Three-dimensional oriented Ca nanoporous carbon with N doping tuned via self-assembly to potentiate P adsorption: The vital role of the micro interfacial electronic environment

Developing green adsorbents with high phosphorus (P) adsorption capabilities is crucial to address the limitations of traditional chemical agents for deep P removal and to improve P purification. In this study, we designed an efficient and eco-friendly calcium/nitrogen nanoporous carbon (Ca/N-NPC) material using a directional nanoscale self-assembly strategy to serve as a novel phosphate (P) remover. By directly pyrolyzing precursors formed through self-assembly, calcite is encapsulated in an in-situ N-doped 3D graphene framework, resulting in a stable porous structure. The Ca/N-NPC (1:2) demonstrated an efficient selective P sorption capacity of 147.674 mg/g and a P/Ca molar ratio of 1.374, which were 1.5 and 4 times higher than those of the non-N-doped version, respectively. Compared with Ca-NPC, the introduction of nitrogen significantly reduced the boundary layer thickness, effectively improving transient adsorption efficiency from 5.03 ± 0.47 to 8.25 ± 1.1 mg/(g·min^0.5). This outstanding performance is attributed to the modulation of the electronic environment of the 3D graphene structure and calcite micro-interface by the introduction of N-functional sites. Pyrrole-N, pyridine-N, graphene-N, and nitrogen oxide formation reconfigure electron cloud distribution on NPC surface, enhancing adsorption energy and effectively enriching adsorption sites for P. The orbital overlap of the N, C, and O produces sp3 hybridization, promoting electron mobility to drop the dynamic barrier for P adsorption reaction. Crucially, N-doping enhances the electron-orbital overlap and electron accumulation between Ca and O, inducing an orderly structure that facilitates the accumulation of Ca-P with high stability. Overall, this work provides a novel approach for the development of Ca-based adsorbents with efficient P adsorption properties and offers a new perspective on regulating phosphate adsorption through the micro interfacial electronic environment.