THE SUCCESSFUL INCORPORATION OF COPPER IN THE WELL-STRUCTURED SILICATE KANEMITE

Copper atoms were chemically inserted into sodium kanemite structures in different Si/Cu molar ratios under hydrothermal conditions, which new synthetic strategy enabled the creation of Bronsted acidity after metal insertion in the pristine siliceous framework. The precursor and the chemically modified silicates from X-ray powder diffraction for sodium and copper kanemites demonstrated that only small changes were observed after silicon atoms were isomorphically substituted by copper in the Si/Cu 50, 100 and 200 molar ratios. 29Si HPDEC NMR confirmed that the silicon atom located in tetrahedral positions is substituted to copper atoms in the original kanemite framework. The sodium kanemite presented only one peak assigned to Q3 at -97.2 ppm, but for copper inserted two peaks with chemical shifts at -101.9 ppm, belonging to the species Q3 and the second at – 110 ppm appeared after isomorphic substitution. 23Na-NMR spectra showed that isomorphic substitution of some silicon per copper atoms caused a partial migration of sodium atoms from the site S1 to S2 and S3 sites. However, the S3 site was only observed for copper derivatives with Si/Cu ratios of 50. The results from 13C-NMR in the solid state are in agreement with a successful intercalation, with SEM images for sodium and copper kanemites showing irregular crystallites in plate morphology. X-ray photoelectron spectroscopy revealed the isomorphic substitution of silicon by copper in the inorganic skeleton, which Si (2p) spectra, demonstrating a decrease of the binding energy and the peak area after incorporation. For copper derivative two peaks are assigned to Cu 2p3/2 and Cu 2p1/2 with binding energy of 931.56 and 951.36 eV, respectively.