Engineered La-Polyurea Aerogel for Fluoride Capture: High Performance and Stability in Complex Water Matrices

The development of adsorbents that combine high adsorption capacity, stability in complex water matrices, and easy handling remains a major challenge for fluoride wastewater treatment. In this work, we report a lanthanum-functionalized polyurea aerogel (La-PUA) as a monolithic adsorbent for fluoride removal. La-PUA features a well-defined mesoporous structure, providing ideal sites for the uniform anchoring of La 3+ ions, thereby enabling effective fluoride capture. Experimental results demonstrate that La-PUA maintains high performance across a broad pH range (2–10), exhibiting a 64.4% increase in fluoride adsorption capacity compared to unmodified PUA, with an optimal removal efficiency exceeding 97%. The adsorbent shows strong anti-interference capability, retaining over 85% adsorption efficiency in the presence of coexisting anions, and preserves approximately 77% of its initial adsorption capacity after six consecutive adsorption–desorption cycles, highlighting its robust stability and reusability. The adsorption process is well-described by the Langmuir isotherm and pseudo-second-order kinetic models, suggesting monolayer chemisorption on homogeneous active sites, with a theoretical maximum adsorption capacity of 98.75 mg/g. Adsorption equilibrium was achieved within 40 min. Mechanistic studies reveal that fluoride removal is primarily governed by a synergistic mechanism involving hydrogen bonding, ligand exchange, and LaF 3 precipitation. This study not only presents a high-performance adsorbent for fluoride sequestration but also provides a viable material design for tackling complex industrial wastewater.