Comparison of MnO2 modified and unmodified magnetic Fe3O4 nanoparticle adsorbents and their potential to remove iron and manganese from aqueous media

Abstract

In this work, several magnetic nanoparticles (Fe3O4) with silica (SiO2) and Mg–Fe–CO32− layered double hydroxide (LDH) as the shell was prepared then modified with manganese dioxide (MnO2) to the removal of iron (Fe2+) and manganese (Mn2+) ions and compared with each other. Results of adsorption experiments showed that magnetic nanoparticles modified by MnO2 are very effective in the adsorption of Fe2+ and Mn2+ from aqueous solutions. The textural properties of the adsorbents were done by FT-IR, TGA, TEM, XRD, FESEM, BET, EDX, and VSM. The central composite design (CCD) defined under response surface methodology (RSM) was employed to optimize and interaction effects of variables on removal efficiency of Fe2+ and Mn2+ with Fe3O4@LDH@MnO2. The optimum adsorption conditions were determined at the pH of 6.0, dose of 0.01 g, contact time 30 min, initial Fe2+concentration of 100 mg/L and initial Mn2+ concentration of 80 mg/L. The maximum adsorption capacity of Fe2+ and Mn2+ at optimum conditions were found to be 238.09 and 81.30 mg/g respectively. The experimental equilibrium data were fitted better by using the Langmuir model than the Freundlich or the Temkin model, suggesting that the adsorption feature be monolayer. The pseudo-first order, pseudo-second order, Elovich, intra-particle diffusion, and particle diffusion kinetic models were used to describe the obtained data. The pseudo-second-order model was found to describe adequately the experimental kinetic data. Thermodynamic parameters studies indicated that heavy metals adsorption onto Fe3O4@LDH@MnO2 is a spontaneous and endothermic. Regeneration process was performed with NaCl and proven it was a suitable desorbing reagent in the discharge of Fe2+ and Mn2+. The reusability of prepared magnetic Fe3O4 nano particle was investigated up to six cycles. The adsorption method was utilized for the adsorptive removal of Fe2+ and Mn2+ in two water samples.