Preparation And Performance Optimization Of Polyamide Composite Membranes With High-flux/Anti-fouling Property

With the rapid development of industrialization in China,the environmental protection industry attracts increasing attention especially in the field of water treatment.The membrane separation technology,which is dominated by nanofiltration?NF?and reverse osmosis?RO?,has been widely used due to its unique advantages.In order to further reduce operating cost,energy-efficient membranes are quite desirable in modern economic system,which could significantly promote the development of this technology.Therefore,polyamide composite membranes with enhanced performance were studied here to meet the above needs.On one hand,highly permeable and selective NF membranes were prepared on ultrafiltration membranes grafted with amino groups.On the other hand,a novel functional monomer was synthesized to fabricate RO membranes with excellent anti-fouling performance based on layer-by-layer assembly.For the NF membranes with enhanced permeation,an innovative strategy for an ultrathin polyaminophenylene?PAP?layer tethered onto substrate membrane surfaces based on a diazonium-induced anchoring process?DIAP?was introduced.This approach could be a new alternative for membrane surface amino-functionalization.Ultrathin polyamide NF membranes with thickness down to 8.5 nm were formed then by interfacial polymerization?IP?on a polysulfone?PSF?substrate with a PAP interlayer.The diamine and triacid chloride monomers were piperazine?PIP?and trimesoyl chloride?TMC?,respectively.Enhanced permeation and desirable selectivity of the NF membranes were achieved thanks to the existence of a PAP interlayer.Surprisingly,the?PAP₅?IP membrane shows outstanding flux which could still reach5.6 L/m²/h/bar even when being tested in 0.4 MPa using tap water as feed solution,with up to nearly two orders of magnitude higher permeation than those prepared on the bare PSF substrates.Considering that ultrafiltration supports and the monomers used to form the NF membranes are both commercially available,such a highly permeable and selective NF membrane has been quite potential for up-scaling in water treatment especially for household water filters to reduce energy consumed by separations.With regard to the novel RO membranes with excellent anti-fouling performance,there are two main strategies introduced here,one is to design the functional acyl chloride monomer5-?N-sulfonamide?isophthaloyl chloride?NSO?at the molecular level to realize self-polymerization,whereas a second approach is to apply layer-by-layer assembly to take the place of traditional IP process.The chemical structure,surface morphology,hydrophilicity,charge property,film thickness and separation ability were investigated as a function of assemble layers.The result shows that the RO membrane with only 5 deposition layers could achieve desirable desalination performance at an order of Na₂SO₄?99.6%?>MgSO₄?99.1%?>NaCl?97.2%?>MgCl₂?96.4%?>CaCl₂?94.2%?with the pure water flux of 1.3 L/m²/h/bar,and more importantly,it outperforms the membrane prepared by conventional IP method in exhibiting excellent antifouling property due to their unique surface morphology with only 13%flux attenuation in the test condition compared to 65%flux decline of that by IP,which is very encouraging in reducing running cost significantly.