Conductive Percolation of CNT Membranes Influenced Anodic Degradation of Aqueous Sulfamethoxazole

Flow-through membranes have demonstrated promising potential in the oxidative removal of antibiotics in water. However, the delicate balance between electron and contaminant transfer during this process has not yet been disclosed. This study employed the continuous percolation theory to reveal the significance of the carbon nanotube (CNT) membrane topology to the anodic degradation of antibiotics. Based on the microscopic current distribution mapped by conductive atomic force microscopy, a conductive percolation threshold (<i>p</i>_c) of 0.51 and a nonuniversal critical exponent (<i>t</i>) of 4.1 were determined for the membranes. The semiconductor-to-metal transition near <i>p</i>_c shifted the conduction mechanism from electron tunneling at the subcritical-percolation region (SBPR) to the ohmic current at the supercritical region (SPPR). Furthermore, the conductive percolation state influenced sulfamethoxazole (SMX) degradation pathways at the membrane anodes: SPPR favored hydroxyl radical (·OH) addition due to rapid electron transfer, while SBPR and critical percolation promoted ring-opening reactions due to strong localized electric fields. Finally, the SPPR membrane having a CNT loading equal to 40 times that at <i>p</i>_c achieved the highest SMX removal (97.3%) and mineralization (50.8%), with a low energy consumption of 0.04 kWh m^-3. Overall, the multiscale percolation analysis provides a suitable paradigm for rational design of electrocatalytic membranes for effective antibiotic pollution control.