Controllability of pore size and porosity on self-organized porous silica particles

Silica powder containing organized pores was prepared by a spray drying method, Silica and polystyrene latex (PSL) nanoparticles colloids were mixed and atomized to form micrometer-sized droplets. Nitrogen carrier gas was used to carry the resulting droplets into a vertical reactor that contained two heating zones: 200 degreesC and 450 degreesC, which were used, respectively, to evaporate the dispersing medium (water) and to decompose the PSL particles to give a porous silica powder. The pores on the surface of the powders were found to be arranged into a hexagonal packing, indicating that a self-organization process occurred spontaneously during evaporation of the solvent. The pore size was controlled by changing the size of the PSL particles. By adding an additional zone (third zone) maintained at high temperatures, the produced powders could be in-situ annealed. A comparison of the average volume of the powder before and after annealing (at 1500 degreesC) indicated that the porosity of the powder was about 70%. Together with the TEM image, this result indicated that pores were present both on the surface of the powders, as well as, inside the powder particles.