Porous biomimetic carbon structure evolution supported by silica for microwave absorption application

This study investigates structural evolution of porous carbon based on the strategy of small molecule cross-linking and carbonization within the silica framework. Cetyltrimethylammonium bromide (CTAB) molecules are introduced into the silica by electrospinning, where abundant Si-OH groups ensure extensive bonding of CTAB moieties. Concurrently, CTAB in the SiO₂ nanofibers slowly releases into the reaction system during the citric acid and urea crosslinking process. Its long hydrophobic alkyl chains and exposed hydrophilic ammonium segments can interact with the organic precursors, forming positively charged 'wrappings' in the aqueous solution. The presence of CTAB guides the growth of carbon nanomaterials along the SiO₂ nanofibers as the skeleton, ultimately forming a vein-like carbon/SiO₂ composite. Microwave absorption performance is investigated based on the complex dielectric constant and magnetic permeability. The vein-like carbon/SiO₂ composite exhibits strong microwave absorption intensity of −37.8 dB when the filler content is only 20 %. A sponge-like porous carbon-based composite structure is also obtained based on citric acid and urea in silica sol without CTAB by electrospraying. It still exhibits microwave absorption intensity of −19.3 dB when the filler content is only 20 %, with effective absorption widths at 4 GHz at thicknesses of 3 mm.