Molded micro- and mesoporous carbon/silica composite from rice husk and beet sugar

A molded carbon/silica composite with high micro- and mesoporosity, as well as a high bulk density, was fabricated by activating a disk-molded precursor made from carbonized rice husk (RH) and beet sugar (BS) at 875 °C in CO2. The pore structure of the RH- and BS-based carbon/silica composite (RBC) was analysed in relation to the bulk density. An activation time of 2.0 h provided the largest BET specific surface area (1027 m2/g) and total pore volume (0.68 cm3/g) and a low bulk density (0.54 g/cm3). An RBC that was first activated for 1 h was immersed again in BS syrup and then activated in CO2 for 1 h. This two-step activation process provided both a high bulk density (0.69 g/cm3) and a highly textured structure (BET specific surface area, 943 m2/g; total pore volume, 0.56 cm3/g). The immersion in BS syrup was useful for improving the texture without reducing the bulk density, in comparison to one-step activation for 1.0 h. The suspension of the RBCs was basic because of the residual inorganic compounds of potassium and calcium. However, the basicity of the suspension was alleviated by washing the RBCs with water.