Separation of reactive dyes using PES/SPEEK blend nanofiltration membrane

Abstract

The objectives of this research are to characterize and evaluate the performance of negatively charged nanofiltration (NF) flat sheet membrane for dyeing wastewater treatment. 20 wt% polyethersulfone (PES) was used to prepare the sheet due to its good structural integrity incorporation the standard of permeability and rejection which are close to NF category. Negatively charged NF membranes with thickness of 150µm were successfully fabricated by blending with sulfonated poly (ether ether ketone) (SPEEK) in the range of 0-4 wt%. Prior to membrane fabrication, the synthesized SPEEK was characterized in terms of the degree of sulfonation (DS) using nuclear magnetic resonance (NMR) spectroscopy. The morphological structure of membrane was determined using scanning electron microscopy (SEM), atomic force microscopy (AFM) and their performances were examined in terms of flux and rejection. It was found that the blend membranes exhibited higher water flux and dye rejection in comparison to pure PES membrane. High water flux is due to increasing SPEEK content, implying that the improvement in the hydrophilicity which was confirmed by contact angle (CA) values. However, controlling the content SPEEK with high DS of 75% is necessary because the integrity of membrane tends to deteriorate at high SPEEK content, resulting in low dye rejection. In the dye separation test, almost complete rejection (>99.1%) of Reactive Black (RB5) and more than 91.4% rejection of Reactive Orange 16 (RO16) was achieved with the use of feed solution contains 200 ppm. The dye rejection was found to be dominated by sieving effect as NF membranes typically possess pore radius in sub-nanometer range, which is relatively smaller than the effective hydrodynamic radius of dye molecules. Hence, the membrane produced in this study is very promising to be used in the separation of dye from textile dyeing wastewater.