Bottom-up assembly of cellulose nanocrystals as a green entry to structured functional carbons

Le résumé fourni par la source

The bottom-up assembly of cellulose nanocrystals (CNCs) into porous scaffolds offers a sustainable route to translate their intrinsic properties into functional 3D materials. This strategy enables precise control over porous architectures, unlocking opportunities for high-performance materials tailored to specific applications. Here, we present the fabrication of structured carbons derived from nanocellulose precursors. CNCs are isolated from cellulosic feedstock in type-I and type-II crystalline allomorphs via a one-pot synthesis process followed by minima processing steps. The resulting aqueous CNC colloids self-assemble into cross-linked hydrogels through controlled hydrothermal aggregation, followed by lyophilization to produce macroporous aerogels (bulk porosities up to 98%). Each allomorph exhibits distinct aggregation behavior, explored for the first time with type-II CNCs. As proof of concept, these aerogels undergo pyrolysis at varying temperatures and subsequent sulfonation, yielding highly porous carbons functionalized with sulfonic acid groups (functionalization degree of ca. 2400 μmol·g −1 ). The resulting materials combine macroporosity from hydrothermal assembly with microporosity generated during pyrolysis and sulfonation, forming a hierarchical structure ideal for catalytic applications. Their performance is demonstrated in solketal synthesis (yielding ∼90% of solketal in consecutive cycles after 4 hours at room temperature) positioning CNC-based sulfonated aerogels as a greener alternative to conventional Brønsted acid catalysts and surpassing classical activated carbons in sustainability and design.

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