Fabrication And Desalination Properties Of Poly (Ionic Liquid) Charged Nanofiltration Membranes

In printing and dyeing industry, a large amount of wastewater with high salinityand chroma are always produced, thereby resulting in seriously environmentalpollution, waste of resources and as well as costs increases. Hence, it is of practicalsignificance to accomplish the treatment and recycling of dye effluents. Usually, inthe practical industrial production, nanofiltration technology is adopted to removingof electrolytes from water-soluble organics. However, conventional nanofiltrationmembranes generally allow monovalent salts to be transmitted effectively butdivalent or multivalent salts. For this reason, based on previous studies, a series oforganic-inorganic hybrid positively charged loose nanofiltration membranes werefabricated in the interest of developing a certain nanofiltration membrane with highdivalent salts passage and organic matter removing. The main research contents andresults in this work are as follows:(1) Preparation of ionic liquid monomer and fabrication of SiO2-PIL/PESorganic-inorganic hybrid positively charged nanofiltration membranesThe quaternary ammonium type ionic liquid was prepared through the reactionbetween triethylamine and allyl chloride. Silicon oxide nanospheres (SiO2) withsmaller size were constructed using the hydrolysis and condensation oftetraethoxysilane (TEOS). Subsequently, a poly (ionic liquid) modified SiO2(SiO2-PIL) were fabricated through a reverse atom transfer radical polymerization(RATRP) method. Then, SiO2-PIL/PES hybrid membranes were prepared usingpolyethersulfone (PES) as membrane material, SiO2-PIL as nanofiller, viablending-phase inversion method. The performance properties of hybrid membraneswere investigated and the results showed that the optimal polymerization time ofRATRP in such system was24h. Moreover, during the first24hours, RATRPdisplayed the “control/living” characteristic with controlled molecular weight andlower polydispersity index (about1.02inhere). The prepared membrane exhibitedenhanced surface hydrophilicity with a lower water contact angle of57.5oand ahigher water permeability of189.23L/(m2h MPa). Additionally, SiO2-PIL/PES hybrid membranes represented better mechanical and thermostable properties, as wellas a good rejection performance for reactive dyes and an enhanced permeationperformance for salts. Under the pressure of0.4MPa, SiO2-PIL/PES hybridmembranes presented a rejection of above85%for reactive red49and above90%forreactive black5, whereas the rejection for MgSO4, MgCl2was only below10%andbelow5%for Na2SO4, NaCl.(2) Fabrication of HNTs-PIL/PES hybrid positively charged nanofiltrationmembranesPoly (ionic liquid) modified halloysite nanotubes (HNTs) were fabricatedthrough RATRP method and thus a positively charged inorganic nanomaterial wasobtained. Then, HNTs-PIL/PES hybrid positively charged nanofiltration membraneswere constructed by a blending-phase inversion method and the performanceproperties were investigated. The results indicated that by the incorporation ofHNTs-PIL, the hybrid membranes displayed an enhanced hydrophilicity with a lowerwater contact angle of60.5o. HNTs-PIL/PES hybrid membranes exhibited asignificantly enhanced thermostable property with an increment of20-40oC and thedecomposition temperature reached435oC. Importantly, HNTs-PIL/PES hybridmembranes also represented a good separation performance for reactive dyes andsalts. Under the pressure of0.4MPa, the rejection of HNTs-PIL/PES hybridmembranes for reactive red49was above85%and above95%for reactive black5,while the rejection for MgSO4, MgCl2was only about10%and about5%for Na2SO4,NaCl.(3) Fabrication of HT-PIL/PES hybrid positively charged nanofiltrationmembranesMg-Al hydrotalcite (HT) with high degree of crystallinity was prepared using a“urea” method and subsequently the interlayer anions were exchanged as NO3-. Thenthe anion exchanged Mg-Al HT was modified with poly (ionic liquid) using RATRPmethod. After the in-situ exfoliation of the modified product (HT-PIL) in N,N-dimethyl acetamide (DMAc), HT-PIL/PES hybrid nanofiltration membranes wereprepared using the exfoliated colloidal solution as membrane solvent. Theperformance properties of hybrid membranes were investigated and the results showed that hybrid membranes represented a good surface hydrophilicity with alower water contact angle of63.5o. The hybrid membranes exhibited enhancedmechanical and thermostable properties whereas with a lower decrease in waterpermeability. The water permeability of hybrid membrane was63.25L/(m2h MPa),which is slightly below the level of individual PES membrane of64.41L/(m2h MPa).Nevertheless, HT-PIL/PES hybrid membranes displayed a better removingperformance for reactive dyes and a relatively higher passage of salts. HT-PIL/PEShybrid membranes represented a rejection of above90%for reactive red49andabove95%for reactive black5; meanwhile, the rejection for MgSO4was below15%and below10%for Na2SO4.The effects of inorganic nanomaterials with different morphologies and spatialsizes on performance of hybrid membranes were investigated. It is found that thethickness of skin layer, ion exchange capacity and the water permeability of hybridmembranes were influenced distinctly by the morphologies and spatial size ofinorganic nanomaterials. The smaller spatial size of inorganic nanomaterials, thebetter uniformity and water permeability the hybrid membranes have. Likewise, thedistribution of inorganic nanomaterials in membrane matrix, the ion exchangecapacity and water permeability of hybrid membranes were prominently affected bythe morphologies of inorganic nanomaterials. Therefore, a hybrid membrane with acertain performance can be prepared through adjusting or altering the morphologiesand spatial size of inorganic materials.