Natural Polyphenol-Promoted Degradation of Emerging Contaminants during Copper Sulfide Mineral Oxygenation: The Synergism of Surface-Bound Radicals and Singlet Oxygen

Natural polyphenols are prevalent in aquatic environments, playing a critical role in the aerobic degradation of contaminants by redox-active minerals. Nevertheless, little is known about how the natural polyphenols influence the environmental behavior of copper sulfide minerals and reactive oxygen species (ROS) generation. In this work, the role of natural polyphenols in the degradation of waterborne emerging contaminants during CuS- x (a composite of Cu 2 S and CuS) oxygenation was investigated, where protocatechuic acid (PCA) was selected as a representative natural polyphenol. It was demonstrated that PCA could significantly enhance the degradation of target contaminant by substantially boosting surface-bound • OH ( • OH bound ) generation via a three-electron O 2 activation pathway. Experimental analysis and theoretical calculations unveiled that PCA favored the adsorption and activation of O 2 on the CuS- x surface, thus facilitating the formation of O 2 •– (an important precursor of both • OH and singlet oxygen ( 1 O 2 )). The contributions of 1 O 2 and • OH bound to contaminant degradation in the CuS- x /PCA system were 31.8% and 60.2%, respectively. Notably, besides PCA itself, the oxidation products (i.e., ortho-quinones and semiquinone radicals) and S vacancies also played a crucial role in accelerating the Cu redox cycle to activate O 2 . These findings provide valuable insights for advancing sulfide mineral-based green remediation technologies.