Investigating the Gas Sorption Mechanism in an rht-Metal–Organic Framework through Computational Studies

详细信息    查看全文

• 作者：Tony Pham ; Katherine A. Forrest ; Juergen Eckert ; Peter A. Georgiev ; Ashley Mullen ; Ryan Luebke ; Amy J. Cairns ; Youssef Belmabkhout ; Jarrod F. Eubank ; Keith McLaughlin ; Wiebke Lohstroh ; Mohamed Eddaoudi ; Brian Space
• 刊名：Journal of Physical Chemistry C
• 出版年：2014
• 出版时间：January 9, 2014
• 年：2014
• 卷：118
• 期：1
• 页码：439-456
• 全文大小：1204K
• ISSN：1932-7455

文摘

Grand canonical Monte Carlo (GCMC) simulations were performed to investigate CO₂ and H₂ sorption in an rht-metal鈥搊rganic framework (MOF) that was synthesized with a ligand having a nitrogen-rich trigonal core through trisubstituted triazine groups and amine functional groups. This MOF was synthesized by two different groups, each reporting their own distinct gas sorption measurements and crystal structure. Electronic structure calculations demonstrated that the small differences in the atomic positions between each group鈥檚 crystal structure resulted in different electrostatic parameters about the Cu²⁺ ions for the respective unit cells. Simulations of CO₂ sorption were performed with and without many-body polarization effects and using our recently developed CO₂ potentials, in addition to a well-known bulk CO₂ model, in both crystallographic unit cells. Simulated CO₂ sorption isotherms and calculated isosteric heats of adsorption, Q_st, values were in excellent agreement with the results reported previously by Eddaoudi et al. for both structures using the polarizable CO₂ potential. For both crystal structures, the initial site for CO₂ sorption were the Cu²⁺ ions that had the higher positive charge in the unit cell, although the identity of this electropositive Cu²⁺ ion was different in each case. Simulations of H₂ sorption were performed with three different hydrogen potentials of increasing anisotropy in both crystal structures and the results, especially with the highest fidelity model, agreed well with Eddaoudi et al.鈥檚 experimental data. The preferred site of H₂ sorption at low loading was between two Cu²⁺ ions of neighboring paddlewheels. The calculation of the normalized hydrogen dipole distribution for the polarizable model in both crystal structures aided in the identification of four distinct sorption sites in the MOF, which is consistent to what was observed in the experimental inelastic neutron scattering (INS) spectra. Lastly, while the experimental results for the two groups are quantitatively different, the sorption mechanisms (for both crystal structures and sorbates) are broadly similar and not inconsistent with either set of experimental data; the theoretical sorption isotherms themselves resemble those by Eddaoudi et al.