Bio-based nanomaterials have become an intense field of research, most notably with cellulose nanocrystals (CNCs) leading the forefront of research interest in regard to its properties including as high surface area, biocompatibility, and tunable self-assembly. A multitude of applications have been shown, ranging from energy and drug delivery to support scaffolds for catalysis. With such advancements of cellulose-based bio-nanomaterials, chitin on the other hand has been scarcely explored in this form. With an annual availability ranging on the order of billions of tons, chitin is mainly derived from the shells of crustaceans, which are often discarded into landfills. This provides a huge biomass resource that can used to create advanced materials. Therefore, it is crucial to develop downstream applications for this very abundant material, enabling the concept of a "shell biorefinery"; akin to a wood biorefinery utilizing wood-based biomass. Much like CNCs, chitin nanocrystals (ChNC) can be formed through hydrolytic treatment. We (Lam group) have recently shown that using ammonium persulfate as a mild oxidant can be used to yield carboxylated ChNC. From this, we describe a novel method using NaBH4 to inhibit "end-peeling," making carboxylated chitosan nanocrystals (ChsNC) that retain its rod-like dimensions for the first time with consistent degree of deacetylation (DDA) values of over 80%. These chitin-based nanomaterials display remarkably high aqueous solubility due to the amine functionality, along with a carboxylate functional handle that may bind to metals for application as a support-based heterogeneous catalyst. We demonstrate that both ChNC and ChsNCs can be used as a catalyst support for metal nanoparticle (NP) catalysis. First, it was seen that supported Au NPs on ChsNCs proved to be extremely effective for aromatic nitro reduction and aldehyde-amine-alkyne coupling reactions, mediated by Au(I) species on the ChsNC surface. Following this, Pd NPs were immobilized onto ChNCs to effectively catalyze the Heck coupling reaction. We explore the non-trivial role that both catalyst supports play in these catalyst systems, and demonstrate its versatility in future applications.

Chitin and chitosan nanocrystals as a biomass-based catalyst support

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.