Tripodal Ligand-Stabilized Layered Double Hydroxide Nanoparticles with Highly Exchangeable CO₃^2–

Layered double hydroxide nanoparticles (LDHNPs) with exceptionally small particle sizes are synthesized using a tripodal ligand of tris­(hydroxymethyl)­aminomethane (THAM). For example, a LDHNP with the average size of 9.7 nm (denoted as LDH­(10 nm), containing CO₃^2– in the interlayer), can be synthesized using a 2.0 M THAM solution. The ¹³C CP/MAS NMR and FTIR analyses show that THAM is ligated to the layer as an alkoxide species. The average particle size of LDH synthesized using l-lysine (buffering base) instead of THAM is larger (47.9 nm) than that of LDH­(10 nm). Therefore, the size reduction is possibly explained by the specific interaction of THAM with the layer via its multiple coordination. In addition, it is confirmed by the ¹³C CP/MAS NMR analysis that LDH­(10 nm) possesses CO₃^2– species weakly interacting with the layers. LDHNPs, in particular, as-synthesized LDH­(10 nm) (denoted as LDH­(10 nm)-as, containing CO₃^2– and Cl^– in the interlayer), possesses the extremely high anion exchange abilities, and almost all anions in LDH­(10 nm)-as are potentially exchangeable with NO₃^–, even under ambient (CO₂-existing) conditions. Furthermore, LDH­(10 nm)-as can act as an efficient reusable scavenger for harmful oxyanions and remove arsenic, selenium, and boron from their dilute aqueous solutions under ambient conditions