Nanofiltration membrane achieving dual resistance to fouling and chlorine for “green” separation of antibiotics

Abstract

Poor fouling and chlorine resistance significantly reduce the service life of traditional aromatic polyamides thin-film-composite (TFC) nanofiltration (NF) membranes, hindering their widespread applications in waste water treatment, pharmaceutical and fine chemicals industries. Herein, novel polyamide (PA) TFC NF membranes synthesized through interfacial polymerization (IP) of amino functional polyethylene glycol (PEG) and trimesoyl chloride (TMC) are designed for achieving dual resistance to fouling and chlorine. The hydrophilic PEG based PA TFC NF membranes show positive charge since the isoelectric points range from pH=8.9 to pH=9.1 and the salts rejection are in the order of R(MgCl2)>R(MgSO4)>R(NaCl)>R(Na2SO4). The high chlorine resistant performance has been proven by maintaining good salt rejections and high water flux of PEG based membranes after treatment by 2000ppm NaClO for 24h. Besides, high hydrophilicity (water angle of 15–18.2°) accounts for the excellent fouling resistance of the PEG based membranes with a water flux recovery of 90.2% using BSA as a model molecule. Importantly, the hydrophilic PEG based NF membranes have been exploited to separate several water soluble antibiotics (such as tobramycin, an aminoglycoside antibiotic applied in the treatment of various types of bacterial infections). By optimizing operating conditions, the advanced membranes show highly stable tobramycin solution flux of 37Lm−2h−1 alongside tobramycin rejections up to 96% with 50ppm feed concentration under 8.0bar. When the feed concentration increases up to 800ppm, our membranes can still exhibit a high rejection over 92%. Therefore, as a promising “green” technique capably declining the solvent emissions and energy-consuming, the designed PEG based NF membranes owning highly efficient antibiotic concentration ability together with dual resistance to fouling and chlorine have great potentials in substituting conventional separation techniques for concentration and purification of active molecules in pharmaceutical and fine chemicals industries.