Adsorption of indole and quinoline from a model fuel on functionalized MIL-101: effects of H-bonding and coordination

Denitrogenation of a model fuel was studied by employing the adsorption of indole (IND) and quinoline (QUI) over a metal-organic framework (MOF), MIL-101, with or without functionalization. Five MIL-101 MOFs were obtained by direct syntheses, grafting, and hydrogenation. The adsorption capacity of IND increased significantly (up to 1.7 times that of MIL-101) upon introducing amino functional groups into MIL-101, despite the decrease in the porosity of the MOF after modification. However, the adsorption of QUI decreased when MIL-101 was modified using both amino and butyl groups because of the reduced porosity. The adsorption capacity for IND (based on the unit surface area of MIL-101s) showed that MIL-101s with amino groups had an adsorption capacity of around 2.3 times those of MIL-101 or MIL-101 with butyl groups, showing the importance of H-bonds for the adsorption of IND over MIL-101s. However, for the adsorption of QUI, only the porosity is important, and coordination of QUI on open metal sites does not play a dominant role, probably because of the low basicity of QUI. Moreover, there is little contribution of H-bonds (between N of QUI and H of -NH2 of MOF) in the adsorption of QUI over amino-MIL-101s, and this is probably due to a similar reason. Preparation methods for MIL-101 having a free amino group did not have any effect on the adsorption (based on surface area) of QUI or IND.