Freeze-crosslinking approach for preparing carboxymethyl cellulose nanofiber/zirconium hydrogels as fluoride adsorbents.

Tough carboxymethylcellulose nanofibers (CMF)/zirconium (Zr) hydrogels were easily obtained by a freeze-crosslinking method, where Zr-containing HCl solution was added to frozen CMF sol and the mixture was allowed to thaw. The Zr content of the hydrogels increased with increasing Zr concentration in the initial HCl solution. Furthermore, the mechanical strength increased with increasing Zr content. The Young's modulus value was improved by approximately 6 times compared to the CMF hydrogel without Zr, i.e. , from 4.5 kPa to 27.2 kPa. The hydrogel had a porous structure with a pore size of 133 ± 37 μm and a CMF-Zr sheet structure around the pores. The obtained CMF-Zr hydrogel exhibited high adsorptivity for fluoride. The maximum adsorption capacity ( Q _max ) was estimated to be 24.1 mg g ^-1 . This simple gelation method provides useful insights for the development of easy-to-handle hydrogel-based adsorbents.