Mesoporous Layer-by-Layer Ordered Nanohybrids of Layered Double Hydroxide and Layered Metal Oxide: Highly Active Visible Light Photocatalysts with Improved Chemical Stability

Abstract

Mesoporous layer-by-layer ordered nanohybrids highly active for visible light-induced O₂ generation are synthesized by self-assembly between oppositely charged 2D nanosheets of Zn–Cr-layered double hydroxide (Zn–Cr-LDH) and layered titanium oxide. The layer-by-layer ordering of two kinds of 2D nanosheets is evidenced by powder X-ray diffraction and cross-sectional high resolution-transmission electron microscopy. Upon the interstratification process, the original in-plane atomic arrangements and electronic structures of the component nanosheets remain intact. The obtained heterolayered nanohybrids show a strong absorption of visible light and a remarkably depressed photoluminescence signal, indicating an effective electronic coupling between the two component nanosheets. The self-assembly between 2D inorganic nanosheets leads to the formation of highly porous stacking structure, whose porosity is controllable by changing the ratio of layered titanate/Zn–Cr-LDH. The resultant heterolayered nanohybrids are fairly active for visible light-induced O₂ generation with a rate of ∼1.18 mmol h^–1 g^–1, which is higher than the O₂ production rate (∼0.67 mmol h^–1 g^–1) by the pristine Zn–Cr-LDH material, that is, one of the most effective visible light photocatalysts for O₂ production, under the same experimental condition. This result highlights an excellent functionality of the Zn–Cr-LDH–layered titanate nanohybrids as efficient visible light active photocatalysts. Of prime interest is that the chemical stability of the Zn–Cr-LDH is significantly improved upon the hybridization, a result of the protection of the LDH lattice by highly stable titanate layer. The present findings clearly demonstrate that the layer-by-layer-ordered assembly between inorganic 2D nanosheets is quite effective not only in improving the photocatalytic activity of the component semiconductors but also in synthesizing novel porous LDH-based hybrid materials with improved chemical stability.