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 (PEO ₂₀-PPO₆₉PEO₂₀) and P85 (PEO ₂₆PPO₃₉PEO₂₆). 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 Å 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.