Photocatalyst based on a transition metal-Schiff base ligand and V-doped Kegging-type polyoxometalate for efficient and stable CO₂ reduction

In order to simultaneously control the greenhouse effect and solve the problem of energy depletion, the strategy of converting CO₂ into other forms of energy can be used. In this work, two Keggin-type polyoxometalate-based compounds were synthesized <i>via</i> the hydrothermal method: [Co(C₁₁H₁₅N₇O₂)(H₂O)₂]₄{[Co(C₁₁H₁₅N₇O₂)(H₂O)]₂(PWVI11V^IVO₄₀)}(PWVI9W^V₂V^IVO₄₀)·14.5H₂O (1) and [Fe(C₁₁H₁₅N₇O₂)(H₂O)₂]₃{[Fe(C₁₁H₁₅N₇O₂)(H₂O)]₂(BW₁₂O₄₀)}(BW₁₂O₄₀)·11H₂O (2). The structural analysis of compound 1 indicated that an interesting V-doped Keggin-type (PWVI11V^IVO₄₀)^5- anion is successfully bonded to the two [Co(C₁₁H₁₅N₇O₂)(H₂O)]²⁺ cations to generate a hybrid [Co(C₁₁H₁₅N₇O₂)(H₂O)]₂(PWVI11V^IVO₄₀) unit. Through a series of photocatalytic CO₂ reduction reaction (CO₂RR) experiments, it was found that compound 1 exhibits good photocatalytic performance. The CO generation rate can reach 7081.4 μmol g^-1 h^-1, and the selectivity was 83.8%. In addition, the stable and efficient photocatalytic activity of compound 1 was verified after four-cycle photocatalytic experiments, which provided a new idea for CO₂ photoreduction to CO. Comparatively, the CO production rates was 103.5 μmol g^-1 h^-1 for compound 2. This is because the adsorption energy of CO on Co is lower than that on Fe. Furthermore, V-modified compound 1 enhances CO₂ adsorption to promote CO₂ conversion.