Physiochemical properties of mixed oxides of iron and silicon

The work presented here deals with the synthesis and characterization of silica, iron hydroxide and their mixed oxides M1 (0.25 M SiO2:0.75 M Fe(OH)3), M2 (0.50 M SiO2:0.50 M Fe(OH)3), and M3 (0.75 M SiO2:0.25 M Fe(OH)3) of various molar ratios. Fe(OH)3 was prepared by precipitation while the rest of the solids were synthesized by the sol–gel method. For the synthesis of mixed oxides, Fe(NO3)2.12H2O and Na2SiO3 were employed as precursors for Fe(OH)3 and silica respectively. The surface charge and structure of the materials were investigated by X-ray diffraction (XRD), surface area analysis (SAA), thermal analysis (TG-DTG), scanning electron microscopy (SEM), electron dispersive X-ray (EDX) analysis, Fourier transform-infrared (FT-IR) spectroscopy and the point of zero charge (PZC) was determined by the salt addition method and by measuring the ζ-potential versus pH. The results obtained from the nitrogen adsorption–desorption isotherms reveal that the sol–gel method is a suitable route for synthesizing materials of high surface area. Moreover, the values of the PZC determined by salt addition method and by electrokinetic potential are found to be close to each other.