Modulation of mixed matrix membranes with positively charged polymer-grafted nanoparticles for enhanced protein separation and fouling resistance

To address the persistent challenges in membrane-based protein separation, including membrane fouling and the permeability–selectivity trade-off, we developed mixed matrix membranes (MMMs) by incorporating positively charged polymer-grafted nanoparticles into the PVDF membrane matrix. The incorporated nanoparticles regulated the membrane microstructure and interfacial physicochemical properties, thereby enhancing water permeation and protein separation performance. Compared with the pristine PVDF membrane, the optimized MMM containing 0.25 wt% polymer-grafted nanoparticles exhibited an increase in BSA permeate flux from 8.2 to 15.3 L m -2 h −1 , corresponding to an 86 % relative increase, together with a 17 % relative improvement in BSA rejection. This simultaneous enhancement was mainly attributed to the combined effects of enlarged effective pore size, improved hydrophilicity, and regulated electrostatic interactions. The modified membrane also showed improved antifouling performance, as evidenced by the increase in flux recovery ratio from 76.1 % to 89.4 % and the decrease in irreversible fouling ratio from 23.9 % to 10.6 %. Static adsorption tests showed that the BSA adsorption capacity decreased from 18.75 to 4.38 μg cm −2 after nanoparticle incorporation, confirming that the positively charged nanoparticles did not promote irreversible protein adsorption. These improvements were mainly associated with the formation of an interfacial hydration layer and the regulation of the pore structure. Notably, the optimized MMM maintained stable permeability and rejection after five cycles of alternating BSA filtration and water cleaning, demonstrating favorable cyclic stability. These results demonstrate that positively charged polymer-grafted nanoparticles can serve as effective interfacial modifiers for regulating membrane structure, hydration behavior, and protein fouling pathways, providing a potentially useful strategy for developing antifouling MMMs for protein-separation applications.