In-situ grown bilayer MOF from robust wood aerogel with aligned microchannel arrays toward selective extraction of uranium from seawater

Metal-organic frameworks (MOFs) have been widely applied in the recovery of specific guest molecules due to their excellent properties including high porosities, adjustable pore size and abundant chelating functions. However, the granular MOF crystals bring a great challenge to the recycling and reusing from aqueous media, and thus seriously limit their practical application. In this work, MOF bonded wood aerogel prepared by means of in-situ growth strategy was developed for uranium extraction from natural seawater. Eco-friendly and biocompatible wood aerogel possesses run-through microchannel arrays enclosed by aligned cellulose nanofibers (CNFs), contributing to the free and fast diffusion of uranyl ions (UO22+), and thus result in the sufficient coordination with active chelation sites of MOF crystals. To increase the loading content of MOF, bilayer MOF architecture (CMPM) was prepared by using hydroxyl functional groups in CNFs and polydopamine (PDA) coating as nucleation centers of MOF, respectively. The resultant CMPM adsorbents exhibited good reversible compressibility and fragility resistance, which were critical to extend its service life. Moreover, the excellent photothermal conversion capability of PDA enabled CMPM to acquire high temperature under simulated sunlight irradiation. Owing to the apparently endothermic behavior of UO22+, light-irradiated CMPM achieved high adsorption capacity (5.81 mg-U/g-Ads) together with excellent UO22+ selectivity in natural seawater after 30 days. Therefore, this work provides a feasible solution in promoting the practical application of MOF adsorbents.