Low-Cost Synthetic Route to Mesoporous Carbons with Narrow Pore Size Distributions and Tunable Porosity through Silica Xerogel Templates

Silica xerogels synthesized by the sol−gel process were used as templates to fabricate mesoporous carbons. The silica was prepared in a two-step process, under acid pH conditions, at a high H 2 O/Si molar ratio of 194 and at different HCl/Si molar ratios. Two sources were used as silica precursors: tetraethoxysilane (TEOS) and sodium silicate. The resulting silica xerogels have surface areas of >500 m 2 ·g - 1, pore volumes of >0.4 cm 3 ·g - 1, and a tunable mesopore size of between 2 and 10 nm, depending on the HCl/Si molar ratio. The mesoporous carbons obtained as inverse replicas of silica xerogel templates have large pore volumes (in the 1.5−2.1 cm 3 ·g - 1 range), large BET surface areas of up to 2200 m 2 ·g - 1, and narrow pore size distributions (PSD) in the mesopore range. The mesopore size of the carbons can be tuned between 3 and 4.5 nm depending on the type of silica xerogel selected as template. Carbons prepared in this way have structural characteristics comparable to those of mesoporous carbons made by templating mesostructured silica materials synthesized by using expensive surfactants as structure-directing agents. The procedure also allows unimodal or bimodal mesoporous carbons to be obtained from the same silica xerogel template. This is achieved by varying the amount of carbon precursor allowed to infiltrate into the silica porosity.