Incorporation of carboxylic monoamines into thin-film composite polyamide membranes to enhance nanofiltration performance

Nanofiltration membrane performance is enhanced to attain an economical water purification system. Herein, we developed a series of high-performance thin-film composite nanofiltration polyamide (PA) membranes by incorporating different monoamines containing carboxylic terminal groups such as 4-aminobenzoic acid (ABA), 6-aminocaproic acid (ACA), and 3-aminopropanoic acid (APA). Each monoamine was added to an aqueous piperazine (PIP) solution, which was reacted with trimesoyl chloride through interfacial polymerization on a porous polysulfone support. The chemical structures and compositions of the obtained membranes were characterized using attenuated total reflectance-Fourier transform infrared and x-ray photoelectron spectrometry. The PA membranes were measured for their contact angle and streaming potential. Both the membrane hydrophilic property and surface charge density were enhanced as a result of introducing carboxylic monoamines. The membrane separation performance was tailored by adjusting the monoamine structure and content. The pure water flux of the membranes increased in the following order: PAM < PAM-APA < PAM-ACA < PAM-ABA. PAM-ABA demonstrated the optimum nanofiltration performance - ABA:PIP = 5:5 (w/w); water flux, J(H2O) = 71.2 L m(-2) h(-1); salt rejections: R-Na2SO4 = 93.2% and R-NaCl = 15.6% (for 1000 ppm aqueous salt solution, operating at 0.6 MPa and 25 degrees C). Moreover, PAM-ABA delivered stable performance at various operating conditions and exhibited excellent antifouling properties.