Laser-Induced Graphitization of Cellulose Nanofiber Substrates under Ambient Conditions

A CO2 laser engraver was used to synthesize conductive graphitic carbon directly on cellulose nanofiber (CNF) substrates under ambient conditions. CNFs were prepared via a TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl radical)-mediated oxidation reaction of bleached pulp, and a porous paper or a transparent film was obtained based on the drying conditions employed. Laser irradiation on a porous CNF paper led to the formation of amorphous carbon owing to an increase in temperature. Subsequent lasing converted the amorphous carbon to conductive graphitic carbon. The conductivity of this carbon increased from 3 mu S/cm to 60 mS/cm as the number of irradiations increased from one to four. Although the CNF paper was converted to graphitic carbon by means of multiple lasing, graphitic carbon was obtained for the CNF film by a single run of lasing owing to its very low oxygen permeability. The conversion of the CNF substrates to graphitic carbon under ambient conditions was attributed to the presence of sodium in CNFs. A control experiment using a CNF in which sodium was replaced with hydrogen demonstrated that only amorphous carbon was produced by laser exposure.