Adsorption Kinetics and Isotherms: A Safe, Simple, and Inexpensive Experiment for Three Levels of Students

Adsorption kinetics and isotherms are taught to chemistry and engineering students and are important to understanding operations such as water pollution treatment, yet many students do not have the opportunity to perform a hands-on experiment that demonstrates the theory in a practical and tangible way. This paper describes an experiment that is inexpensive, safe, and visually conclusive and can be used for a variety of student audiences: non-science and non-engineering students, first-year engineering students, and upper-level engineering students. Adsorption kinetics and isotherms were examined through the dyeing of fabric. All students observed the dyed water becoming colorless, while the adsorbent darkens. Students used the spectrophotometer to measure dye concentrations as a function of time and found that the data followed the first-order process they learned in calculus. Upper-division students noted a systematic error in the first-order model and determined that a second-order model fits the process much better. Students in upper-level courses also developed a procedure to collect data and fit it to isotherms. Data can be obtained at different temperatures for a complete picture of the process.