Ab Initio Molecular\nDynamics Investigation of Water\nand Butanone Adsorption on UiO-66 with Defects

Volatile organic compounds (VOCs) are harmful chemicals\nthat are\nfound in minute quantities in the atmosphere and are emitted from\na variety of industrial and biological processes. They can be harmful\nto breathe or serve as biomarkers for disease detection. Therefore,\ncapture and detection of VOCs is important. Here, we have examined\nif the Zr-based UiO-66 metal–organic framework (MOF) can be\nused to capture butanonea well-known VOC. Toward that end,\nwe have performed Born–Oppenheimer ab initio molecular dynamics\n(AIMD) at 300 and 500 K to probe the energetics and molecular interactions\nbetween butanone [CH<sub>3</sub>C(O)CH<sub>2</sub>CH<sub>3</sub>]\nand open-cage Zr-UiO-66. Such interactions were systematically interrogated\nusing three MOF structures: defective MOF with a missing 1,4-benzene-dicarboxylate\nlinker and two H<sub>2</sub>O; pristine MOF with two H<sub>2</sub>O; and pristine dry MOF. These structures were loaded with one and\nfour molecules of butanone to examine the effect of concentration\nas well. One-molecule loading interacted favorably with the defective\nstructure at 300 K, only. In comparison, interactions with four-molecule\nloading were energetically favorable for all conditions. Persistent\nhydrogen bonds between the O atom of butanone, H<sub>2</sub>O, and\nμ<sub>3</sub>–OH hydroxyl attachments at Zr nodes substantially\ncontributed to the intermolecular interactions. At higher loadings,\nbutanone also showed a pronounced tendency to diffuse into the adjoining\ncages of Zr-UiO-66. The effect of such movement on interaction energies\nwas rationalized using simple statistical mechanics-based models of\ninteracting and noninteracting gases. Broadly, we learn that the presence\nof prior moisture within the interstitial cages of Zr-UiO-66 significantly\nimpacts the adsorption behavior of butanone.