Porous substoichiometric TiO2 anodes as reactive electrochemical membranes for water treatment.

This research investigates the characterization and testing of an anodic reactive electrochemical membrane (REM) for water treatment. The REM consists of a porous substoichiometric titanium dioxide (Ti4O7) tubular, ceramic electrode operated in cross-flow filtration mode. Advection-enhanced mass transfer rates, on the order of a 10-fold increase, are obtained when the REM is operated in filtration-mode, relative to a traditional flow-through mode. Oxidation experiments with model organic compounds showed that the REM was active for both direct oxidation reactions and formation of hydroxyl radicals (OH(•)). Electrochemical impedance spectroscopy data interpreted by transmission line modeling determined that the electro-active surface area was 619 times the nominal geometric surface area. Results from filtration-mode experiments with p-methoxyphenol indicate that compound removal occurred by electro-assisted adsorption and subsequent oxidation. Electro-assisted adsorption was the primary removal mechanism at potentials where OH(•) did not form. At higher potentials (>2.0 V), where OH(•) concentrations were significant, p-methoxyphenol removal occurred by a combination of electro-assisted adsorption and OH(•) oxidation. These removal mechanisms resulted in 99.9% p-methoxyphenol removal in the permeate, with calculated current efficiencies >73% at applied current densities of 0.5-1.0 mA cm(-2). These results illustrate the extreme promise of the REM for water treatment.