Influence of Synthesis Conditions and Heat Treatment on the Structure of Ti3SiC2-Derived Carbons

Abstract

We investigate the characterization and adsorption modeling of Ti3SiC2-derived carbons (Ti3SiC2-DCs) prepared by chlorination at three temperatures (600, 800, and 1000 degrees C) as well as samples heat-treated at 1100 degrees C for one and three day periods. The modeling exploits our recent finite Wall thickness model-based density functional theory approach (Nguyen, T. X.; Bhatia, S. K. Langmuir 2004, 20, 3532), Utilizing experimental adsorption isotherms OF Ar at 87 K for the characterization. In general, characterization results show that the carbon wall structure of carbide-derived carbons (CDCs) is precursor-inherited, and Ti3SiC2-DCs have predominantly graphitic walls whose helium density is close to the true density of graphite (2.27 g/cm(3)), while SiC-derived carbons (SiC-DCs) have predominantly diamond-like walls whose helium density approaches the true density of diamond (3.52 g/cm(3)). This precursor-inherited character is also seen to give rise to two distinct evolutions of the Pore Structure of Ti3SiC2-DCs and SiC-DCs under chlorination temperature or post-heat-treatment conditions. In Particular, both pore enlargement and opening are observed for Ti3SiC2-DCs, but only pore opening, especially in the region of smallest pores (<5 angstrom), is found for SiC-DCs. For adsorption modeling results, the ordering of pore network accessibility, Ar at 87 K < CH4 at (313K and 333K) < CO2 at or above 273 K, has been specifically found for the Ti3SiC2-DC samples prepared by chlorination at 800 degrees C, providing high CO2/CH4 selectivity by the carbon. Heat treatment of this sample at 1100 degrees C for a 1 day period gives rise to significant improvement of pore network accessibility but subtle change in pore bodies. Finally, shrinkage is found for all investigated CDCs and the I day heat-treated sample, but swelling is found for the 3 day heat-treated carbon sample, under high-pressure CO2 adsorption conditions.