Regulated Ionic Channels and Coordinate-Bonded Effect on Enhanced Trivalent-Ion Transport during Electrosorption

The difficulty in clarifying the overlapping ionic transport pathways of the layered Ti₃C₂T_x electrode has led to a lack of clear structural criteria to enhance electrosorption (e.g., ion-selective separation, water treatment, and resource recovery). In particular, a highly charged, large trivalent ion brings harsh pursuits on the electrode transport structure. Interlayer spacing is considered the dominant factor to improve trivalent-ion electrosorption capacity. However, our results reveal a weak correlation between the interlayer spacing and ion electrosorption capacity. Instead, capacitive deionization (CDI) experiments and molecular dynamics simulations demonstrate a strong correlation between coordinate-bonded effects, regulated ionic channels within the electrode, and ion adsorption capacity. Through a protonated pg-C₃N₄/Ti₃C₂T_x//activated carbon asymmetric CDI device, strong C₃N₄-Al³⁺ coordination and induced regulated 3D-structured ion channels achieve an exceptional Al³⁺ adsorption capacity (55.22 mg g^-1) owing to the N-Al bond in electrode-ion interaction, outperforming Mg²⁺ and Na⁺ cases (31.26 and 24.36 mg g^-1, respectively) caused by parallel layer-stacked C₃N₄-Mg²⁺ and C₃N₄-Na⁺. Moreover, in the AlCl₃-adsorbed NaCl solution, the regulated ionic transport channels markedly enhance Na⁺ intercalation, yielding a 2.7-fold increase compared to that of the identical device in fresh NaCl solution after 100 cycles. Practical tests verify the enhanced Al³⁺ enrichment and preferential Al³⁺/Na⁺ separation via the ion-capturing CDI electrode. These findings suggest ways to understand and utilize electrode-ion interactions to achieve the reinforced Na⁺ adsorption performance and overcome challenges associated with large multivalent ion adsorption, with implications for ion-selective removal, resource recovery, and multivalent metal-ion energy storage.