Facile synthesis of resorcinol-melamine-formaldehyde based carbon xerogel

Abstract

A facile sol-gel / ambient drying / pyrolysis process has been developed for the synthesis of a new class of “mixed resin” resorcinol-melamine-formaldehyde (RMF) based carbon xerogels. Such materials display versatile structural features or, more precisely, allow facile tuning of micro and macropores through chemical and processing parameters such as the melamine/ resorcinol ratio (M/R) or the pyrolysis temperature, respectively. The chemical composition and crystalline structure of the RMF xerogels and their corresponding carbon xerogels were characterized by elemental analysis and X-ray diffraction. The specific surface area, agglomerate colloid size, pore volume and pore size distribution were further investigated with scanning electron microscopy (SEM) and nitrogen sorption (BET). Dynamic water uptake behavior of the xerogels was investigated using the dynamic vapor sorption (DVS) method. It was found that ambient dried RMF gels exhibit comparable properties to those of multi-step solvent exchanged and supercritically dried RMF gels. By increasing the pyrolysis temperature from 600°C to 1200°C, the surface area and pore volume of the carbon xerogels decrease. These materials exhibit a rather high water sorption capacity at low relative pressure which makes them potential candidates for sorption based heat pumps. Carbon xerogel synthesized using an M/R ratio of 1.0 and pyrolysis temperature of 600°C showed higher water uptake than those at an M/R ratio of 0.5. Furthermore, a high pyrolysis temperature (1200°C) led to reduced water sorption capacity values of the carbon xerogels.