Unlocking oxidase-mimicking activity in S-block calcium through single-atom engineering for synergistic peroxymonosulfate activation and detection.

S-block elements are conventionally considered catalytically inert for peroxymonosulfate (PMS) activation due to their lack of accessible d-orbital electrons, while rapid PMS detection during its activation remains challenging. Herein, we overcome these limitations by engineering a single-atom calcium catalyst (Ca-NC) with a Ca-N4 coordination structure, which exhibits unprecedented oxidase-mimicking activity for dual activation of molecular oxygen (O2) and PMS. Experimental and theoretical investigations reveal that nitrogen coordination partially populates the previously vacant Ca d-orbitals, enabling electron transfer to O2 for superoxide radical (O2•-) generation. Simultaneously, the Lewis acidic Ca-N4 sites directionally extract electrons from PMS, selectively steering PMS oxidation toward singlet oxygen (1O2), which reconverts to O2. This synergistic process enhances O2 activation and elevates the oxidase-like activity of Ca-NC from an intrinsic 0.19 to 0.65 μmol min-1 with PMS. The amplified absorbance of oxidized 3,3',5,5'-tetramethylbenzidine (oxTMB) at 652 nm linearly correlates with PMS concentration (0-1.5 mM), enabling rapid PMS detection during catalytic activation with a limit of detection (LOD) of 0.01 mM. The Ca-NC catalyst also demonstrates robust stability and multifunctionality in water sterilization and purification applications. This work unlocks the catalytic potential of s-block metals and pioneers an innovative "activate-and-detect" platform for environmental remediation and detection.