Tailoring the Dynamics of Al Metal-Organic Framework Nanocrystals: From Rigid Nanoparticles to Flexible Nanowires

Here we describe the synthesis of a series of 1D anisotropic Al metal-organic framework (i.e., DUT-5(Al)) nanostructures differing in their crystal dimensions and aspect ratios. By using graphene oxide (GO) nanoscrolls as structure-directing agents, we synthesized monodisperse DUT-5(Al) nanowires (NWs) that are >6 μm in length. Shorter DUT-5(Al) nanorods (∼50 nm) and polydisperse samples with broader size distributions were prepared without GO. Remarkably, these nanostructures also differed by their dynamic properties upon the adsorption of guest molecules. While DUT-5(Al) nanorods exhibited a rigid large pore (lp) phase, it was revealed that DUT-5(Al) NWs could present a gating behavior characterized by a structural transition from a disordered narrow pore (np) phase to the lp phase upon adsorption. The structure of DUT-5(Al) NWs and their guest-responsive structural flexibility were fully characterized by coupling high-resolution TEM, 3D electron diffraction, high-resolution synchrotron PXRD and PDF, adsorption isotherms, and in situ PXRD. To the best of our knowledge, this study delivers an unprecedented design of flexible DUT-5(Al) NWs, revising the conventional view of this MOF as a rigid porous material. Moreover, this demonstrates that tuning the aspect ratio of MOF particles can influence their structural flexibility.