Enhanced chlorine activation on Cu-doped goethite via the synergistic effect of Cu+ and oxygen vacancy for efficient organic pollutant degradation

Abstract

The goethite (FeOOH) has become a cost-effective and efficient alternative for triggering chlorine-based advanced oxidation technology towards water purification. However, the performance of FeOOH was limited by the sluggish Fe³⁺/Fe²⁺ cycling. Herein, the Cu doped FeOOH (Cu-FeOOH) catalysts with varying Cu doping levels were designed and synthesized, aiming to enhance the chlorine activation efficiency of FeOOH for efficient organic pollutants removal. The results indicated that the Cu doping significantly enhanced catalytic activity of FeOOH, and the Cu-FeOOH with moderate Cu doping level (15-Cu-FeOOH) performed best. The 15-Cu-FeOOH enabled almost complete removal of atrazine within 30 min, whose reaction rate (0.18 min⁻¹) was 233.6 times higher than that of pristine FeOOH (7.8 ×10⁻⁴ min⁻¹). Additionally, 15-Cu-FeOOH/chlorine system demonstrated universal performance towards diverse organic pollutants, extremely low metal leaching and satisfactory cyclic performance. Quenching and probe experiments elucidated •OH primarily contributed to pollutant degradation, while •Cl and •ClO played subordinate roles. Mechanistic insights revealed that the incorporated Cu⁺ and oxygen vacancy (O_v) synergistically enhanced performance of Cu-FeOOH: Cu⁺ enabled efficient Fe³⁺/Fe²⁺ cycling via formed Cu-O-Fe bond while O_v expedited Cu²⁺/Cu⁺ cycling through Cu-O_v interaction for Cu⁺ recovery, thus resulting in sustained chlorine activation to produce powerful reactive species for pollutant degradation.