Structural modification of aluminum oxides for removing fluoride in water: crystal forms and metal ion doping.

In this paper, the effect of different crystal forms of AlO on fluoride removal was studied. All crystal forms of AlO were based on the same boehmite precursor and were obtained using a hydrothermal and calcination method. -AlO had higher fluoride removal performance (52.15 mg/g) compared with θ-AlO and α-AlO. Density functional theory (DFT) calculations confirmed that fluoride removal was greatest for -AlO, followed by θ-AlO and α-AlO, and -AlO possessed the strongest fluoride binding energy (-3.93 eV). The typical adsorption behaviour was consistent with the Langmuir model and pseudo-second-order model, indicating chemical and monolayer adsorption. Different metal ions were used to modify -AlO, and lanthanum had the best effect. Lanthanum oxide was shown to play an important role in fluoride removal. The best La/Al doping ratio was 20 At%. The adsorption process of the composite was also consistent with chemical and monolayer adsorption. When the La/Al doping rate was 20%, the adsorption capacity reached 94.64 mg/g. Compared with -AlO (1.39 × 10 m/s), the adsorption rate of 20La-AlO was 3.93 × 10 m/s according to the mass transfer model. Furthermore, DFT was used to provide insight into the adsorption mechanism, which was mainly driven by electrostatic attraction and ion exchange.