Colloidal behavior of N-doped graphene quantum dots nanoporous structures in cationic electrolyte

In this study, the colloidal behavior and aggregation mechanism of nitrogen-doped graphene quantum dot aggregates (N-GQDAs) are investigated in a complex pharmaceutical electrolyte matrix consisting of 1 mg/mL cisplatin in a 9 mg/mL NaCl background solvent. Derjaguin–Landau–Verwey–Overbeek (DLVO) theory is used to understand how the charge screening effect influences the colloidal stability of N-GQDAs. Fourier transform infrared and Raman spectroscopy results show that the cisplatin remains intact and chemically inert, indicating that charge screening by monovalent Na⁺ ions governs the stability of N-GQDAs in a cationic electrolyte. Through the charge screening mechanism, free Na + ions in the background electrolyte shield the surface charge of the aggregates, diminishing long-range repulsive forces and fostering aggregation. Rather than forming specific chemical coordinates, the Na + cations act as an electrostatic shield, promoting the short-range van der Waals and π–π attractive forces between aromatic domains of the N-GQDAs in various directions. This physical aggregation, as observed via dynamic light scattering, field-emission scanning electron microscopy, and X-ray diffraction analyses, leads to a dense, cage-like colloidal structure with large aggregates. Understanding the colloidal behavior of N-GQDAs in commercial, complex cationic electrolytes is vital for optimizing their potential in clinical formulations, energy storage, and sensing applications, as well as assessing ecological risks tied to the environmental release of N-GQDs and their derivatives.