Quantitative 2D electrooxidative carbon nanotube filter model: Insight into reactive sites

In this study, the electrooxidative carbon nanotube (CNT) filtration of sorptive methyl orange (MO) and non-sorptive ferrocyanide was investigated by both experiment and numerical simulation. The two-dimensional numerical model includes target molecule; mass transport, adsorption, and electron transfer and product desorption. For MO, the model was calibrated with experimental reaction rates from the mass- and electron-transfer limited regimes and accurately predicted effluent concentrations over a much larger range of conditions. For ferrocyanide, five CNT electrodes of various specific surface area and surface oxygen content were utilized and a similar single reaction site model to MO accurately predicted kinetics at low anode potentials while a two-site model was necessary at higher potentials yielding insight into the CNT reactive sites. For example, at low anode potentials (<= 0.2 V), the kinetics have a linear correlation with CNT surface area indicating the sp(2) conjugated sidewall sites are dominant. In contrast, at higher anode potentials (>= 0.3 V), the kinetics were significantly greater than expected from CNT surface area and the differential kinetics have a linear correlation with the CNT surface oxygen content indicating the CNT tips were also electroactive. The spatial distribution of internal electrode mass transport and surface reactivity is discussed. (C) 2014 Elsevier Ltd. All rights reserved.