Large-scale, surfactant-free, hydrothermal synthesis of lithium aluminate nanorods: optimization of parameters and investigation of growth mechanism.

Lithium aluminate nanorods were successfully synthesized from Al2O3 nanoparticles and lithium hydroxide by a simple, large-scale hydrothermal process without any surfactant or template. The various reaction parameters were optimized to achieve the maximum yield. The as-obtained nanorods had orthorhombic beta-lithium aluminate structure with edges in the range of 40-200 nm and lengths of 1-2 mum confirmed by SEM, TEM, XRD, and NMR. Upon calcination at 1273 K for 12 h it transformed to gamma-lithium aluminate, yet maintained the initial morphology, demonstrating the thermal stability. The ratio of lithium hydroxide to aluminum oxide showed a significant effect on the morphology as Li/Al = 1 gives "microroses", whereas Li/Al = 3 and Li/Al = 15 gave "microbricks" and "nanorods", respectively. Investigation of the mechanism showed that the nanorods were formed via a "rolling-up" mechanism. As we used all-inorganic raw materials and a simple synthetic procedure under mild conditions, the scale-up of this process for large-scale production should be very easy.