Tuning strategies of MIL metal organic frameworks for adsorptive removal of formaldehyde in air.

Materials Institute Lavoisier (MIL) metal organic frameworks (MOFs) are known for their potential to adsorb gaseous organic pollutants. This study explores the synergistic effects between the selection of central metals (e.g., titanium, iron, and aluminum) and the incorporation of -NH groups in terms of adsorption efficiency against gaseous formaldehyde (FA). A group of the pristine MIL MOFs is synthesized using three different metals (i.e., titanium, iron, and aluminum) and terephthalic acid along with their NH derivatives using 2-aminoterephthalic acid. Among the pristine forms, MIL-125(Ti) achieves the highest FA adsorption capacity (Q) of 26.96 mg g and a partition coefficient (PC) of 0.0898 mol kg Pa. Further, amination significantly improves the FA adsorption potential of NH-MIL-125(Ti) with a Q value of 91.22 mg g (PC = 0.3038 mol kg Pa). In situ diffuse reflectance infrared Fourier-transform spectroscopy reveals that the FA adsorption of plain MILs should be governed primarily by physisorption. In contrast, FA adsorption of NH-MILs appears to be regulated by both physisorption and chemisorption, while the latter being affected mainly through FA-NH interactions (Schiff base reactions). These findings provide valuable insights into the utility of aminated MIL sorbents, possibly toward the efficient management of indoor air quality.