Synthesis of carbon xerogel particles and fractal-like structures

Abstract

A variety of dense and open-architecture amorphous carbon xerogel microspheres and folded fractal-like structures were synthesized by sol-gel polycondensation of resorcinol with formaldehyde in a slightly alkaline aqueous solution. Carbon structures were obtained by inverse emulsification of resorcinol-formaldehyde (RF) sol in cyclohexane containing a non-ionic surfactant Span-80, followed by its pyrolysis at 1173 K in nitrogen. We have investigated the effects of synthesis parameters including stirring time, resorcinol/catalyst (R/C) ratio and surfactant concentration on the structures. The average particle size of the carbon microspheres could be modulated from 5 to 46 µm by increasing the stirring time from 2 to 7 h and by varying the R/C ratio from 0.2 to 500. Particles agglomerated as the R/C ratio increases above 100. Increase in the surfactant concentration from 1% to 4% (v/v) produced smaller spherical particles with narrower size distribution. Further increase in the surfactant concentration from 10% to 50% (v/v) produced branched and folded fractal-like structures of large external area. Thus, RF sol-based precursor chemistry can be easily tuned to produce a spectrum of desired carbon particle morphologies with potential applications in printing technology, adsorbents, resonance-based solar cells, thermal detectors and carbon-based micro-electromechanical devices (C-MEMS).