Barpaga Dushyant, Nguyen Van T, Medasani Bharat K, Chatterjee Sayandev, McGrail B Peter, Motkuri Radha Kishan, Dang Liem X
Energy and Environment Directorate, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA, 99352, USA.
Physical and Computational Sciences Directorate, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA, 99352, USA.
Sci Rep. 2019 Jul 16;9(1):10289. doi: 10.1038/s41598-019-46269-7.
The improvement in adsorption/desorption of hydrofluorocarbons has implications for many heat transformation applications such as cooling, refrigeration, heat pumps, power generation, etc. The lack of chlorine in hydrofluorocarbons minimizes the lasting environmental damage to the ozone, with R134a (1,1,1,2-tetrafluoroethane) being used as the primary industrial alternative to commonly used Freon-12. The efficacy of novel adsorbents used in conjunction with R134a requires a deeper understanding of the host-guest chemical interaction. Metal-organic frameworks (MOFs) represent a newer class of adsorbent materials with significant industrial potential given their high surface area, porosity, stability, and tunability. In this work, we studied two benchmark MOFs, a microporous Ni-MOF-74 and mesoporous Cr-MIL-101. We employed a combined experimental and simulation approach to study the adsorption of R134a to better understand host-guest interactions using equilibrium isotherms, enthalpy of adsorption, Henry's coefficients, and radial distribution functions. The overall uptake was shown to be exceptionally high for Cr-MIL-101, >140 wt% near saturation while >50 wt% at very low partial pressures. For both MOFs, simulation data suggest that metal sites provide preferable adsorption sites for fluorocarbon based on favorable C-F ··· M interactions between negatively charged fluorine atoms of R134a and positively charged metal atoms of the MOF framework.
氢氟烃吸附/解吸性能的改善对许多热转换应用具有重要意义，如冷却、制冷、热泵、发电等。氢氟烃中不含氯，可将对臭氧的长期环境破坏降至最低，R134a（1,1,1,2 - 四氟乙烷）被用作常用氟利昂 - 12的主要工业替代品。与R134a结合使用的新型吸附剂的效能需要对主客体化学相互作用有更深入的了解。金属有机框架（MOF）代表了一类新型吸附材料，因其高比表面积、孔隙率、稳定性和可调节性而具有巨大的工业潜力。在这项工作中，我们研究了两种基准MOF，微孔Ni - MOF - 74和介孔Cr - MIL - 101。我们采用实验和模拟相结合的方法来研究R134a的吸附，以利用平衡等温线、吸附焓、亨利系数和径向分布函数更好地理解主客体相互作用。结果表明，Cr - MIL - 101的总吸附量极高，接近饱和时>140 wt%，而在极低分压下>50 wt%。对于这两种MOF，模拟数据表明，基于R134a带负电的氟原子与MOF框架带正电的金属原子之间有利的C - F···M相互作用，金属位点为碳氟化合物提供了优选的吸附位点。
