Surface Chemical Heterogeneity over Defect Density Enhances Glucose Isomerase Immobilization in Acetate-Modified UiO-66 for Efficient Glucose-to-Fructose Isomerization

Metal-organic frameworks (MOFs) represent promising platforms for enzyme immobilization; however, the interplay between surface chemical heterogeneity and defect density in dictating adsorption efficiency remains poorly understood. Herein, we systematically investigated the immobilization of glucose isomerase (GI) on three UiO-66 variants, indicating that the acetic acid (AA)-modified UiO-66 (UiO-66-AA) achieved the highest enzyme loading efficiency of 92.8% and activity recovery of 84.2%, markedly outperforming both pristine UiO-66 and formic acid-modified UiO-66 (UiO-66-FA). The resulting UiO-66-AA-GI composite achieved the highest fructose yield of 37.7% with an excellent selectivity of 94.8% under optimal conditions and retained stable performance over five recycling cycles. Comprehensive characterization demonstrates that acetate modification generates a distinctive chemical mosaic surface, in which hydrophobic methyl domains and residual carboxyl groups synergistically enable multimodal adsorption via hydrophobic interactions, hydrogen bonding, and weak electrostatic forces. This unique surface chemistry, combined with the largest external surface area, maximizes GI loading while preserving the catalytic activity. These findings establish that rationally designed surface chemical mosaics with complementary interaction modes are critical for achieving high-efficiency enzyme immobilization in MOF-based biocatalysts.