Control Synthesis Of 3D Cubic Pm(3|-)n Mesotructure Silica In A Weak Acid System

The 3D channel network and unique cage-type pores of cubic Pm（3|-） n structure mesoporous silica materials is much more desirable for the diffusion and transmission of guest molecules than 2D hexagonal p6 mm mesophase which make them suitable for wide applications in catalysis, adsorption and drug delivery. However the strong acidic medium during the synthesis process not only pollute the environment but also go against the incorporation of active metal into the silica framework, what’s more it’s not benefit to pack the bioactive macromolecules such as protein or enzyme in the channel. Meanwhile, it is difficult to form an ordered mesoporous phase under weak acidic medium.In order to solve the above problems, this paper firstly synthesizes high-quality 3D cubic Pm（3|-） n structure mesoporous silica materials in the mild acid medium provided by H₃PO₄（p H<2） and HAc（p H>2） through adding the inorganic salt（Na Y, Y= Cl-, SO42-, Br- and NO3-）which can only change the ionic strength and without affecting the p H values to induce the condensation of the silicate species in the presence of cetyltriethylammonium bromide（CTEABr）. At the same time, the influence of synthesis parameters on the formation of the mesophase structure was investigated in this work. The main results of the research are as follows:1. high-quality cubic Pm（3|-） n mesoporous materials have been successful synthesized in the system of TEOS-CTEABr-Na Y-H₃PO₄-H2O（p H<2） at room temperature（18℃ to 28℃） under static condition by adjusting the type and concentration of sodium salt for the first time. The presence of various counteranions in the interfacial region of the silicate-surfactant mesophase is helpful for condensation of the silicate species which have no direct association with the strength of the acid and offer opportunities for manipulation of the phase structure. Well-ordered three-dimensional hexagonal P63/mmc, cubic Pm（3|-） n, two-dimensional hexagonal p6 mm mesoporous materials have been synthesized according to the type and concentration of anion of sodium salt, but high-quality cubic Pm（3|-） n mesoporous materials can be only synthesized by adding Na Cl and Na2SO4 and hexagonal p6 mm mesoporous materials can be synthesized by adding Na Br and Na NO3 with the same surfactant. The counteranions of Inorganic sodium salt resulte in increasing of surfactant packing parameter g in the order SO42-<Cl-<Br-<NO3-, which leads to different formation routes to the mesostructures.2. Results are similar in the system of TEOS-CTEABr-Na Y-HAC-H2O（p H>2） by adjusting the type and concentration of sodium salt, it shows that the silicate species and surfactant micelle are self-assembled to form the mesostructures which is not relevant to the way of electronic interaction. In other words, the formation of mesostructures is not relevant to the S+X-I+ pathway in H₃PO₄ system or S+I- pathway in HAc system but up to the influence of anion on surfactant micelle curvature and the higher curvature of spherical micelle is helpful to form cubic Pm（3|-） n mesophases. However, the type of acids affect the morphology of 3D cubic Pm（3|-） n mesoporous materials.There is no doubt that when the 3D cubic Pm（3|-） n mesoporous materials can be prepared efficiently in gentle acidic system, it not only reduces the preparation cost and synthesis difficulties, but also provides a new way to research such a special 3D channel network and unique cage-type pores of the mesoporous materials for its further modification and functionalization. On the other hand, it provides the basis for us to understand the key factor of controlling the self-organization process of mesostructures between the silicate species and surfactants from a new perspective.