Multielement coordination regulates Co sites in high-entropy oxides for selective peroxymonosulfate activation

<title>Abstract</title> <p> High-entropy oxides diversify local coordination, yet their catalytic promise is constrained by a central ambiguity: which metal activates the oxidant, and how do neighbouring elements control reaction selectivity? Here we resolve this site-pathway connection in a mesoporous Co-Fe-Mn-Ni-Cu spinel for peroxymonosulfate (PMS) activation. Co K-edge spectroscopy identifies mixed-valent Co (+ 2.81) within Co-O and Co-M coordination shells. Chemical probes, electron paramagnetic resonance, in situ Raman spectroscopy and isotope experiments collectively support a sequence from high-valent Co-oxo to superoxide and singlet oxygen, with singlet oxygen accounting for approximately 88% of sulfamethoxazole degradation. Calculations further identify an Mn-Co dual-site configuration that strengthens PMS adsorption, increases interfacial charge transfer and polarizes the peroxide bond while retaining electronically accessible Co states. This coordination environment increases the degradation rate constant 6.5-fold relative to mesoporous Co ₃ O ₄ (0.386 versus 0.059 min ^− 1 ) and sustains near-complete removal for 240 h under continuous flow. These findings connect compositionally complex coordination to a defined Co centre and a singlet-oxygen-dominant pathway, without attributing the enhancement to configurational entropy alone. </p>