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.