2D/2D S-scheme heterojunction with a covalent organic framework and g-C3N4 nanosheets for highly efficient photocatalytic H2 evolution

The fabrication of S-scheme heterojunctions with fast charge transfer and good interface contacts, such as intermolecular π–π interactions, is a promising approach to improve photocatalytic performance. A unique two-dimensional/two-dimensional (2D/2D) S-scheme heterojunction containing TpPa-1-COF/g-C3N4 nanosheets (denoted as TPCNNS) was developed. The established maximum interfacial interaction between TpPa-1-COF NS and g-C3N4 NS may result in a π–π conjugated heterointerface. Furthermore, the difference in the work functions of TpPa-1-COF and g-C3N4 results in a large Fermi level gap, leading to upward/downward band edge bending. The spontaneous interfacial charge transfer from g-C3N4 to TpPa-1-COF at the π–π conjugated interface area results in the presence of a built-in electric field, according to the charge density difference analysis based on density functional theory calculations. Such an enhanced built-in electric field can efficiently drive directional charge migration via the S-scheme mechanism, which enhances charge separation and utilization. Thus, an approximately 2.8 and 5.6 times increase in the photocatalytic hydrogen evolution rate was recorded in TPCNNS-2 (1153 μmol g−1 h−1) compared to pristine TpPa-1-COF and g-C3N4 NS, respectively, under visible light irradiation. Overall, this work opens new avenues in the fabrication of 2D/2D π–π conjugated S-scheme heterojunction photocatalysts with highly efficient hydrogen evolution performance.