G.S. Lai

A practical approach to synthesize polyamide thin film nanocomposite (TFN) membranes with improved separation properties for water/wastewater treatment

Thin film nanocomposite (TFN) membranes containing 0.05 or 0.10 w/v% surface-functionalized titanate nanotubes (TNTs) in a polyamide selective layer were synthesized via interfacial polymerization of piperazine (PIP) and trimesoyl chloride (TMC) monomers. Nanomaterials were dispersed into the monomer solution using two different approaches. In the first one, the functionalized TNTs were dispersed into the amine aqueous solution, while in the second approach the same nanomaterials were dispersed in TMC organic solution. The TFN membranes were characterized and compared with a control thin film composite (TFC) membrane to investigate the effect of nanofiller loadings and the fabrication approach on membrane properties. Results showed that introducing nanofillers into the organic phase was more effective to synthesize a TFN membrane of greater separation performance as the use of a rubber roller to remove aqueous solution from the substrate surface could cause the loss of a significant amount of nanofillers, which further affected the polyamide layer integrity. It was also found that the incorporation of a high nanofiller loading tended to interfere with interfacial polymerization and weaken the bonds between monomer blocks, resulting in poor polyamide–nanotube integrity. Compared to the TFC membrane, the TFN membrane made of 2% PIP and 0.15% TMC with 0.5% nanofiller incorporation could achieve greater water flux (7.5 vs. 5.4 L m−2 h−1 bar−1) and Na2SO4 rejection (96.4% vs. 86%) while exhibiting higher resistance against fouling by protein and dye.

Anti-Fouling Double-Skinned Forward Osmosis Membrane with Zwitterionic Brush for Oily Wastewater Treatment

Despite its attractive features for energy saving separation, the performance of forward osmosis (FO) has been restricted by internal concentration polarization and fast fouling propensity that occur in the membrane sublayer. These problems have significantly affected the membrane performance when treating highly contaminated oily wastewater. In this study, a novel double-skinned FO membrane with excellent anti-fouling properties has been developed for emulsified oil-water treatment. The double-skinned FO membrane comprises a fully porous sublayer sandwiched between a highly dense polyamide (PA) layer for salt rejection and a fairly loose dense bottom zwitterionic layer for emulsified oil particle removal. The top dense PA layer was synthesized via interfacial polymerization meanwhile the bottom layer was made up of a zwitterionic polyelectrolyte brush - (poly(3-(N-2-methacryloxyethyl-N,N-dimethyl) ammonatopropanesultone), abbreviated as PMAPS layer. The resultant double-skinned membrane exhibited a high water flux of 13.7 ± 0.3 L/m2.h and reverse salt transport of 1.6 ± 0.2 g/m2.h under FO mode using 2 M NaCl as the draw solution and emulsified oily solution as the feed. The double-skinned membrane outperforms the single-skinned membrane with much lower fouling propensity for emulsified oil-water separation.