Oxygen doping regulates coordination structure of iron-single-atom catalysts for peroxymonosulfate activation and pollutants degradation: high-valent iron-oxo species role - Lin Niu; Qitao Lei; Zhi Tang; Yaqi Cai; Junyu Wang; Guoqing Hou; Xiaoli Zhao; Fengchang Wu (Chemical Engineering Journal, 2026)