(A) study on the synthesis of SBA-15 having macropores induced by colloidal crystal templating and the adsorption of vocs over these materials

Abstract

SBA-15 has obvious advantages such as good hydrothermal stability induced from thicker wall than that of MCM-41, and high surface area generated from mesoporous structures. Furthermore, when mesopores and macropores coexist in a same material, the material has additive advantages like ease access to active sites derived from macroporous structures. In this regard, meso/macroporous SBA-15 should be very attractive for their application in the area of adsorption, catalysis and separation. The meso/macroporous silicates were prepared by a new and simple dualtemplating method, which is the combination of replicating the closed packed array of colloidal crystal and liquid crystal mesophase of surfactant. Monodispersed polystyrene (PS) beads were directly added without any pre-arrangement to a gel solution prepared for the synthesis of mesoporous SBA-15. The macrostructure of biporous MCM-41 and SBA-15 were obtained through impregnation of the latex spheres followed by calcination. Each of the macrophases showed different morphologies due to different textural morphology of pure MCM-41 and SBA-15. Furthermore, the morphology of macrostructure of biporous SBA-15 was affected by the PS bead size and the Si:PS ratio. With the PS bead size or PS:Si ratio, not only was the volume of macroporous space increasing, but also the ordering of macropores was also better. Meso/macroporous silicates should be attractive as adsorbents for adsorption and desorption of VOCs due to high surface area induced from mesopores and also due to the accessibility derived from macropores. The adsorption breakthrough curves with macrostructured MCM-41 and SBA-15 showed that the adsorption dynamics were improved (i.e., the slope was stepper). The temperature programmed desorption of VOCs (toluene and p-xylene) showed that the maximum desorption peaks were shifted to a lower temperature. When bulky materials like p-xylene were used as adsorbate, the differences of adsorption/desorption behavior b...