Preparation of Fe-Si mixed oxide surface and its application in the removal of toxics from water

Abstract

Mixed oxide of iron-silicon adsorbent was synthesized chemically by a sol-gel method. Fe-Si binary oxide adsorbents were prepared by varying the concentration of Fe(III) while the concentration of Na2CO3 and Na2SiO3 were kept constant and also by varying the concentration of Na2CO3 while the concentration of Fe(III) and Na2SiO3 was chosen to be constant. In this study Fe/Si molar ratio and Na2CO3 concentration were selected to be 3:1 and 0.5 M respectively. The mixed oxide thus obtained and characterized by a wide range of EDX, XRD, SEM, UV-Visible and IR spectroscopy techniques. Elemental analysis exhibited the presence of iron, silicon and oxygen elements in the mixed oxide with a composition of Fe1.47 Si0.53 O3. The results showed that the iron-silicon mixed oxide were successfully synthesized. The IR spectra yielded the characteristics signals of silicon oxide (470, 1099 cm-1), iron oxide (457, 545, 569 cm-1) and iron−silicon mixed oxide (962 cm-1) and confirmed the presence of the components in each substrate. The average crystallite size was calculated from the XRD data to be approximately 18 nm. The specific surface area of this binary oxide was found to be 46.79 m2g-1. The point zero charge of this surface was observed to be at pH 8.8. Surface capacity of the mixed metal oxide (MMO) were studied and thus it was used as an adsorbent for the removal of organic dyestuff from water. In that case, organic cationic (methylene blue abbreviated as MB) and anionic (orange green abbreviated as OG) dyes were attempted to be adsorbed on the MMO surface. The adsorption data showed that both the MB and OG dyes can be adsorbed on the mixed oxide surface. But the extent of MB adsorption is much more higher than OG, suggesting the present MMO an attractive adsorbent for the removal of the cationic dye MB. The adsorption property of mixed oxide for removal of organic cationic MB dye was investigated with various parameters including effect of pH, contact time, initial dye concentration, temperature and dose of mixed oxide. The adsorbent was tested for removal of dyes from their aqueous solution. The maximum adsorption capacity of binary mixed (Fe-Si) oxide for MB dye was found at pH 7. Kinetic study showed that MB followed pseudo-second-order kinetics equation for MB. Adsorption isotherm was interpreted by Langmuir equation from the obtained data. This study clearly demonstrated that dye can be removed efficiently by the Fe-Si mixed oxide surface.