Striking analogies and dissimilarities between graphene oxides and humic acids: pH-dependent charging and colloidal stability

Etelka Tombácz, Ildikó Y. Tóth, Krisztina Kovács, Erzsébet Illés, Márta Szekeres, Balázs Barna, Attila Csicsor, Tamás Szabó

Research output: Contribution to journalArticle

Abstract

This study provides a comparative framework on the elucidation of analogies and differences in the interfacial protolytic processes and the associated colloidal behaviour of a typical humic acid (HA) and a set of single-layer graphene oxide (SLGO) and (multi-layered) graphite oxide samples in aqueous electrolyte media. The pH dependence of the surface charge densities of HA and SLGO was explored at three different salt concentrations by potentiometric acid-base titration, along with simultaneous determination of zeta potential and hydrodynamic sizes. Charging curves obtained in the pH range of 3 to 10 by cyclic titrations reveal the presence of a small hysteresis, proving the chemical stability of SLGO and graphite oxides in weakly acidic and alkaline solutions. HA and SLGO display a parallel shift of the pH-dependencies of their negative charge densities with increasing ionic strength, demonstrating a unique combination of particle and polyelectrolyte-like behaviour, which is absent for multi-layered graphite oxide exhibiting charging curves that resemble to “classical” colloidal particles. An accurate purification of SLGO results in inherent change in its surface properties; however, the salt tolerance of aqueous HA solutions is still superior to that of SLGO dispersions.

Original languageEnglish
Article number112948
JournalJournal of Molecular Liquids
Volume306
DOIs
Publication statusPublished - May 15 2020

Keywords

  • Acidic dissociation
  • Graphene oxide
  • Humic substances
  • Particle aggregation
  • Salt tolerance
  • Surface charging

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Condensed Matter Physics
  • Spectroscopy
  • Physical and Theoretical Chemistry
  • Materials Chemistry

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