Synthesis and characterization of copper containing mesoporous silicas

Abstract

A series of copper containing mesoporous silicas has been prepared at room temperature using tetramethylorthosilicate as the source of silicon, a quaternary ammonium chloride salt as organic template surfactant and copper complexes obtained from organofunctional silicon molecules as ligands. Using this synthetic route, it was possible to prepare mesoporous materials containing up to 4.7 wt% copper. The structure and the sorption properties of the obtained materials have been studied by X-ray diffraction, Fourier-transform reflectance IR spectroscopy, transmission electron microscopy and surface area measurements. All experimental data reveal that calcined products containing up to 2.4 wt% copper retain the basic structural characteristics of MCM-41 materials, while higher copper loading leads to progressive destruction of hexagonal structure. Electron paramagnetic resonance was used to study the symmetry and environment of Cu(II) species in the silicate framework of the as synthesized and calcined materials, as well as the accessibility of these centers to polar adsorbed molecules, such as pyridine. The spectra of calcined materials indicate a distorted octahedral geometry for the Cu(II) centers which were easily accessible by pyridine molecules. Cyclic voltammetry showed that calcined copper containing mesoporous samples exhibit a marked electroactivity indicating that most of the copper centers are distributed on the mesoporous surfaces.