| Mesoporous carbon materials with deposited silica were prepared by initially adsorbing silica tetrachloride onto the carbon surface and then converting the silica tetrachloride to silica by reaction with water vapor. Subsequently, the processes of adsorption and hydrolysis were repeated several times (i.e., cycled) to increase the amount of modification. In addition to these experiments, the carbon materials were oxidized prior to carrying out the silica deposition process. The extent of surface modification for the two groups of materials as well as their surface and structural properties were characterized by a combination of thermogravimetry, adsorption, microscopy, and chromatography measurements.; The amount of silica modification reached a plateau after seven cycles for the unoxidized carbon and after four cycles for the oxidized material. Besides determining contaminants and silica residues, thermogravimetry was employed to study surface bound water. It was determined that the greatest adsorption of water occurred with the oxidized carbons with deposited silica. The nitrogen adsorption isotherms were concurrent for the unmodified carbon and the carbon with deposited silica. Likewise, the t-plots and BJH pore size distribution data showed a decrease in the pore volume with increasing amount of deposited silica.; Gas chromatography (GC) was utilized to characterize the surface and energetic properties of the mesoporous carbons before and after silica modification. For most solutes, significant differences in the peak shapes and retention times were noted between the unmodified carbons and the carbons with deposited silica. In addition to GC, liquid chromatography frontal analysis measurements were carried out to study the acid and base properties of the silica-modified carbons. A direct correlation was noted between the extent of silica modification and the retention of both acidic and basic compounds on the modified materials.; Results from the current work have demonstrated that unique materials can be prepared by depositing varying amounts of silica onto a carbon substrate. Further, it has been shown the analytical tools employed in the current work are useful to monitor the surface and structural properties of the modified carbons. |
