Selective and ppb level removal of Hg(ii) from water: synergistic role of graphene oxide and SnS2

Abstract

Mercury (Hg) contamination can cause serious health issues like brain damage, skin diseases and birth defects. An upper limit of 2 ppb for Hg in drinking water has been allowed by the United States Environmental Protection Agency (EPA). Thus, the selective removal of Hg below 2 ppb is an important challenge in the treatment of wastewater. Herein, we report the tremendous selectivity and ppb level removal of Hg^(II) from water by using a graphene oxide and tin(IV) disulfide (SnS₂) composite (GO@SnS₂). The material can remove 99.1% of Hg^(II) from a concoction of Na^(I), K^(I), Cs^(I), Rb^(I), Ca^(II), Mg^(II), Co^(II), Cu^(II), Ni^(II), Zn^(II), Pb^(II), Cd^(II), Mn^(II), Fe^(III) and As^(III) with a high separation factor of the order 10² to 10³. We have achieved a capacity of 342.02 ± 8.02 mg g⁻¹ with a distribution coefficient (K_d) value of 8.68 × 10⁵ mL g⁻¹ and GO@SnS₂ is stable in the pH range of 0.5–11. The material can remove Hg^(II) from even 0.3 ppb Hg^(II) contaminated water. Furthermore, the mechanism behind the synergistic Hg^(II) adsorption is due to the interaction between Hg^(II) and –COOH of GO and the soft Lewis acid-base chemistry between S²⁻ of SnS₂ and Hg^(II). For convenient application, we have designed a tea bag filled with GO@SnS₂ powder which can capture 99.9% of Hg^(II) from contaminated water economically.