The zeta potentials of g-C3N4 nanoparticles: Effect of electrolyte, ionic strength, pH, and humic acid

In this study, zeta potentials of graphitic carbon nitride (g-C3N4) nanoparticles were detailedly investigated under various electrolytes, solution pH, and humic acid (HA) concentration conditions. The hydrodynamic radius of g-C3N4 nanoparticles was measured to be 388.9 ± 24 nm, and the specific surface area of the g-C3N4 nanoparticles was measured to be 46.2 m2 g−1. The absolute values of g-C3N4 zeta potentials significantly decreased with the increasing ionic strength (IS) due to the charge screening. Compared to the monovalent cation, the zeta potentials of g-C3N4 were less negative with the presence of divalent cations. In addition, K+ was more effective than Na+ in decreasing the absolute values of g-C3N4 zeta potentials, and Ca2+ was more effective than Mg2+ in decreasing the absolute values of g-C3N4 zeta potentials. When NaCl and CaCl2 were used as the electrolytes, the zeta potentials of g-C3N4 became less negative with the decreasing pH conditions. When FeCl3 and AlCl3 were used as the electrolytes, the zeta potentials of g-C3N4 became more positive with increasing solution pH due to the changing species of Fe3+ and Al3+. The zeta potentials of g-C3N4 were significantly more negative with the presence of HA. The results from this work indicated electrolytes, solution pH, and HA concentration conditions play a complex role in zeta potentials of g-C3N4 nanoparticles in aqueous environment.