Phenolic acids interactions with clay minerals: A spotlight on the adsorption mechanisms of Gallic Acid onto montmorillonite

Adoum Mahamat Ahmat (1, 2, 3) , Thomas Thiebault (4, 5) , Régis Guégan (1, 2, 6)

1 ISTO - Institut des Sciences de la Terre d'Orléans - UMR7327
2 Biogéosystèmes Continentaux - UMR7327
3 IMT Lille Douai - Ecole nationale supérieure Mines-Télécom Lille Douai
4 METIS - Milieux Environnementaux, Transferts et Interactions dans les hydrosystèmes et les Sols
5 EPHE - École Pratique des Hautes Études
6 Faculty of Science and Engineering, Global Center for Science and Engineering

For a better understanding of the preservation of organic matter in clay minerals, the adsorption of a model humic substance, the Gallic Acid (GA), onto a Na-montmorillonite (NaeMt) was performed in batch situation for various experimental conditions (pH = 2, 5, 7) in order to mimic the natural context. The adsorption efficiency and change in the clay mineral were characterized via a set of complementary experimental techniques (Fourier transform infrared spectroscopy, X-ray diffraction, elemental analyses). Adsorption isotherms at the equilibrium were fitted with the models of Langmuir, Freundlich and Dubinin-Radushkevitch allowing one to precisely quantify the adsorption through the derived fitting parameters. From the adsorption data combined with complementary results of the modeled humic-clay complexes, different types of interactional mechanisms were inferred as a function of background acidity: (i) at pH = 2 while protonated GA was the preponderant form, anionic GA species can be adsorbed to the Na-Mt surface through electrostatic interaction, leading to the a slight covering of the clay surface favoring in a second step the GA adsorption by π-π and Van der Waals forces; XRD patterns corroborated via TGA and FT/IR results suggested the actual intercalation of the phenolic acid within the interlayer space; (ii) At pH = 5, above the pKa of phenolic acid, only 20% of the protonated form subsisted and these species were adsorbed via coordinative bonding, without however any perceptible intercalation; (iii) and in the regime with neutral environment (pH = 7), the preponderance of GA anionic species led to a poor adsorption which appeared to be only located at the external surface of the clay mineral.

Domaines: Géochimie; Environnement et Société; Interfaces continentales, environnement; Chimie organique

Adoum Mahamat Ahmat, Thomas Thiebault, Régis Guégan. Phenolic acids interactions with clay minerals: A spotlight on the adsorption mechanisms of Gallic Acid onto montmorillonite. Applied Clay Science, 2019, 180, pp.105188. ⟨10.1016/j.clay.2019.105188⟩. ⟨insu-02164418⟩