Synthesis and Characterization of Hierarchically Porous Silica with Poplar Tissue as Template with Assistance of Supercritical Co2

Hierarchically porous silica samples, ranging from mesopores to macropores, were prepared by “nanoscale casting using supercritical (SC) fluids” (NCSCF) technology and bionics, achieving a biomineralization process in an environmentally friendly and efficient way. These wood-templated SiO2 samples, having special hierarchical pore sizes from 3.3 nm up to 50 μm, were obtained with SC-CO2 precursor solution by a wood-silication method. For this method, the precursor, tetraethyl orthosilicate (TEOS), was dissolved in SC-CO2 and impregnated into poplar tissue cells using SC-CO2 as a mass carrier. After removal of the wood template by calcination in air at suitable temperatures, the porous silica was obtained. The effects of CO2 pressure and precursor concentration on the impregnating ratio were studied, and the products were characterized. SEM experimental results showed that the obtained silica had the same external and internal structures of the original wood. XRD and N2 absorption-desorption results indicated that the silica was amorphous but crystallized with the calcination temperature up to 1000 o C, and had a preferable BET surface area being up to 469 m 2 /g (600 o C). So this work provides a simple and timesaving route to obtain and control the special microstructure of silica with the aid of a wood template in supercritical CO2.