Materials were prepared hydrothermally based on the method used to synthesize pure silica ZSM-5, a zeolite of MFI-type framework. Water, salt (SDA) or ionic liquid, base (NaOH) and silicon dioxide (SiO2) were combined in a molar ratio 0.072: 0.030: 0.37: 9.2 respectively then stirred for 2 hours. The reaction mixture was charged into autoclaves which were then placed in an oven at 150oC for 44 hours. The precipitate was washed with water, followed by acetone (for [TPA][PF6] only) and air-dried at room temperature. Analysis was done using an X-ray diffractometer and the resulting patterns compared to those available in the literature.
Results
Each of the synthesis mixtures yielded a white product. Only in presence of [TPA][Br] was a product synthesized with X-ray diffractometer patterns (XRD) characteristic of a porous pure silica zeolite with the MFI-type framework. In the presence of either [TBA][Br], [TBA][PF6], [TBA][NO3] or [emim][Br], products synthesized showed X-ray diffractometer patterns characteristic of magadiite (NaSi7O13(OH)3·4(H2O)) which is a dense material with a silicate layer and whose synthesis does not commonly require an SDA. The addition of either [TBA][Br], [TBA][PF6], [TBA][NO3] or [emim][Br] therefore neither enhanced nor inhibited the formation of magadiite; they merely served as co-solvents.
The lengthening of alkyl group from propyl to butyl led to MFI framework not being formed. The larger cation did not provide the necessary van der Waals forces to make MFI.
Comments
The researchers in this experiment should have provided more discussion on the influence of anions in the framework formation. Determining the effect of these anions on the framework was one of the objectives of the experiment but the results are not discussed to this effect. They also could have extended the scope of the experiment by using salts with TPA as the cation but with different anions and determine the influence of anions on the MFI structure.
Small-Angle Neutron Scattering Studies of Model Protein Denaturation in Aqueous Solutions of the Ionic Liquid 1-Butyl-3-Methylimidazolium Chloride.
