Construction of 2D-2D S-scheme heterojunction based graphdiyne (g-CnH2n−2) coupling with highly crystalline nitrogen defect g-C3N4 for efficient photocatalytic overall water splitting

Graphdiyne (GDY) is an up-and-coming two-dimensional all-carbon nanostructured material, which fills the long-standing gap in carbon material science and opens up a whole new way for the research of electronic, optical and semiconductor materials. In this work, a 2D-2D S-scheme heterojunction was constructed by 2D GDY coupling with highly crystalline nitrogen defect g-C3N4 nanosheets (GDY/g-C3N4-VN) for efficient photocatalytic overall water splitting. GDY was fabricated by the cross-coupling reaction of hexaethynylbenzene with CuI as catalyst and substrate. And the highly crystalline nitrogen defect porous g-C3N4-VN was fabricated by the alkali-molten salt-assisted method and the existence of N defects was testified by Transmission Electron Microscopy (TEM) and Electron Paramagnetic Resonance (EPR). In addition, the successful construction of S-scheme heterojunction between GDY and crystalline g-C3N4-VN was strongly demonstrated by in situ XPS, Electron Spin Resonance (ESR) and Density Function Theory (DFT) calculations. The construction of GDY/crystalline g-C3N4-VN (GNG-X) heterojunctions enhances the charge density and raise detaching efficiency of photogenerated carriers. The excellent and photostable photocatalytic hydrogen evolution activity of 17.87 μmol h−1 was acquired on CNG-25, which increased of 25.23 folds than that of GDY alone. Most importantly, photocatalytic overall water splitting experiments were carried out by loading 3 wt% Co3O4 and 1 wt% Pt as cocatalysts on CNG-25, and the yields of H2 and O2 were obtained as 0.48 μmol h−1 and 0.24 μmol h−1, respectively, which further demonstrated the promising application value of CNG-25 photocatalyst. This work presents a simple strategy for the design and manufacture of novel 2D GDY-based S-scheme heterojunction to enhance photocatalytic activity and achieve overall water splitting.