Enhanced adsorptive removal of diclofenac sodium from aqueous solution by bentonite-supported nanoscale zero-valent iron

Abstract

Nano zero-valent iron-bentonite (B-nZVI) is an excellent composite for treating recalcitrant organic pollutants. In this study, B-nZVI was prepared via NaBH4 reduction method and characterized using different instruments including X-ray diffractometer (XRD), Fourier-transform infrared spectrometry (FTIR), Field emission scanning electron microscope (SEM), Transmission electron microscope (TEM), and UV–Vis spectroscopy. Also, the efficiency of B-nZVI as an adsorbent to remove diclofenac sodium (DCF) from aqueous solution was investigated, and compared with activated carbon (AC) under different experimental conditions such as pH, adsorbent dose, DCF initial concentration, temperature, and contact time. The B-nZVI has successfully removed a high percentage of DCF from aqueous solution ((Formula presented.) 80%) within 50 min, 25 °C, and pH = 3. The maximum adsorption capacity of B-nZVI at equilibrium was 140.8 mg g−1 compared to 107.5 mg g−1 via AC. Furthermore, it was found that the DCF adsorption best fitted the Langmuir isotherm and pseudo-second-order kinetic models (R 2 > 0.987). Also, the thermodynamic parameters of adsorption were estimated and the average values showed that the adsorption of DCF via B-nZVI is an endothermic process (Formula presented.) and spontaneous with a positive value of entropy (Formula presented.) at 25 °C. The point of zero charge (PZC) was determined (7.0 ± 0.1) using a salt addition method. Finally, column filtration was demonstrated using a mixture of sand and B-nZVI composite, which showed a significant advantage in comparison with that activated carbon/sand mixture.