Interfacial and electronic dual regulation of metal organic frameworks for enhanced catalytic oxidation of peroxymonosulfate into dyes

Abstract

In heterogeneous advanced oxidation processes, it is important to improve the catalytic performance, which can be achieved by increasing the mass transfer of catalysts and utilization efficiency of reactive oxygen species (ROSs). Herein, the functional groups, amino group (NH₂) and hydroxyl group (OH), were introduced onto the surface of metal organic frameworks (MOFs), FeBDC (Iron terephthalate) by ligand exchange. The synthesized MOFs were used as catalysts to activate peroxymonosulfate (PMS) for the efficient removal of dye from wastewater. The NH₂/-OH groups accumulated at the surface of MOFs to significantly enhanced their hydrophilicity, which favored dye adsorption efficiency on the surface of MOFs from aqueous solution. This dye enrichment was benefited to the high utilization of ROSs due to the shorter transfer distance in solution. Additionally, the introduction of NH₂/OH favored the reduction in electrochemical resistance both within the bulk and at the interface of the MOFs, thereby facilitating the electron transfer from the MOFs to PMS. The efficient utilization of ROSs (the radicals (SO₄^- and O₂^-) and non-radical (¹O₂)) generated by PMS removed nearly all RB171 (96.2-98.5 %) by oxidation reaction. The azo bonds and aromatic rings of dye molecules were susceptible to the attack by these ROSs. At the utilization of 5 cycles, iron leaching from MOFs/PMS was very low, satisfying the value of discharge standards. This work demonstrates that the functional groups presented in MOFs effectively facilitate the dual regulation of dye enrichment and catalytic activity in heterogeneous advanced oxidation processes.

Keywords: Advanced oxidation process; Azo dyes; Electronic transfer regulation; Interfacial enrichment; Metal organic frameworks.