Highly permeable polyamide nanofiltration membrane incorporated with phosphorylated nanocellulose for enhanced desalination

Nanofiltration (NF) membranes with excellent permeability and selectivity are highly desirable for the efficient separation but still remain a great challenge. Herein, a novel thin-film nanocomposite (TFN) membrane with excellent permeability and enhanced desalination was prepared by in-situ incorporating phosphorylated cellulose nanofibers (P–CNF) during interfacial polymerization. The unique attributes of P–CNF, especially the well dispersibility in water, excellent hydrophilicity and highly negative charges, were propitious to the formation of defect-free separation layer with hydrophilic nanochannels and high surface charge density. The composite membrane obtained thereby exhibited not only enhanced permeance of up to 17.0 L m−2 h−1 bar−1 but a high rejection of 95.4% for Na2SO4, successfully overcoming the trade-off effect between permeability and selectivity. Importantly, a low rejection of down to 5.3% for NaCl was achieved for the membrane due to a slight increase in effective pore size. Therefore, this composite membrane demonstrated elevated separation factor of up to 18.0 towards mono/divalent salts, 3–6 times higher than those of the reported TFN membranes and commercial NF membranes. Additionally, this membrane displayed highly efficient antibiotic desalination, suggesting its promising potential in pharmaceutical fields. As a result, the incorporation of P–CNF yielded a great enhancement to the water permeance and desalination ability of the polyamide membranes by tuning the microstructure. This work provided a novel biobased green nanomaterial for the fabrication of advanced NF membrane with outstanding perm-selectivity. The developed highly selective and permeable NF membrane has huge potentials in the efficient separation of divalent salt/antibiotic and monovalent salt.