Construction of Hierarchical Rod-Assembled Ce–Al–La–MOFs@PPy Composites for Highly Efficient Fluoride Removal from Water

In this study, a hierarchical rod-assembled, polypyrrole-modified Ce–Al–La trimetallic metal–organic framework (Ce–Al–La–MOFs@PPy) composite was successfully synthesized through a solvothermal method combined with in situ polymerization for efficient fluoride removal from aqueous solutions. The incorporation of conductive polypyrrole (PPy) into the multimetallic MOFs effectively enhanced the structural stability, surface properties, and adsorption performance of the material. Adsorption experiments demonstrated that the optimal metal-to-ligand molar ratio was 3:1, and the prepared adsorbent exhibited excellent fluoride removal performance under weakly acidic conditions (pH = 5). The maximum adsorption capacity calculated from the Langmuir model reached 216.92 mg·g−1 at 45 °C. Adsorption kinetics were well fitted by the pseudo-second-order model, indicating that the adsorption process was mainly governed by chemisorption. Mechanism investigations based on FTIR and XPS analyses demonstrated that fluoride removal mainly occurred through electrostatic attraction and coordination exchange between fluoride ions and the Ce/La active sites. In addition, the composite exhibited good selectivity, anti-interference ability toward coexisting ions, and satisfactory fluoride removal performance in practical industrial wastewater. These findings suggest that Ce–Al–La–MOFs@PPy is a promising adsorbent for efficient fluoride-contaminated wastewater treatment.