Recyclable high-affinity arsenate sorbents based on porous Fe2O3/La2O2CO3 composites derived from Fe-La-C frameworks

Efficient removal of aqueous arsenic is still a great challenge in particular for producing clean drinking water and for waste water treatment. To this end, a novel magnetic porous Fe-La composite, comprising La 2 O 2 CO 3 and Fe 2 O 3 , was fabricated via a self-sacrificing template method based on bimetallic (Fe, La)-MOFs calcined at 550 °C. Batch adsorption results demonstrated that Fe-LaXY (X and Y represent the feeding mole ratio of Fe and La precursors) exhibited a maximum adsorption capacity of As(V) (241, 251 and 410 mg g −1 for Fe-La51, Fe-La21 and Fe-La11, respectively), and they also showed satisfactory adsorption kinetics, which can be ascribed to a strong coordination between La and arsenate species. Coexisting sorbates including carbonate, silicate, sulfate, and humic acid had a slight influence on adsorption performance of arsenate, while phosphate isostructural to arsenate gave severe interference. More importantly, the Fe-La11 could be easily separated from water due to its magnetism (7.0 emu g −1 ), and it also exhibited excellent recyclability (above 80% of removal efficiency at the fifth cycle) as well as stability in terms of release of Fe and La ions (< 0.5 mg L −1 at pH 4.0–10.0). Based on results from X-ray photoelectron spectroscopy (XPS), Powder X-ray diffraction (PXRD) and Raman spectroscopy, it is demonstrated that ligand exchange of surface hydroxyl groups and the formation of inner-sphere surface complexes are main responsible for the As(V) removal mechanism. Combining the magnetic properties, the absorption properties and the recyclability make Fe-LaXY derived from bimetallic MOFs promising sorbents for arsenate removal.