Cost-effective and efficient: cerium‑lanthanum MOF for superior fluoride ion adsorption from wastewater

Efficient remediation of fluoride pollution is a global priority and an urgent requirement for water security. Adsorption is the most widely employed defluoridation technology, and metal-organic frameworks (MOFs) show great application potential due to their unique advantages. However, the high raw material cost and limited adsorption capacity of current defluoridation MOFs severely restrict their large-scale application. This study selected low-cost metal precursors (cerium and lanthanum) and organic linkers (fumaric acid and formic acid), and further reduced costs by replacing part of the DMF solvent with water, successfully synthesizing a novel MOF (denoted CeLa-FUMFA). The raw material cost for this material was reduced by at least 40 % compared to zirconium-based MOFs. Furthermore, it achieved a high adsorption capacity of 233 mg/g at an initial F⁻ concentration of 25 mg/L, and its capacity after the 5th regeneration cycle remained superior to most reported adsorbents. Adsorption experiments indicated that CeLa-FUMFA exhibits fast adsorption kinetics towards F⁻ and maintains excellent defluoridation performance across a wide pH range, with only HPO₄²⁻ exhibiting an inhibitory effect. The Langmuir and pseudo-second-order kinetic models fitted the defluoridation process well, indicating that the adsorption of F⁻ onto CeLa-FUMFA is dominated by monolayer chemisorption. A series of characterization analyses revealed that the defluoridation mechanism involves ion exchange, electrostatic interactions, hydrogen bonding, and complexation effects. In conclusion, the developed CeLa-FUMFA provides an effective solution for treating fluoride-containing wastewater.