Porous Substoichiometric TiO₂ Anodes as Reactive Electrochemical Membranes for Water Treatment

Abstract

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.

Mineralization of organic pollutants by anodic oxidation using reactive electrochemical membrane synthesized from carbothermal reduction of TiO2

“…This technological constraint also limits the potential for scaling up. Implementation of flow-through porous electrodes is the most promising way to overcome mass transfer limitations (Zaky and Chaplin, 2013;Ganiyu et al, 2015;Radjenovic and Sedlak, 2015;Ronen et al, 2016).…”

“…The reactivity of the material has been investigated by using probe molecules (oxalic acid, coumarin, terephthalic acid) showing that both DET and formation of OH were involved in the oxidation of organic compounds Chaplin, 2013, 2014;Ganiyu et al, 2016). First studies on TiO x REM used either commercial Ebonex ® membranes (Walsh and Wills, 2010;Zaky and Chaplin, 2013) or TiO 2 ultrafiltration membranes reduced to Ti 4 O 7 under 1 atm H 2 during 50 h at 1050 C . The latter showed the most promising results because of a higher permeability and predominance of the Ti 4 O 7 phase but high production costs are associated to the synthesis method.…”

Using TiO2 Mesoflower Interlayer in Tubular Porous Titanium Membranes for Enhanced Electrocatalytic Filtration

“…The observed OEP for the TPTM/TMF/ATO 2.22 V (vs SCE) was significantly higher than that for TPTM/ATO 1.85 V (vs SCE). This OEP of 2.22 V is also higher than reported OEP of carbon nanotube (CNT) membranes (1.27 V) [6,7,36], metallic oxide (e.g., TiO 2 , SnO 2 , and Bi-doped SnO 2 )-coated carbon-based membranes (1.55-1.89 V) [1,4,7], and Ti 4 O 7 membranes (2.14 V) [3]. In addition, TPTM/TMF/ATO also gained a larger Tafel slope of 2.25 V than both TPTM/ATO (0.84 V, inset of Fig.…”

“…Electrocatalytic filtration (EF), a process that takes the advantages of electrochemical oxidation and membrane filtration has drawn much attention recently [1][2][3][4]. In the EF process, mass transfer of the target pollutant from the bulk solution to the membrane surface is significantly enhanced due to forced convection by filtration, while the electrochemical oxidation of pollutants that take place simultaneously on conductive membrane anode can be greatly promoted because of the existence of large amounts of active reaction sites on the anode.…”

“…Among the popular electrochemical catalysts (e.g. boron-doped diamond (BDD) [13], RuO 2 [14], Ti 4 O 7 [3,15], IrO 2 [16], PbO 2 [17], and Sbdoped SnO 2 (ATO) [18]), ATO is considered an excellent candidate owing to its high oxygen evolution potential (OEP), 1.8 V (vs saturated calomel electrode, SCE) [18], easy in preparation and cost efficiency. Electrocatalytic properties (e.g.…”