The effect of dopant PO functional group and OH, O, H2O adsorption on the structural, electronic, and optical properties of triangular g-C3N4 quantum dots by first-principles study

The effect of dopant PO functional group and OH, O, H2O adsorption on the structural, electronic, and optical properties of triangular g-C3N4 QDs has been studied by first-principle calculations. Negative formation energies indicate that the formation processes of these systems are exothermic. PO doping can enhance the stability of C3N4–H QD and weaken the stability of C3N4–F QD. O–C3N4–H QD presents a chemisorption process, whereas the adsorption of OH group or H2O molecule on the C3N4–H QD is proposed to be a physisorption process. The substitutional PO group significantly deforms the geometric structure of the tri-s-triazine unit and induces charge redistribution in the PO-C3N4–H and PO-C3N4–F QDs. For C3N4–H QD, PO-C3N4–H QD, C3N4–F QD, and PO-C3N4–F QD, the calculated HOMO-LUMO gaps are 3.248, 1.583, 2.821 and 1.478 eV, respectively. The charge transfer between the O radical and the C3N4–H QD is +0.522 e, indicating a strong chemical bonding interaction. The tiny charge transfers of +0.107 e and +0.003 e indicate weak interaction between OH or H2O and C3N4–H QD. The study will provide an effective theoretical foundation for the development of new g-C3N4 QDs sensors or catalysis systems.