Sulfur-modified TiO2 nanotube/nitrogen-doped graphene aerogel particle electrodes for enhanced tetracycline hydrochloride degradation in a three-dimensional electrochemical system

S-TNT@NGA integrates S-modified TiO 2 nanotubes with N-doped graphene aerogel. • At 1 mM Na 2 SO 4 , 99.2% TCH removal gave an E EO of 6.12 kWh m −3 order −1 . • Charge-transfer resistance decreased to 223.1 Ω for S-TNT@NGA. • TCH removal remained 88.7% after ten consecutive degradation cycles. • An ‧O 2 - -H 2 O 2 - 1 O 2 network played an important role in TCH degradation. Efficient electrochemical degradation of antibiotics with limited supporting-electrolyte addition remains challenging. Here, sulfur-modified TiO 2 nanotube/nitrogen-doped graphene aerogel (S-TNT@NGA) was developed as a particle electrode for three-dimensional electrochemical degradation of tetracycline hydrochloride (TCH). The composite formed an interconnected porous framework containing sulfur and nitrogen species. KPFM, cyclic voltammetry, and electrochemical impedance spectroscopy showed altered local electronic properties and improved interfacial electrochemical characteristics; the charge-transfer resistance decreased from 558.9 Ω for TNT@GA to 223.1 Ω for S-TNT@NGA. At 15 V, initial pH 7, 1.0 mM Na 2 SO 4 , and an S-TNT@NGA loading of 1.0 g L −1 , 99.2% TCH removal and 64.0% total organic carbon (TOC) removal were achieved within 150 min. The corresponding volumetric electrical energy consumption and electrical energy per order were 12.84 kWh m −3 and 6.12 kWh m −3 order −1 , respectively. Chloride enhanced early-stage removal, whereas bicarbonate and humic acid inhibited degradation. After ten consecutive cycles, TCH removal remained at 88.7%, with the principal anatase structure and porous framework largely retained. Scavenger-based kinetic analysis, H-type-cell experiments, and EPR spectroscopy supported a coupled mechanism involving direct/surface-mediated oxidation and an oxygen-reduction-derived ‧O 2 - -H 2 O 2 - 1 O 2 network, with a secondary SO 4 ‧ - -associated pathway and a comparatively limited ‧OH-associated pathway. These findings show that S-TNT@NGA combines favorable interfacial electrochemical characteristics, reusability, and multi-pathway oxidation for TCH degradation at low added supporting-electrolyte concentration, while highlighting energy demand and water-matrix composition as important considerations for further development. Download: Download high-res image (312KB) Download: Download full-size image