Environmentally benign tannin-modified chitosan aerogel decorated with Zr(IV) enabled high-performance adsorption of fluoride

The contamination of fluoride is a concerned issue from the perspective of drinking water safety. Herein, we reported the controlled synthesis of novel chitosan aerogel functionalized by tannin-chelated Zr(IV), which was capable of accomplishing the high-performance adsorption of fluoride from water. The as-prepared functional chitosan aerogel (BTCA-Zr) featured fast adsorption kinetics and exceptional adsorption capability to fluoride. In static adsorption experiments, the superiority of the functional chitosan aerogels was demonstrated with the removal efficiency higher than 95% in the wide pH range of 3–10. The high porosity (79.08%) combined with surface decoration of amphiphilic tannin provided the functional aerogel with fast adsorption equilibrium in 40 min. Adsorption capacity of 86.0 mg g −1 for fluoride was achieved by the functional aerogel with the low fluoride concentration of 2.0 mg L −1 . The fluoride adsorption on BTCA-Zr exhibits pseudo-second-order (PSO) kinetics and fits the Langmuir isotherm, and the adsorption process is exothermic and spontaneous. The adsorption mechanism was revealed by adsorption experiments combined with the density functional theory (DFT) calculations, which confirmed the critical role to form the species of Zr-oxyfluoride with low binding energy for accomplishing the high-performance adsorption of fluoride. Notably, the functional aerogel achieved 85.59% of fluoride removal by column adsorption of the simulated underground water. The functional aerogel was recycled 5 times in column adsorption of the simulated underground water by retaining 78.38% of its initial adsorption capacity.