Ethylene Glycol (EG)-Derived Chlorine-Resistant Cu/TiO for Efficient Photocatalytic Degradation of Nitrate to N without Sacrificial Agents at Near-Neutral pH Conditions: The Synergistic Effects of Cu and EG Radicals.

The selective photoreduction of nitrate to nontoxic nitrogen gas has emerged as an energy-efficient and environmentally friendly route for nitrate removal. However, the coexisting high-concentration chloride ions in wastewater can exert a significant influence on nitrate reduction due to the competitive adsorption and corrosion of Cl on photocatalysts. Herein, we prepared ethylene glycol-Cu/TiO (EG-Cu/TiO) through a solvothermal reaction of Cu-doped TiO in an EG solution. The photodegradation of nitrate using EG-Cu/TiO without adding sacrificial agents can efficiently occur in near-neutral pH solutions containing 50 mM Cl with 95.26% of NO removal and 76.52% of N selectivity. Moreover, the photocatalyst performance remained at a high level after 8 cycles. In this work, NO was first converted to NH by Cu and Ti, followed by the NH-to-N conversion by photogenerated chlorine free radicals. Compared to HO, Cl, and Cl, ClO is proved to play the predominant role in transforming NH to N. The EG radicals produced by UV light impede Cl adsorption on Cu, protecting Cu from being corroded. What's more, photoelectrons can reduce Ti to Ti and protect Cu from being oxidized, enabling the stability of reactive sites. This work provides novel insights and understanding on designing photocatalysts for NO removal in solutions containing chloride ions, highlighting the significance of eliminating Cl by EG radicals and adjusting the conversion process of NO for the efficient removal of NO.