Silica-free syntheses of hierarchically ordered macroporous polymer and carbon monoliths with controllable mesoporosity

Abstract

Hierarchically ordered macroporous polymer and carbon monoliths with walls containing face-centered cubic or 2D-hexagonal mesopores were synthesized via a facile dual-templating technique using poly(methyl methacrylate) (PMMA) colloidal crystals and amphiphilic triblock copolymer surfactants as templates. A nanocasting step using a silica mold was not required. The as-synthesized nanoporous structures contain both ordered macropores and mesopores, originating from the colloidal crystal and surfactants, respectively. The mesostructures could be conveniently controlled by tuning the concentration of the copolymer surfactant. Starting from the PMMA template, only four major processing stages (precursor infiltration, solvent removal, thermal curing and carbonization) were involved to prepare the bimodal porous carbon materials. A two-step thermal curing method was utilized to improve the robustness of the products. On the basis of nanoindentation measurements, the carbon products were mechanically more stable than hierarchically porous carbon monoliths synthesized by nanocasting, and the product with the cubic mesopore structure was even more stable than 3D-ordered macroporous carbon lacking any templated mesopores in the wall skeleton. Compared with conventional nanocasting strategies, the current method avoids the use of hazardous hydrofluoric acid that is required to remove a silica template, and therefore the synthetic procedure is more environmentally benign.