Controlled synthesis of La(HCOO)3 derived from La-MOF byproduct for efficient fluoride adsorption flotation

Developing materials that combine ultrahigh adsorption capacity with facile solid–liquid separation remains a central challenge in interfacial science for fluoride pollution control. Current research on metal-organic frameworks (MOFs) as adsorption carriers mainly emphasizes structural design, while byproducts generated during MOF synthesis are commonly regarded as useless impurities and consequently neglected. Herein, we report a previously overlooked crystalline byproduct, La(HCOO) 3 , which was initially formed via N , N -dimethylformamide (DMF) hydrolysis during the solvothermal synthesis of La-BDC and can be subsequently controllably synthesized by the deliberate introduction of formic acid. Owing to its uniform and well-defined particle size, La(HCOO) 3 can be readily separated from La-BDC by simple physical sieving, enabling its direct recovery. Inspired by this feature, we propose a “waste-to-resource” strategy by directly employing La(HCOO) 3 as a functional material for fluoride adsorption flotation for the first time. Under optimized conditions, La(HCOO) 3 exhibits a fluoride adsorption efficiency of 96.29% and a flotation separation efficiency of 94.22%, yielding a low effluent turbidity of 4.37 NTU and excellent selectivity. The adsorption process follows a monolayer chemisorption model with a maximum theoretical adsorption capacity of 206.61 mg/g, outperforming many deliberately designed adsorption carriers. Combined characterization and density functional theory (DFT) calculation reveal that fluoride adsorption is governed by the synergistic effects of ligand exchange and electrostatic attraction, while sodium dodecyl sulfate (SDS) enables efficient flotation recovery through chemical adsorption and electrostatic interactions with La(III) sites. This study reveals a novel approach for the interfacial valorization of MOF byproducts and a sustainable route for fluoride remediation.