Carbon Trends (Oct 2022)
Utilization of starch and cellulose toward facile synthesis of high surface area zeolite-templated carbon
Abstract
Starch and cellulose are examined to synthesize high surface area zeolite-templated carbons (ZTCs). In this method, starch or cellulose is mixed with undried NaY zeolite as a template, and the mixture is subject to chemical vapor deposition (CVD) using propylene and subsequent heat treatment, followed by zeolite removal with HF. For maximizing the structural regularity and surface area of ZTC, a necessary amount of starch is only equal to the total pore volume of the zeolite (i.e., 0.5 g per 1 g of the zeolite). Upon heating, starch is decomposed into oligosaccharides and the oligosaccharides are adsorbed inside the micropores of the zeolite before the CVD. The adsorbed oligosaccharides are pyrolyzed into nanographenes, and the nanographenes are extended and interconnected together to form the three-dimensional ZTC framework inside the zeolite pores during the CVD. The resulting gravimetric and volumetric surface areas are 3760 m2 g−1 and 630 m2 cm−3, respectively. Meanwhile, cellulose is not readily decomposed into oligosaccharides, and a necessary amount of cellulose is 1.4 times larger than that of starch to maximize the high structural regularity, yielding the gravimetric and volumetric surface areas of 3330 m2 g−1 and 670 m2 cm−3, respectively. A decrease in the gravimetric surface area is explained by the formation of cellulose-derived amorphous carbons on the surface of ZTC particles. However, the difference between their volumetric surface areas is negligible because the amorphous carbons are so small that they do not expand the volume of the densified ZTC. Consequently, the ZTC prepared using cellulose shows high volumetric capacitance and high capacitance retention even at 10 A g−1 as an electric double-layer capacitor electrode, due to the existence of amorphous carbons that enhance the electrical conductivity of the electrode.
