A multi-walled carbon nanotube electrode based on porous Graphite-RuO2 in electrochemical filter for pyrrole degradation

A novel electrochemical filter has been prepared for the effective adsorption and electrochemical oxidation of aqueous organic pollutants. The adsorptive electrode utilized in the electrochemical filter was a porous Graphite-RuO2 electrode decorated with multi-walled carbon nanotubes (MWCNTs) adsorption layer, which was prepared by sol-gel coating, thermal decomposition, and vacuum filtration synthesis. The morphology and composition of adsorptive electrode characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) revealed a uniform distribution of RuO2 active coating and MWCNTs adsorption layer. Electrochemical measurements indicated that the adsorptive electrode possessed a favorable oxygen evolution potential (OEP) of 1.42 V and inner voltammetric charge 170.05 mC·cm−2, which were higher than that of non-MWCNTs electrode. Furthermore, the mass transfer of adsorptive electrode was enhanced as high as 4.6-fold in the electrochemical filter. The optimal operation parameters obtained was 3 mA·cm−2 and 7 g·L−1 Na2SO4. Under this condition, the electrochemical filter can remove > 97% of pyrrole and >75% of total organic carbon. The pyrrole oxidation mechanism of electrochemical filter was also investigated, revealed three dominant reaction stages: adsorption (≤0.3 V), direct oxidation (0.3-1.2 V) and indirect oxidation (>1.2 V). In general, the high electrochemical performance of Graphite-RuO2-MWCNTs filter on pyrrole removal resulted from the enhanced mass transfer, which attributed to the synergistic effect of adsorption from MWCNTs, electrochemical oxidation and convection by filtration.