**4. Conclusions**

This work introduces a simple and fast way of quantifying the separation degree of a binary solvent mixture by a MOF material with exemplification on UiO-66(Zr) using a small and low-cost single-sided NMR device. The proposed method is based on correlation curves between the proton effective transverse relaxation times *T*2eff and the mass proportions of the two solvents. Once the correlation curves were established, the mass proportions in the filtered mixture can be obtained within a few minutes with great accuracy, as demonstrated by the excellent agreement with the results from liquid-state NMR spectroscopy. The proposed approach can be even applied to characterize solvent mixtures where NMR spectroscopy alone fails. It could help identifying experimental conditions that improve the separation of the mixture components by systematically investigating the impact of particular experimental parameters, such as, e.g., the separation temperature or the presence or absence of a carrier gas. The use of other MOFs with higher separation selectivity for the studied binary mixtures than UiO-66(Zr) would further highlight the potential of this novel method. The whole NMR setup can be introduced inside a synthesis laboratory and it is amenable to automation; thus, helping to save time in searching for adequate separation conditions and MOFs for a particular solvent mixture.

**Supplementary Materials:** The following are available online. Figure S1: Exemplarily ILT spectra of various investigated mixtures. Figure S2: Correlation curves for different binary mixtures. The continuous lines are the fit results using a single exponential function and has for all samples a correlation factor higher than 0.99. Figure S3: Changes in the effective relaxation times before (closed symbols) and after separation (open symbols) with UiO-66(Zr) for all investigated mixtures. Figure S4: Experimental diffraction patterns of activated UiO-66 (Zr) showing the presence of a fully crystalline structure. Figure S5: Typical ILT of the proton CPMG decays (a) and 1H spectra (b) of the solvent mixture after different mixing times with the metal–organic framework. The solvent-MOF system equilibrates within around 2 h, as no changes between the results can be detected at longer times. Figure S6: 1H high-field spectra of the binary mixture cyclohexane—n-hexane before (top) and after the separation (bottom) by UiO-66(Zr). Figure S7: 1H high-field spectra of the binary mixture TiPB—2-pentanone before (top) and after the separation (bottom) by UiO-66(Zr). The two solvents were mixed in a ratio of about 1:12 as described in the experimental section. Figure S8: 1H high-field spectra of the binary mixture n-octane—2-pentanone before (top) and after the separation (bottom) by UiO-66(Zr). The two solvents were mixed in a ratio of about 1:12 as described in the experimental section. For better view of smaller signals, the signals of n-octane are not shown in full amplitude. Figure S9: 1H high-field spectra of the binary mixture cyclooctane—pentanone before (top) and after the separation (bottom) by UiO-66(Zr). The two solvents were mixed in a ratio of about 1:12 as described in the experimental section. For better view of smaller signals, the signal of cyclooctane is not shown in full amplitude. Figure S10: 1H high-field spectra of the binary mixture cyclooctane—n-octane before (top) and after the separation (bottom) by UiO-66(Zr). The two solvents were mixed in a ratio of about 1:12 as described in the experimental section. For better view of smaller signals, the signal of cyclooctane is not shown in full amplitude. Table S1 (in the Supplementary Materials): Proton transverse relaxation times T2eff of the pure solvents measured using the NMR-MOUSE at room temperature and using the experimental conditions described in the experimental section. Diffusion coefficients and viscosity values are also shown for better understanding the obtained values for the T2eff. Table S2: Reproducibility of the NMR relaxation measurements with exemplification on different mixtures.

**Author Contributions:** Conceptualization, A.A.; investigation, M.W. and N.R.; resources, A.K. and A.A.; writing—original draft preparation, M.W., N.R. and A.A.; writing—review and editing, A.A.; supervision, A.A.; funding acquisition, A.K. and A.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** A part of this work was financially supported by National Centre for Research and Development in Poland (contract No. STRATEGMED2/265761/10/NCBR/2015) and by RWTH Aachen University.

**Conflicts of Interest:** The authors declare no conflict of interest.
