Oxygen Vacancies and Surface Hydroxyl Groups in NiFe/Mn-MOF-74 Synergistically Drive Indoor Formaldehyde Mineralization

The challenge in enhancing the room-temperature catalytic oxidation (RTCO) performance of formaldehyde (HCHO) lies in strengthening the ability to activate oxygen. This study synthesized a NiFe/Mn-MOF-74 composite with abundant oxygen vacancies (OVs) and surface hydroxyl groups through an in situ growth strategy. This composite material not only inherits the strong capture capacity of the layered double hydroxides (LDHs) surface hydroxyl groups for HCHO but also generates reactive oxygen species such as O2- and O- by introducing high-density OVs to activate oxygen molecules. Density functional theory (DFT) calculations indicate that the synergistic interaction between OVs and surface hydroxyl groups significantly promotes the adsorption of O2 (-2.93 eV) and HCHO (-3.31 eV). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results further reveal the reaction pathway, in which HCHO is converted via intermediates such as formate and carbonate and is ultimately mineralized into CO2 and H2O. In a 35 L reactor simulating an indoor environment, the optimized 0.25 NiFe/Mn catalyst achieved 93.30% HCHO mineralization, retaining good stability throughout 1800 min of cyclic operation. This study elucidates the synergistic mechanism between OVs and surface hydroxyl groups in the composite material during RTCO of HCHO and advances the fundamental understanding of this reaction process.