Cerium (III)-MOF as a photocatalyst for hydrogen evolution from water splitting

Exploring the photocatalytic application of cerium-based metal-organic frameworks (Ce-MOFs) has attracted special interest due to the high abundance, low cost, and easy availability of Ce as well as the presence of low energy 4f orbitals and redox Ce (III)/(IV) couple. However, in contrast to the recent emerging study on the development of Ce (IV)-MOFs as photocatalysts, there are few reports focusing on the photocatalytic performance of Ce (III)-MOFs. Meanwhile, research on comparing the photocatalytic properties of rare-earth lanthanide (Ln) ions has rarely been reported. Herein, a novel Ce (III)-MOF with a formula of (Ce)6(BDC)9(DMF)6(H2O)3<middle dot>(DMF)3, named CSUST-4 (CSUST stands for Changsha University of Science and Technology), was successfully synthesized and characterized. The comprehensive analysis of the Ce-O distance and Ce 3d spectra of CSUST-4, mixed-valence Ce (III/IV)-MOF CSUST-1, and Ce (IV)-MOF CSUST-3 demonstrated that the Ce-O distance (O from the oxo bridge) can be used as an important reference to assign the valence state of Ce in Ce-MOFs while the satellite peak around 916.0 eV attributed to Ce (IV) can be utilized to distinguish Ce (IV)-containing Ce-MOFs from Ce (III)-MOFs. Furthermore, the photocatalytic hydrogen evolution (PHE) property of CSUST-4 by water splitting was also studied, and by utilizing isostructural MOFs CSUST-4-Ln (Ln = La, Nd, Eu, Er, Yb) as platforms, the PHE performances of these Ln ions were compared, which evidenced that Ce is a suitable Ln ion to construct MOF materials for PHE in terms of cost and performance. This work contributes to the development of the Ce-MOF field as well as sheds light on advancing Ce (III)-MOFs toward potential photocatalytic application. The photocatalytic hydrogen evolution property of a novel Ce (III)-MOF from water splitting was studied and compared to isostructural Ln (III)-MOFs (Ln = La, Nd, Eu, Er, Yb), which evidenced that Ce is a suitable Ln ion to construct MOF materials for photocatalytic hydrogen evolution in terms of cost and performance. image