Oriented generation of long-lived surface-bound sulfate radicals in hydroxyapatite@single-atom cobalt nanoreactors...

Selective generation and effective utilization of sulfate radicals (SO₄^-) in water treatment has been restrained by the multiple reaction pathways of Fenton-like catalysis and the short radical lifetime. Here, we designed a nanocomposite composed of hydroxyapatite (HAP) 'core' and single-atom Co (Co_SA) catalyst 'shell' that creates a nanoconfined environment for selective generation of the surface-bound SO₄^- via peroxymonosulfate (PMS) activation. This surface-confinement strategy markedly prolongs the half-lifetime of sulfate radicals from 40.0 μs (free SO₄^-) to 72.7 μs (surface-bound SO₄^-), thus improving the utilization efficiency of SO₄^- radical. In situ spectroscopy and computations revealed that the Co_SA 'shell' activated PMS and the HAP 'core' with abundant oxygen vacancy stabilized PMS and SO₄^-, resulting in oriented generation of the surface-confined SO₄^-. Mechanisms studies demonstrated that the HAP@Co_SA/PMS system effectively degraded diverse emerging organic contaminants (EOCs) by the inner-surface-bound SO₄^-. Moreover, the HAP@Co_SA catalyst flocculated natural organic matter (NOM) through outer-surface complexation by the released Ca²⁺ ions, excluding coexisting NOM from the nanoconfined inner-surface. The cooperative coupling of nanoclay-mediated flocculation and confined Fenton-like oxidation provides an efficient and robust platform for selective oxidation of EOCs in complex real waters.