Highly graphitic Fe-doped carbon xerogels as dual-functional electro-Fenton catalysts for the degradation of tetracycline in wastewater

Fe-doped carbon xerogels with a highly developed graphitic structure were synthesized by a one-step sol-gel polymerization. These highly graphitic Fe-doped carbons are presented as promising dual-functional electro-Fenton catalysts to perform both the electro-reduction of O2 to H2O2 and H2O2 catalytic decomposition (Fenton) for wastewater decontamination. The amount of Fe is key to the development of this electrode material, since affects the textural properties; catalyzes the development of graphitic clusters improving the electrode conductivity; and influences the O2-catalyst interaction controlling the H2O2 selectivity but, at the same time is the catalyst for the decomposition of the electrogenerated H2O2 to OH• radicals for the organic pollutants oxidation. All materials achieve the development of ORR via the 2-electron route. The presence of Fe considerably improves the electro-catalytic activity. However, a mechanism change seems to occur at around -0.5 V in highly Fe-doped samples. At potential lower than -0.5 eV, the present of Feδ+ species or even Fe-O-C active sites favour the selectivity to 2e-pathway, however at higher potentials, Feδ+ species are reduced favoring a O-O strong interaction enhancing the 4e-pathway. The Electro-Fenton degradation of tetracycline was analyzed. The TTC degradation is almost complete (95.13%) after 7 h of reaction without using any external Fenton-catalysts.