Modulator-controlled nucleation and growth of UiO-66 membranes for C6 isomer separation

The separation of hydrocarbon isomers is essential in petrochemical upgrading; however, conventional distillation processes remain highly energy-intensive. Metal–organic framework (MOF) membranes have emerged as an energy-efficient alternative, yet the fabrication of intercrystalline defect-free membranes with precise microstructural control remains challenging. Herein, we report a modulator-controlled nucleation and growth strategy to direct the crystallization of UiO-66 membranes. Acetic acid (high pK a , weak deprotonation ability) was used to induce rapid nucleation and generate a uniform nanoparticle seed layer, whereas formic acid (low pK a , strong deprotonation ability) competed vigorously with ligands for zirconium coordination, promoting Ostwald ripening and facilitating the formation of a well-intergrown, molecular-sieving membrane. The optimized membrane exhibited a separation factor of 2.27 for (n-hexane + 3-methylpentane) versus 2,2-dimethylbutane. When challenged with a ten-component alkane isomer mixture mimicking light naphtha, a two-stage cascade process enriched low-octane alkanes from 49.0 to 90.5 wt% in the permeate stream, while simultaneously concentrating high-octane alkanes in the retentate. This work constitutes the first demonstration of acidity-modulated MOF membranes for the separation of industrially relevant alkane isomers, highlighting their potential to hybridize or replace energy-intensive distillation in the petrochemical industry.