Adsorption of iron(II, III) cations on pristine heptazine and triazine polymeric carbon nitride quantum dots of buckled and planar structures: theoretical insights

The adsorption of the Fe2+ and Fe3+ cations on four surface models of graphitic carbon nitride quantum dots, including planar and corrugated nanosheets of triazine and heptazine structures has been explored using density functional theory. The adsorption was most favorable on hollow sites but with different coordination numbers and geometrical configurations. A remarkable decrease in the energy gap of the semiconductor (e.g., from 4.10 to 0.01 eV with the buckled triazine-type sensor) delineated the high capability of the 2D material toward the detection of iron cations, particularly the Fe3+ analyte. Remarkable charge transfers (in the range of 0.688-0.908 e and 1.692-1.794 e for Fe2+ and Fe3+, respectively) from the surface to the analyte were identified from the QTAIM charge analysis. Ignoring the surface curvature could overestimate the adsorption energy while underestimating the energy gap and charge transfer of both types of graphitic carbon nitride. The LOL profiles and density of electronic states revealed the mechanism and nature of the interactions.