Preparation of carbon cryogels from wattle tannin and furfural

Wattle tannin-furfural (TFu) hydrogels were synthesized by the sol–gel polycondensation of wattle tannin with furfural by using three types of base catalysts (NaOH, Na2CO3 and NaHCO3). TFu cryogels were prepared by freeze drying of the hydrogels and TFu carbon cryogels were obtained by pyrolysis of the cryogels in an inert atmosphere. The TFu and carbon cryogels were characterized by N2 adsorption and scanning electron microscope (SEM). The effect of catalysts on porous properties of carbon cryogels resulted in different ways: (1) NaOH enhances increasing mesopore volumes and surface area of carbon cryogels and (2) Na2CO3 and NaHCO3 cause decreasing those of carbon cryogels. The TFu and carbon cryogels prepared by using NaOH as a catalyst possessed large mesopore volumes comparing with micropore volumes. Even though the TFu cryogels have surface area and mesopore volumes smaller than the resorcinol-formaldehyde (RF) cryogels, the carbon cryogels have unique porous properties differed from the RF carbon gels. The properties are summarized as follows: (1) the mesopore volume changes insignificantly after pyrolysis, (2) the pore radius is increased after pyrolysis and (3) micropores are not greatly developed during pyrolysis.