New insights on UV-activated transformation of polynuclear Fe-hydroxide and iron(III) (hydr)oxide for enhanced removal of natural organic matter by ferrate

It is important to regulate the in-situ generated iron(III) (hydr)oxides with the function of adsorption/coagulation during ferrate (Fe(VI)) oxidation and hydrolysis which was beneficial for removal of natural organic matter (NOM). This study investigated the effect of UV activation on the Fe(VI) hydrolysis and Fe(III) flocculation performance. Results indicated UV activation can effectively improve the protein and humic acid(HA) removal in natural surface water. In situ UV differential absorption spectroscopy showed that UV effectively activated the hydrolysis of Fe(VI), which converted Fe(VI) into intermediate high-valence iron with higher reactivity, and promoted polynuclear Fe-Hydroxide and iron(III) (hydr)oxide (PnFe-H), which improved the oxidation and flocculation of pollutants. With the radical species analysis, UV activation promoted the generation of Fe(IV) and H 2 O 2 , which greatly increased the generation rate of superoxide radicals (O 2 •- ) and hydroxyl radicals (•OH). Furthermore, the structure analysis of the hydrolysate proved that UV enhanced the hydrogen bond and produced a large number of polar hydroxyl groups combined with iron ions, which further triggered the conversion of Fe(III) into amorphous Fe-hydroxide and ferrihydrite with large specific surface area and high surface activity. Meanwhile, the aggregation behavior and interaction energy of Fe-(oxy)hydroxide indicated that the lower free energy obtained in UV-activation system and increased the aggregation. This study clarified new insights on UV-activated ferrate, which can expand our understanding on ferrate applications in water purification processes.