▎ 摘　　要

Water and ions in the vicinity of grapheme oxide (GO) sheet has achieved much interest recently because of its great potential applications in building grapheme nanocomposites. In this study, molecular dynamics was utilized to study the structural, dynamical and interfacial behavior of calcium and sulfate ions in the vicinity of GO sheet. To better understand the effects of surface properties on the behavior of ions, four surface types were modeled, including graphene sheet (G), GO with carboxylate (GO-COO-, deprotonated carboxyl), GO with carboxyl (GO-COOH) and GO with hydroxyl (GO-OH). We found that the presence of oxygen-containing functional groups restrained the layered packing of water molecules, reduced the water density and changed the dipolar angle distribution in the vicinity of graphene sheet. The OH bond of water molecules preferred to orientate toward the graphene sheet due to the surface hydrophilicity. With increasing polarity of the functional groups, more surface water molecules donated their H to the oxygen sites provided by the -COO-, -COOH and -C-OH. Moreover, the adsorption properties of calcium and sulfate ions were greatly depended on the polarity of GO surface. The adsorption ratios of ions were arranged in the following order: GO-COO- > GO-COOH > G-OH > G. The GO sheets immobilized the calcium ions by forming the Ca-O ionic bond with the functional oxygen atoms. The strength of Ca-O interaction was increased with the increasing polarity of functional groups, which was characterized by the time correlation function. The adsorbed surface calcium ions can further immobilize the sulfate ions by forming Ca-SO4 ionic pair. Comparing with the water and ions near the graphene sheet, the diffusivity of solution on the GO-COO- surface decreased by 73%. The dramactical reduction of the mobility was attributed to longer resident time of ions on the GO surface and longer hydration time of the ions. Hopefully, this study can provide valuable insights on the functional GO sheet design. This study can contribute to the molecular understanding of the immobilization mechanism of GO sheets.