Study of the structural evolutions of mesoporous MCM-48 silica infiltrated with carbon by different techniques

The physico-chemical properties of ordered mesoporous carbons obtained by a negative replication process are strongly influenced by their preparations. In order to get a better understanding of the carbon formation, the structural evolution of the mesoporous MCM-48 silica templates before and after C infiltration by two different processes (and a subsequent oxidation), was studied using various techniques such as XRD, N-2 adsorption/desorption and TEM. It was shown that the use of a liquid carbon precursor such as a sucrose solution led to a strong alteration of the silica template (loss of long-range ordering, disappearance of the narrow mesopore size distribution). This was attributed to (i) the high temperature of the process (1173 K) and (ii) to the water vapor released during the carbonization that hydrolysed the poorly hydrothermally stable silica network. On the contrary, the pyrolytic decomposition of a gaseous carbon precursor such as propylene, performed at lower temperature (1023 K) and without water release, only led to minor modifications. These behaviors may influence the physico-chemical properties of the resulting carbon. For both impregnation processes, carbon acts as a highly stable porogene agent. Heat-treatment at a temperature as high as 1473 K in an inert atmosphere and a subsequent oxidation for the removal of the carbon succeeded in preserving the long-range ordering of the starting silica template and its surface area. (C) 2003 Elsevier Inc. All rights reserved.