Structural and optical properties of exfoliated graphene-like carbon nitride into nanosheets and quantum dots

Abstract

The polymeric carbon nitride possesses the capability to form graphene like novel nanostructures (nanosheets, QDs etc) owing to its layered structure composed of tri-s-triazine units arranged in graphitic fashion by weak Vander Waals forces. Such nanostructures showed improved optoelectronic properties compared to bulk material making them potential candidates as electrode material, interface layer and active layer additive for various optoelectronic devices. Herein graphitic carbon nitride (g-C3N4) based 2D nanosheets (NS) and 0D Quantum Dots (QDs) were prepared by facile green route and acidification of bulk material respectively. Systematic structural and optical investigation were performed on the prepared nanostructures by various characterization techniques viz. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), Atomic force microscopy (AFM), UV–Vis and photoluminescence (PL) to understand their structure-property relationship in details. It was observed that even after exfoliation and acidification the unit chemical structure was preserved both for NS and QDs having thicknesses nearly 3–5 nm (~ 10 layers) for NS and 0.8–1.7 nm for QDs respectively. The g-C3N4 nanostructures showed tunable band gap which increases from 2.78 eV for bulk g-C3N4 to 3.3 eV and 3.58 eV for NS and QDs respectively, as observed from the blue shifted absorption and emission spectrum. Moreover, small Urbach energy (EU) for NS (0.64 eV) and QDs (0.24 eV) and higher stokes shift of QDs compared to bulk counterpart, indicate possibilities for superior charge carrier separation and collection capabilities of such novel nanostructures, making them potential candidate for OPVs and OLEDs applications.