An eco-friendly green and facile synthesis of carbon dots from red propolis wax with photoluminescence dependent of reaction time and thermal treatment in solid state

Although the luminescent properties of carbon dots (CDs) already have been modulated by changing different synthetic parameters, the effect of the reaction time and temperature is still rarely explored. In this work, a facile and eco-friendly synthesis of CDs by hydrothermal method using red propolis wax as a source of carbon was performed in times of 6 (CD6) and 24 h (CD24) and thermally treated. The produced CDs exhibit a size around 2–5 nm, a uniform morphology, and an intense blue light photoluminescence emission under UV irradiation. The photoluminescent properties of CDs display both excitation-dependent/independent emission that are affected by the different reaction times tested in the synthesis. The results showed that the degree of oxidation/defects decreases as the particle size increases providing an unusual emission behavior independent of the excitation with the time increase from 6 to 24 h. In addition, the heat treatment makes the CD6 sample emit independent of the excitation. Moreover, it is noteworthy that to the best of our knowledge, red proprolis wax has not been used as a precursor in the synthesis of CDs and no study has reported changes in dependent/independent emission of CDs by using different reaction times and thermal treatments. Graphic Abstract