Isomorphic substitution of goethite by cobalt: Effects on the pathway and performance of peroxymonosulfate activation

Abstract

Isomorphic substitution of Goethite (α-FeOOH) by metal elements with similar radii can greatly alter its physicochemical properties. Herein, a cobalt-substituted α-FeOOH (FeCox) was synthesized by simple coprecipitation on the atomic scale. The effect on the activation of peroxymonosulfate (PMS) was explored using tetracycline (TC) as a model pollutant. Compared with the α-FeOOH, the performance of FeCo10 on PMS activation was greatly enhanced, and 95.4 % of TC was removed within 10 min. Cobalt substitution significantly decreased the metal ion leaching of the catalyst, and the iron and cobalt leaching of FeCo10 was only 4.023 and 33.614 μg/L. Co substitution altered the activation pathway of α-FeOOH for PMS. Electron paramagnetic resonance (EPR) and quenching experiments indicated that singlet oxygen (1O2) was the dominant reactive oxygen species (ROS) in the reaction system. The activation of PMS was achieved by the process that PMS was first complexed with hydroxyls (–OH) on the surface of FeCo10, after which Fe and Co species in FeCo10 broke the peroxide bond. The reaction system could operate efficiently under different concentrations (2–250 mM) of Cl-, HCO3-, SO42- and NO3-. The excellent catalytic performance of FeCo10 was due to the structural defects caused by the introduction of Co, which significantly increased the –OH sites and electron transmission capacity of the catalyst. This work has proved that isomorphic substitution was an effective strategy for improving the PMS activation performance of α-FeOOH.