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清华大学材料科学与工程研究院《材料科学论坛》
学术报告
Physical adsorption is based on van der Waals interactions between molecules of vapors and atoms on solid surfaces. The physical adsorption proceeds markedly at very low relative pressure in nanopores because of enhancement by superposition of the interactions from different walls of the solid, although the van der Waals interaction is considered to be weak. I will talk about physical adsorption of gases in naopores for vapor and for supercritical gases.
And then, a specific gas sorption behavior, a gate phenomenon, will be introduced. [Cu(bpy)2(BF4)2]n (bpy = 4,4'-bipyridine) is one of metal organic frameworks having a 2-dimensional coordination space, has latent pores, and therefore is called a "latent porous complex (LPC)." LPC shows a unique sorption behavior, the "gate phenomenon", in adsorption of CO2 and other gas molecules. The sorption reaction is well described by a clathrate formation of LPC and CO2 molecules. The mechanism of the gate phenomenon is based on the expansion/shrinkage behavior of the stacking structure of LPC.
We can control the 2-dimensional coordination space by changing metal ions, counter anions, and ligand molecules. For example, [Cu(bpy)2(OTf)2]n (OTf = CF3SO3-) has a wider interlayer distance than that of [Cu(bpy)2(BF4)2]n because OTf anions are more bulky than BF4-, resulting in the micropore filling at very low relative pressure, whereas [Cu(bpy)2(BF4)2]n shows no sorption uptake at such a low pressure. Moreover, [Cu(bpy)2(OTf)2]n indicates a gate phenomenon accompanied by an expansion of the interlayer distance, after the completeness of the micropore filling; the second-step sorption. Gas behaviors of other MOFs with different metals such as [Co(bpy)2(OTf)2]n will be also presented.
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