Host–guest and guest–guest interactions between xylene isomers confined in the MIL-47(V) pore system

Abstract

The porous MIL-47 material shows a selective adsorption behavior for para, ortho, and meta-isomers of xylenes, making the material a serious candidate for separation applications.The origin of the selectivity lies in the differences in interactions (energetic) and confining (entropic). This paper investigates the xylene-framework interactions and the xylene-xylene interactions with quantum mechanical calculations, using a dispersion corrected density functional and periodic boundary conditions to describe the crystal. First, the strength and geometrical characteristics of the optimal xylene-xylene interactions are quantified by studying the pure and mixed pairs in gas phase. An extended set of initial structures is created and optimized to sample as many relative orientations and distances as possible. Next, the pairs are brought in the pores of MIL-47. The interaction with the terephthalic linkers and other xylenes, increases the stacking energy in gas phase (-31.7 kJ/mol per pair) by roughly a factor four in the fully-loaded state (-58.3 kJ/mol per xylene). Our decomposition of the adsorption energy shows various trends in the contributing xylene-xylene interactions. The absence of a significant difference in energetics between the isomers indicates that entropic effects must be mainly responsible for the separation behavior.Corresponding authors: an.ghysels@ugent.be, veronique.vanspeybroeck@ugent.be 2

Prediction of Adsorption Properties of Cyclic Hydrocarbons in MOFs Using DFT-Derived Force Fields

“…36 This method was previously used to assess the stacking energy of xylenes in MIL-47. 37 A force field fitting procedure was performed to determine parameters for the cross-interactions between the toluene The Journal of Physical Chemistry C Article molecules and the atoms in the BDC linker of the framework. The metal atoms of all MOFs and the DABCO linker in DMOF-1 (DABCO = 1,4-diazabicyclo[2.2.2]octane) were described using UFF.…”

Mass transfer of toluene in a series of metal–organic frameworks: molecular clusters inside the nanopores cause slow and step-like release

“…24 Later, computations showed that molecules like CO 2 , CH 4 , benzene and xylene form molecular clusters and dense molecular packings in the pores of various MOF structures. 25–28 In a pioneering experimental study, M. Tsotsalas, S. Kitagawa et al observed the molecular clustering of butanol, diethyl ether and n -pentane in the pores of the prototype MOF HKUST-1. 29 It was found that the desorption process is significantly decelerated by the clustering of the molecules.…”

Theoretical chemistry in Belgium

“…Currently, the CMM members are author of about 437 papers in ISI journals, among which Nature Materials, Angewandte Chemie, Journal of the American Chemical Society, Physical Review Letters, Journal of Catalysis, etc., with more than 6,600 citations. The paper by A. Ghysels et al [7] and A. Cedillo et al [8] in the present issue gives illustrations of the research carried out in the CMM and the GQCG. The first study that has been undertaken was the computation of an extensive series of monosubstituted pyridines and phenolates in the gas phase using semi-empirical (MINDO/3, MNDO, and AM1) and ab initio methods using a program vectorized in the group for the Cyber 205 vector processor.…”