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Membrane-based separation has served as an environmentally friendly technology over many conventional separation technologies in production of clean water, energy, and other materials. However, the vast amount of organic solvents used in membrane fabrication violates its initial intention. Therefore, to meet the needs of green chemistry and sustainable development, the traditional organic solvents must be replaced by environmentally benign solvents to reduce the solvent pollution. Ionic liquids have grabbed increasing interest as a kind of green solvents due to their low vapor pressure, chemical and thermal stability, recyclability, and diversity of ion combination. They have showed great superiority as the solvents for membrane fabrication. Contrary to traditional molecular solvents, the special properties of ionic liquids bring about distinct phenomena during hollow fiber fabrication and unique properties of the membranes. Therefore this chapter discusses the fundamental science of using ionic liquids as the solvents for hollow fiber spinning. The properties of hollow fibers spun from ionic liquids are summarized first, followed by the examination of interactions between polymers and ionic liquids as well as their influences on solution rheology and phase inversion behavior. Afterwards, the effects of spinning parameters on hollow fiber performance are also illustrated. With the further industrialization of ionic liquids and the development of novel recovery technologies, ionic liquids may serve as effective and feasible solvents in the near future for the fabrication of hollow fiber membranes and the realization of green fabrication in the membrane industry.

Thin film nanocomposite membranes have become a feasible technology for heavy metal wastewater treatment. However, how to enhance the dispersibility and compatibility of nanomaterials in the selective layer is an important issue to improve the membrane performance of heavy metal removal. In this study, silica-poly(ionic liquid) nanoparticles were incorporated in the selective layer of TFN membranes. 1-Allyl-3-methyl imidazolium hexafluorophosphate ([AMIm]PF6) was selected to modify silica (SiO2) particles. The formed poly([AMIm]+) brushes provided charge properties to enhance dispersibility and organic part to improve compatibility in the polyamide layer of NF membranes. The resultant TFN membranes incorporated with SiO2-[AMIm]PF6 particles exhibited an increment of 34% water permeation and 41.6% MgCl2 rejection. Moreover, with an average rejection improvement of around 15% for heavy metal ions at pH = 5–6, the SiO2-[AMIm]PF6/PA membrane showed its superiority beyond the PA membrane. The electropositivity and microporous structure of the SiO2-[AMIm]PF6 particles enhanced their dispersibility and compatibility in the polyamide layer. Meanwhile, the proper pore size and structure of the SiO2-[AMIm]PF6 particles contributed to the channels for water transport and the sieving effect for most heavy metal ions. This work may facilitate the applications of TFN membranes in heavy metal wastewater treatment to alleviate the “trade-off” phenomenon.

Electrically conductive membranes have been regarded as a new alternative to overcome the crucial drawbacks of membranes, including permeability-selectivity trade-off and fouling. It is still challenging to prepare conductive membranes with good mechanical strength, high conductivity and stable separation performance by reliable materials and methods. This work developed a facile method of simultaneous phase inversion to prepare electrically conductive polyethersulfone (PES) membranes with carboxylic multiwalled carbon nanotubes (MWCNT) and graphene (Gr). The resultant MWCNT/Gr/PES nanocomposite membranes are composed of the upper MWCNT/Gr layer with good conductivity and the base PES layer providing mechanical support. MWCNT as nanofillers effectively turns the insulting PES layers to be electrically conductive. With the dispersing and bridging functions of Gr, the MWCNT/Gr layer shows an enhanced electric conductivity of 0.10 S/cm. This MWCNT/Gr/PES membrane in an electro-filtration cell achieves excellent retention of Cu(II) ions up to 98 % and a high flux of 94.5 L m−2∙h−1∙bar−1 under a low driven-pressure of 0.1 MPa. The conductive membrane also shows improved anti-fouling capability during protein filtration, due mainly to the electrostatic repulsion and hydrogen evolution reaction on the electrode. This facile strategy has excellent potential in electro-assistant membrane filtration for fouling control and effective separation.

Aminosilane materials, with their low cost and ease of modification, have exhibited great potential for the adsorption of perfluorinated compounds (PFCs) from water. However, this kind of material may be facing two drawbacks during its application: low resistance to hydrolysis and difficulties in separation from the water matrix. This work proposed a strategy of grafting N-(2-aminoethyl) aminopropyltrimethoxysilane (AE-APTMS) on the surface of magnetic γ-Fe2O3 nanoparticles by full utilization of the sorption sites provided by the aminosilane and the magnetism by γ-Fe2O3. The FTIR and XRD results verified the formation of the magnetic AE-APTMS nanocomposite. The core-shell nanocomposite showed a superparamagnetic property and an isoelectric point at pH = 8.2. Particularly, compared to the aminopropyltriethoxysilane (APTES) nanocomposite, the AE-APTMS nanocomposite exhibited improved hydrolytic stability with 60% less loss of the amine groups during the 48 h adsorption process, as the longer alkyl chain hindered the aminosilane detachment. The AE-APTMS nanocomposite exhibited a rapid adsorption with the removal efficiency of 78% for perfluorooctane sulfonate (PFOS) and 65% for perfluorooctanoate (PFOA) due to the electrostatic interaction and hydrophobic interaction. The regeneration and reuse of the magnetic AE-APTMS nanocomposite were conveniently realized with the removal efficiency higher than 70% for both PFOS and PFOA even after 15 adsorption-desorption cycles. The stable magnetic aminosilane nanocomposite with the ease of separation may provide a new strategy to achieve the economical and effective removal of typical PFCs from water.

