Using iron–oxide nanoparticles synthesized at varying temperatures to remove Cr(VI): Characterization, adsorption mechanism, and optimization study

Abstract

Hexavalent Chromium [Cr(VI)] is a toxic heavy metal and a notable health hazard. Thus, proper remediation method must be employed for its removal from contaminated water. Iron–oxide nanoparticles have been employed multiple times as an adsorbent for the removal of Cr(VI); however, the adsorption capacity obtained was not sufficiently high.Therefore, this study attempts to synthesize iron–oxide nanoparticles at different temperatures of 25̊ °C, 60̊ °C, and 90̊ °C, respectively and improve both its adsorption efficiency and capacity substantially. Firstly, the iron–oxide nanoparticles were synthesized by the co–precipitation method and investigations on the surface morphologies, sizes, chemical compositions and magnetic properties were carried out by several characterization methods. Next, iron–oxide nanoparticles were used as adsorbents in batch equilibrium studies to effectively remove Cr(VI). A number of parameters, including dosage and contact time, were examined in order to determine how they affected the adsorption process. Using the iron–oxide nanoparticles synthesised at 25 °C (room temperature), 60 °C, and 90 °C, the optimal removal efficiencies recorded were 81.78%, 82.29%, and 83.82% for a Cr(VI) content of 10 mg/L, respectively. Subsequent optimization experiments were conducted with the Box–Behnken Design approach (BBD) in order to emphasise the interactions among the parameters. The adsorption efficiency was used as the response variable in the development of a 2^nd–order quadratic equation, and the proposed model's feasibility was assessed using an ANOVA test. Several adsorption isotherm and kinetic models were analysed and the most appropriate model to define the adsorption mechanism and the rate–limiting steps were determined.