Issue 43, 2024

Surface accumulation and acid–base equilibrium of phenol at the liquid–vapor interface

Abstract

We have investigated the surfactant properties of phenol in aqueous solution as a function of pH and bulk concentration using liquid-jet photoelectron spectroscopy (LJ-PES) and surface tension measurements. The emphasis of this work is on the determination of the Gibbs free energy of adsorption and surface excess of phenol and its conjugate base phenolate at the bulk pKa (9.99), which can be determined for each species using photoelectron spectroscopy. These values are compared to those obtained in measurements well below and well above the pKa, where pure phenol or phenolate, respectively, are the dominant species, and where the Gibbs free energy of adsorption determined from surface tension and LJ-PES data are in excellent agreement. At the bulk pKa the surface-sensitive LJ-PES measurements show a deviation of the expected phenol/phenolate ratio in favor of phenol, i.e., an apparent upward shift of the Image ID:d4cp02212b-t1.gif at the surface. In addition, the Gibbs free energies of adsorption determined by LJ-PES at the bulk pKa for phenol and phenolate deviate from those observed for the pure solutions. We discuss these observations in view of the different surface propensity of phenol and phenolate as well as potential cooperative interactions between them in the near-surface region.

Graphical abstract: Surface accumulation and acid–base equilibrium of phenol at the liquid–vapor interface

Supplementary files

Article information

Article type
Paper
Submitted
29 May 2024
Accepted
21 Aug 2024
First published
23 Aug 2024
This article is Open Access
Creative Commons BY license

Phys. Chem. Chem. Phys., 2024,26, 27292-27300

Surface accumulation and acid–base equilibrium of phenol at the liquid–vapor interface

C. Richter, R. Dupuy, F. Trinter, T. Buttersack, L. Cablitz, S. Gholami, D. Stemer, C. Nicolas, R. Seidel, B. Winter and H. Bluhm, Phys. Chem. Chem. Phys., 2024, 26, 27292 DOI: 10.1039/D4CP02212B

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