Rational design of 2D-2D porphyrin metal-organic nanosheet/g-CN heterostructure for enhanced production of hydrogen under visible-light.

The development of heterojunction-based photocatalysts is a promising strategy to achieve enhanced green hydrogen (H) production by facilitating the competent separation of photo-induced charge carriers. In this context, two-dimensional (2D) metal-organic nanosheets (MONs) have garnered considerable attention owing to their unique properties of highly exposed active sites, ultrathin thickness, and large surface area. Especially, porphyrin-based 2D MONs have gained significant interest due to their optimum band structure and exceptional visible light harvesting properties. Herein, we efficaciously constructed a group of 2D porphyrin nanosheets (M-PNs, M = Pd, Pt, and Ni) and 2D-2D g-CN/Pd-PNs (CN-Pd) heterojunctions to achieve enhanced photocatalytic H production assisted by visible light irradiation (λ ≥ 420 nm). Among the 2D MONs, Pd-porphyrin nanosheet (Pd-PNs) displayed a substantially higher H evolution rate (HER) of 4910 μmol g h over Pt-PNs (2490 μmol g h) and Ni-PNs (108.6 μmol g h). Furthermore, 2D-2D heterojunction, CN-Pd(1:2) formed by coupling Pd-PNs with g-CN exhibited a remarkably enhanced HER of 8400 μmol g h, significantly higher than pristine Pd-PNs. This enhanced HER performance of heterojunction could be assigned to the synergistic interaction between Pd-PNs and g-CN, facilitating effective visible light absorption, facile charge separation, and migration with reduced recombination rates. The superior HER activity of CN-Pd(1:2) heterostructure was further established by transient photocurrent and time-resolved PL spectroscopy studies. This work highlights the importance of 2D-2D heterojunction photocatalysts for enhanced generation of green hydrogen by leveraging the cooperative effects between porphyrin MONs and g-CN.