Electrochemically activated peroxymonosulfate with modified TiO<sub>2</sub> nanotube array anode for PPCPs degradation and pharmaceutical wastewater detoxification: Mechanistic insights and practical implications.

Abstract

Electrochemically activated peroxymonosulfate (EA-PMS) is a promising process enabling efficient and reliable pharmaceutical wastewater treatment. However, controversial mechanisms, and unrealized efficiency potential limit their practical application. In this work, metoprolol (MET) as model pollutant, a mesh-structured blue TiO₂ nanotube array electrode with a protective TiO₂ coating (BDTNAs) was employed as the anode to drive EA-PMS process at low current density, achieving highly efficient pharmaceutical and personal care products (PPCPs) degradation and pharmaceutical wastewater detoxification. At 5 mA cm^-2, the six common PPCPs removal rate of EA-PMS (2 mM PMS) was approximately 3-12 times higher than that of electrochemical oxidation (EO). The toxicity of pharmaceutical wastewater was also reduced from extreme (TUa ≥100) to low level (TUa <1) by EA-PMS (2 mM), while EO-treated wastewater remained highly toxic (TUa = 13.31). The enhanced oxidative capability of EA-PMS is attributed to activation of PMS to sulfate radicals (SO₄^•-) and singlet oxygen (¹O₂) under an electric field, as well as increased hydroxyl radicals (•OH) production. While both PMS dosage and current density enhanced MET degradation, showing a linear (R² = 0.95) and a logarithmic (R² = 0.99) relationship respectively, excessively high PMS loading in real pharmaceutical wastewater markedly increased its toxicity, with the effluent becoming extremely toxic (TUa = 31.42) after EA-PMS (10 mM) treatment. This work provides fundamental insights into green and sustainable PPCPs degradation via EA-PMS, paving the way for scalable application in industrial settings.