Abstract
In fields of materials science and chemistry, ionic-type porous materials attract increasing attention due to significant ion-exchanging capacity for accessing diversified applications. Facing the fact that porous cationic materials with robust and stable frameworks are very rare, novel tactics that can create new type members are highly desired. Here we report the first family of polyhedral oligomeric silsesquioxane (POSS) based porous cationic frameworks (PCIF-n) with enriched poly(ionic liquid)-like cationic structures, tunable mesoporosities, high surface areas (up to 1,025 m2 g−1) and large pore volumes (up to 0.90 cm3 g−1). Our strategy is designing the new rigid POSS unit of octakis(chloromethyl)silsesquioxane and reacting it with the rigid N-heterocyclic cross-linkers (typically 4,4′-bipyridine) for preparing the desired porous cationic frameworks. The PCIF-n materials possess large surface area, hydrophobic and special anion-exchanging property, and thus are used as the supports for loading guest species PMo10V2O405−; the resultant hybrid behaves as an efficient heterogeneous catalyst for aerobic oxidation of benzene and H2O2-mediated oxidation of cyclohexane.
Highlights
Yamamoto)[16,17,18,19,20], Friedel-Crafts reaction[21,22] and polymerization[23]
Through acid-catalyzed condensation oftriethoxysilane, we successfully synthesize a new rigid reactive POSS building unit, octakis(chloromethyl)silsesquioxane (ClMePOSS), the structure of which is characterized by 1H NMR, 13C NMR, 29Si NMR and MALDI-TOF MS spectra
With the catalyst-free solvothermal process in tetrahydrofuran (THF), ClMePOSS is able to react with 4,4′ -bpy and gives rise to a gel-state product, producing the brittle solid PCIF-1 after drying
Summary
Yamamoto)[16,17,18,19,20], Friedel-Crafts reaction[21,22] and polymerization[23]. The applications of those covalently linked POSS-based porous polymers are always limited to the moderate adsorption capability for gases (e.g. H2 or CO2), mostly owing to the undecorated neutral skeletons. The vital factor for developing one-step quaternization process towards the desired POSS-based porous cationic framework, though a huge challenge, is to seek a rigid alkyl halide functionalized POSS unit This motivates the innovative design of rigid ClMePOSS tethered with the tailored chloromethyl groups, providing eight possible positions/directions around one POSS cage to react with the organic linker 4,4′ -bpy using nucleophilic substitution reaction. Through this synthetic process, we directly fabricate the novel POSS-based porous cationic framework (named as PCIF-1) with a very high surface area up to 1,025 m2 g−1 and enriched cationic sites, which can be regarded as a new member of porous ion-exchange materials, breaking through the neutral networks of previous POSS-based porous materials. The obtained hybrid PMoV@PCIF-1 demonstrates as an efficient and recyclable heterogeneous catalyst for liquid-phase aerobic oxidation of benzene to phenol and H2O2-mediated oxidation of cyclohexane
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