3D crosslinked chitosan for fluoride remediation in industrial wastewater: From structure to performance enhancement

The development of novel adsorbent materials represents a promising approach for the remediation of fluorine pollution and the promotion of a sustainable water cycle. Nevertheless, the complex preparation processes, stringent application conditions, and limited reusability significantly impede the practical implementation of various adsorption materials. Herein, three-dimensional crosslinked chitosan (3D CS) was developed for treating wastewater containing high concentration of fluoride (hundreds and thousands of mg/L). FTIR, FE-SEM and other techniques were used to investigate several key process factors on the structure and performance of 3D CS and the optimal synthesis conditions, including chitosan hydrogel concentration (5 %wt), the amount of crosslinking agent (2.5 %v/v), acetic acid concentration (2 %), drying method (353 K blast drying for 9 h), were determined. Afterwards, the optimized 3D CS demonstrates microporous structure and exceptional fluorine removal capabilities, characterized by a 6-fold enhancement in adsorption capacity (64.7 mg/g), a 5-fold improvement in recycling capacity (more than 17 times), as well as broad pH applicability range (3–12) and high salt tolerance (25000 mg/L NaCl and 5000 mg/L Na₂SO₄). Furthermore, its straightforward and low-carbon synthesis method, customizable macro shape, and ease of separation from wastewater endow the 3D CS with significant potential for practical applications. Ultimately, the adsorption mechanism was investigated and the results show that ion exchange, electrostatic attraction, and hydrogen bonding between 3D CS and HF together determine the good adsorption performance of F⁻.