Ethylene Glycol (EG)-Derived Chlorine-Resistant Cu⁰/TiO_2–<i>x</i> for Efficient Photocatalytic Degradation of Nitrate to N₂ without Sacrificial Agents at Near-Neutral pH Conditions: The Synergistic Effects of Cu<sup>0

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_2-<i>x</i> (EG-Cu/TiO_2-<i>x</i>) through a solvothermal reaction of Cu-doped TiO₂ in an EG solution. The photodegradation of nitrate using EG-Cu/TiO_2-<i>x</i> without adding sacrificial agents can efficiently occur in near-neutral pH solutions containing 50 mM Cl^- with 95.26% of NO₃^- removal and 76.52% of N₂ selectivity. Moreover, the photocatalyst performance remained at a high level after 8 cycles. In this work, NO₃^- was first converted to NH₄⁺ by Cu⁰ and Ti³⁺, followed by the NH₄⁺-to-N₂ conversion by photogenerated chlorine free radicals. Compared to HO^•, Cl^•, and Cl₂^•-, ClO^<b>•</b> is proved to play the predominant role in transforming NH₄⁺ to N₂. The EG radicals produced by UV light impede Cl^- adsorption on Cu, protecting Cu⁰ from being corroded. What's more, photoelectrons can reduce Ti⁴⁺ to Ti³⁺ and protect Cu⁰ from being oxidized, enabling the stability of reactive sites. This work provides novel insights and understanding on designing photocatalysts for NO₃^- removal in solutions containing chloride ions, highlighting the significance of eliminating Cl^- by EG radicals and adjusting the conversion process of NO₃^- for the efficient removal of NO₃^-.