Surfactant-Assisted Synthesis of Mesoporous Metal Phosphonates to Control Surface Properties Including an Opportunity...

A wide variety of properties by the presence of functional organic groups have so far been investigated by using periodic mesoporous organosilica (PMO)-type materials but not yet discussed with surface properties that are controlled through the success in synthesizing analogous non-silica-based hybrid mesoporous materials and subsequent evaluation and/or comparison of their properties. Here, we demonstrated the advance in synthesizing biphenyl group (-Ph-Ph-, also expressed as -2Ph)-containing mesoporous metal phosphonates with a rational understanding of surface properties. Ordered mesoporous films of aluminum and titanium ones (AOP-2Ph and TiOP-2Ph) were fabricated by spin-coating and their powders were recovered by spray-drying with the confined assembly of spherical mesopores. As in the case of PMO-type materials, the possibility to organize a -Ph-Ph- linker at the molecular scale was found in the powder samples of AOP-2Ph and TiOP-2Ph because thick frameworks would give an opportunity to organize the bulky -Ph-Ph- linker as the small-sized domains even around spherical mesopores. Surface properties of AOP-2Ph and TiOP-2Ph were evaluated by using the data of water (H₂O) adsorption isotherms and compared with those containing different organic groups. The unique hydrophilicity starting from the hydration of AlO₄ units was drastically reduced by the presence of -Ph-Ph- groups with a disappearance of the capillary condensation by the presence of mesopores. In addition, a partial replacement of TiO₆ units with AlO₄ and/or its hydrated AlO₆ species was proposed for decreasing the strong hydrophobicity of TiOP-2Ph. The contact angle over the spin-coated films was also measured by using a droplet of H₂O, indicating that the surface of the films, especially TiOP-2Ph, was extremely hydrophilic. Although surface properties at the molecular scale can be evaluated by using molecular H₂O vapor during the measurement of H₂O adsorption isotherms, the interaction of the H₂O cluster (droplet) with the bulk surface seems to be predominated by inorganic moieties.