Embedding Sodium Ions in Graphitic Carbon Nitride Vacancies for Visible Light Photocatalytic H2 Evolution

In this work, through first-principles density functional theory calculations, Na ions embedded in the vacancies of the aromatic ring plane of graphitic carbon nitride (g-C-3 N-4) were predicted to bridge the transfer of photoinduced charge carriers and subsequently enhance its photocatalytic activity. Thereafter, Na-functionalized g-C3N4 (Na/CN) was synthesized via a one-step polymerization of melamine and NaBH4. The formation of coordinative Na-N bonds with the N atoms at the edge of aromatic rings resulted in a bridge that facilitated the transfer and separation of photogenerated carriers, changed the electronic band structure of g-C3N4, enhanced the separation degree of the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO), and increased the visible light absorption, thus realizing efficient photocatalytic hydrogen generation under visible light. The hydrogen evolution rate of 10 mg of photocatalyst 10Na/CN reached 17.4 mu mol/h under visible light irradiation with lambda > 420 nm, which was about 12.8 and 35.0 times higher than those of Nw/CN nanowires and Bulk/CN, respectively.