Structure and properties of vanadium(V)-doped hexagonal turbostratic birnessite and its enhanced scavenging of Pb2+ from solutions

Abstract

Vanadium(V)-doped hexagonal turbostratic birnessites were synthesized and characterized by multiple techniques and were used to remove Pb2+ from aqueous solutions. With increasing V content, the V(V)-doped birnessites have significantly decreased crystallinity, i.e., the thickness of crystals in the c axis decreases from 9.8nm to ∼0.7nm, and the amount of vacancies slightly increases from 0.063 to 0.089. The specific surface areas of these samples increase after doping while the Mn average oxidation sates are almost constant. V has a valence of +5 and tetrahedral symmetry, and exists as oxyanions, including V6O162−, and VO43− on birnessite edge sites by forming monodentate corning-sharing complexes. Pb LIII-edge extended X-ray absorption fine structure (EXAFS) spectra analysis shows that, at low V contents (V/Mn≤0.07) Pb2+ mainly binds with birnessite on octahedral vacancy and especially edge sites whereas at higher V contents (V/Mn>0.07) more Pb2+ associates with V oxyanions and form vanadinite [Pb5(VO4)3Cl]-like precipitates. With increasing V(V) content, the Pb2+ binding affinity on the V-doped birnessites significantly increases, ascribing to both the formation of the vanadinite precipitates and decreased particle sizes of birnessite. These results are useful to design environmentally benign materials for treatment of metal-polluted water.