Phosphate Adsorption on Activated Carbon: An Undergraduate Experiment for Constructing the Thermodynamics of Liquid–Solid Interface Adsorption

A critical component of various water purification technologies is the adsorption of contaminants from solution onto properly designed solid surfaces. This necessitates the understanding of adsorption of species from solution onto solid surfaces. Undergraduate students are typically only introduced to gas on solid adsorption phenomena, and this comprehensive experiment, which systematically compares the adsorption characteristics of phosphate ions on various types of activated carbon surfaces, is designed to enhance junior-year undergraduates’ understanding of the thermodynamics of such adsorption processes, particularly those majoring in materials chemistry, applied chemistry, and related disciplines, and those who are preparing to engage in advanced coursework and engineering practice. The results indicate that, through this experiment, students gain firsthand experience and recognize that multilayer adsorption becomes significant and inevitable under high adsorbate concentrations. Furthermore, by comparing the data, students observe that the multilayer adsorption theoretical models─specifically, the Brunauer–Emmett–Teller (BET) isotherm equation─demonstrate excellent agreement with experimental results. At the same time, through analysis, students come to understand that monolayer adsorption models, including the Langmuir and Dubinin–Radushkevich isotherm equations, effectively describe the thermodynamic behavior of the adsorption process within their respective theoretical domains.