Properties of fluorescent chiral carbon microspheres and nanodots synthesized by a one-step hydrothermal method

Abstract

Fluorescent carbon microspheres (CMSs) and carbon nanodots (CNDs) synthesized together in one pot have received much attention in the past decade. Here we report the use of L- and D-ascorbic acids (AA) to prepare CMSs with different chirality and CNDs with different fluorescent emission by the hydrothermal method. The CMSs emit a blue light while the CNDs emit a green one under 365 nm UV light. The reaction conversions of CMSs prepared with this method are over 25% when the reaction temperature is above 180°C. Circular dichroism, specific rotation, and photoluminescence of CMSs were measured. The analyses show that the L- and D-AA-based CMSs exhibit different chiral spectra. The graphene-like structures of CMSs are revealed by Raman spectroscopy. A possible formation mechanism of the CMSs and CNSs is proposed. In addition, the CMSs after calcination were found to achieve higher electrical and thermal conductivities comparable to those of the commercial carbon black. Photoluminescence analyses of CNDs show that the relative fluctuation between the blue and green emissions determines the shifting of blue and green hybrid color of the synthesized CNDs. D-AA derived CNDs show a higher quantum yield (QY) close to 1% and a stronger green emission. The blue-emitting CNDs and the green-emitting ones could be separated with the larger green CNDs kept inside the dialysis tube.