Adsorptive potential of ZnO/SiO2 nanorods prepared via the sol-gel method for the removal of Pb (II) and Cd (II) from petroleum refinery wastewater.

Abstract

BACKGROUND: The adsorption technique is considered one of the most effective and economical methods for the removal of heavy metals, due to its excellent advantages of low cost, high efficiency and easy handling. This research looks into the possibility of using ZnO/SiO2 nanorods to remove Cd(II) and Pb(II) from refinery wastewater and their reusability. RESULTS: ZnO/SiO2 nanorods were synthesized via the sol–gel method. The analysis of ZnO/SiO2 shows the formation of a rodlike structure and surface area of 33 m2 g−1 compared with the 0.3 and 8.620 m2 g−1 for ZnO and SiO2, respectively. Effects of adsorption contact time, adsorbent dosage and temperature were examined via batch adsorption. The result indicates that the ZnO/SiO2 rods exhibited higher adsorption removal efficiency of 85.06% and 84.12% for Pb(II) and Cd(II), respectively, compared to Pb(II) (80.00% and 74.25%) and Cd(II) (76.48% and 70.99%) using ZnO and SiO2 nanoparticles. A thermodynamic study indicates that the adsorption process was endothermic. The data from the adsorption isotherm were well fitted to the Langmuir isotherm. The pseudo-second-order kinetic model best described the adsorption process. An adsorption–desorption study indicated the adsorption to be concentration-dependent and maintained up to 80.65% and 76.90% for Pb(II) and Cd(II) after the fourth regeneration cycle. CONCLUSIONS: These findings demonstrated that ZnO/SiO2 nanorods are a better nanoadsorbent for the removal of Pb(II) and Cd(II) than ZnO and SiO2 nanoparticles due to their high adsorptive potential and stability.