Effective removal of mercury(II) from aqueous solutions by chemically modified graphene oxide nanosheets

Improved graphene oxide (IGO) is chemically modified with chloroacetic acid and ethylene diamine to form carboxylated improved graphene oxide (IGO-COOH), aminated improved graphene oxide (IGO-NH2), and imino-diacetic acid improved graphene oxide (Imino-IGO). These novel solid phase adsorbents are utilized to adsorb mercury ions from aqueous solutions. The IGO, IGO-COOH, IGO-NH2, and Imino-IGO adsorbents are fully characterized by FT-IR, UV-Vis, XPS, XRD, SEM, TEM, and Raman spectroscopy. Batch adsorption experiments are conducted to evaluate the adsorption of Hg(II) ions by IGO, IGO-COOH, and Imino-IGO under different conditions. The effects of pH, adsorbent dose, temperature, contact time, and initial concentrations on the removal of Hg(II) ions are studied. The results reveal that, at pH 5, the maximum adsorption capacity for the removal of mercury (mg Hg/g adsorbent) follows the order: Imino-IGO (230.0) > IGO-COOH (122.0)> IGO (24.0 mg/g), in which mercury ions' complexation is highly dependent on the concentrations of (NH), and (OH) containing functional groups in the adsorbent. The IGO-COOH, and Imino-IGO adsorbents show 100% removal of Hg(II) at concentrations as low as 10 ppm. The equilibrium isotherms for evaluating the mechanism of adsorption process show good fits to the Langmuir model. The Imino-IGO could retain more than 93.0% of its original adsorption capacity after six adsorption-desorption cycles. All data confirmed that the Imino-IGO is a promising material to extract Hg (II) from wastewater. (C) 2018 Production and hosting by Elsevier B.V. on behalf of King Saud University.