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The Measurement of the Gibbs Energy of Transfer Between Oil and Water Using a Nano‐Carbon Paste Electrode
Author(s) -
Gan Patrick,
Lowinsohn Denise,
Foord John S,
Compton Richard G
Publication year - 2014
Publication title -
electroanalysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.574
H-Index - 128
eISSN - 1521-4109
pISSN - 1040-0397
DOI - 10.1002/elan.201300478
Subject(s) - aqueous solution , dissolution , adsorption , chemistry , electrochemistry , electrolyte , electrode , gibbs free energy , cyclic voltammetry , ferrocene , carbon fibers , redox , analytical chemistry (journal) , voltammetry , inorganic chemistry , materials science , organic chemistry , physics , quantum mechanics , composite material , composite number
The use of nano‐carbon paste electrodes for the measurement of Gibbs energies of transfer between oil and aqueous phases is reported. In this method the oil of interest is used as the binder for the nano‐carbon paste electrodes and the molecule of interest is dissolved in the organic or aqueous phase. Voltammetry is performed over a period of time and used to monitor the transfer of the molecule between the two phases. The method is illustrated for the transfer of ferrocenemethanol between water and oil using the ferrocenemethanol / ferroceniummethanol (FcCH 2 OH/FcCH 2 OH + ) redox couple. Three pairs of voltammetric peaks were observed in a 0.1 M KCl solution when the nano‐carbon paste electrode was modified by dissolution of FcCH 2 OH in the binder oil: P1 [ E =0.23 V, 0.17 V vs. Ag/AgCl (1 M KCl)], P2 [ E =0.36 V, 0.32 V vs. Ag/AgCl (1 M KCl)] and P3 [ E =0.55 V, 0.46 V vs. Ag/AgCl (1 M KCl)]. These are assigned to the FcCH 2 OH species existing in the aqueous solution [FcCH 2 OH(aq)/FcCH 2 OH + (aq)], originating in the oil (o) [FcCH 2 OH(o)/FcCH 2 OH + (aq)] and to oxidation of adsorbed (ads) material on the nano‐carbon [FcCH 2 OH(ads)] respectively. When supporting electrolyte containing the anions Cl − , NO 3 − or SCN − was used, an expulsion of the oxidised ferrocene occurred and the difference in midpoint potentials ( E mid ) between the peaks P1 and P2 observed in these experiments allowed the calculation of the Gibbs energy (Δ G° ) of transfer of ferrocenemethanol from water to oil. The average Δ G° value thus obtained was (−12.7±0.2) kJ mol −1 . For more hydrophobic anions (X − =PF 6 − , AsF 6 − ), the electron transfer is coupled to the transfer of the anion into the oil and the Δ G° for the transfer of the ion pair of FcCH 2 OH + and X − ions from water to oil was found to be −1.3 and −3.9 kJ mol −1 for PF 6 − and AsF 6 − respectively.