Tetraethyl orthosilicate-assisted synthesis of nitrogen-containing porous carbon spheres

It is shown that the pore size and pore volume of carbon spheres (CSs) can be effectively tuned by varying the amount of tetraethyl orthosilicate (TEOS) during the one-pot modified Stöber synthesis that involves polymerization of resorcinol and formaldehyde in the presence of ethylenediamine used as a basic catalyst and nitrogen source. Namely, an increase in the amount of added TEOS caused a considerable reduction in the micropore volume accompanied by a three-fold increase in the total pore volume. This substantial increase in porosity was achieved after dissolution of the TEOS-generated silica and additional activation. Importantly, the controlled addition of TEOS was effectively used to tune the structure of the composite carbon-silica spheres to obtain, for instance, the composite spheres with uniformly distributed carbon and silica, and core-shell structures with single shells (silica core/mixed silica-carbon shell), and double shells (silica core/mixed silica-carbon shell/silica shell), which upon suitable post-synthesis treatment can be respectively converted to mesoporous CSs, hollow mesoporous CSs, and yolk-shell silica spheres. Beside the well-developed porosity and interesting morphology, the resulting CSs were N-doped and featured high surface area in the range of 1000-1439 m2/g.

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