RESUMEN
The synthesis of SBA-15 with or without ethanol using a one-step method and its porosity were investigated. Well-ordered SBA-15 with a rod like morphology could be obtained from starting mixtures by aging at a low (60 degrees C) or high (80 degrees C) temperature in the presence of an appropriate amount of ethanol. By contrast, mesoporous materials containing aggregates of particles obtained in the absence of ethanol at high aging temperatures (70 or 80 degrees C) had complex poorly ordered structures, indicating that ethanol can affect the structure of mesoporous materials. In addition, the poorly ordered mesoporous materials had unusual desorption characteristics, namely they possessed a two-step desorption branch.
Asunto(s)
Cristalización/métodos , Nanoestructuras/química , Nanoestructuras/ultraestructura , Dióxido de Silicio/síntesis química , Sustancias Macromoleculares/química , Ensayo de Materiales , Conformación Molecular , Nanotecnología/métodos , Tamaño de la Partícula , Propiedades de SuperficieRESUMEN
The accuracy of thermoporometry (TPM) in terms of the characterization of SBA-15 is examined based on a model that classifies the water in the mesopores into two different types: freezable pore water, which can form cylindrical ice crystals, and nonfreezable pore water, which cannot undergo a phase transition during a differential scanning calorimetry (DSC) measurement. Applying the empirical relationship between the sizes of the ice crystals formed in the mesopores and the solidification temperature of the freezable pore water to a thermogram (a recording of the heat flux during the solidification of the freezable pore water) yielded a size distribution of the ice crystals. The size of the ice crystals increased slightly with repetitive freezing, indicating that the mesopores were enlarged by formation of the ice crystals. Adding the thickness, t(nf), of the nonfreezable pore water layer to the ice crystal-size distribution calculated from the thermogram allowed for the determination of the porous properties of SBA-15. The porous properties attained from TPM experiments were compared with the results attained through the combination of Ar gas adsorption experiments and nonlocal density functional theory (NLDFT) analysis. The porous properties determined by TPM were confirmed to be quite sensitive to the t(nf) value.
