Directional Shunting of Photogenerated Carriers in POM@MOF for Promoting Nitrogen Adsorption and Oxidation

Abstract

The efficient catalysis of nitrogen (N₂ ) into high-value N-containing products plays a crucial role in the N economic cycle. However, weak N₂ adsorption and invalid N₂ activation remain two major bottlenecks in rate-determining steps, leading to low N₂ fixation performance. Herein, an effective dual active sites photocatalyst of polyoxometalates (POMs)-based metal-organic frameworks (MOFs) is highlighted via altering coordination microenvironment and inducing directional shunting of photogenerated carriers to facilitate N₂ /catalyst interaction and enhance oxidation performance. MOFs create more open unsaturated metal cluster sites with unoccupied d orbital possessing Lewis acidity to accept electrons from the 3σ_g bonding orbital of N₂ for storage by combining with POMs to replace bidentate linkers. POMs act as electron sponges donating electrons to MOFs, while the holes directional flow to POMs. The hole-rich POMs with strong oxidation capacity are easily involved in oxidizing adsorbed N₂ . Taking UiO-66 (C₄₈ H₂₈ O₃₂ Zr₆ ) and Mo₇₂ Fe₃₀ ([Mo₇₂ Fe₃₀ O₂₅₂ (CH₃ COO)₁₂ {Mo₂ O₇ (H₂ O)}₂ {H₂ Mo₂ O₈ (H₂ O)}(H₂ O)₉₁ ]·150H₂ O) as an example, Mo₇₂ Fe₃₀ @UiO-66 shows twofold enhanced adsorption of N₂ (250.5 cm³ g^-1 ) than UiO-66 (122.9 cm³ g^-1 ) at P/P₀ = 1. And, the HNO₃ yield of Mo₇₂ Fe₃₀ @UiO-66 is 702.4 µg g^-1 h^-1 , ≈7 times and 24 times higher than UiO-66 and Mo₇₂ Fe₃₀ . This work provides reliable value for the storage and relaying artificial N₂ fixation.