Performance and Mechanism of Calcium Peroxide for Fluoride Removal and Site Energy Distribution
Calcium peroxide (CaO2) with a rich porous structure was synthesized via chemical precipitation for efficient fluoride removal from aqueous solutions. The adsorbent was characterized by SEM, BET, LPSA, and XRD, revealing a mesoporous material with a total pore volume of 0.51 cm3·g−1. Batch experiments investigated the effects of adsorbent dosage, initial fluoride concentration, reaction time, pH, and coexisting anions. Adsorption kinetics followed a fractal-like pseudo-first-order model, with intraparticle diffusion as the rate-limiting step. Equilibrium data were well described by the Sips isotherm, predicting a maximum adsorption capacity of 479.8 mg·g−1. Site energy distribution analysis indicated a normal distribution with an average energy of 13.36 kJ·mol−1. Mechanistic studies using FTIR and XPS revealed that fluoride removal proceeds via surface precipitation, ligand exchange, and electrostatic attraction. The high density of active sites contributes to the exceptional defluoridation performance, positioning CaO2 as a promising adsorbent for fluoride-contaminated water treatment.