Mechanism and pathway for the electrocatalytic degradation of an organic phosphine scale inhibitor by a novel Ti/IrO₂-RuO₂(Bi+[Emim]BF₄) electrode

Organic phosphine scale inhibitors are widely used chemical additives in industrial water treatment. Due to its high stability, high solubility and anti-biodegradability, it can persist in water bodies for a long time and is a potential long-term source of phosphorus pollution. This study developed a novel Ti/IrO₂–RuO₂ electrode co-modified with bismuth and ionic liquid [Emim]BF₄ via thermal decomposition for electrocatalytic degradation of hydroxyethylene-1,1-diphosphate (HEDP) in reverse osmosis concentrate (ROC). Analyses with scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD) revealed that adding (Bi+[Emim]BF4) to the electrode reduced the crystal grain size by 33 %, enhancing compactness while maintained the typical oxide crystals rutile crystal structure. Electrochemical tests demonstrated that the Ti/IrO2-RuO2(Bi+[Emim]BF4) electrode significantly outperformed its Ti/IrO2-RuO2 counterpart and had a lifespan 1.2 times longer. Then, at optimal conditions, current density of 30 mA/cm2, initial pH of 3, 0.25 mol/L NaCl electrolyte, and a reaction time of 120 min, the removal of HEDP reached 84.22 %. Mechanistic studies indicated that indirect oxidation by active chlorine dominated. Ultimately, the Ti/IrO2-RuO2(Bi+[Emim]BF4) electrode system removed 82.77 % of HEDP, 83.16 % of COD, and 49.73 % of UV254 from actual ROC within 60 min, albeit with a limited TOC removal rate of 30.23 %. Notably, it achieved a 91.55 % removal rate for fluorescent substances within 10 min. This research provides valuable insights for enhancing the performance of iridium-ruthenium electrode and designing efficient electrocatalytic oxidation systems for treating phosphorus-containing wastewater.