Luminescent Single-Atom Eu-Coordinated Graphitic Carbon Nitride Nanosheets for Selective Sensing of Acetone and Cyclohexane

The doping of Eu3+ within a framework of exfoliated g-C3N4 nanosheets (Eu/nanoC3N4) was achieved via a straightforward one-step pyrolysis process using dicyandiamide and EuCl3·6H2O as precursors in N2 at 550 °C by the conjoint use of NH4Cl as a dynamic gas template. Physicochemical characterization by means of X-ray diffraction, X-ray photoelectron spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, and Eu LIII-edge X-ray absorption fine structure analyses provided evidence for the generation of a single-atom Eu3+ complex in the cavity bonded with six N atoms constructed by three heptazine units in the g-C3N4 framework. Eu/nanoC3N4 exhibited characteristic Eu3+ emissions attributed to the 5D0 → 7F2 transitions, which are quickly quenched at room temperature upon exposure to particular volatile organic compounds (VOCs) with moderate adsorption energies, such as acetone and cyclohexane, as evidenced by density functional theory calculations. Fourier transform infrared analysis indicated that the sensing properties are due to a ligand–metal energy transfer mechanism between adsorbed VOC molecules and the single-atom Eu doped within the C3N4 framework. The results provide insight into the utilization of single-atom Eu3+ complexes within the framework of exfoliated g-C3N4 nanosheets for the development of potential luminescent sensing materials with high sensitivity and selectivity.