Gas Storage and Diffusion through Nanocages and Windows in Porous Metal鈥揙rganic Framework Cu2(2,3,5,6-tetramethylbenzene-1,4-diisophthalate)(H2O)2

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• 作者：Liangjun Li ; Jon G. Bell ; Sifu Tang ; Xiaoxia Lv ; Chao Wang ; Yanlong Xing ; Xuebo Zhao ; K. Mark Thomas
• 刊名：Chemistry of Materials
• 出版年：2014
• 出版时间：August 26, 2014
• 年：2014
• 卷：26
• 期：16
• 页码：4679-4695
• 全文大小：912K
• ISSN：1520-5002

文摘

A novel nanoporous metal鈥搊rganic framework NPC-4 with excellent thermal stability was assembled from 2,3,5,6-tetramethylbenzene-1,4-diisophthalate (TMBDI) and the paddle-wheel secondary building unit (Cu₂(COO)₄). The porous structure comprises a single type of nanoscale cage (16 脜 diameter) interconnected by windows (5.2 脳 6.3 脜), which give a high pore volume. CH₄ (195鈥?90 K), CO₂ (198鈥?03 K), N₂ (77 K), and H₂ (77 K) adsorption isotherms were studied for pressures up to 20 bar. NPC-4 exhibits excellent methane and carbon dioxide storage capacities on a volume basis with very high adsorbate densities, under ambient conditions. Isobars were investigated to establish the relationship for adsorption capacities over a range of storage temperatures. The isosteric enthalpies of adsorption for both CH₄ and CO₂ adsorption did not vary significantly with amount adsorbed and were 鈭?5 and 鈭?5 kJ mol^鈥?, respectively. The adsorption/desorption kinetics for CH₄ and CO₂ were investigated and activation energies, enthalpies of activation, and diffusion parameters determined using various kinetic models. The activation energies for adsorption obtained over a range of uptakes from the stretched exponential kinetic model were 5.1鈥?.3 kJ mol^鈥? (2鈥?3.5 mmol g^鈥?) for CO₂ and 2.7鈥?.6 kJ mol^鈥? (2鈥? mmol g^鈥?) for CH₄. The activation energies for surface barriers and diffusion along pores for both CH₄ and CO₂ adsorption obtained from a combined barrier resistance diffusion model did not vary markedly with amount adsorbed and were <9 kJ mol^鈥?. Comparison of kinetic and thermodynamic parameters for CH₄ and CO₂ indicates that a surface barrier is rate determining at high uptakes, while intraparticle diffusion involving diffusion through pores, consisting of narrow windows interconnecting with nanocages, being rate determining at very low uptakes. The faster CH₄ intraparticle adsorption kinetics compared with CO₂ for NPC-4 was attributed to faster surface diffusion due to the lower isosteric enthalpy of adsorption for CH₄.