Self-assembly of mixed valence polyoxovanadate-based metal-organic frameworks for enhanced CO2 photoreduction

The design of efficient catalysts for photocatalytic CO2 conversion is extremely significant to alleviate greenhouse effect and energy crisis. In this study, two novel structurally clear polyoxovanadates (POVs)-based metal-organic frameworks, that is, {[Co(CH3OH)2(bbbm)][H6VIV12VV6O42(SO4)]}& BULL;3CH3OH & BULL;3H2O [abbr. V18-Co, bbbm = 1,1 & PRIME;-(1,4-butanediyl)-bis-1H-benzimidazole], {[Mn(CH3OH)2(bbbm)][H6VIV12VV6O42(SO4)]}& BULL;5CH3OH & BULL;2H2O (V18-Mn), were successfully synthesized under solvothermal conditions. It is noticed that the ball-shaped octadecanuclear vanadium cluster is quite rare as a building block in POV-based hybrids. The structural characterizations and the photocatalytic CO2 conversion, are explored systematically. It can be confirmed that the cobalt containing POV-based metal-organic frameworks can photoreduce CO2 under visible light, and V18-Co has higher photocatalytic performance. In the heterogeneous catalytic system, V18-Co exhibited a robust CO formation rate up to 10371 & mu;mol g- 1h- 1 with high CO selectivity of ca. 93.1%, which outperforms most reported polyoxometalate-based MOF systems. Moreover, cycling tests confirmed that V18-Co was a high-efficient and stable photocatalyst for CO2 reduction, which could be repeatedly applied multiple cycles without losing its catalytic activity.