Effects of N mono- and N/P dual-doping on H2O2, [rad]OH generation, and MB electrochemical degradation efficiency of activated carbon fiber electrodes

Abstract

Pure N mono- and N/P dual-doped cotton-stalk-derived activated carbon fibers (CSCFs) were synthesized by steam, HNO3(CSCF-N), NH3(CSCF-A), and (NH4)3PO4(CSCF-N/P) treatments. This study investigated how three different N/P modifiers affected the pore structure, chemical property, H2O2 generation ability, and electrocatalytic activity of methylene blue (MB) degradation of CSCFs in an electric-Fenton system. Results confirmed that the three employed treatments effectively doped N/P in the carbon lattice and slightly changed the pore structures. NH3 and (NH4)3PO4 were the most effective modifiers for the N mono-doping and N/P dual-doping of CSCFs, respectively. Among the fabricated CSCFs, the N/P dual-doped CSCF-N/P demonstrated the highest electrochemical activity in an electro-Fenton system, followed by the N mono-doped CSCF-A, the CSCF-N, and the raw CSCF. In contrast to the CSCF electrode, the CSCF-N/P electrode exhibited enhanced H2O2, OH generation, and MB degradation efficiency by 42%, 41%, and 35%, respectively. Under optimum conditions, the electrochemical decolorization efficiency of MB (initial concentration, 100 mg L−1) of the CSCF-N/P reached 93% after 150 min and was 24.1% higher than that of the CSCF. By the tenth cycle, 82.2% of the MB could still be decomposed, suggesting the excellent stability and reusability of the N/P co-doped CSCF electrode. The outstanding electrocatalytic performance of the CSCF-N/P electrode is primarily due to the simultaneous doping of active N/P sites with low activation energy and introduction of mesopores with strong trapping forces for MB. The MB reduction catalyzed by CSCF electrodes followed pseudo-first-order kinetics, and the reaction rate depended on the modifiers.