Interlayer-active layered oxysulfides NaMTiO₂.₂S₁.₈ (M = Nd, Sm) with an 𝘯 = 1 Ruddlesden–Popper structure acting as photocatalysts for visible light water splitting

Layered compounds that utilize interlayer space as a reactive field are known as “interlayer-active” compounds and have been gaining attention, particularly in photocatalysis for water splitting. However, most of the reported “interlayer-active” photocatalysts are oxide semiconductors that possess a wide bandgap. Thus, they cannot utilize visible light essential for efficient water splitting. In this study, we synthesized novel Ruddlesden–Popper (RP) (n = 1) layered oxysulfides, NaMTiO2.2S1.8 (M = Nd, Sm), by heating “interlayer-active” layered oxides, NaMTiO4, under H2S flow. In NaMTiO2.2S1.8, the sulfur atoms occupy the apical oxygen sites and contribute to the elevated valence band maximum (VBM) to enable visible light absorption. Additionally, NaMTiO2.2S1.8 exhibits both proton exchange and interlayer hydration capabilities as well as photocatalytic activity for hydrogen and oxygen evolution under visible light. Hence, NaMTiO2.2S1.8 is the first example of both a n = 1 RP and an “interlayer-active” oxysulfide with the potential for visible-light-driven overall water splitting. The “interlayer-active” RP (n = 1) oxysulfide is expected to find application in various fields beyond photocatalysis by utilizing interlayer reactions such as ion exchange and interlayer hydration.