Axial Co–O–Cu Pairs Enable Superexchange Interaction for Efficient Co IV =O Formation toward Water Purification

Heteronuclear dual-metal site catalysts (DACs) featuring unique coordination structures enable precise manipulation of metal spin-states, offering great potential for efficient peroxymonosulfate (PMS) activation. In particular, they enable highly efficient generation of high-valent cobalt-oxo (Co^IV = O) species. However, the identification and mechanism functions of DACs with axially coordinated diatomic structures remain elusive. Herein, we show a DAC featuring axial Co-O-Cu (CoN₄-O-CuN₄) pairs embedded in carbon nitride (CoCu-CN). This unique configuration significantly stabilizes the medium-spin state of Co, thereby enhancing PMS activation for efficient Co^IV = O generation. Combined experimental and theoretical analyses reveal that superexchange-mediated electron transfer from Co to Cu occurs via Co 3d (d_xz/d_yz) and O p (p_x/p_y) orbitals. This strong Co-O hybridization upshifts the d-band center to -0.41 eV, facilitating PMS adsorption. Furthermore, the orbital polarization optimization of the d orbitals in Co and Cu promotes the simultaneous cleavage of both O-O and O-H bonds for PMS, enabling direct Co^IV = O formation. Consequently, this catalyst design achieves high degradation performance, including a sulfisoxazole degradation rate of 1.98 min^-1 (5.8 times and 19.8 times higher than Co-CN and Cu-CN). This work establishes a new paradigm for designing PMS activation catalysts that concurrently exhibit spin activity and persistent stability.