Nanocellulose is the most promising natural nanofibers produced from renewable woody bioresources. Especially, TEMPO-oxidized nanocellulose, developed by Prof. Akira Isogai (the University of Tokyo), possesses a very unique nanoarchitecture, i.e. an ultra-fine crystalline nanofiber on which carboxylates are regularly arranged along the nanofiber axis with high density. Herein, we present three concept-driven nanocomposites as below. Emergent functions of nanocellulose will open up a new phase in green materials chemistry and industries. (1) Molecular-sieving gas-separation films: Polymer membranes containing nanoporous metal-organic frameworks (MOFs) have attracted much attention for selective gas separation. The MOFs were topologically synthesized in situ via carboxy groups on crystalline TEMPO-nanocellulose in tight contact to avoid gas leaking. The nanocellulose-MOF films coated on paper demonstrated extremely high CO2/CH4 selectivity up to 123 for CO2 at 73,200 Barrer of high gas flux, through such unique combination of nanoporous MOFs and gas-barrier nanocellulose. (2) Nanocatalysts on nanocellulose matrix. Metal ions and nanoparticles (NPs) were successfully immobilized on the TEMPO-nanocellulose with high density of catalytic active sites for heterogeneous catalysis. Huisgen[3+2] cycloaddition was accelerated by Cu(I) loading on the nanocellulose. Topochemical synthesis of gold NPs on the TEMPO-nanocellulose was achieved, and the exposed AuNPs demonstrated ca. 800 times higher catalytic efficiency than conventional polymer-supported AuNPs in an aqueous reduction of 4-nitrophenol to 4-aminophenol. As-synthesized organic-inorganic hybrid nanocatalysts would be promising in practical applications. (3) Organocatalysis with proline and nanocellulose Organocatalysts have occupied attention instead of metals and enzymes, and proline is well known as a first organocatalyst for an aldol reaction. Here, we show the combination of proline and TEMPO-nanocellulose. The aldol reaction of 4-nitrobenzaldehyde and acetone proceeded enantioselectively to synthesize (4R)-4-hydroxy-4-(4-nitrophenyl)-2-butanone. High-concentration proline yielded racemic products; but the combination with nanocellulose promoted only R-isomer formation. Our challenge in pairing nanocellulose with versatile organocatalysts would provide new insights to interfacial asymmetric synthesis.

Combination of nanocellulose and nanomaterials for functional applications

251st National Meeting (2016)

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