Covalent S-I Interactions for Mesoporous TM Oxides

Apart from the above-mentioned advantages of the LAT method, there are some major drawbacks preventing the method to be a major approach for the synthesis of mesoporous materials. First, the method is applicable to very limited TMs (T, Nb, and Ta), because not all TM sols are strong Lewis acids. 

Likewise, the number of available surfactants (Lewis bases) are also limited, since not all of them have available orbitals to form molecular orbitals with Lewis acid TM centers [74,76,82]. Typical surfactants used in the LAT method are alkyl phosphates and alkyl amines [72,74,76,82]. The second major drawback is the thermal stability of the formed mesostructure. Due to the strong S-I interaction, conventional solvent extraction methods are not enough to remove surfactant from mesostructured TM oxides to form mesoporous oxide materials. In addition, low metal to surfactant ratios ( 1) and essentially high temperature treatments ( 500 °C) to remove hydrophobic alkyl chains, which make these materials thermally unstable. 

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