants with high current efficiency.1-10Anodic oxidation of organics may proceed by several mechanisms including direct and indirect oxidation.

Electrochemical Promotion of Catalysis

A review with refs. concerning electrochem. promotion of catalysis is presented. Recent progress made in our lab. in the field of electrochem. promotion of heterogeneous catalytic gas reactions is presented. The phenomenon consists of non-Faradaic modification of the catalytic reaction rate as the result of electrochem. polarization of the interface between the catalyst and the solid electrolyte support. Two main aspects are addressed, the description of the phenomenon and the development of bipolar cell configurations suitable for practical applications. It is shown that the necessary condition to achieve electrochem. promotion is the formation of a double layer at the catalyst/gas interface by mechanism of ion backspillover from the solid electrolyte support. Electrochem. promotion is only feasible in an adequate temp. range, limited by the mobility and the lifetime of the promoting ion, and it is favored by high porosity and low film thickness of the catalyst. On the application side, two new cell designs have been developed, a ring-shaped and a multiple-channel configuration, both operated in bipolar polarization mode. The ring-shaped cell is shown to be almost free of current bypass. Feasibility of electrochem. promotion is successfully demonstrated with both configurations. Realization of efficient bipolar cell configurations for electrochem. promotion is very promising in view of future applications in dispersed catalytic systems. [on SciFinder (R)]

Retention on non-polar adsorbents in liquid—solid chromatography: Effect of grafted alkyl chains

Abstract The retention of 39 molecular probes was measured on chemically bonded dense layers of (3,3-dimethylbutyl)dimethylsiloxy (DMB) and tetradecyldimethylsiloxy (C 14 ) substituents on silica as a function of the composition of the binary acetonitrile-water eluent. The sign of the “associated system peak” was also noted. The composition dependence of retention, measured as areal retention volume, could be described on both non-polar stationary phases by the two-parameter Snyder-Soczewinski equation and by the three parameter Schoenmakers equation in a broad but restricted composition range. The areal retention volume on the surface with grafted alkyl chains was equal to or higher than that on the non-swellable, smooth, non-polar DMB surface. Additional retention on the C 14 surface increased with increasing adsorption force (retention) on the DMB surface and it was a function of the composition of the eluent. A possible interpretation of the sign of the “associated system peak” generated by the injection of a pure solute is also given in terms of salvation of the solute in the mobile phase and in terms of the modification of the non-polar adsorbent by the adsorbed solute.

Packing density of organyldimethylsiloxy-covered silica gel and hydrolytic stability of the coating

Abstract Packing densities of different surface-modified silicon dioxide preparations were determined. Packing densities relative to thesilicon dioxide matrix were nearly independent of the nature of the modifying monolayer. Also, the surface concentration of dense organyldimethylsiloxy layers did not diminish during contact with acetonitrile-water mixtures for two years.

Classical Retention Mechanism in Ion Exchange Chromatography. Theory and Experiment

The classical model for ion exchange chromatography is characterized by firmly adsorbed driving ions at the surface of the stationary phase in an amount required by electroneutrality and stoichiometric ion exchange between the bulk of the eluent electrolyte and this immobilized Stern layer. Retention equations have been derived for system peaks, labeled eluent ions, and analytes in a system containing only strong electrolytes by strictly respecting this model. It is shown that the classical model described dependence of retention data on concentration and composition of the binary eluent with excellent precision, but the resulting system parameters were not self-consistent. Inconsistency of the results might be due to contributions from another retention mechanism.

Note on the net retention volume in chromatography with a real gas as a carrier

The problem of the calculation and interpretation of the net retention volume with a real gas as carrier is revisited. The properties of the carrier are described by a first order virial equation of state. The net retention volume of a solute is related to the mean flow rate of the carrier, therefore determination of the mean flow rate of a real gas carrier is reviewed. It is shown that the mean flow rate cannot be calculated from the mean column pressure. With a real gas carrier the local capacity factor depends on the local pressure of the real gas. The basic relationship between the net retention volume and the function describing this pressure dependence is also reviewed. Precise formulae as well as practical approximations are presented for the calculation of the mean flow rate, of the mean column pressure, and of a representative pressure related to the mean capacity factor.

Anodic Oxidation of Organics on Oxide Anodes

The electrochemical oxidation (or combustion) of organics with simultaneous oxygen evolution has been investigated using different oxide electrodes. A simplified mechanism for the electrochemical oxidation of organics is presented, according to which selective oxidation occurs with oxide anodes (MOx) for which the formation of higher oxides (e.g.: MOX+1,) is possible. Combustion occurs at electrodes with oxidatively saturated surface. Detection of OH radicals formed by water discharge at different anodes using N,N dimethyl-p-nitrosoaniline (RNO) as a spin trap and preparative electrolysis confirmed the proposed mechanism.