Improvement Of Hydrothermal Stability Of Mesoporous Materials And Novel Mesoporous Carbon Materials Water-phase Synthesis

Ordered mesoporous materials were first discovered by researchers of Mobil Company in 1992. For their unique properties and thus derived great potential application in catalysis, sorption, sensors, biology etc, mesoporous materials soon became one of the hottest research fields in the world. To date, numerous mesoporous materials with variable composition, structure, pore size, functions etc have been obtained, and more synthetic pathways and application fields have been explored and demonstrated. However, there are still a lot of questions to answer and many problems to solve in the research fields on mesoporous materials.This thesis mainly focuses on two aspects: 1) Systematically investigate the hydrothermal stability of SBA-15 and find effective methods to improve it. 2) Explore new synthetic pathway and synthesize novel materials. Explore an aqueous route to synthesize novel mesoporous carbon materials. Synthesize bimodal mesoporous silica in a W/O system.In chapter 2, the effect of the pore wall structure, of samples on the hydrothermal stability of pure silica SBA-15 in pure steam at 600 and 800℃, which is similar to industrial condition, was systematically investigated. In the steam of 600℃, SBA-15 materials show very good hydrothermal stability and the materials with thicker walls and more micropores possess better stability. The structures of SBA-15 materials are easily destroyed under steam of 800℃. High-temperature thermal treatment is proved to be an effective method to increase the polymerization degree and improve the hydrothermal stability. Nevertheless it will cause severe shrinkage of the mesopores. A carbon-propping approach was proved to dramatically increase the hydrothermal stability of SBA-15 under such critical condition, in pure steam of 800℃for 12 h. Al-SBA-15 shows very good hydrothermal stability in steam of 800℃(> 12 h). Nevertheless, Al-SBA-15 lost most of its acidity after steam treatment at 600℃for 3 h, which is a result of the hydrolyzation of framework Al.In chapter 3, novel bimodal ordered mesoporous silica materials possessing tunable small pore of 5-10 nm and large pore of- 30 nm were synthesized by using triblock copolymer P123 as a template and liquid paraffin as a swelling agent in the water-in-oil (W/O) system following a solution sol-gel pathway. The solubility of liquid paraffin in P123 solution is much smaller than that of TMB or other short chain hydrocarbon. Thus, two types of micelles may exist in the liquid paraffin/P123/HCl/ H₂O solution. After the addition of TEOS, bimodal mesoporous materials are formed on the W/O surface as a result of the co-assembly of the two types of micelles with inorganic precursors (TEOS) at the same time. The two length scale pores are all uniform and well-controlled framework pores and homogeneously interconnected. The small pores are derived from the micelles of P123 and the pore size can be easily tuned from 5 to 10 nm by varying the aging temperature. The bimodal mesoporous materials display morphologies of thin sheets or shells of hollow spheres, with a thickness of 100 - 200 nm, which can be tuned by varying the P123 concentration.In chapter 4, a facile aqueous route to synthesize ordered mesoporous carbon frameworks with tailored mesostructures (Im3m, p6m, and Ia3d) and well controlled morphologies were demonstrated by employing the organic-organic cooperative self-assembly of resols and triblock copolymers. Mesoporous carbons FDU-14 (Ia3d) with bicontinuous cubic structure were synthesized by using Pluronic P123 (EO20PO70EO20) as a template. A mesophase transformation from Ia3d to p6m was observed as the P123/phenol ratio decreased. Hydrocarbons were employed as swelling agents in the organic-organic self-assembly, and 2-D hexagonal (p6m) mesoporous carbons FDU-15 were successfully obtained as a result. The pore size of the obtained FDU-15 can be tuned from 4.1 to 6.8 nm by varying the hydrocarbon molecules. Highly ordered mesoporous carbons FDU-16 with body-centered cubic structure (Im3m) were first obtained from the aqueous route by using Pluronic F127 (EO₁₀₆PO₇₀EO₁₀₆) with a large PEO segment as a template. The morphology of the obtained carbons can be controlled on the micrometer scale (FDU-15, FDU-16) or millimeter scale (small pellets of 1-5 mm). One-layer hydrogen bond interaction between resols and PEO segments was proposed to be the essential driving force that induces the organic-organic cooperative assembly.In chapter 5, 3-D cubic mesoporous carbon FDU-16 single-crystals were prepared by employing an aqueous solution induced organic-organic assembly of triblock copolymer F127 and phenol/formaldehyde resols. The morphologies of the obtained materials are perfect rhombdodecahedron with the uniform size of - 5μm, which are commensurate with the crystallographic point group symmetry (Im3m). The scanning electron microscope (SEM) and transmission electron microscope (TEM) images directly show a layer-by-layer growth mode of face-centered cubic FDU-16 mesostructured carbon single-crystals from the centers of twelve {110} planes. Simultaneously, 2-D hexagonal mesoporous carbon FDU-15 crystals with discus-like morphologies are the products if mixed templates of F127 and P123 are used. The ordered circular mesopore channels with hexagonal packing of FDU-15 can be directly observed by the FE-SEM images.