Extensive void defects in mesoporous aluminosilicate MCM-41

Mesoporous MCM-41 materials with a distinct N-2-sorption hysteresis behavio r have been prepared from pure silica and aluminosilicate-C-16 trimethylamm onium (TMA)Br systems by a delayed neutralization procedure. On the basis o f the analysis of transmission electron microscopy micrographs of these MCM -41 materials, we observed that the sample with large type-H4 hysteresis lo op at p/p(0) between 0.5 and 1.0 contains extensive structural defect holes amid the nanochannels. These holes are irregular in shape and their size d istributes between 5.0 and 30.0 nm. The pore-blocking effect leads to the h ysteresis in desorption. Aluminosilicate MCM-41 often possesses a larger hy steresis loop than pure silica MCM-41. The linear channel system of MCM-41 becomes effectively interconnected through these defect holes. The unusual adsorption hysteresis is associated with the pore-blocking effect around th e embedded voids in the framework structures. The size of the adsorption-de sorption hysteresis loop is proportional to the volume of hole defects in t he nanochannels, and it is dependent on the synthesis conditions such as wa ter content, Si/Al ratio, and morphology. Tubular morphology is often assoc iated with large hysteresis behavior and thus more hole defects. The interc onnecting channels through defect holes thus makes the diffusion of molecul es inside the MCM-41 structure more effective, which is important in cataly sis applications.