Equilibrium, kinetic and thermodynamic study of diazinon adsorption from water by clay/GO/Fe3O4: Modeling and optimization based on response surface methodology and artificial neural network

Abstract

In this study, a new magnetic composite consisted of clay/graphene oxide/Fe3O4 was used for elimination of Diazinon (pesticide) from aqueous solutions. Analysis of the structural properties and surface morphology of the composite showed that the composite was well-synthesized and had a crystalline and multilayere structure. Magnetic saturation value was determined to be 39.9 emu/g. Its pHZPC value and active surface area was 7.1 and 185.7m2/g, respectively.In order to investigate the effects of pH, temperature, contact time, initial concentration of Diazinon and composite dosage on adsorption efficiency and modeling adsorption process, the response surface methodology-central composite design (RSM-CCD) and artificial neural network methods (ANN) were used. The results obtained through analysis using response surface methodology showed that the maximum amount of adsorption was 98.79% at 25.91 °C, while pH, initial concentration, contact time, and adsorbent dose were 6.9, 1.2 ppm, 24.6 min, and 1.1 g/L, respectively. Comparison between results obtained from CCD modeling and artificial neural network proved that both methods had high ability to predict the adsorption process but the CCD method had higher coefficient of determination and lower error. The equilibrium and kinetic study of the process showed that the Langmuir-Freundlich isotherm model, pseudo-second-order, and Elovich kinetics are all suitable for expressing the adsorption process. In addition, the adsorption mechanism obeyed double-exponential model that combines external and internal diffusions.Results of thermodynamic study suggested that the Diazinon adsorption on clay/GO/Fe3O4 was a spontaneous and exothermic process. The results of the equilibrium process study revealed that the adsorption process was physical and desirable. Therefore, the adsorption-desorption process was performed which showed that the composite was reusable up to 20 cycles.