States of orientation of pyridine and 1,4-pyrazine as a function of electrode potential and surface charge at a high-area, porous C electrode

In the course of earlier work on development of electrochemical procedures for adsorptive removal of noxious organic impurities from waste waters, using high specific-area carbon-cloth electrodes, we have found a major promoting influence of electrode potential applied through galvanostatic or potentiostatic polarization. In the present paper, those effects are examined more quantitatively using pyridine and 1,4-pyrazine as model adsorbates. The effects of electrode-potential changes are followed by means of double-layer capacitance measurements and related changes of surface charge-density with variation of electrode potential. Extents of adsorption as a function of potential and time are directly evaluated by means of in situ UV–Vis spectrometry in a combined electrochemical optical absorbance cell. The effects of changes of electric polarization of the C electrode surface are interpreted in terms of an Esin and Markov type of effect through evaluations of surface-potential (χ) changes due to adsorption and interfacial orientation of the organic adsorbates in the double-layer interphase, coupled with changes of the solvent–water orientation. The results obtained for C are analogous to those found at Hg.