Postsynthesis Hydrothermal Restructuring of M41S Mesoporous Molecular Sieves in Water

Abstract

A high-quality Si−MCM-41 was prepared with the composition of SiO2, 0.2; TEAOH, 0.25; CTMABr, 35 in H2O using fumed silica as the silica source. The quality of the compounds was assessed using different analytical techniques such as XRD, N2 adsorption−desorption measurement, UV−vis absorption, FTIR, and 29Si MAS NMR. The quality of M41S mesoporous materials, synthesized using a single C16TMA+ surfactant, could be further improved by a postsynthesis hydrothermal treatment of the as-synthesized materials in water. In comparison with the ordinary preparation, the water-treated materials exhibited a higher long-distance order, a higher BET surface area, and a larger pore size. The postsynthesis water treatment method provided an easy and mild way to prepare high-quality M41S molecular sieves with the pore size controllable by altering either the treatment time or the temperature. The postsynthesis treatment also enhanced the stability, especially the hydrothermal stability, of Si−MCM-41. The 29Si MAS NMR results demonstrated that the water treatment promoted the wall polymerization or local atomic arrangement. It was suggested that the pH lowering of synthesis mixture by replacing the mother liquor with water played a crucial role in the restructuring toward a high-quality Si−MCM-41. The quality of Ti−MCM-41, Al−MCM-41, and Si−MCM-48 was also improved by a similar postsynthesis hydrothermal treatment.

Adsorptive desulfurization of diesel with mesoporous aluminosilicates

“…Weak acidity also leads to weak ion-exchange ability and small adsorptive capability. Many efforts have been made to improve the disadvantage of mesoporous molecular sieves, including postsynthesis grafting of aluminum to the silica wall [13] . But the acid sites that aluminum can offer are limited, whereas the problem of poor stability and poor hydrothermal stability still exists.…”

Synthesis and Characterization of Ordered Mesoporous Aluminosilicate Molecular Sieves with High Stability in High‐Temperature Steam

“…, 11 the addition of some salts [12][13][14] or HF 15 during the crystallization synthesis, the post-synthesis hydrothermal treatment, 16,17 the post-synthesis grafting route, [18][19][20][21][22][23] and the post-synthesis re-crystallization. [24][25][26][27] However, the stability of these materials in the high-temperature steam (e.g.…”

Postsynthesis Vapor-Phase Functionalization of MCM-48 with Hexamethyldisilazane and 3-Aminopropyldimethylethoxylsilane for Bioseparation Applications

“…13,16,[20][21][22] The formation of strained siloxane bridges is influenced by the synthesis conditions (e.g., silica precursor, pH) and treatment of the materials. Efforts to increase the hydrothermal stability of these materials often involve strategies that facilitate a relaxation of the framework structure, 13 postsynthesis restructuring, 23 the use of salt solutions during synthesis, 24,25 or the use of nonionic surfactant templates. 21 Another approach to the optimization of mesoporous molecular sieves for separations is their surface functionalization.…”