Advanced carbon films derived from nanocellulose.

Abstract

Cellulose nanofibre (CNF) films are an underexplored precursor for carbon materials. They have an intrinsically dense packing, and their surface charge offers a pathway for doping with functional ions. To study this, CNF films crosslinked with varying concentrations of CaCl2 were carbonized. The carbonization resulted in carbon films with a multicolour metallic lustre. The structural colour occurred due to a thin film of calcium oxide which formed on the surface and was effectively tuned by adjusting the holding time of the carbonization. The presence of calcium ions reduced the graphitic crystallite size and increased the microporosity of the films. The macroporosity, however, significantly reduced, resulting in carbon films with a compact structure. The optically smoothness facilitated thin film interference and formed structural colour with potential use as a visual sensor for humidity.