Morphology control of mesoporous silica-carbon nanocomposites via phase separation of poly(furfuryl alcohol) and silica in the sol–gel synthesis

Due to the different rates of silica alkoxide hydrolysis and furfuryl alcohol polymerization, hydrophobic poly(furfuryl alcohol) network became incompatible with hydrophilic silica network, PFA-rich spheres were formed in the sol–gel process. The presence of the amphiphilic triblock copolymers P123 could help reduce the degree of phase separation. Slower drying rate, higher aging temperature, and higher C/SiO₂ ratio accelerated the polymerization of FA and tend to aggregate more PFA spherical domains. However, in the sample with a fast increased viscosity, the temperature effect would be small since the PFA is hard to agglomerate, leading a homogenous mesoporous structure. If the C/SiO₂ ratio is quite high to get a more hydrophobic system, there will be no phase separation too. The understanding of the phase separation of poly-furfuryl alcohol-silica systems offers great opportunities in controlling of the mesoporous carbon-silica nanocomposites.

Schematic diagrams of the formation of PFA/silica hybrids: during the sol–gel process, once an alkoxide molecule is hydrolyzed, the resulting hydroxy groups make the molecule more polar, which are more hydrophilic. At the same time, FA polymerized to form PFA oligomers, which are hydrophobic. The incompatibility between these two precursors could be reduced by the amphiphilic triblock copolymers P123, because the long PEO chains are hydrophilic while the PPO block is hydrophobic. Either homogenous or phase separated PFA/silica/P123 can be obtained by tailoring the chemical ratio and the sol–gel process parameters.