Acid-catalyzed hydrolysis of semi-aromatic polyamide NF membrane and its application to water softening and antibiotics enrichment

- We systemically investigated post-treatment on semi-aromatic polyamide membrane.
- Hydrolyzed amide group increased hydrophilicity, absolute value of surface charge.
- Post-treatment increased water flux by increasing MWCO value of membrane.
- In water softening, 10% water flux and 20% ideal selectivity was improved.
- Optimum membrane showed better performance for enrichment of antibiotics.

The effect of post-treatment by acid-catalyzed hydrolysis of a commercial NE70 semi-aromatic polyamide (PA) membrane was systemically investigated to determine feasibility of use in water softening and antibiotic enrichment applications. The surface of a post-treated PA membrane was characterized using various analytical tools: SEM (Scanning Electron Microscopy) for surface morphology, ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy) for chemical bonds, contact angle for hydrophilicity of membrane surface, and electrophoretic light scattering spectrophotometer for surface charge of membrane surface. Conversion of amide groups to amine and carboxyl groups by post-treatment increased hydrophilicity and absolute value of surface charge as well as pore size and molecular weight cut off (MWCO) value. Post-treated membrane under optimal condition showed enhancement of water flux (∼10%) as well as ∼20% ideal selectivity (Na+/Mg2+) for water softening using a single electrolyte solution. In addition, mixture selectivity (Na+/Mg2+) using a mixture solution at pH 3 was also improved ∼2.6 times. Post-treated membranes at pH 0.25 for 7 and 14 days as optimization points were also applied to enrichment of antibiotics which are erythromycin (ERY) and vancomycin (Van). Optimized post-treatment membranes showed higher water flux and lower NaCl rejection as well as competitive rejection of antibiotics when compared to virgin NE70 membrane or other commercial/fabricated membranes. The approach to post-treatment of semi-aromatic membrane by the acid-catalyzed hydrolysis method can be utilized as a multipurpose usage in the future depending on characteristics of the target compound (e.g. surface charge (positive/negative) or size diversity).