Rieth Adam J, Wright Ashley M, Skorupskii Grigorii, Mancuso Jenna L, Hendon Christopher H, Dincă Mircea
Department of Chemistry , Massachusetts Institute of Technology , 77 Massachusetts Avenue , Cambridge , Massachusetts 02139 , United States.
Materials Science Institute, Department of Chemistry and Biochemistry , University of Oregon , Eugene , Oregon 97403 , United States.
J Am Chem Soc. 2019 Sep 4;141(35):13858-13866. doi: 10.1021/jacs.9b06246. Epub 2019 Aug 23.
The reversible capture of water vapor at low humidity can enable transformative applications such as atmospheric water harvesting and heat transfer that uses water as a refrigerant, replacing environmentally detrimental hydro- and chloro-fluorocarbons. The driving force for these applications is governed by the relative humidity at which the pores of a porous material fill with water. Here, we demonstrate modulation of the onset of pore-filling in a family of metal-organic frameworks with record water sorption capacities by employing anion exchange. Unexpectedly, the replacement of the structural bridging Cl with the more hydrophilic anions F and OH does not induce pore-filling at lower relative humidity, whereas the introduction of the larger Br results in a substantial shift toward lower relative humidity. We rationalize these results in terms of pore size modifications as well as the water hydrogen bonding structure based on detailed infrared spectroscopic measurements. Fundamentally, our data suggest that, in the presence of strong nucleation sites, the thermodynamic favorability of water pore-filling depends more strongly on the pore diameter and the interface between water in the center of the pore and water bound to the pore walls than the hydrophilicity of the pore wall itself. On the basis of these results, we report two materials that exhibit record water uptake capacities in their respective humidity regions and extended stability over 400 water adsorption-desorption cycles.
在低湿度条件下可逆地捕获水蒸气能够实现一些变革性应用，如大气水收集以及以水作为制冷剂的热传递，从而取代对环境有害的氢氟烃和氯氟烃。这些应用的驱动力取决于多孔材料孔隙充满水时的相对湿度。在此，我们通过阴离子交换展示了对一类具有创纪录水吸附容量的金属有机框架材料中孔隙填充起始点的调控。出乎意料的是，用亲水性更强的阴离子F和OH取代结构桥连的Cl并不会在更低的相对湿度下引发孔隙填充，而引入更大的Br则会导致显著地向更低相对湿度偏移。基于详细的红外光谱测量，我们从孔径变化以及水的氢键结构方面对这些结果进行了合理解释。从根本上说，我们的数据表明，在存在强成核位点的情况下，水填充孔隙的热力学有利性更多地取决于孔径以及孔隙中心的水与结合在孔壁上的水之间的界面，而非孔壁本身的亲水性。基于这些结果，我们报道了两种材料，它们在各自的湿度区域展现出创纪录的水吸收容量，并在400次水吸附 - 解吸循环中具有良好的稳定性。
