Engineering of a hierarchical S-scheme 2D/3D heterojunction with graphdiyne (g-C_nH_2n−2) coated 3D porous CoAl₂O₄ nanoflowers for highly efficient photocatalytic H₂ evolution

Solar photocatalytic hydrolysis of hydrogen is one of the most important ways to solve energy and environmental problems. Rational design and modulation of interfaces in S-scheme heterojunctions still present significant challenges for solar hydrogen production. Herein, a novel 2D/3D hierarchical graphdiyne/CoAl₂O₄ (GCA) S-scheme heterojunction was successfully constructed by coupling graphdiyne (GDY) nanosheets onto porous CoAl₂O₄ nanoflowers. GDY was synthesized by a cross-coupling reaction and ultrathin 3D porous CoAl₂O₄ nanoflowers were transformed from CoAl-LDH. This unique 3D hierarchical porous structure of CoAl₂O₄ nanoflowers not only provides a larger specific surface area, sufficient active sites and enhanced light harvesting, but also significantly reduces the aggregation of GDY. Notably, hierarchical GCA-15 shows an exceptional photocatalytic hydrogen production rate of 5009.28 μmol g⁻¹ h⁻¹ under visible-light irradiation, which was 4.78 times higher than that of pristine CoAl₂O₄. This excellent photocatalytic activity can be attributed to the synergistic effect of the formed S-scheme heterojunction between GDY and CoAl₂O₄ and the 2D/3D hierarchical architecture. In situ irradiated XPS, UPS and DFT unveil the S-scheme electron transfer for GDY/CoAl₂O₄. The work functions and charge density difference further indicate the electrons transferring from GDY to CoAl₂O₄. This work provided a simple strategy for designing and constructing hierarchical graphdiyne-based S-scheme heterostructures for photocatalytic hydrogen production.