The Electronic Origin of the Zeta Potential is Supported by the Redox Mechanism on an Aqueous Dispersion of Exfoliated Graphite

• Published in: Angewandte Chemie 2022-12, Vol.134 (52), p.n/a
• Main Authors: Damasceno, João Paulo Vita, Kubota, Lauro Tatsuo
• Format: Article
• Language: English
• Subjects: Ammonia; Aqueous solutions; Chemistry; Colloids; Dispersion; Electrons; Fermi level; Functional groups; Graphite; Interfaces; Nitrogen; Nitrogen atoms; Redox reactions; Sonication; Surface Chemistry; Zeta potential
• ISSN: 0044-8249; 1521-3757
• DOI: 10.1002/ange.202214995

Herein we have proposed that a redox mechanism can produce surface charges and negative zeta potential on an aqueous graphite dispersion. Graphite was kept in contact with a concentrated ammonia aqueous solution, washed, and exfoliated in water, resulting in a dispersion with lyophobic nature. Ammonia treatment did not provide functional groups or nitrogen doping to graphite. Moreover, this material was washed twice before sonication to remove most hydroxide. Therefore, neither functional groups, nitrogen atoms, nor hydroxide excess is responsible for the zeta potential. Kelvin probe force microscopy has shown that the ammonia‐treated and exfoliated graphite has higher Fermi level than the water‐treated material, indicating that the contact between ammonia and graphite promotes redox reactions that provide electrons to graphite. These electrons raise the Fermi level of graphite and generate the negative zeta potential, consequently, they account for the colloidal stability. An aqueous graphite dispersion was prepared without passivating agents and a minimal amount of functional groups by treating graphite with ammonium hydroxide. This approach has raised the Fermi level above the original value. The negative zeta potential has been revisited and attributed to the electrons accumulated on the material.