Novel synthesis of high hydrothermal stability and long-range order MCM-48 with a convenient method

The high quality MCM-48 has been easily synthesized at 120 °C for 24 h, and the results of which showed that not only long-range ordering of MCM-48, but also hydrothermal stability could be significantly improved by direct addition of NaF with F−/Si ratio of 0.1 and 0.2 to initial reacting gel without post-treatment and pH adjustment. The results of XRD, N2-adsorption and TEM analyses indicated that MCM-48, which was synthesized via appropriate procedure, maintained their structural integrity after boiling in water at 100 °C for at least 3 days. Additionally, the optimum condition was F−/Si ratio of 0.1 at a Na2O/SiO2 ratio of 0.25. The adding time of NaF was critical in the formation of this high quality MCM-48. When the addition of fluoride ions was 60 min earlier than that of surfactant, the mesoporous structure of the synthesized MCM-48 could be maintained after refluxing in boiling water for 3 days. When the additions of fluoride ions and surfactant were simultaneous, however, the structure of MCM-48 was collapsed after 12 h refluxing in boiling water. The result clearly showed that the long-range structural ordering and hydrothermal stability could be improved only when adding NaF at the early stage of hydrolysis and polymerization of silicate. The different effects of fluoride anions at the different reacting periods of synthesizing MCM-48 are also discussed.