Experimental and DFT Cross-Validation: Synergistic Adsorption Mechanisms and Water Stability Improvement of Core-Shell Hierarchically Porous Multimetallic MIL-100(Fe)@hollow Ni/Co-BTC Composites for Perfluorooctanoic Acid Removal.

Efficient perfluorooctanoic acid (PFOA) capture requires synergistic optimization of adsorption kinetics and capacity. Defect-free metal-organic frameworks (MOFs) with well-defined hierarchical pores are key to addressing this challenge, yet single-component MOFs face inherent limitations including monotonous pores, insufficient unsaturated metal sites, and poor water stability, which restrict their practical application. To overcome these drawbacks, this study designed and synthesized a core-shell structured dual-MOF composite, MIL-100(Fe)-on-(Ni/Co-BTC) (abbreviated as M-on-(NCB)), via a polyvinylpyrrolidone (PVP)-assisted hydrothermal strategy. The composite integrates a hollow Ni/Co-BTC core and a micro-mesoporous MIL-100(Fe) shell: the hollow core constructs diffusion pathways for target molecules and reduces mass transfer resistance; the shell provides high-density Fe active sites, enhances hydrophobicity, and acts as a protective barrier to significantly improve the water stability of the fragile Ni/Co-BTC framework. Systematic characterizations confirm the well-defined core-shell structure, distinct hierarchical pore distribution, uniform elemental composition, and intact hollow core of the composite. Benefiting from structural synergy and multiple adsorption mechanisms, M-on-(NCB) exhibits remarkably superior PFOA adsorption performance relative to single-component MOFs and their physical mixtures. A cross-validation system combining experimental characterizations and density functional theory (DFT) calculations fully elucidates the adsorption mechanism: spectroscopic and zeta potential analyses verify the synergistic roles of electrostatic attraction, ligand exchange, hydrophobic interactions, and pore filling; DFT calculations reveal the nature and strength of each interaction from an electronic structure perspective, confirming that coordination interactions dominate the adsorption process, with electrostatic attraction, hydrogen bonding, and π-CF hydrophobic interactions synergistically enhancing binding. The composite also possesses excellent water stability and cyclic reusability. This work develops a highly efficient and stable PFOA adsorbent via structural innovation, clarifies the adsorption mechanism through experimental-theoretical cross-validation, and proposes a generalizable "structural-functional complementary integration" strategy for MOF-based composite design, providing theoretical support and technical reference for efficient remediation of persistent organic pollutants (POPs).