Intrinsic Thermal Management Capabilities of Flexible Metal-Organic Frameworks for Carbon Dioxide Separation and Capture
Intrinsic Thermal Management Capabilities of Flexible Metal-Organic Frameworks for Carbon Dioxide Separation and Capture
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DOI：
10.1021/acsami.7b13771
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发表时间：
2017-11-22
影响因子：
9.5
通讯作者：
Miyahara, Minoru T.
中科院分区：
文献类型：
--
作者：
Hiraide, Shotaro;Tanaka, Hideki;Miyahara, Minoru T.
研究表明，柔性金属有机框架（mof）对CO2具有“闸门打开/关闭”的特性，可以从本质上抑制吸附释放的放热和解吸获得的吸热，这两者都降低了CO2在近绝热条件下分离过程中的工作能力。我们使用弹性层状结构金属有机框架-11 (ELM-11) [Cu（4,4'-联吡啶）(2)(BF4)(2)]，它具有两步门吸附等温线，作为柔性mof的模型系统，并借助大规范蒙特卡罗模拟对由Rietveld方法确定的ELM-11结构进行自由能分析，该结构使用原位同步x射线粉末衍射数据。我们证明了ELM-11在低压力和高压力下的热管理能力几乎相同，并且非常有效（在298 K下分别为41%和44%）。此外，我们发现ELM-11在298 K下对CO2/N-2和CO2/CH4混合物具有极高的CO2选择性，除了固有的热管理能力外，这是应用于碳捕集与封存（CCS）的关键因素。ELM-11的多闸口关闭压力不一定与CCS中使用的操作压力相匹配；然而，我们的研究结果，以及基于自由能分析的观点，关于修改主机框架结构以调整浇注压力，表明具有多栅极开口/关闭的柔性mof是进一步开发成具有CCS应用固有热管理机制的系统的有前途的材料。
We show that flexible metal organic frameworks (MOFs) exhibiting "gate openings/closings" for CO2 can intrinsically suppress the exothermic heat released by adsorption and the endothermic heat gained by desorption, both of which reduce the working capacity of CO2 in a separation process under near-adiabatic conditions. We use the elastic layer-structured metal organic framework-11 (ELM-11) [Cu(4,4'-bipyridine)(2)(BF4)(2)], which exhibits a two-step gate-adsorption isotherm, as a model system for flexible MOFs, and perform free energy analyses with the aid of grand canonical Monte Carlo simulations for ELM-11 structures that were determined by the Rietveld method using in situ synchrotron X-ray powder diffraction data. We demonstrate that the thermal management capabilities of ELM-11 showing the two-step gating for CO2 at lower and higher pressures are nearly identical and quite effective (41% and 44% at 298 K, respectively). Moreover, we show that ELM-11 has an extremely high CO2 selectivity for both CO2/N-2 and CO2/CH4 mixtures at 298 K that, in addition to the intrinsic thermal management capability, is a crucial factor for application to carbon capture and storage (CCS). The multigate closing pressures of ELM-11 are not necessarily matched to the operating pressures used in CCS; however, our findings, and perspectives based on free energy analyses regarding modification of the host framework structure to tune the gating pressure, suggest that flexible MOFs exhibiting multigate openings/closings are promising materials for further development into systems with intrinsic thermal management mechanisms for CCS applications.