Fouling resistant polyvinyl chloride ultrafiltration membranes containing functionalized chitosan nanoparticles

Organic nanoparticles, such as chitosan nanoparticles, are promising alternatives to inorganic ones to fabricate nanocomposite ultrafiltration membranes. Surface modification of nanoparticles is necessary to realize their full potential in membranes. However, the coupling of nanoparticles surface modification with nanoparticles size makes it difficult to isolate their effects in membranes, resulting in a lack of understanding of how surface functional groups affect membrane performance. To decouple these effects, we first used a combined self-consistent field theory/density functional theory to predict the optimal size of chitosan nanoparticles with a specific surface chemistry leading to high performance ultrafiltration membranes by maximizing nanoparticles interfacial segregation-to-leaching ratio during nonsolvent-induced phase separation. Then, we prepared corresponding functionalized chitosan nanoparticles containing carboxymethyl, sulfonate or phosphate groups and investigated their effects on the ultrafiltration performance of polyvinyl chloride (PVC) membranes. Compared to pristine PVC membrane, the membrane containing sulfonated nanoparticles exhibited 300% and 13% improvement in water flux and alginate (a typical model foulant) rejection, respectively. The same membrane also showed the best antifouling properties in terms of increased flux recovery ratio (FRR) and reduced irreversible fouling ratio (IFR), 280% and 83%, respectively, compared to pristine PVC membrane. This, in addition to the interplay of thermodynamic and rheological effects on phase separation and membrane morphology, was attributed to the highest interfacial segregation-to-leaching ratio in the presence of sulfonated chitosan nanoparticles compared to other functionalized nanoparticles. Finally, the interfacial segregation-to-leaching ratio normalized by the nanoparticle/nonsolvent interaction parameter correlates well with the FRR and 1/IFR values of the nanocomposite membranes.