Adsorption and determination of Cr(VI) in environmental samples using triazine-modified Fe₃O₄ nanoparticles: kinetics and equilibrium modeling

A facile and highly sensitive adsorbent for the determination of Cr(VI) ions has been developed for the first time. The sorbent was based on triazine-functionalized Fe₃O₄ nanoparticles and was prepared by direct silylation of magnetic nanoparticles with 3-aminopropyltriethoxysilane-2,4-bis(3,5-dimethylpyrazol)-triazine and was characterized by infrared spectroscopy, transmission electron microscopy, X-ray powder diffraction, and electron-dispersive X-ray analyses. The sorbent was applied to adsorption, preconcentration, and determination of chromate anions by the solid-phase extraction method. The effects of various factors including the pH of the solution, concentration of the adsorbate, adsorption time, and temperature on removal of Cr(VI) ions were optimized. The Cr(VI) removal efficiency of 85.8 % was achieved at the optimum initial pH of 3. The maximum adsorption capacity was 170.68 mg g⁻¹ at an initial concentration of 75.0 mg L⁻¹ and adsorbent dosage of 0.1 g L⁻¹. The equilibrium data were analyzed using the Langmuir and Freundlich isotherm models by nonlinear regression analysis. The results obtained from adsorption isotherm indicated that these data can be better fitted to the Langmuir equation than the Freundlich equation. The kinetic analysis revealed that the adsorption process was successfully fitted with the pseudo-second-order kinetic model. The thermodynamic investigation demonstrated that the adsorption process is endothermic, spontaneous, and feasible in nature. Furthermore, the new sorbent was successfully applied for the determination of Cr(VI) anions in a few environmental samples using a continuous method.