Incorporation of NU-1000 into Cellulose Acetate Membranes with Preserved Indoxyl Sulfate Adsorption

Abstract

Zirconium-based metal–organic framework (MOF) NU-1000 was successfully synthesized and exhibited the expected structural and chemical properties, confirming its suitability as an adsorbent for protein-bound uremic toxins (PBUTs). In batch experiments, NU-1000 removed approximately 53% of indoxyl sulfate (IS), corresponding to an adsorption capacity of 17.7 mg IS g^-1 NU-1000. To translate this adsorption capability into a membrane platform, mixed matrix membranes (MMMs) were prepared by incorporating NU-1000 into a cellulose acetate (CA) matrix via phase inversion. Structural characterization confirmed the uniform dispersion of NU-1000 microcrystals within the polymer, with no evidence of agglomeration or degradation during fabrication. The resulting membranes exhibited an asymmetric morphology, consisting of a dense selective layer supported by a porous substructure, while maintaining good hydrophilicity (contact angle < 60°) and structural integrity. Under crossflow filtration of buffered IS solutions, CA/NU-1000 membranes showed a 1.3-fold increase in IS transport compared to pristine CA membranes. This enhancement indicates that NU-1000 retains its adsorption functionality after incorporation into the polymer matrix and contributes to adsorption-assisted transport. The reversible interactions between IS and NU-1000 enhance solute partitioning within the membrane, promoting diffusion and increasing permeation. Overall, these results demonstrate that CA/NU-1000 MMMs combine the processability and transport properties of conventional polymeric membranes with MOF-based adsorption, offering a promising strategy for adsorption-assisted transport and improved clearance of PBUTs in hemodialysis.