Synthesis and characterization of cerium substituted hematite by sol-gel method

摘要

Fine particles of cerium substituted hematite with different compositions were prepared by the sol-gel method from the aqueous solution of their corresponding metal salts. Mixed hydroxides of Fe~(3+) and Ce~(4+) were obtained by reacting aqueous NH_3 with the aqueous solution of FeCl_3 and Ce(NH_3)_2(NO_3)_6 at pH 2.5-3.0) and they were heat treated at different temperatures between 400 and 1200 deg C in air for 2 h to get the mixed oxide product. Thermal analysis and X-ray diffraction studies revealed the coexistence of Fe_2O_3 and CeO_2 phase separately up to 900 deg C, and covalent interaction between them above 1000 deg C, which was evidenced by the shifting of the XRD peaks. Unit cell parameters and the cell volumes (V) of the samples derived between 1000 and 1200 deg C were found to be in the range a = 5.045-5.048+-0.007 A, c= 13.774-13.815 + 0.041 A and V=303.608-304.874 A~3 respectively. It was observed that both the lattice parameters and the cell volumes were higher than that of the pure alpha-Fe_2O_3 (a=5.036 A, c = 13.749 A, V=301.976 A~3) system. The expansion of lattice parameters further supported the incorporation of the large Ce~(4+) ion into the alpha-Fe_2O_3 matrix. The lattice parameter increased with increasing Ce~(4+) ion loading. FESEM studies showed the growth of the particles with increasing temperature though it was suppressed due to the presence of Ce~(4+) ions as compared to the pure system.