The wetting transition on submersed superhydrophobic surfaces with hierarchical structures and the influence of trapped air on superhydrophobic stability are predicted based on the thermodynamics and mechanical analyses. The dewetting transition on the hierarchically structured surfaces is investigated, and two necessary thermodynamic conditions and a mechanical balance condition for dewetting transition are proposed. The corresponding thermodynamic phase diagram of reversible transition and the critical reversed pressure well explain the experimental results reported previously. Our theory provides a useful guideline for precise controlling of breaking down and recovering of superhydrophobicity by designing superhydrophobic surfaces with hierarchical structures under water.

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Ionic metal–organic frameworks (MOFs) with an ionic skeleton and unique porous structures could selectively adsorb charged dyes with specific dimensions. However, the ion-exchange-based and size-exclusion-based process as a chromatography method needs to be further explored. In this study, a new microporous anionic MOF, JUC-210, was synthesized using a spirobifluorene-based ligand and trivalent metal indium. JUC-210 has a two-fold interpenetrated pts framework with a large void space, possessing suitable pore sizes and an anionic skeleton for efficient separation of certain organic dyes. Different types of dyes were used to observe the selective adsorption ability of the as-synthesized MOF. JUC-210 displayed high selective adsorption toward the cationic dye methylene blue with positive charges based on ion exchange and size exclusion. Moreover, the effect of solvent on the selective adsorption behaviors of JUC-210 was investigated. The exploration of novel MOF materials would provide potential efficient adsorbents for separation of organic dyes.

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