Thermally Induced Transition between Open and Closed Spherical Pores in Ordered Mesoporous Silicas

Silicas with ordered arrays of closed (isolated) spherical mesopores of diameters on the order of 10 nm were synthesized using block-copolymer templating followed by a thermally induced pore closure process, which is described herein for the first time. Closed-pore materials with face-centered cubic structure and body-centered cubic structure were obtained using appropriately modified synthesis procedures for SBA-16 silica and large-pore FDU-12 silica templated by a common Pluronic F127 block copolymer. In some cases, the transition from open to closed mesopores was observed at temperatures of 550 °C or lower, while in other cases, the pore closure required temperatures close to 1000 °C. The cagelike pore shape, the significant degree of structural shrinkage upon the thermal treatment, and the small pore entrance size relative to the pore cage size emerge as main factors contributing to the facile formation of ordered arrays of closed mesopores. The thermally induced pore closure takes place not only for silicas but also for organosilicas, which suggests a wide applicability of the proposed approach.