High active radicals induced from peroxymonosulfate by mixed crystal types of CuFeO2 as catalysts in the water

Delafossite CuFeO2 is a promising material for heterogeneous activation of peroxymonosulfate (PMS), while effect of different crystal types on its activity has not been reported. In this work, pure rhombohedral CuFeO2 (3R-CFO) and a mixture of rhombohedral and hexagonal phases CuFeO2 ((3R + 2H)-CFO) are successfully synthesized by a simple hydrothermal method, and an efficient PMS activation system is set up. Compared with pure 3R-CFO, the introduction of hexagonal phase (2H-CFO) markedly enhances the removal of Orange I (OI). Visible-light response accelerating PMS conversion is observed, and 3R-CFO plays a critical role in such synergetic reaction under natural light illumination. Moreover, it is uncovered that the mixed (3R + 2H)-CFO crystals enhance the exposed Lewis sites of Cu+ and Fe3+, the concentration of surface hydroxyl groups, and the electron transfer. These are important for excellent activity of (3R + 2H)-CFO. SO4− and OH both take part in the oxidation process, accompanying the dominant contribution of SO4−. The electron transfer of Cu2+/Cu+ and Fe3+/Fe2+ cycles facilitates the decomposition of PMS to generate reactive radicals.