Hydrothermal Synthesis of MCM-22: Effect of Aging and Alkalinity

فاقد چكيده فارسي

In this research, the possibility of hydrothermal synthesis of MCM-22 via static approach is investigated. Silicic acid was used as a silica source since it has high specific surface area which helps better dissolution of silica source. In general static approach is a difficult process for obtaining MCM-22 phase, however by using aging step, before the actual synthesis, this phase was successfully formed under specific OH-/SiO2 molar ratio of 0.15. XRD results confirms the crucial role of this aging step on the formation of MCM-22 phase. It also confirms the role of alkalinity of the reaction mixture on the degree of product crystallinity. At the OH-/SiO2 molar ratio of 0.15, higher degree of crystallinity was achieved compared to the 0.1 one. SEM images show the importance of the OH-/SiO2 molar ratio on the shape and structure of the MCM-22 crystalls. At the ratio of 0.15 (as an optimum value), MCM-22 crystalls are formed as rose-like structures made of petal plates with the thickness of about 70 nanometer, but for the case with OH-/SiO2 molar ratio of 0.1, MCM-22 crystalls are donut-shape which is composed of much smaller parts, agglomerated with a bulk thickness of 160 nm.