High-efficiency fluoride removal using hierarchical flower-like magnesium oxide: adsorption characteristics and mechanistic insights

Abstract

In this study, hydrothermally synthesized magnesium oxide demonstrated effective fluoride adsorption, with a maximum capacity of 199.67 mg g⁻¹ and equilibrium was achieved within 60 min. The morphology of magnesium oxide and the adsorption mechanism were investigated by SEM, FTIR, BET and XPS. The adsorption process conformed to the Freundlich isotherm and pseudo-second-order kinetic models. The ΔH and ΔS of fluoride adsorption by this material were 44.58 kJ mol⁻¹ and 163.31 J mol⁻¹ K⁻¹, respectively, indicating surface heterogeneity and specific adsorption kinetics. Optimal fluoride removal was observed in the pH range of 4–11, with the highest adsorption capacity achieved at pH 5.0. Co-existing ions significantly influenced the adsorption performance (Cl⁻ < NO₃⁻ < SO₄²⁻ < HCO₃⁻ < PO₄³⁻). These findings underscore the potential application of magnesium oxide in water treatment and suggest avenues for further optimization of synthesis and operational parameters.