Abstract: A new synthetic approach based on the co-precipitation method was explored to synthesize regularly hexagonal Mg-Al-NO3-LDHs nanoparticles by taking the advantages of the conventional urea hydrolysis method. The effects of precipitator, solvent, reaction time and the dropping speed of precipitator on the crystallinity and morphologies of LDHs were systematically studied. Nearly monodispersed and regularly hexagonal morphology of LDHs with high crystallinity and particle size in the range of 100~250 nm could be obtained using NH4OH as precipitator and a mixture of alcohol and water as solvent. The addition of alcohol might slow down the ionization rate of NH4OH into OH- and benefit the reduction of the supersaturation degree. In addition, the alcohol could be absorbed on the surface of LDHs particles and the hydroxyl groups play a steric repulsion effect, which prevent the aggregation of the particles. Our results also show that an incomplete particle growth occurred at short reaction time(1 h) will lead to the formation of irregular and hexagonal particles, while the aggregation of particles tends to take place when the reactions are prolonged(4 h). Furthermore, the effect of dropping speed of precipitators was also investigated. A low dropping speed(0.025 mL/s) of precipitator favors the formation of regularly hexagonal particles with good monodispersity, and the particle size increases with the decrement of dropping speed.

Key words: nanoparticles, layered compouds, layered double hydroxides, hexagonal