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

Defective MIL-88B(Fe) nanorods are exploited as exemplary iron-bearing metal-organic framework (MOF) catalyst for molecular oxygen (O-2) 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 A, larger enough for the diffusion of O-2 (3.46 angstrom) and HCHO (2.7 angstrom). The Lewis acid-base interaction between Fe-CUSs and accessible HCHO accelerates the Fe-III/Fe-II cycle, catalyzing Fenton-like O-2 activation to produce reactive oxidative species (ROSs), including superoxide radicals (center dot O-2(-)), hydroxyl radicals (center dot OH), and singlet oxygen (O-1(2)). 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 (center dot CHO) are recorded as the main reaction intermediates during HCHO oxidation. HCHO, H2O, and O-2 are captured and activated by abundant Fe-III/Fe-II-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 O-2 activation and reliable indoor air purification at ambient temperature.

Automated summary

Defective MIL-88B(Fe) nanorods are used as a catalyst for catalytic oxidation of formaldehyde by activating molecular oxygen at ambient temperature. The Fe-CUSs on the nanorods facilitate efficient O-2 activation and generation of ROSs, leading to the successful oxidation of formaldehyde with high mineralization efficiency. This study provides new insights into utilizing novel MOF catalysts for efficient O-2 activation and reliable indoor air purification at ambient temperature.