Photo-catalytic H2 evolution, structural effect and electron transfer mechanism based on four novel [2Fe2S] model complexes by photochemical splitting water

• Four new bionic photocatalysts (1–4) with [2Fe2S] model complexes were reported.
• H2 evolution of 1–4 was evaluated, the max H2 yield reached 52.9 ± 1.6 TON (vs. 4).
• Inactivity of system was mainly due to photo-degradation of EBS2− and catalyst (1–4).
• Reduced FeIFe0 species could be formed by ET from 1*EBS2− to FeIFeI.
• The effect of [2Fe2S] complexes’ structure on H2 production mechanism was discussed.

Four novel [2Fe2S] model complexes (1–4) had been synthesized and characterized by IR, 1H NMR, elemental analysis and single crystal X-ray crystallography (for 2). The key parameters affecting H2 evolution of title compounds (1–4) were optimized by constructing homogeneous photo-catalytic system consisting of title compounds (1–4) as catalyst, erythrosin B sodium salt (EBS2−) as photo-sensitizer (PS) and triethylamine (TEA) as sacrificial reagent in CH3CN/H2O solution under the irradiation of visible light. The maximum H2 evolution was separately 211.4 ± 6.5 μmol (52.9 ± 1.6 TON vs. 4), 199.4 ± 13.5 μmol (49.9 ± 3.4 TON vs. 1), 124.8 ± 7.6 μmol (31.2 ± 1.9 TON vs. 3) and 34.9 ± 6.9 μmol (8.7 ± 1.7 TON vs. 2) under the optimal conditions with catalyst of 2 × 10−4 mol·L−1, EBS2− of 4 × 10−4 mol·L−1, TEA of 10% (v/v) and pH 12 in CH3CN/H2O (1/1, v/v) solution. Furthermore, the structural effect and mechanism of electron transfer in the present system was carefully discussed by fluorescence spectra and cyclic voltammetry (CV) measurements.

We have constructed a homogeneous photo-catalytic system using [2Fe2S] model complexes 1–4 as biomimetic photo-catalysts, EBS2− as PS and TEA as sacrificial reagent in CH3CN/H2O (v/v, 1/1) solution under the visible light irradiation. The H2 evolution performance and mechanism of target complexes 1–4 were evaluated. The result suggested that the different structures of [2Fe2S] simulate complexes affect on H2 evolution performance and mechanism, the maximum H2 evolution was 211.4 ± 6.5 μmol (52.9 ± 1.6 TON vs. 4). The H2 generation mechanism might be able to firstly form an intermediate Fe0FeI by electron transferring from 1*EBS2− to [2Fe2S] center, and then underwent an ECEC (for 1, 2 and 4) or EECC (for 3) process to form the important H2–Fe2S2 (η2-H2–FeIIFeI) species of H2 production. The result indicated the target complexes are potential candidates as photo-catalysts for H2 generation.Figure optionsDownload as PowerPoint slide