Synthesis and investigation of SBA-15 lined with ethylenediamine to create charge-transfer complexes

Abstract

The purpose of this research was a study of selected physical properties of a class of absorbents with large specific surface area (some of them including self-assembled monolayers on mesoporous supports). A polycrystalline powder of silica-based material with crystalline honeycomb structure (of SBA-15 type) was synthesized. The primary material was calcined and then lined with N-[3-(tri-methoxy-silyl)propyl]ethylenediamine to coordinate to cations Ba2+, Sn2+, Fe2+ or Cu2+. All six specimens’ properties were investigated using X-ray diffraction, X-ray photoelectron spectroscopy and nitrogen adsorption techniques. The unit-cell constant being edge-length of the hexagonal frame was determined for each sample and occurred the largest one for the pure silica material, smaller for the ethylenediamine-covered silica support and the smallest one (and approximately the same) for immobilized specimens. The shrinkage of internal nanotubes resulted from subsequent treatment of the basic siliceous skeleton with N-[3-(tri-methoxy-silyl)propyl]ethylenediamine and creating the charge-transfer complexes with cations Ba2+, Sn2+, Fe2+ or Cu2+. The specific surface areas of mesopores and whole crystallites, together with the volume of mesopores, were determined from low-temperature N2-physisorption isotherms. A mathematical model of crystalline microstructure explaining the sizes and shapes of crystalline grains in relation to adsorption features was proposed and successfully confronted with the results following experimental data. The roughness of the surface is different from one that occurred to be necessary to explain the experimental characteristics quantitatively. The estimated silicon-organic layer thickness was close to the corresponding molecule length for hybrid specimens.