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Separating water isotopologues using diffusion-regulatory porous materials


The discovery of a method to separate isotopologues, molecular entities that differ in only isotopic composition1, is fundamentally and technologically essential but remains challenging2,3. Water isotopologues, which are very important in biological processes, industry, medical care, etc. are among the most difficult isotopologue pairs to separate because of their very similar physicochemical properties and chemical exchange equilibrium. Herein, we report efficient separation of water isotopologues at room temperature by constructing two porous coordination polymers (PCPs, or metal–organic frameworks) in which flip-flop molecular motions within the frameworks provide diffusion-regulatory functionality. Guest traffic is regulated by the local motions of dynamic gates on contracted pore apertures, thereby amplifying the slight differences in the diffusion rates of water isotopologues. Significant temperature-responsive adsorption occurs on both PCPs: H2O vapour is preferentially adsorbed into the PCPs, with substantially increased uptake compared to that of D2O vapour, facilitating kinetics-based vapour separation of H2O/HDO/D2O ternary mixtures with high H2O separation factors of around 210 at room temperature.

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Fig. 1: The diffusion-regulatory mechanism for dynamic discrimination of water isotopologues.
Fig. 2: Structural depictions of the diffusion-regulatory PCPs.
Fig. 3: Adsorption kinetics of water isotopologues for FDC–1a and FDC–2a.
Fig. 4: Mixed vapour separation.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding authors upon request. The X-ray crystallographic coordinates for structures reported in this Article have been deposited at the Cambridge Crystallographic Data Centre (CCDC), under deposition numbers CCDC 2100317–2100320. These data can be obtained free of charge from the Cambridge Crystallographic Data Centre via


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This work was supported by the National Natural Science Foundation of China (grant no. 21975078), the Guangdong Basic and Applied Basic Research Foundation (grant no. 2021A1515010311), the Natural Science Foundation of Guangdong Province (grant no. 2019B030301003), the 111 Project (grant no. BP0618009), the Thousand Youth Talents Plan, the KAKENHI Grant-in-Aid for Scientific Research (S) (grant nos. JP18H05262/JP22H05005) from the Japan Society of the Promotion of Science (JSPS). The synchrotron radiation experiments were performed at BL02B1 and BL02B2 of SPring-8 with the Japan Synchrotron Radiation Research Institute (JASRI) (Proposal nos. 2020A0649, 2020A1469, 2020A0617, and 2021A1104). We thank S. Kawaguchi and Y. Kubota for their help with VT-XRD measurements at SPring-8, the iCeMS analysis centre for access to the analytical instruments, and S. Sakaki at Kyoto University for access to VASP and computer resources. Y.S. acknowledges the scholarship support from the China Scholarship Council (grant no. 202006150059).

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Authors and Affiliations



Y.S. performed experiments associated with molecular synthesis, crystal growth, vapour sorption and vapour separation. K.O. and Y.S. conducted single-crystal and powder X-ray diffraction studies and structure analyses. J.-J.Z. carried out calculation studies. S.H. performed NMR analysis. C.G. and S.K. conceived the project and directed the research. All authors contributed to the writing and editing of the manuscript.

Corresponding authors

Correspondence to Susumu Kitagawa or Cheng Gu.

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The authors declare no competing interests.

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Nature thanks Randall Snurr, Vincent Guillerm and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data figures and tables

Extended Data Fig. 1 Vapour sorption for control materials.

H2O and D2O sorption curves at 298 K for (a) zeolite 3A (pore aperture 3 Å), (b) microporous active carbon (pore aperture 3 Å), (c) ZIF-7 (pore aperture 3 Å)27, (d) FMOF-Cu (pore aperture 2.5 Å)28, (e) Ni2(bipy)3(NO3)4-M (pore aperture 2.4 Å)29, (f) Ni2(bipy)3(NO3)4-E (pore aperture 2.1 Å)29, (g) Cu(OPTz) (pore aperture 3 Å)21, and (h) HKUST-1 (pore aperture 9 Å)30. For microporous active carbon and Cu(OPTz), their curves for H2O and D2O sorption were the same, and no discrimination was observed. For FMOF-Cu, the adsorption amounts for H2O and D2O were too low for adsorption-based separation. For ZIF-7, the difference in adsorption amounts for H2O and D2O were only 4.1 and 3.1 cm3 g–1 at P/Ps = 0.5 and 0.98, respectively, not as large as in FDC–1a and FDC–2a (10.2 and 9.9 cm3 g–1 at P/Ps = 0.98, respectively). For zeolite 3A, despite the surface condensation at high P/Ps, a distinguishable difference between H2O and D2O was observed at low P/Ps < 0.2, which was attributed to the cluster formation of H2O or D2O at different P/Ps. In principle, this difference could be used in discriminating water isotopologues by controlling the relative pressure. However, in the real recognition/separation systems, an ambient pressure (P/Ps around 1) is more favorable, whereas low pressure is difficult to control. For Ni2(bipy)3(NO3)4-M and Ni2(bipy)3(NO3)4-E, they underwent a sudden gate open and a gradual gate open toward H2O and D2O molecules in the adsorption process, and therefore, they could not separate water isotopologues. For HKUST-1, it represents the systems using large pores and strong binding sites for the separation of water isotopologues (thus thermodynamic separation). However, no difference could be observed in the sorption curves. Therefore, the demonstrated preferential adsorption of H2O over D2O by FDC–1a and FDC–2a at 298 K was not found for other small-pore adsorbents, including zeolite, activated carbon, and other PCPs/MOFs. Even though some compounds show a slight difference in preference of adsorption behavior for water isotopologues, the difference is not comparable to adsorption behavior by FDC–1a and FDC–2a.

