Enhanced removal of arsenic from water by using sub-10 nm hydrated zirconium oxides confined inside gel-type anion exchanger

Abstract

Given high selectivity and excellent stability, zirconium oxides are very promising in selective removal of arsenic, fluorine, and phosphorus from water. Nevertheless, it remains challenging to prepare sub-10 nm zirconium oxides of ultra-high adsorptive reactivity. Herein, we prepared hydrated zirconium oxides (HZO) of 4.88 ± 1.02 nm by conducting in-situ precipitation of nanoparticles (NPs) inside the gel-type anion exchanger (GAE). GAE was swollen in water and contained lots of < 10 nm swollen pores, restricting excess growth of HZO NPs. In comparison, the NPs formed inside the macroporous anion exchanger (MAE) possessed an average diameter of 30.91 ± 8.98 nm. XPS O1s analysis indicated that the oxygen sites in the gel-type nanocomposite (HZO@GAE) possessed a much higher proportion (48.9%) of reactive terminal oxygen (-OH) than the macroporous nanocomposite (HZO@MAE, 21.2%). Thus, HZO@GAE exhibited significantly enhanced adsorption reactivity toward As(V)/As(III) than HZO@MAE. The exhausted HZO@GAE could be fully regenerated by alkali treatment for repeated use without any loss in decontamination efficiency. In column assays, the HZO@GAE column successively produced ~2400 bed volume (BV) clean water ([As]<10 μg/L) from synthetic groundwater, exceeding twice the amount produced by the HZO@MAE column. This study may shed new light on developing highly efficient nanocomposites for water decontamination.