The role of sodium citrate in the formation of platinum nanoparticles through colloidal synthesis

We report the systematic variation of the citrate-to-platinum ratio during the colloidal synthesis of platinum nanoparticles and its correlation with the resulting particle size and aggregative stability. Our study reveals that higher citrate concentrations lead to smaller particle and aggregate sizes. This decrease is the result of an interplay between the kinetics of platinum precursor reduction, particle nucleation, and subsequent growth. When the reaction is conducted with an excess of ascorbic acid as a reducing agent, the presence of citrate does not affect the rate of the precursor reduction. In contrast, increasing the amount of citrate accelerates the process of nucleation and slows down particle growth, leading to the conclusion that citrate primarily serves as a stabilizing agent.