Comparison of core-shell and hollow Fe3O4/silica/chitosan magnetic nanoparticles in vanadium removal: experimental design and optimization analysis

In this work, iron oxide (Fe3O4), silica-coated Fe3O4 (Fe3O4@SiO2), chitosan-coated Fe3O4 (Fe3O4@CT), chitosan/silica-coated Fe3O4 (Fe3O4@SiO2@CT) core-shell magnetic nanoparticles and hollow Fe3O4/silica/chitosan (Hollow Fe3O4@SiO2@CT) magnetic nanoparticle were prepared and compared for vanadium (V) uptake from the aqueous media. The successful synthesis of magnetic nanoparticles (MNPs) was characterized by different methods. The results obtained indicate that the Hollow Fe3O4@SiO2@CT has a further decontamination potential than that of the other synthesized MNPs. Central composite design (CCD) was employed for experimental design according to response surface methodology (RSM) analysis, the model of V adsorption proved to be highly significant with very low probability value (< 0.0001) and high determination coefficient (R-2 > 0.9998). Based on the RSM optimization, the optimal operational conditions were 50 (mg/L) V concentration, 15 min reaction time, 0.01 g adsorbent dose, 160 rpm agitation speed, pH 4.5 and temperature 298 K for having 80 (mg/g) of V adsorption capacity. The Langmuir isotherm model exhibited a much better fitting for the adsorption data than the Harkins-Jura, Jovanovic, Temkin, Dubinin-Radushkevick and Freundlich isotherm models, revealing that the V uptake onto Hollow Fe3O4@SiO2@CT is a monolayer uptake. Five different kinetic models were studied and found that pseudo-second-order kinetic model was recommended to explain the rate of adsorption. Free energy change, Entropy, Enthalpy, and reflected feasible spontaneous and exothermic character of process. The Hollow MNPs showed preferential V ions adsorption with the existence of competing ions. The good recyclability and adsorption capacity made sure that the Hollow Fe3O4@SiO2@CT has great potential in treating V species pollution in water. Also, this work dealt with an effective method to spent Hollow Fe3O4@SiO2@CT after the removal of V ions for efficient adsorption of lead from aqueous media.