Control of Surface Defects and Agglomeration Mechanism of Layered Double Hydroxide Nanoparticles

Agglomeration is a common problem in the production and application of nanoparticles. The degree of agglomeration of layered double hydroxide (LDH) nanoparticles is difficult to control in its industrial production. The properties of industrial scale MgAl–CO3–LDH products obtained using an aging reactor composed of a 1 m3 kettle with a water cooling jacket have been compared with MgAl–CO3–LDHs prepared using different aging times in a model laboratory scale reactor [a 500 mL flask]. The effect of varying aging times on the agglomeration of the LDH nanoparticles has been studied experimentally. The crystallinity, surface defects, and surface zeta potential of the LDHs have been studied in an effort to understand the mechanism of agglomeration of the nanoparticles. The results show that in poorly crystalline LDHs, accumulation of Al3+ cations at different points in the layers results in an increase in local charge density. Consequently, the zeta potential and the electrostatic repulsion between particles decrease, resulting in serious agglomeration of LDH nanoparticles. In contrast, for LDHs with higher crystallinity produced with extended aging times, the layer cations become uniformly distributed resulting in an increase in zeta potential and increased electrostatic repulsion between the particles. As a result, the degree of agglomeration is reduced.