Novel thin-film composite nanofiltration hollow fiber membranes with double repulsion for effective removal of emerging organic matters from water

A novel thin-film composite nanofiltration (NF) membrane was fabricated by interfacial polymerization of hyperbranched polyethyleneimine (HPEI) and isophthaloyl chloride (IPC). For the first time, a dual-layer hollow fiber membrane was employed as the substrate for interfacial polymerization. The substrate possesses a unique cross-section structure comprising a layer full of macrovoid located in the middle and sandwiched by two thin spongy-like layers. Such a sandwich-like sublayer structure provides minimal transport resistance and sufficient mechanical strength for water permeation under high pressures. After interfacial polymerization, the NF membrane possesses a negatively charged substrate and a positively charged selective layer with a mean effective pore radius of 0.36 nm, molecular weight cut off of 500 Da, and pure water permeability of 4.9 l m−2 bar−1 h−1. Due to this double-repulsion effect, together with the steric-hindrance and the solute electro-neutrality effects, the newly developed NF membrane shows superior rejections (over 99%) for both positively and negatively charged dye molecules. By adjusting the pH of cephalexin aqueous solution to modify the ionization states of this zwitterionic molecule, the NF membrane shows high rejections over a wide pH range. The NF membrane may potentially be useful to reduce waste, recycle valuable products and reuse water for textile, pharmaceutical and other industries.