The effect of dopant P=O 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 P=O functional group and OH, O, H2O adsorption on the structural, electronic, and optical properties of triangular g-C(3)N(4 )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.