Magnetic sustentation process as a new adsorption characterization technique
In this paper we present a direct and low-cost characterization technique taking advantage on the intrinsic magnetic properties of paramagnetic metal-organic frameworks (MOFs) for the in situ study of adsorption processes in solution. This method does not rely on the complex magnetic interactions that usually only emerge at temperatures well below room temperature. Instead, it is based on the weak attraction exerted by an external magnetic field on paramagnetic materials measured at room temperature (see video). We have developed the theoretical equations that guide magnetic sustentation experiments to better understand the process and experimentally verify its feasibility using four well-known paramagnetic MOFs (MIL-88A(Fe) isostructural Cu(II)- and Co(II)-MOF-74 and ZIF-67(Co)). The adsorption of different organic molecules was quantified, and it was confirmed that there is a linear relationship between the critical magnetic field and captured mass. All in all, this technique allowed obtaining adsorption isotherms curves, which altogether provides the advantage of performing a direct and in situ measurement of captured molecules and without the need for any sample preparation that conventional techniques such as ultraviolet spectroscopy usually require.
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Communications Chemistry, 2023, 6:4, DOI: 10.1038/s42004-022-00799-w