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

Abstract

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).