Exceptional sorption behaviour of porous tungsten oxide for aqueous lead
A nanoporous WO3 sorbent was found to be highly reactive towards Pb2+, exhibiting a molar sorption capacity of 42.5% and sorption half-lives as low as 47 s. The sorbent lowers the concentration of Pb2+ to less than 0.5 ppb (the instrumental detection limit), a level well below the WHO and EPA action limits. Powder X-ray diffraction and Raman spectroscopy performed on the sorbent after loading with lead demonstrated that the formation of crystalline stolzite (PbWO4) had taken place. Therefore, lead sorption occurs via a chemical reaction between Pb2+ and nanoporous WO3 accounting for the high sorption capacity. Scanning electron microscopy showed that the sorption reaction led to a large morphology change from non-descript smaller tabular particles of the sorbents to large clusters of octahedral crystallites of the stolzite product.