Enhanced Surface Area of Mesoporous Alumina Fibers for Fluoride Removal

Mesoporous alumina fibers (MAFs) combine strong fluoride affinity with a readily recoverable fibrous form, but calcination-induced shrinkage and pore collapse can reduce the surface area available for adsorption. MAF and nine variants doped with alkali metals (Li, Na, and K), alkaline earth metals (Mg, Sr, and Ba), or rare earth metals (Y, La, and Ce) were prepared by CTAB-assisted electrospinning to evaluate how dopant selection affected post-calcination pore structure, BET surface area, and fluoride removal. Li, Na, and K doping mainly increased the pore volume and average pore diameter, whereas Mg, Sr, Ba, Y, La, and Ce doping increased the BET surface area and reduced the average pore diameter relative to MAF. Across the ten samples, fluoride removal efficiency was strongly and positively correlated with BET surface area (R2 = 0.9149, p < 0.001). MAF-Y exhibited the highest BET surface area (237.89 m2·g−1) and fluoride removal efficiency (68.00%). Its Langmuir-estimated maximum adsorption capacity was 51.49 mg·g−1 at 50 °C and pH 7. Overall, dopant selection effectively regulated the post-calcination pore structure of MAF. Y doping most effectively preserved the mesoporous structure, thereby increasing BET surface area and fluoride removal.