Adsorption of fluoride on polyfunctional γ-AlOOH/EG composites: adsorption behavior and mechanism

Adsorption is commonly used for the treatment of fluoride-containing wastewater, a series of multifunctionalized EG/γ- AlOOH composite defluorination adsorbents was synthesized. Among these, the mesoporous D-A@EG exhibited an adsorption capacity (Qe) of 89.33 mg/g, which is 7.30 times higher than that of expanded graphite (EG), and achieved a defluorination efficiency (RE) of up to 96.82%. The adsorption process is spontaneous and endothermic, involving either monolayer chemisorption or multilayer adsorption, which can be described by the Freundlich and PFO models. Investigation of the factors influencing fluoride removal by D-A@EG revealed an optimal adsorbent dosage of 2.085 g/L, an optimal contact time of 50 min, and an optimal pH of 8.82. Furthermore, the adsorption process was largely unaffected by the presence of coexisting anions. The fluoride removal mechanisms of D-A@EG were elucidated through XPS, FT-IR and other characterizations. Fluoride removal occurs via hydroxyl (-OH), amino (-NH₂), and sulfonic acid (- SO₃H) groups, as well as active aluminum sites. The adsorption mechanisms include ion exchange, electrostatic attraction, pore filling, precipitation, and hydrogen bonding. D-A@EG offers a promising new strategy for the remediation of fluoride-contaminated wastewater.