Imperfect oriented attachment of lanthanum hydroxide nanoparticles
Oriented attachment (OA) is a significant growth mechanism in the formation of highly anisotropic and dimensionally amassed nanocrystals. The shape dependent anisotropy and quantization effect can be tuned via OA. Selective surface capping activity of organic linkers can modify the OA mechanism and drives isotropic growth into two-dimensional (2D) nanocrystals. Here we report the 2D OA of La(OH)3 nanoparticles as primary building blocks, which transformed into highly anisotropic nanosheets with both atomic coherence and long-range periodicity, achieved with 3-mercaptopropionic acid (MPA) as a surface passivating organic linker. A three-stage conversion process is proposed: (i) aggregation of NPs, (ii) amorphous nanosheet formation due to the partial surface solubility, attributed to the strong adsorption of MPA and (iii) conversion into crystalline nanosheets. The 2D nanosheets demonstrated the existence of surface defects and dislocations, which elucidated an imperfect OA mechanism and led to an enhanced photo-electrochemical water splitting activity.