Magnetic nanoparticles augmented composite membranes in removal of organic foulant through magnetic actuation

Abstract

Exploring ways to remove foulants is of great importance for sustainable membrane operation in wastewater treatment. This study investigates the efficiency of humic acid removal by a magnetic responsive Fe3O4–PES nano-composite membrane. Magnetic responsive iron oxides (Fe3O4) were first end-capped onto the surface of a polyethersulfone (PES) membrane using a polyelectrolyte modification method. The amount of end-capped Fe3O4 was varied by adjusting the concentration of suspended magnetite nanoparticles from 100ppm to 2500ppm. A quartz crystal microbalance with dissipation (QCM-D), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), contact angle measurement and X-ray photoelectron spectroscopy (XPS) were used to determine the adsorption kinetics and the morphology of Fe3O4 deposited on PES membranes. The combined results of frequency shifts (Δf) and changes in the dissipation factor (ΔD) from QCM-D demonstrated an increased deposition rate of Fe3O4 as the concentration of suspended magnetite nanoparticles was increased. As for filtration studies, when the Fe3O4–PES nano-composite membranes were exposed to an alternatively switching oscillating external magnetic field, torque effects on the nanoparticles were generated and twisted the deposited Fe3O4 nano-colloids. This magnetic nanoparticles augmented nano-composite membrane was able to retain a normalized flux of 0.96 (J=32.8Lm−2h−1) with rejection of 99.4±0.14%. This was due to the twisting effect of the Fe3O4 nanoparticles that reduces concentration polarization near the top surface of the membrane and consequently reduces the potential for membrane fouling.