ESR Study of the Impregnation Process of Silica Gels with CU(NO 3 ) 2 · 6H 2 O

The use of electron spin resonance in the study of the different steps in the impregnation process of hydrated Cu(NO 3 ) 2 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.