Engineering of a hierarchical S-scheme 2D/3D heterojunction with graphdiyne (g-CnH2n-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 mu mol 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.