[Preparation of porous silica microspheres with high porosity using base-dissolving method]

A novel method was proposed and studied for the preparation of porous silica with high porosity using base-dissolving technology. The relationships between the removal of silica and the base concentration, the reaction temperature as well as the reaction time were evaluated. The amount of silica removed from silica spheres was increased and silica-dissolving rate was also accelerated along with the increase of NaOH concentration. This was due to the damage of some inner walls of the porous silica and the dissolution of small fragments into the base solution. The amount of silica removed was in direct proportion to the reaction temperature and reaction time. Moreover, the specific pore volumes were linearly increased along with the increase of the amount of silica removed. The treated silica particles remained as homogeneous spheres and the changes of the particle diameter were not observed. Under the optimized conditions with the NaOH solution of 1.25 mol/L, the reaction temperature of 25 degrees C and the reaction time of 3.0 h, the original silica spheres with the diameter of 4 - 5 microm, the pore size of 8 nm and the specific pore volume (V(p)) of 1.4 cm3/g were modified to the high-porosity silica with the diameter of 4 - 5 microm, the pore size of 14 nm and the V(p) of 3.2 cm3/g. The porosity of the silica microspheres was changed from 75% to 88%. This high-porosity silica was suitable for the preparation of high performance gel filtration packings.