Tubular carbon nanotube-based gas diffusion electrode removes persistent organic pollutants by a cyclic adsorption – Electro-Fenton process

[Display omitted] •Cyclic adsorption – electro-Fenton process overcomes drawbacks of electro-Fenton process.•Microtube out of MWCNT functions as a gas diffusion electrode and porous adsorber.•Pollutants are first removed electroless by adsorption on the CNT-microtube.•Pollutants are then degraded electrochemically on CNT-microtube electrode. We report a novel tubular electrochemical cell which is operated in a cyclic adsorption – electro-Fenton process and by this means overcomes the drawbacks of the traditional electro-Fenton process. A microtube made only of multi-walled carbon nanotubes (MWCNT) functions as a gas diffusion electrode (GDE) and highly porous adsorber. In the process, the pollutants were first removed electroless from the wastewater by adsorption on the MWCNT-GDE. Subsequently, the pollutants are electrochemically degraded in a defined volume of electrolyte solution using the electro-Fenton process. Oxygen was supplied into the lumen of the saturated microtubular GDE which was surrounded by a cylindrical anode made of Ti-felt coated with Pt/IrO2 catalysts. For the proof of concept the model pollutant Acid Red 14 (AR14), an azo dye, was used. The decomposition of AR14 was studied at different applied current densities and initial concentrations of ferrous iron in the electrolyte solution. At optimal conditions, complete regeneration of the adsorption capacity of the MWCNT-GDE, complete decolorization and TOC and COD removal rates of 50% and 70% were achieved, respectively. The MWCNT-GDE is regenerated and again available for adsorption. This approach allows water treatment independent of its composition, thus does not require any addition of chemicals to the wastewater.