Extensive Void Defects in Mesoporous Aluminosilicate MCM-41

Abstract

Mesoporous MCM-41 materials with a distinct N 2 -sorption hysteresis behavior have been prepared from pure silica and aluminosilicate-C 16 trimethylammonium (TMA)Br systems by a delayed neutralization procedure. On the basis of the analysis of transmission electron microscopy micrographs of these MCM-41 materials, we observed that the sample with large type-H4 hysteresis loop 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 distributes between 5.0 and 30.0 nm. The pore-blocking effect leads to the hysteresis in desorption. Aluminosilicate MCM-41 often possesses a larger hysteresis 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 the embedded voids in the framework structures. The size of the adsorption-desorption hysteresis loop is proportional to the volume of hole defects in the nanochannels, and it is dependent on the synthesis conditions such as water content, Si/Al ratio, and morphology. Tubular morphology is often associated with large hysteresis behavior and thus more hole defects. The interconnecting channels through defect holes thus makes the diffusion of molecules inside the MCM-41 structure more effective, which is important in catalysis applications.

Synthesis and optical properties of covalently bound Nile Red in mesoporous silica hybrids – comparison of dye distribution of materials prepared by facile grafting and by co-condensation routes

“…[35][36][37] This behavior is also found for the co-condensed and graed materials but with a less pronounced hysteresis loop. In addition, these materials show a H1 hysteresis loop in the region of the capillary condensation step which can be rationalized with a high degree of pore-size uniformity.…”

Synthesis of para‐Amino Benzoic Acid–TiO2 Hybrid Nanostructures of Controlled Functionality by an Aqueous One‐Step Process

“…Such hysteresis loops have already been observed in samples having aggregates of plate-like particles, which leads to a slit-shape structure, [21] and in mesoporous aluminosilicate MCM-41 with void defects. [22] These N 2 -sorption isotherm patterns reflect an extensively interconnected porous network and a so-called "poreblocking effect". This is due to the opening of many intergranular pores at the same pressure, and this happens only for pore sizes lower than 4 nm.…”

Structural and Morphological Control of Cationic Surfactant-Templated Mesoporous Silica

“…It was found that the extent of voids could be controlled in the synthesis. 42 Figure 7A shows the N 2 adsorption-desorption isotherms of the mesoporous materials in microparticle form (sample I), TWT structure (sample II), and particulates (sample III). The defectless MCM-41 silica (TEM micrograph in Figure 7B) possesses a sharp capillary condensation at p/p 0 of about 0.33, while the TWT structure has an additional type-H4 hysteresis loop at p/p 0 ) 0.5-1.0.…”