Size-controlled and large-scale synthesis of organic-soluble Ag nanocrystals in water and their formation mechanism

Organic-soluble Ag nanocrystals (NCs) with tunable sizes in the range from 5.4 to 22.1 nm were synthesized by a facile, reproducible and easily scaled up route using water as solvent in the presence of oleic acid and an alkylamine. The synthetic Ag NCs exhibits excellent hydrophobicity and can be well re-dispersed in various non- or weak-polar media. The tunable sizes of the Ag NCs were achieved by simply adjusting the initial precursor AgNO3 concentration. Large-scale synthesis of the Ag NCs was realized at a high AgNO3 concentration (0.4 mol/L). As much as 16.2 g highly uniform organic-soluble Ag NCs with 5 nm average diameter can be readily synthesized at low cost in a single reaction only using 400 mL water as solvent, which is adaptable to the industrial scale production. The structure of the obtained Ag NCs was investigated in detail by X-ray diffractometry, transmission electron microscopy, Fourier transform infrared and thermal gravimetric analysis measurements. The results reveal that the surface of the organic-soluble Ag NCs is coated with the monolayer surfactants consisting of oleic acid and the alkylamine. In addition, on the basis of the sufficient evidences, a proposed mechanism based on the “bilayer surfactant-controlled reaction” successfully demonstrates the formation of high quality organic-soluble Ag NCs in the aqueous solution.