A simple and effective route for the synthesis of nano-silver colloidal dispersions

In this work we develop a simple method to synthesize nanosized Ag colloids with the addition of urea which produce intermediates AgOCN and Ag2CO3 before the formation of silver. These intermediates are beneficial to obtaining high conversions of narrow size distributions of silver colloids from this synthesis process. At the molar ratio of [Urea]/[Ag+] = 4, [NaOH]/[Ag+] = 0.8, the weight ratio of PVP/AgNO3 = 1 g/g, using dextrose as a reducing agent and a reaction temperature of 70 °C, we obtain silver colloids of average size 22 nm with a standard deviation of 4.7 nm after separation and washing procedures. The conversion under these conditions was nearly complete at about 98%. After a thorough washing procedure, the purity of silver colloids is up to 94.4% and its dried film is electrically conductive at room temperature. The electrical resistivity reached 4.5 × 10−6 Ω cm after 250 °C heating for 30 min.