Iron Nanoparticles to Catalyze Graphitization of Cellulose for Energy Storage Applications

The production of highly graphitic carbon from bioresources is an environmentally friendly approach to synthesize graphene for energy storage applications. Iron catalytic graphitization of cellulose, the most abundant biopolymer on earth, is an alternative approach as until now, cellulose has been classified as poorly graphitizable material. In this study, the impact of processing temperature and iron impregnation on the extent of graphitization of the cellulose-derived graphitic carbon nanostructure is uncovered by combining Raman spectroscopy, X-ray diffraction, transmission electron microscopy, and X-ray pair distribution function analysis. Raman spectroscopy is used in an innovative way to describe the evolution of the average graphitic phase size where the ash content misguides the X-ray diffraction analysis. A correlation was established between (i) the in-plane crystallite size L_a and the I_D″/I_G first-order ratio, (ii) the out-of-plane L_c crystallite size and the I_G/I_tot′ second-order ratio, and (iii) the second-order Raman I_G′/I_tot′ ratio and the average number of carbon layers per carbon crystallite. For iron-impregnated cellulose, phase quantification and analysis of the spatial distribution reveal highly crystalline rhombohedral graphite surrounded by a nanocrystalline carbon matrix. We explicitly show that traditionally non-graphitizable carbons can be used to form a graphite-like structure with multilayers of graphene sheets by careful addition of widely available nontoxic metal as catalysts. The study also shows that the impact of the catalyst is much more effective than the temperature in the nanostructure transformation. The proposed approach and the results obtained provide interesting insights that should stimulate further works aimed at extending the knowledge in the field.