Separating water isotopologues using diffusion-regulatory porous materials

Abstract

The discovery of a method to separate isotopologues, molecular entities that differ in only isotopic composition¹, is fundamentally and technologically essential but remains challenging^2,3. 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.