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.