Preparation and characterization of SiO2@C nanocomposites from rice husk for removal of heavy metals from aqueous solution

This study focused on preparation and characterization of two activated SiO2@C nanocomposites from rice-husk waste material through a controlled method. Both of them contain different percentages of silica and carbon. After chemical and thermal activations of the prepared composites, high energy ball milling was utilized to prepare nano powders. The percent of silica in the prepared nanocomposites was determined by HF method. Moreover, their chemical compositions were determined by XRF technique. The prepared materials were also examined by x-ray diffraction technique, FT-Infrared, scanning electron microscope, high resolution transmission electron microscope, Zeta Sizer, and Surface-Area-Analyzer. The prepared SiO2@C nanocomposite that contains higher silica percent was selected as adsorbent for removing of Cu, Zn and Pb from aqueous solutions. The effects of pH and contact time on the adsorption process were also studied. The results showed that SiO2@C nanocomposites with different percentages of silica and carbon were prepared successfully by the proposed method. The sample that contains higher silica, exhibited smaller particle size (20-50 nm), higher specific surface area (262.39 m(2)g(-1)) and higher negative zeta potential (-71 mV). On the other hand, the sample that contains lower silica exhibited higher particle size (20-70 nm), lower specific surface area (42.95 m(2)g(-1)), and lower zeta potential (-6 mV). The adsorption efficiencies of prepared SiO2@C nanocomposites at pH 6 for removing of Cu, Zn, and Pb from aqueous solutions were 96.5, 97, 9 and 88.66%, respectively. The kinetic study revealed that the adsorption process proceeded by pseudo-second order reaction.