Hexamolybdenum clusters supported on graphene oxide: Visible-light induced photocatalytic reduction of carbon dioxide into methanol

Hexamolybdenum (Mo6) cluster-based compounds namely Cs2Mo6Bri8Bra6 and (TBA)2Mo6Bri8Bra6 (TBA = tetrabutylammonium) were immobilized on graphene oxide (GO) nanosheets by taking advantage of the high lability of the apical bromide ions with oxygen-functionalities of GO nanosheets. The loading of Mo6 clusters on GO nanosheets was probed by Fourier-transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), high resolution transmission electron microscopy (HRTEM) and elemental mapping analyses. The developed GO-Cs2Mo6Bri8Brax and GO-(TBA)2Mo6Bri8Brax composites were then used as heterogeneous photocatalysts for the reduction of CO2 under visible light irradiation. After 24 h visible light illumination, the yield of methanol was found to be 1644 and 1294 μmol g−1 cat for GO-Cs2Mo6Bri8Brax and GO-(TBA)2Mo6Bri8Brax, respectively. The quantum yields of methanol by using GO-Cs2Mo6Bri8Brax and GO-(TBA)2Mo6Bri8Brax as catalysts with reference to Mo6 cluster units presented in 0.1 g amount of catalyst were found to be 0.015 and 0.011, respectively. The role of immobilized Mo6 clusters-based compounds on GO nanosheets is discussed to understand the photocatalytic mechanism of CO2 reduction into methanol.