Pillared Layered Compounds: Their Synthesis, Structure and Properties

Texas A&M Research Foundation, College Station TX

Investigators

Abstract

There is great current interest to design multifunctional micro- or mesoporous materials. A main goal of this project is the synthesis of organic-inorganic hybrid materials Most of the research is directed towards carboxylic acids as the organic complexing agent. The effort also involves the more complex phosphonic acids. The strategy is to prepare pillared layered materials in which the inorganic portion constitutes the layer and the organic the pillars. The products can have high surface areas (~400m2/g), with small pores (~7-8 diameter) up to mesopores (~25 diameter). The pillars can be functionalized with sulfonic acid, carboxylic acid, amino, etc. groups. Furthermore, the pillars can be further separated by small spacers which themselves carry functional groups. Thus, they can be prepared as ion exchangers, as specific complexants, catalysts and as luminescent materials. When the metal is four valent, the particles formed are nanoparticles in which insufficient Bragg reflections to solve their crystal structures are obtained. The mystery of their structure is further compounded by the fact that the pores grow without the use of templates or spacer groups and are often larger than the interlayer distances and yield type I gas sorption isotherms. This is unprecedented as the pore formation depends upon the solvent used. Therefore, we employ a variety of tools such as extended x-ray absorption fine structure and high resolution electron microscopy as well as in-situ methods to probe their structures along with the more usual infra-red, visible, nuclear magnetic resonance, and neutron scattering and gas sorption methods to characterize the pores. The research is also directed towards molecules that breathe by using flexible alkyl, polyether and polyimine pillars separated by high levels of spacer groups. Thus students learn to synthesize unusual materials and employ cutting edge spectroscopic tools as well as the latest crystal structure methodology. %%% Research in chemistry often leads to unexpected results. There exist a large number of mineral-like compounds that contain pores. These pores are of the order of 4-13 Angstroms, where one Angstrom is about a hundred-millionth of an inch. So these pores are the sizes of small molecules. These mineral-like materials are principal catalysis used in petroleum refining and many other useful reactions. Therefore, they are of great interest to chemists and chemical engineers. This project aims to produce porous materials from layers of inorganic material bonded together with organic (carbon based) pillars. Visualize a parking garage with the floor and ceiling made of inorganic minerals connected by the pillars that are carbon based. Samples with pores that range from 7 angstroms to 25 angstroms are synthesized. The pillars can be made highly reactive by attaching acid or basic groups. They can be made to conduct protons for use in fuel cell membranes and to carry out a variety of useful reactions. One such reaction converts relatively useless compounds to those useful to the pharmaceutical industry. They can also separate molecules by size and finally a variety that breathes by using flexible pillars I sbeing synthesized. They swell when taking up solvent and deflate when emptied. A large number of uses for these fascinating materials is predicted. Research on these materials provides students with special skills in synthesis and techniques of handling nano-sized particles and state of the science spectroscopic X-ray, neutron and electron microscopy methodology. A partnership with a historically African-American University augments the already high diversity (Hispanic, women, Puerto Rican) of our research group.