Aqueous interfaces methodology

Tejedor-Tejedor, M.L Yost, E.C. Anderson, M.C. (1990a) Characterization of benzoic acid and phenolic complexes at the goethite/ aqueous solution interface using cylindrical internal reflectance Fourier transform infrared spectroscopy. Part 5 Methodology. Langmuir 6 979-987... 

The transfer of bromine across liquid-liquid and gas-liquid interfaces is of considerable interest, for example, for sensor systems or for fundamental insights in the effects of bromine in the environment. A new methodology for kinetic studies at a lipid layer has been reported by Zhang etal. ]138]. A microelectrode immersed in the aqueous phase is placed in close distance to a lipid surface layer in contact with a gas phase. The oxidation of bromide at the electrode causes the formation of bromine, which in part escapes through the lipid layer into the gas phase (see Scheme 4). 

The membrane system considered here is composed of two aqueous solutions wd and w2, separated by a liquid membrane M, and it involves two aqueous solution/ membrane interfaces WifM (outer interface) and M/w2 (inner interface). If the different ohmic drops (and the potentials caused by mass transfers within w1 M, and w2) can be neglected, the membrane potential, EM, defined as the potential difference between wd and w2, is caused by ion transfers taking place at both L/L interfaces. The current associated with the ion transfer across the L/L interfaces is governed by the same mass transport limitations as redox processes on a metal electrode/solution interface. Provided that the ion transport is fast, it can be considered that it is governed by the same diffusion equations, and the electrochemical methodology can be transposed en bloc [18, 24]. With respect to the experimental cell used for electrochemical studies with these systems, it is necessary to consider three sources of resistance, i.e., both the two aqueous and the nonaqueous solutions, with both ITIES sandwiched between them. Therefore, a potentiostat with two reference electrodes is usually used. 

The dry surface chemistry, i.e. chemistry of solid-gas interfaces has its own methodology and language. A substantial difference between wet and dry surface chemistry is that adsorption from solution is always an exchange, the empty surface is in fact occupied by solvent. In spite of an obvious relationship between dry and wet surfaces, only wet surface chemistry will be discussed here, although some quantities (e.g. the BET surface area) and relationships involve results obtained for dry surfaces. In particular, certain adsorbates considered show substantial vapor pressure at room temperature, and sorption of their vapors has been studied. Such results, albeit related to sorption of the same species from aqueous solution are beyond the scope of the book. 

Tejedor-Tejedor, M. I., Yost, E. C., and Anderson, M. A., Characterization of benzoic complexes at the goethite/aqueous solution interface using cylindrical internal reflection Fourier transform infrared spectroscopy. Part I. Methodology, Langmuir, 6, 980-987 (1990). 

Further development of the SLM-ionic liquid methodology has been coupled with lipase-catalyzed esterification and ester-hydrolysis reactions in the feed gas (interface 1) and receiving phase (interface 2), respectively, to facilitate selective transport of various organic acids with aryl groups (via their esters) from aqueous solutions by utilizing different substrate specificity of lipases in a SLM system (Fig. 5.6-11) [118]. In the enzymatic SLM systems a poly(propene) membrane with water-immiscible [RMIM][X] (R = butyl, hexyl, octyl and X = [PFe]" and [(CF3S02)2N] ) ionic liquid phases were used. 

---