Surfactant/inorganic precursor ratio

A series of experiments have been eonducted in an attempt to improve the thermal stability of the Ti-Zr mesoporous mixed oxide prepared Ifom inorganic precursors. The results show that the crystallinity of the Ti-Zr mesoporous mixed oxide depends strongly on the Ti/Zr molar ratio in the gel mixtures, and a better crystalline mesoporous structure can be obtained on the sample with the 1 1 Ti/Zr molar ratio. It is also found that surfactant content, addition of sulfate species and auxiliary organic additive such as DDA, TritonX-lOO, triethanolamine and ethanol would play a key role in tailoring the mesopore structures and improving thermal stability of the obtained materials. In addition, the mixing order of organic surfactants, i.e., CTAB and DDA, also affects the the crystallinity of the product. 

Other factors that affect the structure of mesophases include the concentration ratio between surfactants and inorganic precursors. For example, MCM-41 was prepared at a Ci6H33(CH3)3N+/Si ratio of less than 1. As the Ci6H33(CH3)3N+ /Si ratio increases beyond 1, the cubic phase (Ia3d) can be produced. Similarly, Nb-TMSl (/ 6m), Nb-TMS2 (E63/WWC), Nb-TMS3 (Pm-3n), and Nb-TMS4 (p2) were prepared at various surfactant to Nb ratios. ... 

The formation of self-assembled materials is governed by a number of experimental parameters the choice of inorganic precursors and surfactants, the inorganic to surfactant ratio, amount of water and other solvents used, pH during synthesis, additives, reaction time and temperature, treatments used to stiffen the inorganic framework, and treatments to remove surfactant and obtain porosity, all decide the final ordering, porosity and surface area. It is well known that successful... 

In these syntheses the films with mesophase order form spontaneously at an interface from a dilute solution ofsurfactant micelles and sihca precursor via a co-assembly route. The surfactant concentration is higher than that used for evaporation induced self-assembly, and the concentration of volatile solvents is lower. Films will self-assemble from these solutions in closed containers and on submerged substrates, so the development ofmesoscale order does not rely on evaporation as in the work described above. These films form after an extended induction period, the length of which is dependent on solution concentration, ionic strength, inorganic surfactant ratio, pH and surface to volume ratio. Most of the work on films grown at the solution/air interface concerns the formation mechanisms of these films, and since these are likely to be similar for solid/solution interface films, film growth at the solution/air interface will be treated first. 

Route C mobilizes routes A and B to combine complex precursor systems (aerosol cocktails) in different ratios and yield multifunctional materials with hierarchically structured porosity [18-21]. For instance, latex beads can be combined with a diluted sol-gel surfactant dispersion that contains small inorganic nanoparticles of metallic oxides, metals, and so on. This approach then leack by EISA to micrometer-sized porous spheres with an independent control of dimensions at four levels of size. 

---