In this work, we have examined and compared the interactions between cellulose acetate and different ionic liquids at a molecular level and explored their effects on dope rheology, hollow fiber morphology, and performance. Ionic liquid, 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), was found to interact with cellulose acetate (CA) more closely with intensive hydrogen bonds than 1-ethyl-3-methylimidazolium thiocyanate ([EMIM]SCN). Thus, the CA/[EMIM]OAc solution exhibits a more pronounced charge-ordered network than the CA/[EMIM]SCN solution. In addition, the former does not obey the Cox–Merz rule, whereas the latter obeys the rule with its shear viscosity η identical to its complex viscosity |η*| at the equivalent shear rate and angular frequency. These dissimilar factors have contributed to an instantaneous liquid–liquid demixing and resulted in a dense outer skin surface and a porous cross-sectional structure comprising macrovoids for the CA/OAc membrane. In contrast, the CA/SCN membrane has a looser...

Electric membrane bioreactor (E-MBR) for wastewater treatment and water purification has attracted significant interest due to its remarkable performance in fouling mitigation. The performance is much relevant to the electric and physicochemical properties of the conductive membranes in E-MBR. This study proposed a facile method to prepare a conductive membrane with low electrical resistance and enhanced hydrophilicity. Oxidative polymerization of pyrrole doping with ionic liquids was conducted on the surface of polyvinylidene fluoride (PVDF) membranes. Among the studied ionic liquids, 1-butyl-3-vinylimidazolium tetrafluoroborate (BVIMBF4) was the most suitable in this work. The electrical resistance of the PVDF membrane modified by pyrrole and BVIMBF4 (PPy-BVIMBF4/PVDF membrane) was as low as 9.76 Ω/sq, and its water contact angle reduced from 81° to 45°. In the fast-filtration tests, these conductive microfiltration membranes exhibited high rejections of Cu2+ ions (~85%) and Ni+ ions (~65%) and enhanced antifouling performance during the bovine serum albumin filtration with the application of an electric field. A long-term E-MBR operation demonstrated that the transmembrane pressure (TMP) rise and the flux decline of the PPy-BVIMBF4/PVDF membrane were significantly alleviated due to its improved conductivity and hydrophilicity. Its total membrane resistance for water transport was only 27% of the base PVDF membranes under a minute electric field of 0.8 V/m. Overall, the incorporation of ionic liquids in the oxidative polymerization of pyrrole offers a novel and effective strategy in conductive membrane fabrication and serves as an excellent method in fouling mitigation in MBR.

Adsorption is well accepted as an effective method for perfluorinated compounds’ (PFCs) removal from water among various conventional methods. However, development of adsorbents that combine good performance of PFC removal and regenerability has not yet been realized. This work demonstrated the fabrication and application of an ammoniated magnetic adsorbent for efficient and economical PFOS and PFOA removal. Functional ammonium groups and γ-Fe2O3 were effectively incorporated in the particle with the proposed method. These fabricated magnetic particles presented superior adsorption performance for PFOS and PFOA with short equilibrium time of 120 min and high adsorption capacity. The isotherms revealed that the adsorption process belonged to multilayer sorption with their intricate interactions including anion exchange and hydrophobic interaction. The magnetic particle maintained its removal efficacy over a wide pH range of 3–9 or with coexisting substances. Moreover, the regeneration and reuse of the magnetic particle were successfully carried out with PFOS and PFOA removal efficiency sustained higher than 80% in 15 consecutive treatment cycles. Along with the efficient adsorption and easy separation of adsorbents, we expect that this ammoniated magnetic particle can serve as an excellent alternative for PFOS and PFOA removal from water.

We have provided two feasible methods to prepare stable organic solvent nanofiltration (OSN) membranes by chemically cross-linking the polybenzimidazole (PBI) membranes fabricated from environmentally benign ionic liquids for the first time. A glutaraldehyde (GA)–water solution and a 1,2,7,8-diepoxyoctane (DEO)–n-heptane solution were employed to cross-link PBI membranes. The effects of these cross-linking agents on membrane stability and separation performance toward various solvents, including polar aprotic solvents, have been carefully examined. The GA cross-linking method, with little consumption of traditional organic solvents and energy, yielded a PBI membrane with a high and steady ethanol flux [3.69 L (m2 bar h)−1] and ethyl acetate flux [5.21 L (m2 bar h)−1]. Although PBI membranes cross-linked by DEO showed lower ethanol and ethyl acetate fluxes, they displayed impressive stability in aggressive solvents such as dimethyl sulfoxide (DMSO), N-methyl-2-pyrrolidinone (NMP) and N,N-dimethylacetamide (DMAc). Overall, PBI membranes cross-linked by both agents exhibited reasonable rejections which varied slightly from solvent to solvent due to different solute–solvent–membrane interactions. This study not only offers a new range of membrane materials and fabrication approaches for OSN, but will also enhance membrane-based green technology for the recovery of organic solvents.

