Preparation of La(OH)₃-Ce(OH)₃/PAN composite nanofibers by electrospinning and its defluoridation performance

In order to overcome the difficult problem of separation between adsorbent and water phase, this study using polyacrylonitrile (PAN) as a carrier, lanthanum nitrate hexahydrate (La(NO₃)₃·6H₂O) and cerium nitrate hexahydrate (Ce(NO₃)₃·6H₂O) as materials, electrospun PAN nanofibers membranes loaded with La(OH)₃ and Ce(OH)₃ nanoparticles (La(OH)₃-Ce(OH)₃/PAN ENFMs) were fabricated through electrospinning method and a subsequent in situ precipitation under alkaline condition, and then used as an efficient fluoride scavenger. The morphology and structure of La(OH)₃-Ce(OH)₃/PAN ENFMs were characterized by SEM-EDS, TEM, XRD, BET, FTIR and XPS. The BJH pore size distribution of La(OH)₃-Ce(OH)₃/PAN ENFMs is 3.41 nm, and the total pore volume and specific surface area are 0.089 cm³·g⁻¹ and 28.81 m²·g⁻¹, respectively. The effect of fabrication conditions (mass ratio of PAN to total rare earth salt, and alkali treatment time), solution pH value, initial concentration of F⁻, dosage of adsorbent, in addition to co-existing anions on the adsorption of F⁻ by La(OH)₃-Ce(OH)₃/PAN ENFMs were investigated by static adsorption tests. The results reveal that La(OH)₃-Ce(OH)₃/PAN ENFMs prepared with the mass ratio of PAN and total rare earth salt being 1∶1 and treated with 0.1 mol·L⁻¹ NaOH for 12 h possess the best defluorination efficiency at pH 3, and the adsorption capacity can reach 57.83 mg·g⁻¹. The adsorption isotherm of fluoride on La(OH)₃-Ce(OH)₃/PAN ENFMs is consistent with Langmuir model, and the pseudo-second-order kinetic model can explain the adsorption of fluoride on La(OH)₃-Ce(OH)₃/PAN ENFMs. The thermodynamic results indicate that the adsorption of fluorine ions on La(OH)₃-Ce(OH)₃/PAN ENFMs is a spontaneous, endothermic, along with entropy increase process in nature.