Process for manufacture of nanometric, monodisperse, stable metallic silver and a product obtained therefrom
The present invention relates to a procedure for preparation by wet reduction method of nanometric particles of metallic silver, with diameter in the range of 1 to 100 nm and an average diameter of 20 to 40 nm, with monodispersion characteristics, stability greater than 12 months and in a wide range of concentrations. The process comprises 4 steps: a) preparation of the reducing agent solution, taken from the group of tannins and preferably being tannic acid; b) preparation of a solution of a soluble silver salt; c) reaction and, d) solid-liquid separation; the particle size is determined by the nature of the reducing agent and by the pH control of the currents. The final step is designed for separating and concentrating the material after which the user can prepare the product for integration thereof in the desired medium. The particles obtained are redispersable in different media, such as water, alkydalic and phenolic resins, nitrocellulose, polyurethane, vinylics, acrylics, alcohols and in a wide variety of organic and polymeric materials such as high and low density polyethylene, Nylon, ABS and/or mixtures thereof.
1. A wet reduction process to produce monodisperse and stable nanoparticles of metallic silver, comprising the following steps:
a) preparing an aqueous solution of silver salts at room temperature containing from 0.01% to 20% in weight of silver soluble salt, and adjusting the pH of the aqueous silver salts solution to a value between 10.5 and 11.5 by the addition of a first hydroxide;
b) preparing an aqueous solution of a reducing agent at room temperature containing from 0.01% to 20% in weight of tannic acid, and adjusting the pH of the aqueous reducing agent solution to a value between 10.5 and 11.5 by the addition of a second hydroxide;
c) mixing the aqueous solutions of silver salts and reducing agent to react, and adjusting the pH of the mixture to a value between 10.5 and 11.5 by the addition of a third hydroxide, to synthesize silver nanoparticles at room temperature; and
d) separating the resulting mother liquor and the silver nanoparticles produced in the reaction, to obtain silver nanoparticles with average particle sizes from 10 nm to 20 nm.
2. The process to produce monodisperse and stable nanoparticles of metallic silver according to claim 1 wherein the first hydroxide is selected from the group consisting of hydroxide of sodium, hydroxide of potassium, hydroxide of ammonium, and ammonia.
3. The process to produce monodisperse and stable nanoparticles of metallic silver according to claim 1 wherein the silver salts solution is prepared no more than 15 minutes before the mixing step.
4. The process to produce monodisperse and stable silver metallic nanoparticles according to claim 1 wherein the mixing step takes place in the presence of light.
5. The process to produce monodisperse and stable metallic silver nanoparticles according to claim 1 wherein the mixing step has a duration of at least 15 minutes but not more than 30 minutes.
6. The process to produce monodisperse and stable metallic silver nanoparticles according to claim 1 wherein, during the mixing step, the progress of the reaction after 15 minutes is at least 95%.
7. The process to produce monodisperse and stable nanoparticles of metallic silver according to claim 1 , wherein the second hydroxide is selected from the group consisting of hydroxide of sodium, hydroxide of potassium, hydroxide of ammonium, and ammonia.
8. The process to produce monodisperse and stable nanoparticles of metallic silver according to claim 1 , wherein the third hydroxide is selected from the group consisting of hydroxide of sodium, hydroxide of potassium, hydroxide of ammonium, and ammonia.