Mesocrystals of Rutile TiO2: Mesoscale Transformation, Crystallization, and Growth by a Biologic Molecules-Assisted Hydrothermal Process

Using N,N'-dicyclohexylcarbodiimide (DCC) and L-serine as biologic additives, rutile TiO2 hollow spheres assembled by nanorods can be synthesized by a simple hydrothermal reaction route, A distinctive crystallization and transformation route of the rutile TiO2 hollow spheres has been proposed, which includes emergence of polycrystalline, mesoscale transformation to mesocrystals with morphologies of sectors, transformation of mesocrystals to bundles of rods based on oriented attachment, the simultaneous assembled process of sectors to solid spheres, and a cavitating process of solid spheres through the Ostwald ripening mechanism. Two ways of oriented attachment, side-by-side and end-to-end, were observed during the assembly process. It has been found that the presence of DCC and L-serine and their synergistic effects are essential for the formation of rutile TiO2 hollow spheres. The stability of the rutile TiO2 mesocrystals has been studied. The results have demonstrated that the mesocrystals could be maintained longer at lower temperature, while proper choice of organic additives can also enhance the stability of mesocrystals at higher temperature under solution conditions.