Metal-Organic Frameworks for Energy, Environmental and Pharmaceutical Applications: A Computational Perspective
作者单位：Department of Chemical and Biomolecular EngineeringNational University of Singapore
会议名称：《The 1st International Congress on Advanced Materials 2011》
会议日期：2012年
学科分类：07[理学] 070303[理学-有机化学] 0703[理学-化学]
关 键 词：Metal-Organic Frameworks CO2 Storage and Capture Drug Delivery.
摘 要：Metal-organic frameworks (MOFs) have emerged as a new class of hybrid nanoporous materials. Composed of metal-oxide clusters and organic linkers, MOFs possess extremely large surface area (up to 6000 m 2 /g) and high porosity (up to 90%) ever recorded for crystalline materials. The judicious choice of controllable organic linkers and the variation of metal oxides allow the pore sizes, volumes and functionalities of MOFs to be tailed in a rational way for designable architectures. MOFs provide a wealth of opportunities for engineering new functional materials and are considered as versatile candidates for storage, separation, sensing, catalysis, and other important applications. An overview will be presented for the recent state-of-the-art computational studies on energy, environmental and pharmaceutical applications of MOFs. A few typical examples will be given: (1) CO 2 storage is examined in a series of MOFs by varying metal center, organic linker, functional group and framework topology. The affinity with CO 2 is enhanced by the addition of functional groups and the formation of constricted pores;both lead to a stronger adsorption at low pressures. The organic linker plays a critical role in tuning the free volume and accessible surface area, and thus largely determines CO 2 adsorption at high pressures. The capacities at high pressures correlate well with framework density, free volume, porosity and accessible surface area of MOFs. These molecular-based structure-function correlations are useful for a priori prediction of CO 2 capacity and for rational screening of MOFs toward the high-efficacy CO 2 storage. (2) The separation of CO 2 /CH 4 mixture is studied in MOFs with unique characteristics such as exposed metals, catenation and extra-framework ions. The catenated MOFs have a higher selectivity than their non-catenated counterparts. CO 2 /CH 4 selectivity in charged MOF is substantially higher than in neutral MOFs, and the highest among various MOFs reported to date. The study reveals that the selectivity of CO 2 over CH 4 in MOFs is enhanced slightly by exposed metals, catenation and significantly by extra-framework ions and that charged MOFs are promising candidates for upgrading natural gas. The separation of alkane isomer mixtures is also simulated in different MOFs. Competitive adsorption between isomers is observed, particularly at high pressures, in which a linear isomer shows a larger extent of adsorption due to the configurational entropy. The catenated MOFs exhibit larger adsorption and diffusion selectivities for alkane mixtures than the noncatenated counterparts. (3) The microscopic properties of drug (ibuprofen, IBU) in mesoporous MOFs (MIL-101 and UMCM-1) are examined. The predicted maximum loading of IBU is in good agreement with experimental measurement and approximately four times greater than in silica MCM-41. The lowest-energy conformation of IBU in MIL-101 is preferentially located near the metal-oxide. From the highest-occupied molecularorbitals and band gap, a coordination bond is found to form between the carboxylic group of IBU and the exposed metal site of MIL-101. IBU exhibits a stronger binding energy and a smaller mobility in MIL-101 than in UMCM-1. These factors are crucial for the delayed release of IBU from MIL-101, which was observed experimentally. This work unravels the energetics and dynamics of IBU in MOFs at the molecular level and provides useful insight into the interactions of drug with host MOFs.