Removal of Safranin dye from aqueous solution using magnetic mesoporous clay: Optimization study

Iron oxide/sepiolite magnetite composite (MSep) was prepared by a chemical precipitation method. The composite was characterized by using X-ray diffraction, scanning electron microscopy, Fourier transform infrared spectroscopy and specific surface area analysis. The response surface methodology (RSM) based on central composite design (CCD) was successfully applied to the optimization of the Safranin removal process. Three independent variables namely initial pH, dye ion concentration and adsorbent dosage were investigated. Analysis of variance (ANOVA) of the quadratic model suggested that the predicted values were in good agreement with experimental data. Detailed kinetic and equilibrium studies were performed for liquid phase adsorption of Safranin using MSep. The adsorption process could be well described by Langmuir isotherm and the maximum monolayer adsorption capacity was calculated as 18.48 mg g^{- 1}. The adsorption kinetics was evaluated by pseudo-first-order and pseudo-second-order models; pseudo-second-order model was found to describe the process better. The adsorption was analyzed thermodynamically and the results revealed that the adsorption process was spontaneous and endothermic.