Citric acid-assisted hydrothermal carbonaceous nanostructures: Filling factor-driven morphological study through TEM

This study investigates how precursor composition and reactor filling volume influence the hydrothermal synthesis of carbonaceous nanomaterials derived from sucrose and citric acid. Transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) were used to examine morphological evolution and elemental composition at specific filling volumes in a hydrothermal reactor. Variations in the filling factor (30, 50, and 70%) significantly affected nucleation, growth dynamics, and final morphology. Lower filling ratios favored the formation of quasi-spherical carbon dots, while higher ratios promoted anisotropic architectures such as hierarchical nanoflower-like structures. The average particle size decreased from 60 to 20 nm when the filling volume was maintained at 50%. TEM analysis revealed distinct structural features, including dense graphitic cores, functionalized shells, and hierarchical assemblies. EDS confirmed substantial oxygen content attributed to –COOH and –OH groups introduced by citric acid. These functional groups enhanced hydrolysis and facilitated self-assembly, enabling controlled particle growth and stabilization. This synthetic control provides a pathway for advanced research in carbon nanomaterials.