Controllable synthesis of peryleneimide-based nanocrystals as bifunctional photocatalyst for water splitting

Perylene-based organic semiconductors have been widely applied in excellent photocatalytic hydrogen/oxygen evolution (PHE/POE) from water splitting, however, there are no reports on their bifunctional activity. Herein, the nanocrystals of one-dimensional metal-organic framework (Co-PDI) are successfully transformed from nanorods to nanosheets with the thickness of ∼ 7 nm through adjusting the acetic acid-assisted reaction between bis(N-carboxymethyl) peryleneimide and cobaltous nitrate. As compared to Co-PDI nanorods as photocatalyst, its nanosheets can not only keep the suitable energy level for more excellent POE activity, but also exhibit its structure advantages for PHE process. Under visible-light irradiation (λ > 420 nm), the PHE rate of 71.2 mmol•g^-1•h^-1 can be achieved with ascorbic acid as sacrificial agent, meanwhile, the POE rate of 18.2 mmol•g^-1•h^-1 can be reached with silver nitrate as electron acceptor at pH = ∼3.0. The performance surpasses the reported values obtained with bifunctional single-component, even heterojunction photocatalysts. The systematical characterizations reveal that for Co-PDI crystal with an intrinsic high POE activity, the enough exposure of its {002} facet with no reactive carboxyl groups should be a crucial for PHE process. This work presents an effective route of facet engineering to develop bifunctional photocatalysts for water splitting.