In-situ green assembly of spherical Mn-based metal-organic composites by ion exchange for efficient electrochemical oxidation of organic pollutant.

In this study, we develop a facile ion exchange strategy for in-situ assembly of novel spherical metal-organic composites on a large scale. The functional groups (-NH2, -COOH and -SO3H) on chelating and exchange resins had significant effects on improving uniform distribution of metallic sites and metal-support interaction. Without any addition of H2O2, Mn-based metal-organic composites realized the recovery of waste metallic ions and exhibited high activity for methylene blue (MB) electro-Fenton degradation (97.8% decoloration and 54.7% TOC removal) within 150 min under low current density (7.53 mA·cm-2) and 3.0 g·L-1 catalyst dosage. Analyses of performance on different active sites (FeII, MnII, CoII, CeIII and CuII) and supports clearly indicated that synergetic effect of MnII and organic supports played crucial roles in electrochemical oxidation. Kinetic rate constant of 0.037 min-1 and turn over frequency of 0.23 h-1 were much better than those of inorganic supported catalysts, which were attributed to intramolecular electron transfer greatly accelerating MnII/MnIII autocatalytic cycle. Meanwhile, possible degradation pathway of MB was proposed by analysis of oxidative intermediate products. Benefiting from excellent properties and millimeter-level size structure, metal-organic composites can be applied in wide pH range of 2.0-9.0 and easily separated in the industrial application.