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

Abstract

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·(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.