Nanoporous material-based separation technology is vital in many applications due to its ability to precisely distinguish between and separate nearly identical chemical or biochemical molecules.
Previous research by Professor Susumu Kitagawa, from Kyoto University’s Institute for Integrated Cell-Material Sciences (WPI-iCeMS), and colleagues, published in Nature, had applied this technology to the separation of two very similar types of water molecules—regular water (H 2 O) and heavy water (D 2 O), which have similar properties overall but slightly different masses. But the underlying mechanics of that separation weren’t well understood.
Now, a study led by Professor Shinji Saito from the Institute for Molecular Science (IMS) in Japan and published in Nature Communications in July has provided the theoretical explanation for that phenomenon, using molecules of H 2 O and D 2 O to study nanopore behavior in a metal-organic framework.
Metal-organic frameworks are highly porous materials consisting of metal nodes connected by organic linkages and are ideal for use in molecular separation in a range of settings. How well nanopores perform this task is influenced by the structure of the molecules in question and the structure and size of the nanopores. But nanopore structure can fluctuate over time and in response to interactions with the molecules it is exposed to, which makes understanding and modeling the behavior of nanopores challenging.
Using quantum-chemical calculations that represent the behavior of soft porous crystals like metal-organic frameworks, the research team investigated how the size of the fluctuations in the nanopore energy barrier affects the separation performance of the nanopore. Their findings indicate that the fluctuation in nanopore structure is the most important factor influencing the transport and separation of molecules, and that there exists an optimal fluctuation rate to maximize the diffusion of molecules through the nanopore framework.
The mass differences between the two forms of water also proved to be a key factor. Even the very small difference between these two molecules led to significant differences in how they diffused through the nanoporous framework. “The optimal fluctuation rate exhibits mass dependence, enabling specific nanopore dynamics to preferentially accelerate one species over another and achieve transport selectivity”, Professor Saito wrote.
The research points to a new strategy for maximizing the performance of diffusion in structures like metal-organic frameworks. “Instead of relying only on static pore size, materials can use their own dynamic ‘breathing’ motions to selectively accelerate the transport of one molecule over another”, says Professor Saito. “This concept is both scientifically surprising and broadly applicable, offering a new way to design smarter separation materials that could reduce energy consumption and improve industrial separation technologies”.
Nature Communications
Computational simulation/modeling
Not applicable
Fluctuation-driven mass-selective transport in dynamic nanopores
15-Jul-2026