Preparation and dispersion of metal oxide nanostructures using amino acid-assisted chemical routes: An overview

The preparation of various oxide nanostructures via amino acid-assisted self-assembly reaction is reviewed. An amino acid is a molecule containing both amine and carboxyl functional groups. These groups can be ionized to positive (NH ⁺ ₃) or negative (COO _-) ions by protonation or deprotonation, which provide the electrostatic interactions with cations and other directing agents for self-assembly reaction. The NH ⁺ ₃ can form N-H..O hydrogen bonds with oxygen atoms in carboxyl functional groups and the formation of a peptide (amino) bond between the amine and carboxyl groups is also possible. Moreover, the amino acids can be used as capping agents for tuning the growth and dispersion of nanoparticles. The formation mechanisms of various self-assembled structures such as hollow and hierarchical nanostructures using amino acid-assisted reaction are discussed.