Role of citric acid in the formation of silver nanoplates through a synergistic reduction approach.

This study discusses the function of citrate ions in the synthesis of silver nanoplates through a synergetic reduction approach in ambient conditions. It was found that the citrate ions can play multiple roles in the synthesis process, including a reducing agent, a stabilizer, and a complex agent, and they show some unique features under the reported conditions. The reducing ability of these citrate ions was shown to be weaker than that of sodium borohydride and/or L-ascorbic acid used in the same system. The stability in the shape/size control of silver particles is weaker than that of other surfactants tested in the present system, such as bis(2-ethylhexyl)sulfosuccinate (AOT) and thiols. Citrate ions could form a silver complex with silver ions as [Ag(2)(+)...citrate] or [Ag(3)(C(6)H(5)O(7))(n+1)](3n-), as confirmed by electrospray ionization (ESI) mass spectrometry and the kinetic analysis that the molar ratio of citric acid or sodium citrate to silver ions can greatly influence the reaction rate and, hence, the particle growth of silver nanoparticles. Such a complexing effect is further confirmed by the use of chelating ions (e.g., [Fe(CN)(6)](4-)) to form Ag(n)[Fe(CN)(6)](n-4), which can largely influence the synthesis of silver nanoparticles. These results show some formation results of generating silver nanoplates involving citrate ions, which are useful in the shape-controlled synthesis of other metallic nanoparticles with desirable functionalities.