Non-covalent polyhedral oligomeric silsesquioxane-polyoxometalates as inorganic–organic–inorganic hybrid materials for visible-light photocatalytic splitting of water

Abstract

A new series of visible light responsive and water-stable inorganic–organic–inorganic hybrid materials such as polyoxometalate (POM) and polyhedral oligomeric silsesquioxanes (POSS) with different metals was prepared, and these materials include {[PW₁₂O₄₀][(NH₃CH₂CH₂CH₂)(ⁱBu)₇Si₈O₁₂]₃ (POM(W)–POSS), [PMo₁₂O₄₀][(NH₃CH₂CH₂CH₂)(ⁱBu)₇Si₈O₁₂]₃ (POM(Mo)–POSS) and [PMo₁₀V₂O₄₀][(NH₃CH₂CH₂CH₂)(ⁱBu)₇Si₈O₁₂]₅ (POM(MoV)–POSS)}; these materials containing a cationic electron donor of amino-substituted POSS (POSS-NH₂) on an anionic electron acceptor of POM have been developed for efficient and sustainable photocatalytic H₂ production. It is interesting to note that the synthesized hybrid materials exhibit remarkable photocatalytic H₂ production activities under visible-light irradiation. The maximum H₂ production rate of 485 μmol h⁻¹ g⁻¹ is achieved using POM with heterometallic sites, i.e., (MoV)–POSS rather than that having homometallic sites. The enhanced photocatalytic H₂ production is mainly due to improved charge carrier separation by electron-deficient metal sites and a red shift in the absorption, as revealed from photoluminescence and UV-vis spectra. Importantly, POM–POSS hybrid materials demonstrate excellent water stability during photocatalysis due to the hydrophobicity of the hybrid materials, which results from the integration of hydrophobic POSS-NH₂ with POMs in contrast to free POMs. Additionally, the successful integration of POSS-NH₂ into POMs is confirmed using FT-IR, NMR, ESI mass spectroscopy, and elemental and thermogravimetric analyses. The present study may open new possibilities in the design and development of stable POM organic/inorganic hybrid materials for solar energy conversion applications.