We
report on the preparation of hybrid, organic–inorganic porous
materials derived from polyhedral oligomeric vinylsilsesquioxanes
(vinylPOSS) via a single-step molding process. The monolithic, large
surface area materials are studied with a particular focus on morphology
and porous properties. Radical vinyl polymerization of the nanometer-sized
POSS building blocks is therefore utilized via a thermally initiated
route and in porogenic diluents such as tetrahydrofuran and polyethylene
glycols of varying composition. Careful choice of these porogenic
solvents and proper choice of initiator concentration lead to highly
porous monolithic building entities which show a rigid, 3D-adhered,
porous structure, macroscopically adapting the shape of a given mold.
The described materials reflect Brunauer–Emmett–Teller
(BET) surface areas of 700 m2/g or more and maximum tunable
mesopore volumes of up to 2 cm3/g. Experimental investigations
demonstrate the option to tailor nanoporosity and macroporosity in
the single-step free-radical polymerization process. While studies
on the influence of the used porogenic solvents reveal tuneability
of pore sizes due to the unique pore formation process, tailored existence
of residual vinyl groups allows facile postpolymerization modification
of the highly porous, large surface area hybrid materials exploited
via thiol–ene “click” chemistry. Our developed,
simply realizable preparation process explores a new route to derive
porous organic–inorganic hybrid adsorbents for a wide variety
of applications such as extraction, separation science, and catalysis.
A single-step molding process utilizing free-radical cross-linking reaction of vinyl POSS in microliter-sized dimensions leads to hierarchically-structured, mechanically robust, porous hybrid structures tailored for catalytic applications.
We report on the preparation of new hybrid organic–inorganic multiporous monolithic capillary columns carrying gold nanoparticles of 5, 10, 50, and 100 nm size and their use as flow‐through catalytic platforms for aqueous liquid‐phase reduction reactions. We found that the flow‐through performance of the reactors depends not only on the size of the gold nanoparticles but also on the interplay of the pore size of the scaffolds and the catalytically available gold surface within the system, that is, loading an increased number of gold nanoparticles of smaller size does not necessarily result in strictly improved performance. This indicates the importance of the interplay between the nanopore size of the scaffolds and the catalytically active gold surface existing within the system. Demonstration of the highly efficient catalytic flow‐through operation within seconds and the repeated use of the reactors without loss of performance indicates their excellent suitability as microfluidic device elements.
The cover picture shows the conceptual approach to miniaturized flow chemistry enabled by highly porous hybrid materials created in situ from polyhedral oligomeric silsesquioxanes (POSS). The materials contain gold nanoparticles that are strongly held within their porous structure by thiol–gold interactions. The tubular reactors are operated with an aqueous liquid phase at room temperature. The size of the gold nanoparticles and the pore size of the scaffolds themselves can be tailored to create highly efficient platforms for small‐scale chemical processes using the “green” solvent water. Details are discussed in the Communication by I. Nischang et al. on . For more on the story behind the cover research, see the .
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