PHOTOCHEMICAL REDUCTION OF CARBON-DIOXIDE TO METHANOL USING ZNS MICROCRYSTALLITE AS A PHOTOCATALYST IN THE PRESENCE OF METHANOL DEHYDROGENASE

Photoinduced reduction of formate to methanol has been achieved using ZnS microcrystalline colloid which contained formate, methanol dehydro genase (MDH), pyrroloquinoline quinone (PQQ) as an electron mediator f or MDH, and 2-propanol. This reaction was combined with photoreduction of carbon dioxide to formate on the ZnS microcrystallite which had al ready been reported to provide a new photosynthetic route for producti on of methanol from carbon dioxide. The production of methanol showed a saturation tendency when it was accumulated to 0.25 mmol dm-3, proba bly due to oxidation of the produced methanol at MDH or on the ZnS pho tocatalyst or both. The concentration of PQQ influenced the amount of formate production but not the methanol production. The quantum effici ency obtained at 280 nm for the reduction of carbon dioxide to methano l was 5.9%, which is the highest value that has ever been reported for the photochemical reduction of carbon dioxide to methanol.