Surfactant-templated mesoporous materials

Lu Y (2006) Surfactant-templated mesoporous materials from inorganic to hybrid to organic. Angew Chem Int Ed 45 7664—7667... 

Solvent extraction is the most important technique for recovering surfactants from mesoporous materials. However, it is not very effective when applied to microporous compounds. Davis et al. [186] successfully extracted borosilicate and silicate BEA stractures with acetic acid while a small template fraction could be removed for the aluminosilicate. 

Ordered mesoporous materials of compositions other than silica or silica-alumina are also accessible. Employing the micelle templating route, several oxidic mesostructures have been made. Unfortunately, the pores of many such materials collapse upon template removal by calcination. The oxides in the pore walls are often not very well condensed or suffer from reciystallization of the oxides. In some cases, even changes of the oxidation state of the metals may play a role. Stabilization of the pore walls in post-synthesis results in a material that is rather stable toward calcination. By post-synthetic treatment with phosphoric acid, stable alumina, titania, and zirconia mesophases were obtained (see [27] and references therein). The phosphoric acid results in further condensation of the pore walls and the materials can be calcined with preservation of the pore system. Not only mesoporous oxidic materials but also phosphates, sulfides, and selenides can be obtained by surfactant templating. These materials have pore systems similar to OMS materials. 

Many studies that have focused on the formation mechanism of various types of templated mesoporous materials have been summarized in a number of recent reviews,46 9 and it is still an ongoing topic of research.50 51 Here, we want to recapitulate only very briefly the useful interaction classification scheme between the surfactants (S) and the inorganic species (I), which was suggested by Huo et al.52,53... 

Surfactant-templated mesoporous siUcates have been the subject of intense research effort since the publication by Mobil scientists in 1992, of the syntheses for MCM-41, MCM-48 and MCM-50. Some have su ested that similar materials were prepared earlier, however... 

The AMS (anionic surfactant-templated mesoporous silicas) materi-aisi30,i40,i42 family of well-ordered organosilicas prepared using anionic... 

In general, the procedures used for the preparation of mesoporous materials are similar to those utilized in the synthesis of zeolites except that a surfactant instead of an inorganic cation or base is used as the template. Mesoporous materials (e.g., mesoporous silica) are prepared under room temperature or mild hydrothermal conditions (typically below 150°C) in the presence of anionic, cationic, or neutral surfactants, in either basic or acidic conditions. 

The silicate network can also act as an efficient size exclusion membrane. The pore size distribution can be controlled, at least to some extent, by incorporation of water soluble polymers such as poly(ethyleneglycol) or by pH changes (Brinker, 1989). Carefully tailored silicate membranes, using low pH synthesis even exhibit Knudsen flow, facilitating the separation of air components (Brinker, 1993). Incorporation of zeolites, surfactants, templated mesoporous silicates, and leaving template materials can be used to generate tailored size excluding films. 

A non-surfactant templating route to mesoporous silica materials. Advanced Materials, 10, 313—316. 

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