Method of making silver nanoparticles

A method of detecting mercury ions in an aqueous solution, comprising:

• preparing an orange peel extract by:
• cutting a portion of an orange peel into pieces having a surface area of 0.01-0.4 cm2;
• washing the cut orange peel pieces with deionized water to form a washed orange peel;
• forming a mixture of 5-20 wt % washed orange peel and 80-95 wt % deionized water, based on the total weight of the washed orange peel and deionized water;
• boiling the mixture in water for at least 3 mins to form an extract solution;
• filtering the extract solution from the peel to obtain the orange peel extract;
• then
• forming a synthesis mixture of at least one silver salt and the orange peel extract, wherein
• the silver salt is at a concentration of 0.01-0.03 M in solution and the orange peel extract is present in a 1:5-10 volume ratio of orange peel extract to silver salt solution;
• reacting the silver salt and the orange peel extract to form the silver nanoparticles by heating the synthesis mixture to 40-60° C. and adjusting the mixture pH to 8-10 while stirring thereby forming a colloidal solution of the silver nanoparticles;
• wherein the reacting of the silver salt and the orange peel extract to form the silver nanoparticles occurs in less than 1 minute;
• mixing the silver nanoparticles with the aqueous solution;
• and
• detecting a color change following the mixing that indicates a presence of Hg2+ in the aqueous solution by UV-Vis spectroscopy,
• wherein the silver nanoparticles are amorphous, and
• wherein the silver nanoparticles have a mean particle size of 25-75 nm.