Generating High-valent Iron-oxo ≡Fe =O Complexes in Neutral Microenvironments through Peroxymonosulfate Activation by Zn-Fe Layered Double Hydroxides.

The universal limit on the pH conditions is disturbing peroxymonosulfate (PMS)-triggered high-valent iron-oxo systems in environmental applications. Here, we propose for the first time the construction of a neutral microenvironment on the surface of Zn-Fe layered double hydroxide (ZnFe-LDH) by using the amphoteric properties of zinc hydroxide, which continuously generates ≡Fe =O over a wide pH range of 3.0-11.0 in activating PMS. The ≡Zn(OH) moiety offers a neutral microenvironment at the phase interface, which mitigates the self-decomposition of ≡Fe =O by protons and the hydrolysis reaction of iron by hydroxyl groups, which is supported by the Mossbauer spectra, density functional theory calculations and designed experiments. Consequently, ZnFe-LDH/PMS can satisfy the stability in long-term experiments, selectivity under conditions with high salinity or natural organic matter and efficient treatment of actual wastewater.