Effects of preparation conditions on the synthesis of nano-sized Ag metal particles by the wet-process using 3-mercapto-propionic acid

By the addition of sodium borohydride as a reducing agent into an aqueous solution of AgNO₃ mixed with 3-mercapto-propionic acid as a protective agent, nano-sized Ag metal particles could be synthesized. Using this advanced wet-process the synthesis of an aqueous Ag colloid system with a high density became possible, because the surfaces of the synthesized nano-sized Ag metal particles were covered and protected by the adsorbed 3-mercapto-propionic acid. By changing the mix ratio of AgNO₃ to 3-mercapto-propionic acid, the particle size of synthesized nano-sized Ag metal particles could be controlled; a higher 3-mercapto-propionic acid/AgNO₃ ratio was preferable in the synthesis of smaller Ag metal particles. From the relationship between the Ag metal particle size and the residual S content adsorbed on the metal particles, the mechanism of dispersion of Ag particles can be proposed as that the 3-mercapto-propionic acid having a thiol group adsorbs on Ag particles by forming Ag-S bonds as a protective agent.