The composite materials Fe2O3–SiO2 were prepared by two procedures. Thefirst (I) consisted of the simultaneous hydrolysis of Fe3þ and −SIO32 ions followed by the formation of a coprecipitated non-structured composite material. For this purpose,SiO2nH2O was dissolved in 5 M NaOH, then the solution, under vigorous stirring, was slowly added to FeCl36H2O dissolved in 5%HCl at room temperature. Adding a relevant volume of HCl maintained the acidity at a predetermined constant level. The precipitate was centrifuged, washed with water and acetone andthen air dried for 1h at 105°C (sp. I-1–I-11 in Table 1)
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