Highly efficient removal of arsenite from water by using renewable sub-5 nm Zr-Mn binary oxides confined inside gel-type ion exchanger

Efficient removal of As(III) from groundwater remains an urgent but still challenging task. The X-Mn (X = Fe, Zr, Al ... ) binary oxide nanoparticles enable simultaneous oxidation and sequestration of As(III), yet facing the challenges in facile synthesis of the ultra-small nanoparticles with extraordinary decontamination reactivity, and in effective regeneration of oxidation capability. Herein, we prepared a novel nanocomposite Zr-Mn@N201 by conducting stepwise precipitation of hydrated oxides of zirconium (HZO) and manganese (HMO) inside the commercial gel-type anion exchanger N201, i.e., the quaternary ammoniated poly(styrene-co-divinylbenzene) bead. Owing to restriction of nanopores, the HZO/HMO inside N201 possessed an ultra-small size around 4.78 nm. The kinetics and spectroscopic results suggested that As(III) was transformed into As(V) by HMO prior to adsorption onto HZO, and the negatively charged HMO captured most of the produced Mn2+ ions. Alkaline treatment could regenerate Zr-Mn@N201 through simultaneously desorbing As(V) and transforming Mn2+ into HMO again. During a 10-cyclic adsorption-regeneration assay, Zr-Mn@N201 could steadily reduce As(III) from 500 mu g/L to < 10 mu g/L with negligible HMO loss (< 0.3%) in each run. In fixed-bed assays, the integration of HMO increased the effective treatment amounts of the Zr-Mn@N201 column toward the realistic groundwater by -11.5 times over the single nano-HZO (i.e., HZO@N201) column, reaching to -4600 bed volume with < 1% HMO loss.