In this study, we aimed to design PBI (poly-2,2′-(m-phenylene)-5,5′-bibenzimidazole) blend membranes with a higher water flux by using a less amount of the expensive PBI material and by employing environmentally friendly ionic liquids as the solvent. Five commercially available polyimides and polyimide–amides were screened and P84 (BTDA-TDI/MDI, co-polyimide of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride and 80% methylphenylenediamine +20% methylenediamine) was chosen to blend with PBI because it formed miscible blends with PBI and interacted closely with the ionic liquid of 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc). An interesting interconnected network of the PBI/P84/[EMIM]OAc solution was evolved based on the highly charge-ordered characteristics of [EMIM]OAc. The blend solution displayed unusual rheological behavior: an initial shear thinning behavior under low shear rates followed by a Newtonian plateau. The incorporation of P84 in the blend system not only lowered the overall viscosity for easier membrane fabrication but also retarded the phase inversion process favorably to form a macrovoid-free morphology. PBI/P84 blend membranes were therefore fabricated for ultrafiltation via non-solvent induced phase inversion method. The effects of PBI/P84 composition and casting temperature on membrane morphology and separation performance were studied according to their phase inversion mechanisms. Compared to plain PBI ultrafiltration membranes, the newly developed PBI/P84 blend membranes exhibit an open cell structure and a reduced thickness which leads to a 50% higher pure water permeability and a larger pore diameter.

We report an atomic-scale characterization of ZrTe_{5} by using scanning tunneling microscopy. We observe a bulk band gap of ∼80 meV with topological edge states at the step edge and, thus, demonstrate that ZrTe_{5} is a two-dimensional topological insulator. We also find that an applied magnetic field induces an energetic splitting of the topological edge states, which can be attributed to a strong link between the topological edge states and bulk topology. The relatively large band gap makes ZrTe_{5} a potential candidate for future fundamental studies and device applications.

Ionic liquids have gained worldwide attention as green solvents in the past decade. This study explores, for the first time, the fundamental science and engineering of using ionic liquids as a new generation of solvents to replace traditional organic solvents for the fabrication of flat sheet membranes and hollow fiber membranes. The fundamentals and characteristics of membrane formation of cellulose acetate (CA) membranes have been investigated using 1-butyl-3-methylimidazolium thiocyanate ([BMIM]SCN) as the solvent via phase inversion in water. For elucidation, other solvents, i.e., N-methyl-2-pyrrolidinone (NMP) and acetone, were also studied. It is found that [BMIM]SCN has distinctive effects on phase inversion process and membrane morphology compared to NMP and acetone because of its unique nature of high viscosity and the high ratio of [BMIM]SCN outflow to water inflow. Membranes cast or spun from CA/[BMIM]SCN have a macrovoid-free dense structure full of nodules, implying the paths of phase inversi...

This study has investigated the molecular interactions between ionic liquids and PBI and discovered a potentially green solvent to fabricate polybenzimidazole (PBI) membranes for water reuse and protein separation. Ionic liquid, 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), exhibits superior efficiency in dissolving PBI under much lower temperatures and pressures compared to the traditional toxic N,N-dimethylacetamide (DMAc). this is because the acetate anions of [EMIM]OAc could form hydrogen bonding with PBI chains and effectively break up the interchain hydrogen bonding in PBI molecules. Molecular simulations have verified this mechanism by showing the largest amount of hydrogen bonding and the lowest interaction energy in the PBI–[EMIM]OAc system among the studied PBI–ionic liquid systems. The PBI–[EMIM]OAc solution also displays unique rheological properties significantly deviated from the traditional Cox-merz rule, and the shear thinning rheology at low shear rates implies a strong charge-ordered structure resulting from the intense hydrogen bonding. In addition, PBI ultrafiltration membranes have been prepared from PBI–[EMIM]OAc solutions by the non-solvent induced phase separation method and displayed a relatively thick sponge-like structure with a few macrovoids. After thermal treatment in ethylene glycol at 140 °C and chemical cross-linking by dichloro p-xylene, the PBI membranes achieve a high separation factor of 94.55 for a binary protein mixture containing bovine serum albumin and hemoglobin with the aid of combined effects from size exclusion and charge repulsion. This study provides a viable alternative to the current fabrication technology of PBI membranes in a “green” process with the aid of ionic liquids.

Some theoretical results are reported, 1) Proximity effects of N-S interface. 2) The spatial variation of order parameter in S-N-S structure and the dependence of supercurrent on the thickness of normal film d N . 3) The semi-infinite periodic N-S structure.