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Gold and Silver Nanoparticles

In this lab, students will make and filter three different gold and silver colloidal mixtures. Gold and silver solutions will be reduced and stabilized with sodium citrate in a boiling water bath. The colloidal dispersions formed will be poured into Petri dishes, drawn into a Luer-Lok™ syringe, and filtered through 20nm pore size ceramic filters. The colloidal gold should be deep red in color and pass through the filter. Gold colloid particles are about 13nm in size. The silver colloid should be yellow in color and get caught in the filter. Silver colloidal particles are 20-50nm in size. If the silver filter is cut open along the seam with a single edged razor blade, the silver metal can be seen on the inside of the filter. Interestingly, the color will be the color of bulk silver, not the yellow color of the colloid. The red gold colloid in the filtrate can be coagulated into larger particles using sodium chloride. This will change the color of the gold colloid from red to blue. The blue gold colloid can then be refiltered and the students will find that it will be caught on the filter. Cutting open the filter will reveal the gold color of the metal. From their observations, students can draw conclusions about the sizes of red and blue gold and yellow silver colloids.

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