ATR–FTIR Spectroscopy in the Undergraduate Chemistry Laboratory. Part II: A Physical Chemistry Laboratory Experiment on Surface Adsorption

Attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy is a useful technique for measuring the infrared spectra of solids and liquids as well as probing adsorption on particle surfaces. The use of FTIR-ATR spectroscopy in organic and inorganic chemistry laboratory courses as well as in undergraduate research was presented in Part I as well as background information and the fundamentals of the ATR-FTIR technique. In Part II, the use of ATR-FTIR spectroscopy in the upper-level physical chemistry laboratories is discussed. A new experiment involving the adsorption of ions from solution onto oxide particle surfaces is introduced. In this laboratory experiment, students use ATR-FTIR spectroscopy to determine the Langmuir adsorption constant, K ads, for sulfate ion adsorbed on 2 particles at pH = 3. A thin film of oxide particles deposited onto the ZnSe ATR element is exposed to solutions of different sulfate concentrations. The infrared spectrum of adsorbed sulfate can be measured in this way. This experiment, which can be easily implemented into an upper-level chemistry curriculum, introduces students to several concepts including surface adsorption, oxide surface chemistry, and environmental interfacial processes.