Phosphorylation Overcomes the Chaotropic Effect of Li ⁺ in Two-Dimensional Confined Channels and Reverses Li ⁺ /Mg ²⁺ Permeability

Poorly solvated low-charge-density Li + exhibits a chaotropic effect in 2D confined channels: strong interfacial affinity hinders its transport. Conversely, high-charge-density Mg 2+ resides between water layers, facing less obstruction. This distinct behavior severely limits Li + /Mg 2+ separation. To address this challenge, we graft phosphate groups onto graphene oxide (GO). Molecular dynamics simulations show that phosphate groups eliminate Li + ’s interfacial effect, increasing its central distribution from 0% in pristine GO to 100% in GO- g -P and reducing its friction coefficient with the wall from 18.8 to 0.33. In contrast, Mg 2+ shifts from fully central to predominantly interfacial, with its friction coefficient rising from 20.6 to 244. Ion permeation simulations reveal that GO- g -P reverses the Li + /Mg 2+ permeation ratio from 0.17 (GO) to 2.40, a 14.12-fold improvement, validating the strategy. This work establishes a conceptual framework for efficient ion separation using 2D confined channels.