Scalable synthesis of an environmentally benign graphene-sand based organic-inorganic hybrid for sulfide removal from aqueous solution: an insight into the mechanism

In this study, a graphene-sand hybrid (GSH) was successfully synthesized from locally available desert sand and sugar using a green chemistry approach and used as an adsorbent for the removal of dissolved sulfides from aqueous solutions. The structure, composition, and morphology of the new GSH adsorbent were characterized in detail by Raman spectroscopy, scanning electron microscopy equipped with energy dispersive X-ray spectroscopy, zeta potential and Fourier-transform infrared spectroscopy. Batch experiments were conducted to evaluate the effect of several process parameters such as contact time, pH, adsorbent dosage and ionic strength on the removal of sulfide using the GSH adsorbent. These results indicated that GSH exhibited good sulfide removal capacity from aqueous solutions with a maximum uptake capacity of 370 mg g⁻¹, so far the highest value reported in the literature. Langmuir and pseudo-second order models well fitted the equilibrium and kinetic data, respectively. Comparison of linear and non-linear regression methods for the adsorption isotherms revealed that a non-linear model was a better way to obtain the isotherm parameters. The spectroscopic and microscopic and thermogravimetric analysis demonstrated that chemical interaction with oxygen rich functional groups played a major role in adsorption, resulting in the formation of elemental sulfur and sulfates as byproducts. The obtained results illustrated that the prepared graphenic material is an effective, environmentally friendly and economically viable adsorbent for removing toxic and malodorous sulfide ions from aqueous solutions.