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Membrane capacitive deionization (MCDI) is a promising technique to achieve desalination of low-salinity water resources. The primary requirements for developing and designing materials for MCDI applications are large surface area, high wettability to water, high conductivity, and efficient ion-transport pathways. Herein, we synthesized ionic covalent organic nanosheets (iCONs) containing guanidinium units that carry a positive charge. A series of quaternized polybenzimidazole (QPBI)/iCON (iCON@QPBI) nanocomposite membranes was fabricated using solution casting. The surface, thermal, wettability, and electrochemical properties of the iCON@QPBI nanocomposite membranes were evaluated. The iCON@QPBI anion-exchange membranes achieved a salt adsorption capacity as high as 15.6 mg g−1 and charge efficiency of up to 90%, which are 50% and 20% higher than those of the pristine QPBI membrane, respectively. The performance improvement was attributed to the increased ion-exchange capacity (2.4 mmol g−1), reduced area resistance (5.4 Ω cm2), and enhanced hydrophilicity (water uptake = 32%) of the iCON@QPBI nanocomposite membranes. This was due to the additional quaternary ammonium groups and conductive ion transport networks donated by the iCON materials. The excellent desalination performance of the iCON@polymer nanocomposite membranes demonstrated their potential for use in MCDI applications and alternative electromembrane processes.

The strongly implicit procedure is used to model the diffusion-only chronoamperometric responses of microband electrode geometries which deviate from the ideal. Specifically, attention is focused on four electrode shapes: elevated microband electrodes (with conducting supporting sides), recessed microband electrodes (with insulating pit walls), platform electrodes (with insulating supporting sides) and, for the purposes of comparison, a hypothetical line electrode without any support which permits diffusional mass transport to both sides of the infinitesimally thin electrode. In all cases the short time transient is found to be described by simple analytical expressions in which the contributions from linear diffusion over the electrode area(s) and non-linear diffusion to the electrode perimeters are clearly distinguishable. © 1995 Elsevier Science S.A. All rights reserved.

The efficient dehalogenation of aromatic substrates by electrochemical means is of potential synthetic value given the possibility of controlled and selective halide loss at low temperatures. Mechanistically the general picture [l-111 which has emerged is that whereas alkyl halides undergo one-electron reduction with simultaneous carbon-halogen cleavage, aryl halides follow a sequential route in which bond breaking follows electron transfer and radical anions of varying stability are formed as intermediates. The purpose of the work described in this preliminary note is to study whether photochemical activation of the electrogenerated radical anion intermediates can usefully influence the course of reaction. In particular, we examine the influence of light of wavelengths between 300 and 600 nm on the electroreduction of the p-halo-nitrobenzenes (p-X-N no evidence for nitrite loss is observed.

The reduction of m-iodo-nitrobenzene, m-I-φ-NO2, in acetonitrile solution was studied using both microdisk and channel electrodes. A voltammetric wave with a halfwave potential of -1.09 V (vs. saturated calomel reference electrode) was observed and both techniques showed that more than one electron was passed per molecule of the substrate. The rates of mass transport were varied in both electrode systems by changing either the electrode radius in the case of microelectrodes, or the electrolyte flow rate in the case of channel electrodes so as to identify the kinetics and mechanism of the electrode process. Both approaches indicated an ECE mechanism operates: m-I-φ-NO2 + e- → [m-I-φ-NO2]·- [m-I-φ-NO2]·- → I· + ·C6H4NO2 ·C6H4NO2 + HS → φ-NO2 φ.NO2 + e- → [φ-NO2]·- where HS denotes the solvent-supporting electrolyte system. The rate constants for the decomposition of the radical anion, [m-I-φ-NO2]·-, as determined by the two methods, were in excellent agreement and equal to 0.30 (0.05) s-1. Comparisons between the use of microdisks and channel electrodes for such studies are reported and their relative sensitivity assessed.

The 'strongly implicit procedure' is shown to be a general, easy-to-use, stable and computationally efficient method of solving the mass transport equations necessary to predict transient voltammetric responses of electrode processes to which diffusion, convection and homogeneous chemical reaction may all contribute. The method is illustrated with a diversity of problems relating to electrodes of both micro- and milli-dimensions. In all cases excellent agreement with experiment and/or existing analytical or numerical theory is noted. Comparisons are made with alternative computational methods. © 1996 Chapman and Hall.

