Enhanced fluoride removal via adsorption flotation based on La-MOF carrier morphology modulation strategy

Herein, the morphology of a La metal–organic framework (La-MOF) was modified from aggregated granules to a reticular structure possessing a large specific surface area by altering the solvothermal temperature. Thereafter, the La-MOF was applied as an adsorption carrier for fluoride ions removal. Batch adsorption experiments indicated that the morphological structure of La-MOF considerably affects its adsorption performance. The maximum adsorption capacity of the La-MOF-130 comprising the highest dispersion of the reticular structure for fluoride ions was 142.86 mg/g, which was 28.29 % higher than that of the granular-structured La-MOF. Furthermore, La-MOF-130 exhibited an excellent adsorption performance and strong affinity for fluoride ions in a broad pH range (3–10) and a short adsorption time (60 min). The pseudo-second-order kinetic and Langmuir adsorption isotherm models indicated that fluoride ions adsorption of La-MOF was dominated by monomolecular layer chemisorption. Furthermore, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analyses revealed that the coordination exchange and electrostatic attraction were the interaction mechanism between La-MOF and fluoride ions. Moreover, an efficient solid–liquid separation of the adsorption aggregates (La-MOF-F) and removal of fluoride ions were accomplished via microbubble flotation under the action of the anionic surfactant sodium dodecyl sulfate. The fluoride ions adsorption efficiency was 95.57 % and the solid–liquid separation efficiency was 99.08 %. The research results indicate that the La-MOF carrier adsorption flotation method has broad application prospects in industrial wastewater treatment.