Mechanistic regulation of calcium single-atom anchoring in porous carbon microenvironments to enhance formaldehyde capture capacity

Conventional carbon-based sorbents, such as activated carbon, exhibit limited formaldehyde uptake due to a lack of sufficient specific binding sites. In contrast, calcium single-atom adsorbents anchored on porous carbon significantly enhance formaldehyde capture; however, the role of the coordination environment in this process remains insufficiently understood. Here, we report a coordination-environment-regulated carbon-supported calcium single-atom adsorbent that markedly improves formaldehyde adsorption. The adsorption behavior of calcium single-atom adsorbents was systematically investigated through a combination of density functional theory (DFT) calculations and static adsorption experiments. A clear linear correlation was identified between the number of oxygen ligands in the divacancy configuration and the adsorption energy. Among the studied configurations, the tetra-oxygen-coordinated Ca/DV-O 4 structure exhibited the highest adsorption energy (-1.90 eV), demonstrating superior performance. Comprehensive geometric optimization, charge-density difference, and density-of-states analyses revealed that the enhanced adsorption arises from the electron-bridging role of calcium and the strengthened hybridization between Ca-3d and O-2p orbitals. In static adsorption experiments, the Ca/DV-O 4 configuration achieved an equilibrium removal efficiency of 63.5 %, representing a 51.2 % improvement compared to conventional activated carbon. This work elucidates the adsorption mechanism of calcium single-atom adsorbents toward formaldehyde and provides design principles for the rational manipulation and optimization of calcium single-atom coordination environments.