The difficulty in clarifying the overlapping ionic transport pathways of the layered Ti3C2Tx 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/Ti3C2Tx//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.
Qian et al. (Thu,) studied this question.