(7e) Partial Etching of Titanium Carbide-Derived Carbon for VOC Adsorption

Volatile organic compounds (VOCs) are produced in many chemical processes and can cause harm to human health and the environment.  Specifically, methanol may adversely react with other VOCs to form smog.  Carbide-derived carbons (CDCs) offer one solution to remove methanol from waste gas streams via adsorption.  Control over pore size and distribution, chemical selectivity, and chemical and thermal stability make CDCs ideal for this process.  CDCs are formed selectively by removing the metal atoms within a metal carbide using a high temperature etching process.  This selective removal of metal atoms with chlorine leaves behind a narrow distribution of pore sizes in a carbon complex.  Additionally, partial etching of the carbide yields a carbon complex with residual metal species that add active sorption and catalytic sites. Partial etching and post-etching modification negates the need for metal doping seen in activated carbons because the metal is present in the precursor. Titanium has been shown to catalyze methanol in the reduced metal state, while titanium dioxide has been shown to photocatalytically degrade it.  Based upon these metal-to-VOC interactions, titanium carbide-derived carbon (TiCDC) has excellent potential to be tuned for methanol adsorption.  In this work, we use a horizontal bed reactor to partially etch TiC to create TiCDC with various amounts of residual metal. However, partial etching in a horizontal bed reactor shows a significant downside: the development of two layers in the bed which consist of completely etched TiCDC and unreacted TiC.  Methanol adsorption studies show that the TiCDC samples with various residual metal contents are surface area dependent, rather than dependent on the amount of residual metal. This suggests that much of the residual metal remains inaccessible for use as active sorption sites. Further control over metal extraction in CDCs is necessary to optimize active sorption sites.