Single-Site Copper by Incorporation in Ambient Pressure Dried Silica Aerogel and Xerogel Systems: An X-ray Absorption Spectroscopy Study

Abstract

Copper incorporated silica aerogels and xerogels were prepared by adding the metal during the sol–gel stage and applying the ambient pressure drying (APD) method. The materials were characterized using inductively coupled mass spectrometry (ICP-MS), the Brunauer–Emmet–Teller (BET) method, X-ray diffraction (XRD), thermograviometric analysis–differential scanning calorimetry (TGA–DSC), and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The introduction of copper led to changes in the aerogel architecture, seen by considerable expansion of average pore size, while maintaining a hydrophobic nature. The valence state and local chemical environment of copper was studied by X-ray absorption spectroscopy (XAS) before and after annealing to evaluate the interaction with the gel systems. X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectra showed that copper was divalent and present in a tetragonally distorted environment in both a...