Application of metal-organic frameworks in the purification of indoor hexanal: Experiments and DFT calculations

Given that the toxic hexanal in indoor air is primarily originated from the cooking oil fumes, it is necessary to purify hexanal in the cooking oil fumes to prevent the adverse health effects of hexanal to human beings. In this study, four typical metal-organic frameworks (MOFs), namely MIL-101 (Cr), UiO-66, ZIF-8 and Cu-BDC were synthesized and applied to purify the indoor hexanal, and their adsorption capacities to hexanal were compared with the commercial activated carbon (AC). Our results show that the adsorption capacities of hexanal follow the order of MIL-101(Cr) (135 mg g(-1))> UiO-66 (64.3 mg g(-1))> ZIF-8 (40.3 mg g(-1))> AC (35.8 mg g(-1))> Cu-BDC (32.5 mg g(-1)), and the desorption capacities (by air) follow the order of MIL-101(Cr) (55.5 mg g(-1))> UiO-66 (26.1 mg g(-1))> AC (24.5 mg g(-1))>ZIF-8 (19.3 mg g(-1))> Cu-BDC (5.5 mg g(-1)), indicating that hexanal adsorbed on MIL-101 (Cr)/UiO-66 is more appropriate than the commercial AC to be desorbed. FTIR analysis confirms that O-H in Cr-OH/Zr-OH, O-C-O and aromatic C-H in H2BDC in both MIL-101 (Cr) and UiO-66 are possible sites for hexanal adsorption. DFT calculations further reveal that Cr-OH/Zr-OH and aromatic C-H in H2BDC are important sites to interact with C-O in hexanal. This study provides a possibility to purify indoor aldehyde contaminants by the highly porous MOF materials.