Visible-light CO2 photoreduction of polyoxometalate-based hybrids with different cobalt clusters

2019 
The photoreduction of carbon dioxide (CO2) into valuable energy gas (CO and H2) is an efficient approach to addressing the fossil fuels crisis and mitigating the global warming effect. The development of effective photocatalysts for CO2 reduction is still desirable and challenging. Herein, two novel polyoxometalate-based hybrids with multinuclear cobalt clusters, [Co2.67(SiW12O40)(H2O)4(Htrz)4]·Cl1.33 (Htrz = 1,2,4-triazole) (1) with binuclear cobalt cluster and [Co3(SiW12O40)(H2O)3(Htrz)6Cl]·Cl·6H2O (2) with trinuclear cobalt cluster, have been synthesized under hydrothermal conditions. Both of them are characterized by single-crystal X-ray diffractions, PXRD, IR, TG and UV-Vis spectra. Compound 1 exhibits a 3D structure with 4-connected [SiW12O40] and 3-connected [Co2(Htrz)3(H2O)3] secondary building units (SBUs). The 1D chain of compound 2 is constructed from [SiW12O40] and [Co3(Htrz)6(H2O)3Cl] SBUs. Furthermore, photoreduction of CO2 under visible light of the two cobalt-based POMs has been investigated by using [Ru(bpy)3]Cl2·6H2O as a photosensitizer. The CO yields of compounds 1 and 2 were 15705 and 18501 μmol g−1 for CO2 photocatalytic reduction under three hours irradiation at 293 K, respectively. The different photocatalytic performance of 1 and 2 was explained by comparing the energy of the valence band, band gaps and conduction band. The results show that photocatalysts incorporated with multinuclear Co clusters can effectively improve photocatalytic activities, thus providing a valuable view to design high-performance and cost-acceptable molecular catalysts for CO2 photoreduction.
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