A systematic study of long-range ordered 3D-SBA-15 materials by electron tomography

The structures of a series of 3D-SBA-15 materials have been systematically studied by X-ray diffraction (XRD), nitrogen sorption, and electron tomography (ET) techniques. All the 3D-SBA-15 materials possess an ordered 2D hexagonal mesostructure with similar cell parameters, while the pore size measured from nitrogen sorption increases with the hydrothermal treatment temperature, in some cases even larger than the cell parameter calculated from X-ray diffraction. Taking advantage of the ET technique, it is shown that there exist two types of pores in 3D-SBA-15 materials: one is the ordered channels associated with the hexagonal symmetry, and the other is locally disordered and randomly distributed merged pores. During the hydrothermal treatment events at various temperatures, the size of ordered channels changes little, while the volume fraction and the overall size of the latter type of pores increase and eventually become dominant. Thus, the attribution of the pore sizes obtained from nitrogen sorption analysis to which types of pores is synthesis condition dependent and ET is an important tool to answer this question.