Inhibitory effect of hydrogen ion on the copper ions separation from acid solution across graphene oxide membranes.

Graphical abstract Highlights • Permeation across GO membranes for mixed solution was concerned. • Concentration and recovery of Cu2+ with GO membranes was investigated. • Inhibitory effect of hydrogen ion on the transport of copper ions was demonstrated. Abstract Graphene-based materials have many unique features including atomic thickness and well-defined nanochannels, making their great properties for filtration and separation. The removal of low-level heavy-metal ions (e.g. Cu2+) by graphene oxide sheets has been discussed to ascertain their adsorption capacity, but separation and recovery of massive copper ions with graphene oxide (GO) membranes remain to be further studied. Besides, the permeation across GO membranes involving different ions in the very same solution is rarely investigated. Hence, the permeation properties of GO membranes concerning single and mixed solutions of acid and salt were examined in this study, and inhibitory effect of hydrogen ion on the copper ions transport was observed. Expectedly, GO membranes perform obvious permeation rate differences to acid (i.e. H 2 SO 4 , HCl) and copper salts (i.e. CuSO 4 , CuCl 2) when they are tested individually. The diffusion coefficient of H+ is 16 times larger than that of Cu2+ when the anion is SO 4 2−, and twice in the case of Cl−. The differences are mainly determined by physical screening of the capillary channels in the film for ions with different hydration radii and the rapid migration of hydrogen ions in solution. Furthermore, Experiments were carried out using mixed solution of acid and copper salt with the same anion and concentration. It was shown that the existence of H+, whose own transmission decreased by only 1.6 times, reduced the penetration of Cu2+ by an order of magnitude in the same time interval. We supposed this remarkable inhibitory effect is associated with shrink of interlayer spacing and competitive adsorption of H+ against Cu2+ on the surface of GO membranes in mixed solution. The properties of GO membranes show great application prospects in separation and wastewater reuse. [ABSTRACT FROM AUTHOR]