Covalent hydrothermal synthesis

Supported zeolite membranes have been prepared using numerous procedures [4] such as alignment of crystals in electrical fields, electroplating, self-assembly, growth on organic molecular layers, covalent linkages, hydrothermal synthesis (in situ and ex situ), hydrothermal method microwave heating assisted, dry gel method (vapor-phase transport method and steam-assisted crystallization), synthesis at the interface between two fluid phases, etc. 

The traditional methods, such as hydrothermal synthesis, impregnation, and chemical vapor deposition (CVD), can be employed to incorporate heteroatom and metal/metal oxide nanoparticles as catalysts into the nanopores of MSs. The advances in this area have been well summarized in recent reviews [35 - 38]. Herein, we will mainly focus on the assembly of molecular catalysts in the nanopore of MSs and MOFs. Using the molecular chiral catalyst as a model, we will address the general strategies for incorporating molecular catalysts in the nanoreactor, including the covalent and noncovalent bonding methods. 

In contrast to these post-synthetic modifications, it is also possible to functionalize the pore walls directly during the synthesis, as was first shown by Mann and co-workers [7,8] and Stucky and coworkers [9], who used trialkoxysilanes R-Si(OR )3. In our approach, such R Si(OR )3 molecules substitute for part of the TEOS. After hydrolysis, they serve as additional framework components during the hydrothermally induced condensation. An essential condition for this approach is that the trialkoxysilane does not destroy the micellar arrangement of the surfactant, which gives rise to the mesostructure. In mesostructures produced in this way, the R residues should be covalently linked to the silica walls. After the synthesis, the organic surfactant molecules can be removed by extraction so that a modified mesoporous material should remain. For example, when using phenyltrimethoxysilane (PTMOS), phenyl groups may become attached to the walls of the mesopores these can be utilized for further modifications, e.g. the immobilization of metal complexes. 

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