Influence of catalyst amount on properties of resorcinol-formaldehyde xerogels

The effect of catalyst amount on properties of resorcinol-formaldehyde xerogels was investigated. The samples were prepared by sol-gel polycondensation of resorcinol with formaldehyde at three different levels of catalyst (Na2CO3, molar ratios of resorcinol/catalyst R/C = 1000, 2000, 3000). The influence on mechanical, thermal and thermomechanical properties of organic xerogels and on properties of carbon xerogels (surface, adsorption and oxyreactivity) was evaluated. The higher R/C ratio leads to increased particle size of the materials, which affects mechanical strength, residual humidity and shrinkage during heating (all parameters decrease). The R/C ratio does not affect significantly pyrolysis process and microporosity of the materials, the effect on oxyreactivity was negligible. Contrary, higher catalyst content (R/C = 1000) lead to relative high volume of ink-bottle shaped mesopores, but this pores are practically unavailable for adsorption of large molecules of methylene blue or hydrated chromate anions, which negatively influenced adsorption of both adsorbates from aqueous solution on the carbon xerogels.