Water molecules bonded to the carboxylate groups at the inorganic-organic interface of an inorganic nanocrystal coated with alkanoate ligands

Abstract

Abstract High-quality colloidal nanocrystals are commonly synthesized in hydrocarbon solvents with alkanoates as the most common organic ligands. Water molecules with approximately equal number of the surface alkanoate ligands are identified at the inorganic-organic interface for all types of colloidal nanocrystals studied, which is investigated quantitatively using CdSe nanocrystals as the model system. Carboxylate ligands are coordinated to the surface metal ions and the first monolayer of the water molecules are found to bond to the carboxylate groups of alkanoate ligands through hydrogen bonds. Additional monolayer(s) of water molecules can further be adsorbed through hydrogen bonds to the first monolayer of water molecules. The nearly ideal environment for hydrogen bonding at the inorganic-organic interface of alkanoate-coated nanocrystals helps to rapidly and stably enrich the interface-bonded water molecules, most of which are difficult to be removed through vacuum treatment, thermal annealing, and chemical drying. The water-enriched structure of the inorganic-organic interface of high-quality colloidal nanocrystals must be taken into account for understanding synthesis, processing, and properties of these novel materials.