Al-doping chitosan–Fe(III) hydrogel for the removal of fluoride from aqueous solutions

• Al-doping chitosan–Fe(III) hydrogel has relatively high ability to remove fluoride.
• Al is micro doped in the complex but do a contribution to the defluorination.
• After regeneration, this adsorbent performs high defluorination efficiency.

The current problem of excess fluoride in drinking water around the world makes people looking toward low-cost but efficient adsorbents. In the present study, aluminum and doping chitosan–Fe(III) hydrogel (Al–CS–Fe) was prepared and investigated as a possible adsorbent for the removal of fluoride from aqueous solutions. Besides, a series of single metal impregnated chitosan were also synthesized to compare their defluorination ability with Al–CS–Fe. These adsorbents were characterized using FTIR, SEM, EDS and STXM and the adsorption of fluoride is well described by the pseudo-second-order model and Langmuir isotherm model. The results indicate that Al–CS–Fe has a good ability to resist co-existing anions and the change of pH value, and owns a relatively high adsorption capacity of 31.16 mg/g. After regeneration, this adsorbent performs higher defluorination efficiency than before. The mechanism of adsorption may be described by the ligand and ions exchange happened on the active sites. Overall, the results obtained in this study indicate Al–CS–Fe possesses a potential of practical application for fluoride removal from aqueous solutions.