Octahedral rhenium K4[Re6S8(CN)6] and Cu(OH)2 cluster modified TiO2 for the photoreduction of CO2 under visible light irradiation

•Octahedral rhenium cluster supported to Cu(OH)2 cluster modified TiO2 for the photoreduction of CO2.•Solar assisted production of methanol under visible light.•A novel heterogenized homogeneous photoredox catalyst for solar fuel generation.•Easily recoverable and efficiently recyclable photoredox catalyst for CO2 conversion.

Octahedral hexacyano rhenium K4[Re6S8(CN)6] cluster complexes were grafted onto photoactive Cu(OH)2 cluster modified TiO2 {Cu(OH)2/TiO2} support. The rhenium and copper cluster modified TiO2 photocatalyst combines the advantages of heterogeneous catalyst (facile recovery, recycling ability of the catalyst) with the reactivity, selectivity of the soluble molecular catalyst. The synthesized heterogeneous catalyst was found to be highly efficient photoredox catalyst for the reduction of CO2 under visible light irradiation. Methanol was found to be the major liquid product with the formation of hydrogen as a by product as determined with GC-FID and GC-TCD, respectively. The methanol yield after 24 h irradiation was found to be 149 μmol/0.1 g cat. for Re-cluster@Cu(OH)2/TiO2 photocatalyst that is much higher than 35 μmol/0.1 g cat. for Cu(OH)2/TiO2 and 75 μmol/0.1 g cat. for equimolar rhenium cluster in the presence of triethanolamine (TEOA) as a sacrificial donor. The quantum yields (ϕMeOH) of Re-cluster@Cu(OH)2/TiO2 and Cu(OH)2/TiO2 were found to be 0.018 and 0.004 mol einstein−1, respectively. These values are much higher than those reported for other heterogeneous catalysts for six electron transfer reaction.

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