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

Abstract

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.