Fouling resistant microfiltration (MF) membrane modified with thermo-reverisble magnetite nanoparticles

Abstract

We developed a dual stimuli-responsive Poly(tetrafluoroethylene) (PTFE) microfiltration (MF) membrane by thermo-responsive covalent attachment of magnetite nanoparticles. Magnetite-modified PTFE membrane had an excellent anti-fouling performance by magneto-rotation induced vortex as well as enhanced cleaning efficiency. To achieve this, a dynamic covalent bonding that responds to the change of temperature called as Diels-Alder cycloaddition, was introduced. Maleimide-terminated magnetite nanoparticles were synthesized by co-precipitation method of two precursors and polyethylene glycol methyl ether maleimide (PEG-Mal). Various concentration of PEG-Mal was tested to measure the optimized amount of PEG-Mal. A common PTFE MF membrane with the average pore diameter of 0.1 μm was modified with furan functionality by surface UV treatment under hydrazine vapor followed by addition of furfuryl glycidyl ether. Furan-modified PTFE membrane and maleimide-terminated magnetite nanoparticles were coupled by heat treatment. Successful synthesis of maleimide-terminated magnetite nanoparticles was observed by various characterization methods such as Fourier transform infrared spectroscopy (FT-IR), X-ray diffractometry (XRD), thermogravimetric analysis (TGA) and vibrating sample magnetometry (VSM). Also, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE- SEM) and contact angle measurement were additionally used to define characteristics of magnetite-coupled PTFE membrane. Especially, movement of magnetite nanoparticles by rotating external magnetic field was observed by particle image velocimetry (PIV). Finally, water filtration with deionized (DI) water and foulant solution was conducted to evaluate the performance of magnetite-coupled membrane. The modified membrane shown slow decrease of flux in spite of existence of foulant in the feed solution. Also, backwashing efficiency was remarkably enhanced from 44.6% to 80.9%, compared to neat-PTFE membrane. Contamination of membrane surface could be easily recovered by replacement of maleimide-terminated magnetite nanoparticles to new one. Declined water flux was restored to 80% of initial flux after regeneration of magnetite nanoparticles. This combination of magneto-induced foulant rejection and renewable surface can make synergetic effect of anti-fouling performance. This membrane can be efficiently applied to submerged membrane filtration system using feed solution with various type of foulants and thick concentration.