Charge Distribution Controls On-Target Separation of Low Nucleophilicity Anions in Layered Double Hydroxides

Host-guest chemistry principles and mechanisms have been exploited to separate harmful and valuable ionic species. However, separating low nucleophilicity anions using these protocols is difficult due to weak host-guest interactions. Herein, using layered double hydroxides (LDHs), it is demonstrated that guest-guest interactions considerably influence the separation of a low nucleophilicity nitrate. LDHs exhibit considerably low nitrate ion storage capacities due to the co-precipitation synthesis method. Hence, a topochemical reaction is applied to control the cation arrangement in the LDHs. Structural analyses determine that a hexagonal cation arrangement is facilitated. Isotherm analysis reveals that the obtained LDHs improve the capacity up to 250% of that of typical less-ordered LDHs. Finally, further isotherm analysis in combination with theoretical calculations, it is revealed that the hexagonal arrangement effectively facilitates a stable guest-guest interactions-hydrogen-bond between the interlayer nitrate ions and water molecules, which contributes to high ion-storage.

Automated summary

This study demonstrates that guest-guest interactions significantly influence the separation of low nucleophilicity nitrate using layered double hydroxides (LDHs). By applying a topochemical reaction to control the cation arrangement in LDHs, a hexagonal cation arrangement is facilitated, leading to improved ion storage capacity and effective separation.