Spontaneous Co-Assembly of Cellulose Nanocrystals and TiO₂ Nanorods Followed by Calcination to Form Cholesteric Inorganic Nanostructures

Chiral nanomaterials possess unique electronic, magnetic,and opticalproperties that are relevant to a wide range of applications includingphotocatalysis, chiral photonics, and biosensing. A simple, bottom-upmethod to create chiral, inorganic structures is introduced that involvesthe co-assembly of TiO2 nanorods with cellulose nanocrystals(CNCs) in water. To guide experimental efforts, a phase diagram wasconstructed to describe how phase behavior depends on the CNCs/TiO2/H2O composition. A lyotropic cholesteric mesophasewas observed to extend over a wide composition range as high as 50wt % TiO2 nanorods, far exceeding other examples of inorganicnanorods/CNCs co-assembly. Such a high loading enables the fabricationof inorganic, free-standing chiral films through removal of waterand calcination. Distinct from the traditional templating method usingCNCs, this new approach separates sol-gel synthesis from particleself-assembly using low-cost nanorods.