Ruddlesden-Popper compound Sr2TiO4 co-doped with La and Fe for efficient photocatalytic hydrogen production

Doping techniques generally serve as effective means for tailoring the physicochemical properties of a target compound. In this work, we successfully co-doped La/Fe into Ruddlesden-Popper (RP) compound Sr2TiO4 and performed a detailed investigation on the crystal structure, morphology, optical absorption and photocatalytic hydrogen production reactions after doping. Our findings suggest that La/Fe co-doping slightly expand the unit cell of Sr2TiO4 while maintains the structure lamination. Incorporating La/Fe into Sr2TiO4 efficiently reduces the band gap and the level of band gap reduction can be controlled by varying the amounts of dopants. La/Fe co-doping significantly improves the photocatalytic properties of Sr2TiO4 under both full range (λ ≥ 250 nm) and visible light illumination (λ ≥ 420 nm). A fivefold enhancement in hydrogen production rate (∼106.2 μmol/h) is seen in sample Sr1.9La0.1Ti0.9Fe0.1O4 (x = 0.1). Efficient photocatalytic hydrogen production under visible light illumination (λ ≥ 420 nm) is also achieved in sample Sr1.7La0.3Ti0.7Fe0.3O4 (x = 0.3) with AQE as high as ∼1.18% at 420 nm. DFT calculations confirm the critical role of Fe in reducing the band gap of Sr2TiO4 by forming additional spin-polarized bands (SPB). The anisotropic charge transportation in Sr2TiO4 is also verified by our calculations as both conduction band minimum (CBM) and valence band maximum (VBM) are buried in TiO6 octahedron layers. The 2D charge transportation properties are particularly useful for photocatalytic reactions since interlayer charge recombination is essentially prevented.