Synthesis and characterization of high-surface-area millimeter-sized silica beads with hierarchical multi-modal pore structure by the addition of agar

• Millimeter-sized spherical silica foams (SSFs) are successfully prepared.
• SSFs exhibit high BET surface area and ordered hierarchical pore structure.
• Agar addition improves BET surface area and micropore volume of SSFs.
• Foaming process generates interconnected 3-D network macropore structure of SSFs.

Millimeter-sized spherical silica foams (SSFs) with hierarchical multi-modal pore structure featuring high specific surface area and ordered mesoporous frameworks were successfully prepared using aqueous agar addition, foaming and drop-in-oil processes. The pore-related properties of the prepared spherical silica (SSs) and SSFs were systematically characterized by field emission-scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), small-angle X-ray diffraction (SAXRD), Hg intrusion porosimetry, and N2 adsorption–desorption isotherm measurements. Improvements in the BET surface area and total pore volume were observed at 504 m2 g− 1 and 5.45 cm3 g− 1, respectively, after an agar addition and foaming process. Despite the increase in the BET surface area, the mesopore wall thickness and the pore size of the mesopores generated from the block copolymer with agar addition were unchanged based on the SAXRD, TEM, and BJH methods. The SSFs prepared in the present study were confirmed to have improved BET surface area and micropore volume through the agar loading, and to exhibit interconnected 3-dimensional network macropore structure leading to the enhancement of total porosity and BET surface area via the foaming process.

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