Effective purification of phosphate from water using ultra-small hydrated cerium oxides encapsulated inside gel-type polymer

Abstract

Deep removing phosphate from waters is crucial in managing eutrophication, and adsorption has been widely regarded as an effective option. However, it is still lack of adsorbents with high reactivity and applicability. Herein, a novel nanocomposite HCO@N201 was introduced by impregnating hydrated cerium oxides (HCO) NPs inside a gel-type polymer N201. Due to the unique pore structure of N201 that contained plenty of micropores of <5 nm, the in-situ generated HCO NPs were regulated to sub-5 nm level (with the average size of 3.99 ± 0.06 nm), much smaller than the HCO NPs formed inside the widely-used macroporous host D201 (27.64 ± 2.55 nm). Adsorption isotherms demonstrated that HCO@N201 exhibited the saturated adsorption capacity of 218.43 mg/g toward phosphate, reaching to 1.52 times that of the macroporous analogue HCO@D201 (144.04 mg/g). In addition, HCO@N201 exhibited highly enhanced decontamination performance in terms of adsorption selectivity, stability, and reusability. XPS analyses of O 1s and Ce 3d spectra indicated that HCO@N201 possessed elevated proportions of surface hydroxyl groups (−OH, 53.35 %) and Ce(III) species (38.13 %) than HCO@D201 (37.31 % and 29.13 % for –OH and Ce(III) species, respectively). Various techniques including FT-IR, SEM-EDS, and STEM-HAADF have also been applied to deeply explore the internal mechanism of decontamination. In cyclic fixed-bed operations, HCO@N201 could consistently produce approximately 1150 bed volumes (BV) of clean water from the influent containing ∼2 mg/L of phosphate, exceeding twice that of HCO@D201. This study may provide a promising phosphate purifier with high reactivity and applicability.