Glucose-Derived Fluorescent Carbon Dots: Effect of Synthesis Temperature on Structural Evolution

Glucose-derived carbon dots (CDs) were synthesized via a solvent-free pyrolysis method under air at temperatures ranging from 160 °C to 250 °C. The synthesis temperature significantly influenced the structural evolution and optical properties of the resulting CDs. Thermogravimetric and spectroscopic analyses confirmed that higher pyrolysis temperatures promoted extensive carbonization and evolution from amorphous to turbostratic graphitic structures. Progressive loss of oxygen-containing functional groups and development of conjugated domains were supported spectroscopically. X-ray photoelectron spectroscopy (XPS) reveals the chemical transformations, where the O/C ratio decreased systematically from 0.76 at 160 °C to 0.44 at 250 °C, while C 1s deconvolution showed an increasing sp² contribution and the emergence of carboxylic species at higher temperatures. Photoluminescence (PL) studies revealed excitation-dependent emission, with CD-250 displaying a pronounced redshift and spectral broadening, further corroborated by time-resolved PL spectroscopy which indicated stronger contributions from surface trap states. The temperature-dependent structural and surface tuning of CDs highlights the potential of glucose-derived CDs with a tunable structure and photophysical properties.