Surface modification of HKUST-1 for enhanced activity of immobilized formate dehydrogenase used in CO2 hydrogenation

Post synthetic modification of a hydrophilic metal–organic framework (MOF), HKUST-1, with stearic acid (SA) was carried out to enhance the stability of HKUST-1 in aqueous solution to be used as a support for formate dehydrogenase (FDH) used for CO₂ conversion to formate. SA modification improved the hydrophobicity without affecting the morphology and crystal structure of MOF. Adsorption of FDH on the modified MOF (SA@HKUST-1) was compared to that of the native HKUST-1 and ZIF-L. The adsorption kinetics on all MOFs was found to follow pseudo-second order kinetics and the isotherm was best described by Freundlich model. The high stability of SA@HKUST-1 and enhanced hydrophobic interaction between support and CO₂ resulted in high catalytic efficiency and stability of FDH@SA@HKUST-1. The immobilized enzyme retained 95.1% of its initial activity after 4 cycles of repeated use. It was also shown that FDH@SA@HKUST-1 retained morphology and crystal structure after repeated use. Results of the present work provide novel insight into the influence of hydrophobic MOFs on the activity and stability of immobilized FDH. These findings are expected to assist in developing highly active and stable biocatalysts for CO₂ hydrogenation at commercial level.