Abstract
Thermoporosimetry, i.e., DSC measurements of melting point depression of water and heptane confined in mesopores, has been used for determination the pore size distribution of several mesoporous silicas synthesized with the use of micelle templates. Porosity of these materials was additionally characterized by low-temperature nitrogen adsorption and quasi-equilibrated thermodesorption of nonane. The pore size distributions obtained using the water thermoporosimetry were similar to those determined using the other methods, but the pore size values found for the narrow pore materials were underestimated by ca 1 nm. Too large pore sizes obtained for the wide pore silica from heptane thermoporosimetry were attributed to nonlinear dependence of the melting point depression on the reciprocal of the pore size.
Highlights
Thermoporosimetry, i.e., differential scanning calorimetry (DSC) measurements of melting point depression of water and heptane confined in mesopores, has been used for determination the pore size distribution of several mesoporous silicas synthesized with the use of micelle templates
The desorption isotherm used in determination of the pore size distribution (PSD) is affected by the pore network: when pressure is reduced, liquid will evaporate from large open pores, but pores of the same size that are connected to the surface with narrower channels remain filled [6]
The pore size increases is series MCM-41, HMS, SBA-15 to MCM-41/TBM, as indicated by the increasing pressure corresponding to the capillary condensation step in the adsorption isotherms and decreasing temperature of the thermodesorption peaks
Summary
Thermoporosimetry, i.e., DSC measurements of melting point depression of water and heptane confined in mesopores, has been used for determination the pore size distribution of several mesoporous silicas synthesized with the use of micelle templates. Porosity of these materials was characterized by low-temperature nitrogen adsorption and quasi-equilibrated thermodesorption of nonane. The freezing point depression observed for the trapped liquid can be related to the size of the pore it is possible to calculate the PSD of the medium under study This idea is the basis of the TPM, derived by Brun at el. Soaking the porous material in the liquid and measuring the melting or crystallization temperature by differential scanning calorimetry (DSC) is enough to perform pore characterization
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