Extended Data Fig. 2 H2O and D2O sorption curves for FDC–1a and FDC–2a at 298 K using different exposure time.

a, H2O sorption curves for FDC–1a. b, D2O sorption curves for FDC–1a. c, H2O sorption curves for FDC–2a. d, D2O sorption curves for FDC–2a. We measured the H2O and D2O sorption curves with the exposure time of each plot as 600 s, 1800 s, and 4800 s, respectively, resulting in a total measurement time of 26.4, 74.2, and 221.5 h, respectively. The adsorption amounts markedly increased with the prolonged exposure time, which indicated that the diffusion kinetics of adsorbates was the determining factor for this thermoresponsive adsorption behavior.

Extended Data Fig. 3 Temperature-dependent sorption curves of H2O and D2O.

a, H2O sorption curves in FDC–1a from 278 to 323 K. b, D2O sorption curves in FDC–1a from 278 to 323 K. c, H2O sorption curves in FDC–2a from 278 to 323 K. d, D2O sorption curves in FDC–2a from 278 to 323 K. The uptake amounts of H2O and D2O in both the two PCPs obviously increased as increasing the temperature, indicating a diffusion-controlled sorption behavior which was determined by the kinetic factor. On the other hand, the uptake amounts of H2O in both the two PCPs were substantially higher than that of D2O at the same temperature (e.g., H2O 36.1 mL g–1 vs. D2O 25.9 mL g–1 in FDC–1a at 298 K, and H2O 25.2 mL g–1 vs. D2O 15.4 mL g–1 in FDC–2a at 298 K), revealing that the diffusion of H2O was faster than that of D2O. Finally, under otherwise identical conditions (same temperature and vapor), the uptake amounts of H2O and D2O in FDC–1a were substantially higher than that in FDC–2a, demonstrating that the diffusion rate of the former was higher than the latter.

Extended Data Fig. 4 Variable-temperature synchrotron PXRD of FDC–1a under vacuum conditions.

The curves from blue to red denote the temperature changing from 273 to 373 K. The ranges of dominant peaks are enlarged to clearly show the slight change of peak position with temperature.

Extended Data Fig. 5 Diffusion-rate calculation.

Diffusion rates (k) of H2O and D2O in (a) FDC–1a and (b) FDC–2a. Calc.1 represents the calculated diffusion rates considering that all rotational and translational movements were changed to vibrational modes for the adsorbed H2O or D2O. Calc.2 represents the calculated diffusion rates by considering that one rotational movement remains and other rotational and translational movements of H2O or D2O were changed to vibrational modes at the initial state.

Extended Data Table 1 Current methods of the separation of deuterated species

Supplementary information

Supplementary Information

This file includes Table of Contents; Supplementary Materials and Methods; Supplementary Figures 1–89; Supplementary Tables 1–6; captions for crystallographic Data 1–4 and Supplementary References (1–18).

Crystallographic Data 1

Crystallographic information file (CIF) of the as-synthesized PCP (FDC–1). CCDC number: 2100317.

Crystallographic Data 2

Crystallographic information file (CIF) of the as-synthesized PCP (FDC–2). CCDC number: 2100318.

Crystallographic Data 3

Crystallographic information file (CIF) of the water-adsorbed phase of FDC–1a (FDC–1a–water). CCDC number: 2100319.

Crystallographic Data 4

Crystallographic information file (CIF) of the water-adsorbed phase of FDC–2a (FDC–2a–water). CCDC number: 2100320.

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Su, Y., Otake, Ki., Zheng, JJ. et al. Separating water isotopologues using diffusion-regulatory porous materials. Nature 611, 289–294 (2022).

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