Synthesis and optimization of a green and efficient sorbent for removal of three heavy metal ions from wastewater samples: kinetic, thermodynamic, and isotherm studies

Abstract

A novel, green, and stable sorbent (Fe3O4@SiO2@l-Cysteine functionalized magnetic graphene oxide nanocomposites) was synthesized based on a chemical procedure to remove chromium(VI), lead(II), and cadmium(II) ions from wastewater samples. The l-Cysteine functionalized magnetic graphene oxide as a sorbent component was prepared based on the formation of the covalent bonding between graphene oxide and l-Cysteine. The percentages of the sorbent components, including Fe3O4 NPs, SiO2, and C-FGO were optimized using a D-optimal mixture design to enhance the sorbent stability, selectivity, and affinity toward the heavy metal ions. Besides, the critical factors on the heavy metal ion adsorption were investigated and optimized by a two-level full factorial central composite design. Electrostatic attraction is responsible for the adsorption of these ions on the sorbent, which is highly dependent on pH value. The kinetic study shows that the adsorption of these metal ions onto the sorbent follows the pseudo-second-order rate. The experimental results were investigated using the Freundlich and Langmuir models to determine the isotherm model, indicating the Freundlich isotherm model can well describe the adsorption procedure on the sorbent. The maximum adsorption capacity of 476.19, 526.32, and 588.23 mg g−1 was calculated for the Cr(VI), Pb(II), and Cd(II) ions with favorable adsorption and high affinity, respectively. The study of thermodynamic parameters indicates that the adsorption of these ions onto the sorbent is endothermic and chemical in nature. Moreover, the adsorption process is spontaneous in the temperature range of 278–328 K for removing these heavy metal ions. The obtained results confirm that the proposed sorbent is very suitable for the removal of the Cr(VI), Pb(II), and Cd(II) ions from electroplating wastewater samples with many advantages such as high efficiency, environment-friendly, low cost, and short absorption time.