Nanoconfinement Enhances Electrochemical Oxidation in Saline Wastewater Treatment

Electrochemical oxidation (EO) is a promising technology for saline wastewater treatment, but its application is hindered by limited efficiency and the generation of toxic chlorinated byproducts. Here we introduce a nanoconfinement-assisted EO strategy using TiO₂ nanotube (NT) anodes that overcomes these challenges. Compared with TiO₂ film and nanoparticle electrodes, the TiO₂ NT system achieved 95.6% phenol removal (vs 61.3% and 78.1%), a 3-fold higher degradation rate constant, 71.9% mineralization efficiency (vs 10.8% and 17.9%), and ∼80% lower chlorinated byproduct conversion. Six representative pharmaceutical and personal care products were removed by >90% with concurrent toxicity reduction. Mechanistic investigations combined with density functional theory revealed that spatial confinement enriches pollutants and reactive species at the electrode interface, strengthening direct electron transfer (DET) and indirect direct electron transfer (IDET). More importantly, confinement promoted radical-radical cross-coupling, establishing a synergistic pathway between DET and IDET with the lowest thermodynamic barrier, driving deep mineralization while minimizing chlorination. The nanoconfinement-assisted EO system further demonstrated efficient pollutant removal, toxicity control, and long-term stability in treating biologically treated coking wastewater. These findings highlight nanoconfinement as a powerful design principle for advancing EO toward practical saline wastewater treatment.