Synergetic Molecular Oxygen Activation and Catalytic Oxidation of Formaldehyde over Defective MIL-88B(Fe) Nanorods at Room Temperature.

Abstract

Defective MIL-88B(Fe) nanorods are exploited as exemplary iron-bearing metal-organic framework (MOF) catalyst for molecular oxygen (O2) activation at ambient temperature, triggering effective catalytic oxidation of formaldehyde (HCHO), one of the major indoor air pollutants. Defective MIL-88B(Fe) nanorods, growing along the [001] direction, expose abundant coordinatively unsaturated Fe-sites (Fe-CUSs) along extended hexagonal channels with a diameter of ca. 5 Å, larger enough for the diffusion of O2 (3.46 Å) and HCHO (2.7 Å). The Lewis acid-base interaction between Fe-CUSs and accessible HCHO accelerates the FeIII/FeII cycle, catalyzing Fenton-like O2 activation to produce reactive oxidative species (ROSs), including superoxide radicals (•O2-), hydroxyl radicals (•OH), and singlet oxygen (1O2). Consequently, adsorbed HCHO can be oxidized into CO2 with a considerable mineralization efficiency (over 80%) and exceptional recyclability (4 runs, 48 h). Dioxymethylene (CH2OO), formate (HCOO-) species, and formyl radicals (•CHO) are recorded as the main reaction intermediates during HCHO oxidation. HCHO, H2O, and O2 are captured and activated by abundant FeIII/FeII-CUSs as acid/base and redox sites, triggering synergetic ROS generation and HCHO oxidation, involving cooperative acid-base and redox catalysis processes. This study will bring new insights into exploiting novel MOF catalysts for efficient O2 activation and reliable indoor air purification at ambient temperature.