ESR Study of the Impregnation Process of Silica Gels with CU(NO3 )2 · 6H2O

The use of electron spin resonance in the study of the different steps in the impregnation process of hydrated Cu(NO onto silica gels with pore size of 20, 50 and 100 nm is described. The desolvation step with concomitant beginning of the salt decomposition step occurred at ~100 °C in silica with pores of 50 and 100 nm while a temperature higher than 200 °C were necessary for 20 nm pores. In the range 300 to 500 °C the decomposition step was completed and the adsorption of Cu(II) on ≡ SiO surface sites started. Well-defined localization was completed after heating at 650 °C. The bond features of the surface adsorbed Cu(II) species are also described.