A pH-Controlled Reversible Phase Transfer and Electrolytic Size-Fractionation of Stable Silver Nanoparticles Capped with a Long Amino Amide Dicarboxylic Acid

The synthesis of a long alkylaminoamide dicarboxylic acid amphoteric species has been achieved. Employed as capping agent, the reduction of ionic silver in water led to the formation of small (10–100 nm) and hydrophobic diacid bilayer coated silver nanoparticles (AgNPs). In a biphasic system (e.g. H2O–CHCl3), a pH-controlled and reversible phase transfer phenomenon was observed. At different stages, the formation of these nanoparticles was studied by UV–vis spectroscopy, their stability was controlled by zeta-potential measurement and both shape and morphology were observed by transmission electron microscopy (TEM). The ionic strength of the AgNPs was tested by the addition of inorganic salt electrolyte (NaCl, CaCl2). A NaCl concentration dependant size fractionation of the AgNPs between the same above biphasic system was also studied by means of analytical techniques such as dynamic light scattering (DLS), TEM, and UV–vis spectroscopy.