Synthesis and Study of Silver Nanoparticles

A laboratory experiment introduces students to a unique property of a nanomaterial: the intense yellow color exhibited by silver nanoparticles compared to ionic or bulk silver. Students synthesize colloidal silver, estimate particle size using visible spectroscopy, and study aggregation and its prevention by addition of a polymer stabilizer. This experiment, intended as a laboratory activity for general chemistry, introduces students to nanotechnology while reinforcing topics such as redox chemistry, limiting and excess reactants, spectroscopy, and atomic size. The experiment requires dilute solutions and simple equipment such as the Spectronic-20 spectrophotometer and a magnetic stir plate. The reaction used for the synthesis of silver nanoparticles is the borohydride reduction of silver nitrate. The method produces 12 ± 2 nm particles and plasmon absorbance near 400 nm. In developing the experiment, transmission electron microscope (TEM) images were used to determine particle size; however, TEM is not involved in the student experiment. The experimental design is discussed, including the choice of concentrations of reactants, the relationship of particle size to optical properties, as well as a discussion of aggregation and stabilizers. The experiment was tested on laboratory classes of science majors.