Nitrogen-Doped Graphitized Carbon Electrodes for Biorefractory Pollutant Removal

A novel material was fabricated by deposition of graphitized nitrogen-doped porous carbon layer (NPC) on commercial carbon felt (CF). The NPC was obtained via atomic layer deposition of zinc oxide (ZnO) and its subsequent solvothermal conversion to zeolitic imidazolate framework (ZIF-8) followed by its carbonization under controlled atmosphere. Both physical and electrochemical properties have been evaluated by scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, nitrogen sorption, contact angle, and cyclic voltammetry measurements. The parameters affecting the growth of NPC, such as the amount of ZnO/ZIF-8 material before calcination and thermal treatment temperature, have been investigated in detail. The versatility of the as-prepared NPC/CF material was assessed by studying (i) its adsorption ability and/or (ii) its behavior as cathode in electro-Fenton process (EF) for the elimination of a model refractory pollutant (acid orange 7 (AO7)). Once used as adsorbent, the NPC/CF proved good adsorption capacity with 97% color removal of initial 0.02 mM dye concentration after 30 min. Moreover, the application of such novel cathode could also reduce the cost for EF technology by using lower energy consumption at 0.54 kWh g(-1) TOC (total organic carbon). The apparent rate constant (k(app) similar to 0.8 min(-1)) obtained for NPC/CF was more than 7 times higher compared to pristine CF commercial electrode, thus leading to more than 90% TOC removal in 8 h. In addition, high reaction efficiency and system durability were attributed to continuous regeneration of the NPC/CF sorption capacity upon total mineralization of the pollutants accumulated at the electrode surface. Results confirmed that the new NPC/CF material behaves as a highly active electrode with attractive adsorption efficiency and at the same time it possesses an excellent electrochemical activity in the EF oxidation process for the removal of persistent water pollutants.