Fig. 3.

Ion uptake in the 2D channels. (A) Uptake by the MoS₂-COOH membranes in the single ion solution (~4 mM). (B and C) Uptake by the pristine MoS₂ membrane and the MoS₂-COOH membrane in the mixed ions solution, respectively. Ion labels in B and C from left to right are K⁺/Na⁺/Li⁺/Ba²⁺/Pb²⁺/Ca²⁺/Cd²⁺/Mn²⁺/Mg²⁺/Zn²⁺/Co²⁺/Cu²⁺/Ni²⁺/La³⁺/Y³⁺/Yb³⁺/Al³⁺, which are the same as those in Fig. 2A. (D and E) HAADF-STEM image of the MoS₂-COOH membrane and the MoS₂ membrane after ion uptake in the mixture solution, respectively. Blue circles represent the adsorbed single-site cations. Mixture: ~ 4 mM, Cl⁻/NO₃⁻ (~96 mM:44 mM) anions, pH ~ 4.13.