Construction of a recyclable magnetic chitosan/AlOOH/PEI composite with hierarchical porous structure for enhanced adsorption of fluoride ions from wastewater.

Al(III)-based adsorbents have a strong affinity for F, but suffer from problems such as poor structural stability, easy decomposition, and recycling difficulties in the powdered form. Herein, for the efficient removal of F from wastewater, magnetic chitosan/AlOOH/polyethyleneimine (MCAlP) adsorbents with a hierarchical porous structure, multifunctional groups, and structural stability were constructed through chelation, cross-linking, and immobilization strategies using chitosan as a carrier. The adsorption capacity of MCAlP for F was found to be 14.9 mg g (59.8 %) greater than that of AlOOH, and the adsorption equilibrium time was reduced by 120 min. The adsorption of F by MCAlP was better represented by the pseudo-second-order and Langmuir isothermal models (q = 126.4 mg g for F). Chitosan, as a carrier, improved the structural stability of AlOOH, whereas the hierarchical porous structure and polyethyleneimine groups of MCAlP shortened the adsorption equilibrium time. Furthermore, MCAlP showed excellent adsorption capability, where the concentration of F in actual wastewater was reduced from 10.1 to 1.2 mg L in 10 min. Coexisting ions in fluoridated wastewater had no significant effect on the adsorption of F by MCAlP. The main mechanisms of F adsorption on MCAlP were found to be ion exchange, electrostatic interaction, and surface complexation.