Jerry Y S Lin

Ordered mesoporous silica prepared by quiescent interfacial growth method - effects of reaction chemistry

Acidic interfacial growth can provide a number of industrially important mesoporous silica morphologies including fibers, spheres, and other rich shapes. Studying the reaction chemistry under quiescent (no mixing) conditions is important for understanding and for the production of the desired shapes. The focus of this work is to understand the effect of a number of previously untested conditions: acid type (HCl, HNO3, and H2SO4), acid content, silica precursor type (TBOS and TEOS), and surfactant type (CTAB, Tween 20, and Tween 80) on the shape and structure of products formed under quiescent two-phase interfacial configuration. Results show that the quiescent growth is typically slow due to the absence of mixing. The whole process of product formation and pore structuring becomes limited by the slow interfacial diffusion of silica source. TBOS-CTAB-HCl was the typical combination to produce fibers with high order in the interfacial region. The use of other acids (HNO3 and H2SO4), a less hydrophobic silica source (TEOS), and/or a neutral surfactant (Tweens) facilitate diffusion and homogenous supply of silica source into the bulk phase and give spheres and gyroids with low mesoporous order. The results suggest two distinct regions for silica growth (interfacial region and bulk region) in which the rate of solvent evaporation and local concentration affect the speed and dimension of growth. A combined mechanism for the interfacial bulk growth of mesoporous silica under quiescent conditions is proposed.

Preparation Chemistry of Inorganic Membranes

Publisher Summary Membranes are thin films allowing for selective transport of mass species, such as gases, liquids, or ions. The major advantages of inorganic membranes as compared to polymeric membranes are their better thermal, chemical, and mechanical stability and higher permselectivity. The disadvantages are higher membrane costs and an increased difficulty toward making membrane modules with high packing densities. Inorganic membranes will find applications that require high permselectivity and good chemical and thermal stability beyond what can be offered by polymeric membranes. The most important properties of inorganic membranes include permeance and selectivity. These properties of microporous and mesoporous membranes are determined by the pore size, porosity, and membrane thickness. Chemistry plays a very important role in controlling these properties. Microporous amorphous silica membranes can be prepared by the acid catalyzed solegel method using an alkoxide precursor. The intercrystalline defects and zeolitic pores of crystalline zeolite membranes can be eliminated or narrowed by chemical vapor deposition through proper control of the surface chemistry of the zeolite framework. The membranes are very thick because synthesis chemistry gave large metal-organic framework crystals. Synthesis chemistry controls the pore size and structure of ordered mesoporous materials as well as orientation of the pore of the ordered mesoporous membranes.

NOVEL CERAMIC MEMBRANE FOR HIGH TEMPERATURE CARBON DIOXIDE SEPARATION

This project is aimed at demonstrating technical feasibility for a lithium zirconate based dense ceramic membrane for separation of carbon dioxide from flue gas at high temperature. The research work conducted in this reporting period was focused on several fundamental issues of lithium zirconate important to the development of the dense inorganic membrane. These fundamental issues include material synthesis of lithium zirconate, phases and microstructure of lithium zirconate and structure change of lithium zirconate during sorption/desorption process. The results show difficulty to prepare the dense ceramic membrane from pure lithium zirconate, but indicate a possibility to prepare the dense inorganic membrane for carbon dioxide separation from a composite lithium zirconate.