Síntese, caracterização e controle da densidade de estados de superfície de pontos de quânticos de carbono

Abstract

In this work we report the synthesis of three types of carbon dots (CDs), the first with nitrogen on the surface, derived from chitosan and the other two with nitrogen and sulfur on its surface, derived from cysteine and dansyl. The change in temperature causes the optical properties of all CDs to change. To unravel these changes, we performed spectroscopic measurements in solid state in two stages at temperatures ranging from 303 to 453 K. For the first heating stage, the emission spectrum showed a 20 nm redshift for chitosan CDs, from 67 nm for cysteine and a small blue deviation for dansyl CDs. For the cysts of CDs, after the heating a change in the absorption profile was obtained, this indicated that there was a change in the surface states, in addition to its low Huang-Rhys factor and the non-dependence of the bandwidth with the temperature, showed a weak electron-phonon interaction. For the cysteine CDs, the increase in temperature also caused a change in the absorption profile, and na increase in the average size of the CDs, which indicates that the red shift was caused by the change in their surface states and by the increase in particles. It is Worth mentioning that the values of the Huang-Rhys factor showed low values, however their bandwidth had a dependence on temperature, but their values were also low, indicating a low electron-phonon interaction. The dansyl CDs, in addition to the blue shift, showed no change in the absorption spectrum. However, its FTIR spectrum varied considerably, making the blue shift justified. In addition, C-CDs and D-CDs marked the cell cytoplasm. This work can open a new perspective for the development of new strategies of surface modulation for carbon points submitted to heat treatment after synthesis.