The superior surface activity and self-assembly behavior of nanosurfactants amphiphilic carbon dots (CDs) in aqueous solution

Nanosurfactants are amphiphilic nanometer molecules with hydrophilic headgroups and hydrophobic tail chains similar to surfactants, showing excellent interfacial properties. In this work, four amphiphilic carbon quantum dots (CDs) as nanosurfactants with different hydrocarbon chains (abbreviated as C[Formula: see text]-CDs, C[Formula: see text]-CDs, C[Formula: see text]-CDs and C[Formula: see text]-CDs) were investigated for surface activity and the self-assembly behavior. First, four amphiphilic CDs were synthesized by pyrolysis and characterized by high-resolution transmission electron microscopy (HRTEM), Fourier transform-infrared spectrometer (FTIR) and X-ray photoelectron spectroscopy (XPS). The results confirmed the successful synthesis of CDs with an average particle size of 3.3 nm. Thermogravimetric (TG) analysis showed that all CDs have certain high-temperature resistance properties. In addition, through surface tension measurements, CDs as nanosurfactants exhibited superior surface activity due to their amphiphilic structure. To further study the self-assembled aggregates formed by CDs, dynamic light scattering (DLS) measurements were carried out. It was found that when the concentration of CDs was increased to critical aggregation concentration (CAC) and above, the size of aggregates did not change. Finally, the effects of temperature and NaCl concentration on the surface activity and CAC values of CDs were investigated. As the temperature increased, the surface tension of the solution decreased and CAC values increased due to the weakening of the hydrogen bond interactions. As the NaCl concentration increased, the particle bilayers were compressed, resulting in the reduction of the surface tension and CAC values. We expect to deepen our understanding of nanosurfactants through this research work, so as to expand their potential applications in the future.