Efficient Defluoridation of Water by Utilizing Nanosized Ce-Fe Bimetal Oxyhydroxides Encapsulated Inside Porous Polystyrene Anion Exchanger

Fluoride contamination is a serious problem of global concern, and water decontamination from fluoride remains an imperative but also a challenging task. Recently, Ce-Fe bimetal oxyhydroxides (CFBOs) nanoparticles of sufficient hydroxyl group and high reactivity have exhibited unique advantages for specific fluoride elimination. Unfortunately, they are difficult to apply directly in scale-up water treatment due to their ultrafine nature. Herein, we fabricated a novel polymer-based Ce-Fe bimetal oxyhydroxides nanocomposite, i.e., CFBOs@201, by co-precipitation of Ce/Fe oxides nanoparticles inside a porous polystyrene anion exchanger D201. The material characterization results confirmed that CFBOs were successfully immobilized inside the pores of D201 with nanoscale and micro crystalline nature, and the shielding effect of the host D201 significantly improved the chemical stability of CFBOs against pH variation (3-12). As compared with cerium and ferric (hydr)oxides nanocomposites (HCO@201 and HFO@201) and its host D201, CFBOs@201 exhibited superior capacity and better selectivity for fluoride adsorption. Thanks to the inner-sphere complexation between immobilized CFBOs and fluoride, the concomitant competing anions exerted negligible effect on the defluoridation efficiency of CFBOs@201. Fluoride uptake onto CFBOs@201 agreed well with the pseudo-second-order kinetic model and the Langmuir isotherm model, and the calculated maximum adsorption capacity was 65.99 mg/g. The exhausted CFBOs@201 could be efficiently regenerated by a simple alkaline treatment for cyclic utilization with constant defluorination performance. Fixed-bed assays demonstrated that the encapsulating of CFBOs nanoparticles enhanced the effective treatment capacity of CFBOs@201 by 10-12 times over the host D201 irrespective of whether synthetic wastewater or mine drainage was the feeding solution. The above results verified that CFBOs@201 is a new kind of efficient defluoridation adsorbent with practical application prospect.