A novel method of quantifying the u-shaped pores in SBA-15

As diffusion plays an important role in various applications of ordered mesoporous structures, e.g., in catalysis, it is essential to know the exact shape of the pores to estimate or calculate the diffusion rates of molecules in the pores. In the present work, for the first time, we show thermoporometry to be an effective method of separating two types of pores in the SBA-15 samples: straight pores and u-shaped ones. This is based on the observation that water melts at lower temperatures in u-shaped pores compared with the straight pores, whereas the freezing takes place at the same temperature in both types of pores. This kind of hysteresis phenomenon is not observed with nitrogen sorption measurements. Mesoporous MCM-41 and two types of mesoporous SBA-15 materials, siliceous and aluminum-containing SBA-15, are characterized using thermoporometry. The amount of u-shaped pores is found to be 65 and 27% in siliceous and aluminum containing SBA-15, respectively. The observations are supported by high-resolution scanning electron microscopy imaging.