University of Mary Washington Research and Creativity Day 2025

Beyond Langmuir and Freundlich: Quantifying Adsorbate-Adsorbate and Adsorbate-Substrate Interactions Using the ABC Isotherm.

By Grayson Camp

Faculty Mentor: Dr. Leanna Giancarlo

Abstract

Adsorption processes are essential in environmental science and industry, especially for contaminant removal. Many of these adsorption processes have been described utilizing traditional adsorption isotherms such as the Langmuir and Freundlich. Even with these known isotherms a clear understanding of the underlying adsorbate-adsorbate and adsorbate-substrate interactions has not been achieved. Therefore, using a novel ABC isotherm to account for adsorbate-adsorbate and adsorbate-substrate interactions at the interface will allow for a better understanding of the adsorption behavior of methylene blue (MB) on activated carbon (AC) and anionic Congo red on carbon fiber. For the adsorption of methylene blue on activated carbon using this model, the A parameter (6.12×10-7) indicates low strength or potentially equal MB-AC interactions, while the negative B parameter (-0.0181) shows repulsive forces between the absorbates that are relatively weak. The adsorption behavior of anionic Congo red onto carbon fiber indicates qualitatively that electrostatic interactions between the anionic dye and the positive carbon fiber and repulsive interactions between Congo red molecules at the interface are present. Future research is required to clarify the physical significance of the A, B, and C parameters and to refine the ABC model for systems involving repulsive interactions. Exploring such systems, like those involving methylene blue and anionic organic dyes on carbon substrates, will provide deeper insights into molecular interactions underlying adsorption processes.

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One response to “Beyond Langmuir and Freundlich: Quantifying Adsorbate-Adsorbate and Adsorbate-Substrate Interactions Using the ABC Isotherm.”

  1. William A. Wachter Avatar
    William A. Wachter

    Research in the physical sciences often requires more instrumentation than a liberal arts college can afford or maintain. The poster led me to ask what are the most basic questions which one has a reasonable chance to answer. This study had two materials for study, a microporous carbon and a filamentous carbon. How well were they characterized? How well could they be characterized? Cabot Corporation is the American go-to organization for different types of carbons. They make toners for copying machines an many other carbon types. I would get some samples of their well-characterized materials for testing. Adsorption studies from solution were done using two different dyes, neither of whose structures were presented. I related a personal (embarrassing) story about my failure to know my system well. The apparent degree of adsorption was measured by tracking the disappearance of color from a solution as a function of the initial concentration in the solution. How well do we know whether equilibrium was reached? What was the difference between the two carbon types? How could one make and characterize two carbon types well enough to allow comparison of adsorption rates of two different dye types? At that point one might be in a position to fit a three parameter model to the data. A real pleasure talking with the student.

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