Close-packed Langmuir Monolayers of Saccharide-Based Carbon Dots at the Air-Subphase Interface

Carbon dots (CDs) are zero-dimensional carbon-based spherical nanoparticles with diameters less than 10 nm. Here we report for the first time CDs forming stable Langmuir monolayers at the air-subphase interface. Langmuir monolayers are of great interest both fundamentally to study the interactions at the interfaces and for many applications such as the development of sensors. However, CDs usually don’t form Langmuir monolayers because of their highly hydrophilic nature. In this study, amphiphilic CDs were prepared through hydrothermal carbonization using saccharides as the precursor. The surface chemistry behavior and optical properties of CDs at the air-subphase interface were studied. CDs derived from saccharides are consistently formed stable Langmuir monolayers which show all the essential phases, namely gas, liquid expanded, liquid condensed and solid phases. Compression-decompression cycle method showed minimum hysteresis (4.5%) confirming the retaining capacity of the CDs as a monolayer. Limiting C...