Large-scale Investigations of Water Diffusion in Metal–Organic Frameworks with One-Dimensional Channels

Metal–organic
frameworks (MOFs), known for their highly
versatile nature, show considerable promise as adsorbents and membranes
for water-related applications such as water harvesting and water
filtration. One of the key factors that may influence their efficiency
is the diffusion of water within MOFs. However, the behaviors and
mechanisms of water diffusion in MOFs remain relatively underexplored.
To this end, this study utilizes molecular dynamics (MD) simulations
to comprehensively analyze water diffusion in hundreds of distinct
MOFs. Herien, MOFs that exhibit rapid water diffusion under saturated
conditions are identified. Moreover, structure–property relationships
and underlying atomistic mechanisms are explored, showing that water
mobility depends on a subtle interplay between pore topology and host–guest
interaction. For instance, MOFs with similarly small pores can exhibit
markedly different water diffusivities. In hydrophobic MOFs, weak
framework-water interactions allow ultrafast single-file diffusion,
but mobility plunges when the pores narrow further. In hydrophilic
MOFs, strong framework-water interactions immobilize a layer of water
on the pore walls; these fixed water molecules can interestingly shield
strong adsorption sites, enhancing transport in wider pores yet impeding
diffusion in narrower ones. Finally, to address the high computational
cost associated with computing diffusivity, this work further evaluates
the feasibility of using surrogate descriptors for rapid diffusivity
estimation. Overall, this work offers molecular-level key insights
into water transport phenomena.