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Title: Computational study of adsorption and diffusion in metal- organic frameworks
Keywords: Adsorption, Diffusion, Metal-organic Frameworks, Covalent-organic Frameworks, Selectivity, Simulation
Issue Date: 20-Aug-2009
Source: BABARAO RAVICHANDAR (2009-08-20). Computational study of adsorption and diffusion in metal- organic frameworks. ScholarBank@NUS Repository.
Abstract: Adsorption and diffusion in nanoporous materials lie at the heart of many large-scale industrial applications such as gas separation, storage and selective catalysis. As the number of nanoporous materials to date is extremely large, selecting a promising material from discovery to applications is a challenge. The development of particular technological applications for nanoporous materials requires the fundamental understanding of their microscopic properties. In this sense, computational study plays an important complementary role to experiments by making predictions prior to experimental studies. The selection of a suitable adsorbent is a key step in the design of adsorption-based storage or separation processes. While most studies have focused on zeolites and carbon-based adsorbents, a new class of hybrid materials has been recently developed, i.e. metal-organic frameworks (MOFs) which consist of metal-oxide clusters and organic linkers. MOFs allow the formation of tunable porous frameworks with a wide variety of architectures, topologies and pore sizes. Because of their high porosity and well-defined pore size, MOFs are promising candidates for the storage and separation of gases, ion-exchanges, catalysis, sensing, etc. In this thesis, molecular simulation techniques have been used to elucidate the adsorption and diffusion phenomena of fluids in a wide variety of MOFs. (1) The adsorption and diffusion of CO2 and CH4 were examined in three different nanoporous materials (silicalite, C168 schwarzite, and IRMOF-1). IRMOF-1 has a significantly higher adsorption capacity for CO2 and CH4 than silicalite and C168 schwarzite; however, the adsorption selectivity of CO2 over CH4 is similar in all the three adsorbents. (2) Further, a series of metal-organic frameworks (MOFs) with unique characteristics such as exposed metals (Cu-BTC, PCN-6I and PCN-6), catenation (IRMOF-13 and PCN-6) and extra-framework ions (soc-MOF) were considered. It was found that catenated MOFs have a higher selectivity than their non-catenated counterparts. Much higher selectivity is observed in charged soc-MOF compared with other IRMOFs and PCN structures. (3) CO2 storage in a series of MOFs was studied with different characteristics. In addition, covalent-organic frameworks (COFs), a sub-set of MOFs were also considered. The gravimetric and volumetric capacity of CO2 at a moderate pressure correlates well with the framework density, free volume, porosity and accessible surface area of both MOFs and COFs. These correlations are useful for a priori prediction of CO2 capacity and for the rational screening of MOFs and COFs toward high-performance CO2 storage. (4) For the first time, the extra-framework ions were characterized and gas separation was examined in a charged MOF, rho-ZMOF, with anionic framework. The selectivity was ~ 1800 for CO2/H2, 80 for CO2/CH4, and 500 for CO2/N2 mixtures. Compared with other MOFs and nanoporous materials reported to date, rho-ZMOF exhibits unprecedentedly high selective adsorption for gas mixtures. (5) The effect of catenation on the separation of alkane isomers and the microscopic properties of a model drug, ibuprofen, were also studied. As a relatively new class of materials, MOFs will continue to attract extensive interest in both academia and industry. They exhibit high potential for adsorptive storage in energy applications as well as separation and purification in industrial applications.
Appears in Collections:Ph.D Theses (Open)

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