Pore expansion in mesoporous silicas using supercritical carbon dioxide

In this paper we report the controlled expansion of pores within mesoporous silicas using supercritical carbon dioxide (sc-CO2). Our method uses the tunable density of sc-CO2 to induce the controlled swelling of the triblock copolymer surfactant templating agents, P123 (PEO20-PPO69PEO20) and P85 (PEO26PPO39PEO26). This swelling process ultimately leads to the control of pore diameters and hexagonal spacing within the mesoporous silicas. At pressures of approximately 482 bar, pore diameters of up to 100 A can be achieved, representing a pore expansion of 54% compared to the conventionally formed mesoporous silicas. Powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), and nitrogen adsorption techniques were used to establish pore diameters, silica wall widths, and the hexagonal packing of the pores within the sc-CO2 treated mesoporous silicas. The sc-CO2 was shown not to effect the hexagonal ordering of the silica, a distinct advantage over conventional pore-swelling techniques.