Insights into the synthesis of layered double hydroxide (LDH) nanoparticles: Part 2. Formation mechanisms of LDH

This study demonstrates the effect of (co)intercalated anion compositions on nanostructure evolution to understand the formation mechanisms of layered double hydroxide (LDH) nanoparticles following coprecipitation and hydrothermal treatments (HT). Initially, the room temperature coprecipitation resulted in amorphous primary nanoparticles that agglomerated at the edges due to low surface charge densities. The reversibility of such agglomeration was determined by the crystalline quality upon HT and consequent surface charge density, which in turn were strongly influenced by the composition of the intercalated anions. Upon crystallization, the agglomerated Zn₂Al(OH)₆(NO₃)_0.3(CO₃)_0.35{dot operator}xH₂O primary nanoparticles re-dispersed, but the Zn₂Al(OH)₆(NO₃){dot operator}xH₂O nanoparticles with much lower stability and higher disorder (especially at the edges) exhibited irreversible agglomeration, and transformed into secondary nanoparticles via aggregational growth. Additionally, the stability studies on Zn₂Al(OH)₆(NO₃)_y(CO₃)_0.5(1-y){dot operator}xH₂O nanoparticles (y=0-1) showed that the size difference between the cointercalated anions caused phase separation when 0.9≥y≥0.6, leading to bimodal size distributions. Moreover, the coarsening rates were controlled through the cointercalated anion compositions. By gradually varying the ratio of cointercalated NO₃^- to CO₃^2-, monodispersed Zn₂Al(OH)₆(NO₃)_y(CO₃)_0.5(1-y){dot operator}xH₂O (0.5≥y≥0) nanoparticles with systematic variation in the particle size of ~200-400nm were obtained after HT at 85°C for 12h.