Synthesis of texturally biphasic mesoporous carbon-silica composites and carbons

We report a new synthesis of texturally biphasic carbon-silica composites and carbons that exhibit high surface areas (up to 1500 m2 g−1), pore volumes (up to 1.9 cm3 g−1) and mesopores (4.6–6.9 nm). The composite materials have ordered mesoporous carbon domains embedded in a disordered mesoporous composite carbon-silica phase. This biphasic texture is preserved for the carbons obtained after silica etching. The synthesis involves the addition of tetraethoxysilane (TEOS) into an alkaline triblock copolymer (PEO140PPO39PEO140) aqueous solution, followed by addition of phenol and formaldehyde. The resol-silica composites, obtained after several days under stirring and heating, are pyrolyzed at 500 °C or 800 °C. TEOS and resin monomers effects on the copolymer self-assembly to form micelles and vesicles were studied by dynamic light scattering (DLS) before flocculation. We propose a formation mechanism, where siliceous species, are localized mainly in micelles outside the vesicles and in the vesicles bilayers, modifying their properties. The hydrophilic resol monomers are absorbed by micelles outside the vesicles as well as by those inside the vesicles core. After flocculation, biphasic materials, with a resol containing phase embedded in a resol–silica composite phase, are obtained. The in-situ formation of silica reduces the mesopores shrinking occasioned by pyrolysis in both the hybrid carbon-silica and carbon domains although causes disorder in the pores of the hybrid domain.

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► Mesoporous materials with ordered domains embedded in a disordered phase are obtained.
► The micelles and vesicles formed by the surfactant originate the biphasic porosity.
► The TEOS and phenolic resin monomers role on the materials porosity is visualized.
► The silica decreases the mesopores shrinking allowing the obtaining of wide mesopores.