Electro-activating of peroxymonosulfate via boron and sulfur co-doped macroporous carbon nanofibers cathode for high-efficient degradation of levofloxacin

To address the difficulty of precisely regulating the two-electron oxygen reduction reaction (2e-ORR) and investigate the synergistic effect of hydrogen peroxide (H2O2) and peroxymonosulfate (PMS), a heterogeneous electro-catalyst was synthesized via carbonation of boron (B) and sulfur (S) co-doping electrospun nanofibers containing iron and cobalt (B, S-Fe/Co@C-NCNFs-900), and used to degrade levofloxacin (Levo) in the electro-activating PMS with self-made cathode material (E-cathode-PMS) system. The morphological, structural, and electrochemical characteristics have been investigated. The results showed that B and S co-doping could remarkably enhance electron transfer and manage two-electron oxygen reduction, which was more favorable for H2O2 generation. Levo degradation efficiency could reach 99.63% with a reaction rate of 0.3056 min−1 in 20 min under the appropriate conditions (pH = 4, current = 20 mA, and [PMS] = 8.0 mM). The steady-state concentration of singlet oxygen (1O2) was calculated to be 669.17 × 10−14 M, which was 15.42, 29.74, and 45.00 times respectively than that of HO2·/O2·- (43.40 × 10−14 M), ·OH (22.25 × 10−14 M) and SO4-·(14.87 × 10−14 M), signifying that 1O2 was the predominant reactive oxygen species (ROS) involved in Levo removal. The high TOC removal (74.19%), low energy consumption (0.14 kWh m−3 order−1), few intermediates toxicity, and excellent Levo degradation efficiency for complex wastewater with various anions and matrixes showed the prospective practical applications of the E-cathode-PMS system. Overall, this study provides a useful strategy to regulate and control the 2e-ORR pathway.