The electroreduction of pentafluoronitrobenzene in dimethylformamide solution resulting in the formation of the dimer, octafluoro- 4, 4′-dinitro-biphenyl, is studied. The dimeric species is reduced further at the potentials applied to the corresponding di-anion. Microband electrodes are used in conjunction with a high speed channel flow cell to explore the mechanism of this process and to quantify the associated very fast homogeneous kinetics. In particular, the formation of the dimer is seen to proceed via the rate determining loss of fluoride anion from the initially formed radical anion of pentafluoronitrobenzene with a first order rate constant of 4.2 × 10 5 s −1 . The reduction of the dimer to its di-anion is seen to occur via a DISP2 mechanism in which the rate determining step is the disproportionation of the mono-anions of octafluoro,4,4′-dinitro-biphenyl with a rate constant of 2 × 10 8 M −1 s −1 . The merits of high speed channel electrodes for the measurement of fast homogeneous kinetics are examined and compared with those of microdisc voltammetry in stationary solution.

The application of channel electrodes for quantitative in situ electrochemical ESR studies of unstable radicals is discussed with reference to two systems. First, the reduction of 1-bromo-anthraquinone in acetonitrile solution in the presence of laser light of wavelength 488 nm is shown to lead to the loss of bromide and the formation of the anthraquinone radical anion via a photo-ECE process. The kinetics of this reaction as determined by channel electrode ESR studies are found to be in good agreement with those measured by independent methods. Second, the one-electron reduction of the methyl viologen dication in aqueous solution is shown to lead to the formation of viologen radicals which are known to dimerise. However, it is shown that since this reaction is rapid and reversible, measurements of the ESR signal as a function of electrolyte flow rate and current are essentially blind to this reaction. Lower estimates for the dimerisation rate constant are deduced.

Numerical simulations are used to predict the chronoamperometric current transients resulting from an ECE process at both hemicylinder and band microelectrodes. Working curves are presented to permit the analysis of experimental data. It is demonstrated that the long-time behaviour at a band of width w and length xe is identical with the current at a hemicylinder of width w and radius a = xc 4, as has previously been shown to be the case for electrode processes involving simple electron transfer in the absence of coupled homogeneous kinetics. © 1995.

The photoelectrochemical reduction of p -bromo-nitrobenzene in acetonitrile solution, containing tetrabutylammonium perchlorate as supporting electrolyte, was studied using a platinum channel electrode. It is shown that p -bromo-nitrobenzene is reduced at a half-wave potential of −0.98 V (vs. Ag pseudo-reference electrode) to form a radical anion which is stable in the absence of light. On irradiation with light of wavelength 330 nm, corresponding to an absorption band in the radical anion, appreciable photocurrents flow and in situ electrochemical electron spin resonance (ESR) shows the formation of the nitrobenzene radical onion. The mechanism of formation is shown to occur via a “photo-ECE” mechanism rather than either “photo-ECEE” or “photo-DISP” processes by means of (i) the variation in photocurrent with flow rate, and (ii) novel phototransient experiments in which the photocurrent is followed after the step-wise application of light to the system after steady-state transport l imited currents have been established in the dark at various flow rates. Experiments conducted in the presence of different concentrations of added Br − show steady-state photocurrents that are diminished relative to those flowing under corresponding conditions in the absence of added Br − . The kinetic modelling of this effect is consistent with a light-induced breakage of the carbon-bromine bond in the C-step of the ECE process followed by reaction of the ·φNO 2 radical thus formed with both Br − and the solvent system.

The in situ measurement of EPR spectra of radical ions generated at the polarized liquid/liquid interface is described in relation to the 7,7,8,8-tetracyanoquinodimethane (TCNQ), 2,3,5,6-tetrachloro-p-benzoquinone (TCBQ), and 2,3,5,6-tetrafluoro-p-benzoquinone (TFBQ) radical anions and the tetrathiafulvalene (TTF) radical cation. TCNQ and TTF were chosen as model compounds with which to quantify the performance of a novel liquid/ liquid electrochemical EPR cell. The anion radical of TCNQ and the cation radical of TTF in 1,2-dichloroethane (DCE) were produced at the water interface by electron transfer from/to the aqueous-phase ferricyanide/ferrocyanide redox couple by applying a potential difference between the two phases with a four-electrode potentiostat. The EPR signal intensity (at constant magnetic field) of the resultant organic radicals was monitored during potential step experiments which indicated that the EPR data could be modeled in terms of diffusional transport. TCBQ and TFBQ were chosen as compounds to model the electron transfer behavior of biologically important quinones at the oil/water interface. The EPR and voltammetric data obtained from TCBQ/TCBQ-· and TFBQ/ TFBQ-· indicated unambiguously that the two semiquinones are stable at the DCE/water interface and do not undergo immediate protonation.

The strongly implicit procedure is shown to be an easy-to-use stable, rapid and computationally efficient method of solving the coupled mass transport equations which describe complex electrode reactions involving diffusion, convection and homogeneous chemical steps. The method is illustrated with a diversity of problems pertaining to both microelectrodes and electrodes of conventional dimensions located in a rectangular channel through which electrolyte is pumped under laminar conditions. In all cases excellent agreement with experiment and/or existing analytical or numerical theory is noted.