Synthesis, Characterization, and Adsorption Properties of a Graphene Composite Sand (GCS) and Its Application in Remediation of Hg(II) Ions

In this study, graphene-based adsorbent was successfully prepared following a thermal treatment method. The prepared material, named as graphene-coated sand (GCS), was used as an adsorbent for the removal of Hg(II) ions from aqueous solutions. Structure, composition, and morphology of the GCS were characterized by Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), X-ray diffractometer (XRD), Raman spectroscopy, electron diffraction (ED) measurements, energy dispersive X-ray spectroscopy (EDX), surface area measurements, particle size, and zeta potential measurements, respectively. A batch adsorption method was used to assess the ability of GCS towards removal of Hg(II) ions from aqueous solutions. The results of batch studies revealed that the GCS required a pH value 6.0, contact time 120 min, and adsorbent dose of 200 mg to attain adsorption equilibrium. Langmuir, Freundlich, Temkin, and D-R adsorption isotherm models were employed to evaluate the isotherm constants and other parameters related to the adsorption process. The Hg(II) ions uptake by the GCS was found to follow Freundlich isotherm model with R ² value of 0.97695, under optimized conditions and at 40 °C with a maximum adsorption capacity of 299.40 mg/g. The adsorption process followed the second-order kinetic path. The thermodynamic parameters such as ΔH°, ΔS°, and ΔG° were also calculated which suggested that the adsorption processes of Hg(II) ions onto the GCS was endothermic and entropy favored. The values of ΔG° at 283, 303, and 313 K were − 1.10, − 0.025, and − 4.55 kJ, respectively, and ΔH°, ΔS° were calculated to be 26.60 kJ mol⁻¹ and ΔS° 1.35 J mol⁻¹ K⁻¹, respectively. The obtained results revealed that the prepared materials could be effectively and economically beneficial.