Ordered Coimmobilization of a Multienzyme Cascade System with a Metal Organic Framework in a Membrane: Reduction of CO 2 to Methanol.

Enzymatic reduction of CO2 is of great significant, which involves an efficient multienzyme cascade system (MECS). In this work, Formate dehydrogenase (FDH) & Glutamate dehydrogenase (GDH) & reduced pyridine nucleotide (NADH), Formaldehyde dehydrogenase (FalDH) & GDH & NADH and Alcohol dehydrogenase (ADH) & GDH & NADH were respectively embedded in ZIF-8 (one kind of metal organic framework) to prepare three kinds of enzymes & coenzymes/ZIF-8 nanocomposites. Then, by the dead-end filtration these nanocomposites were sequentially located in microporous membrane, which was combined with a pervaporation membrane to timely achieve the separation of product methanol. The incorporation of the pervaporation membrane was helpful to control reaction direction, and the methanol amount increased from 5.8 ± 0.5 μmol to 6.7 ± 0.8 μmol. The reaction efficiency of immobilized enzymes ordered distribution in membrane was higher than that disordered distribution in membrane, and the methanol amount increased from 6.7 ± 0.8 μmol to 12.6 ± 0.6 μmol. Moreover, it appeared that the introduction of NADH into ZIF-8 enhanced the transformation of CO2 to methanol from 12.6 ± 0.6 μmol to 13.4 ± 0.9 μmol. Over 50 % of their original productivity was retained after 12 h using. This method has wide applicability and can be used in other kinds of multi-enzyme systems.