Synthesis and Characterization of Fe3O4@n-SiO2 Nanoparticles from an Agrowaste Material and Its Application for the Removal of Cr(VI) from Aqueous Solutions

The present study dealswith the synthesis and subsequent application of Fe3O4@n-SiO2 nanoparticles for the removal of Cr(VI) from aqueous solutions. Rice husk, an agrowaste material, was used as a precursor for the synthesis of nanoparticles of silica. Synthesized nanoparticles were characterized by XRD and SEM to investigate their specific characteristics. Fe3O4@n-SiO2 nanoparticles were used as adsorbent for the removal of Cr(VI) from their aqueous solutions. The effects of various important parameters, such as initial Cr(VI) concentration, adsorbent dose, temperature, and pH, on the removal of Cr(VI) were analyzed and studied. A pH of 2.0 was found to be optimum for the higher removal of Cr(VI) ions. It was observed that removal (%) decreased by increasing initial Cr(VI) concentration from 1.36x10(-2) to 2.4x10(-2) M. The process of removal was found to be endothermic, and the removal increased with the rise in temperature from 25 to 45 degrees C. The kinetic data was better fitted in pseudo-second-order model in comparison to pseudo-first-order model. Langmuir and Freundlich adsorption capacities were determined and found to be 3.78 and 1.89mg/g, respectively, at optimum conditions. The values of Delta G(0) were found to be negative at all temperatures, which confirm the feasibility of the process, while a positive value of Delta H-0 indicates the endothermic nature of the adsorption process. The present study revealed that Fe3O4@n-SiO2 nanoparticles can be used as an alternate for the costly adsorbents, and the outcome of this study may be helpful in designing treatment plants for treatment of Cr(VI)-rich effluents.