(122a) Structural Control of Resorcinol-Formaldehyde Xerogels and Their Subsequent Processing into Magnetic Carbon Rods

Resorcinol-formaldehyde (RF) gels were originally produced by Pekala et al. and were the first organic aerogels prepared by sol-gel polycondensation. The traditional monolithic gels are isotropic. Current synthetic methods do not permit to impart anisotropy to the macrostructure of the final material, and neither allow for a control of pores direction. By adapting a procedure developed by our group, we show that the macroporous structure of pure polymer gels can be rendered naturally anisotropic by adding superparamagnetic colloids to the sol-gel precursor solution, and by applying a uniform magnetic field during the sol-gel transition. By ensuring that the superparamagnetic colloids are incorporated into the polymer phase, the magnetic colloids will self-assemble into chain-like structures in the direction of the magnetic field and become templates for the growing gel. Hard carbons obtained by the pyrolysis of resorcinol-formaldehyde xerogels are easily prepared, are non-toxic and have low production costs because of the simple sol-gel process that can used to prepare them. The meso- and macroporosity and overall architecture of the xerogels can be controlled by tuning the composition of the sol mixture, and the concentration of the catalyst (pH). Aging and drying conditions also have a substantial effect on the final surface area and pore volume of these gels. Conversely, the microporosity is created during the pyrolysis step. The dry RF xerogels still containing magnetic colloids for structural control, can be sonicated with a horn sonicator for a few minutes. During the sonication process, the rod-structured gel will be broken down into small individual rods of fairly uniform length. After another drying step, these monolithic rods can be pyrolyzed into hard carbon. The rod structure is preserved during the pyrolysis, which is performed at 1000 °C under argon atmosphere. The superparamagnetic iron oxide inside the magnetic template is reduced during the pyrolysis to elemental iron. The structurally controlled RF xerogels are terminating in a highly magnetic carbon material.