Membranes with unprecedented solvent permeance and high retention of dissolved solutes are needed to reduce the energy consumed by separations in organic liquids. We used controlled interfacial polymerization to form free-standing polyamide nanofilms less than 10 nanometers in thickness, and incorporated them as separating layers in composite membranes. Manipulation of nanofilm morphology by control of interfacial reaction conditions enabled the creation of smooth or crumpled textures; the nanofilms were sufficiently rigid that the crumpled textures could withstand pressurized filtration, resulting in increased permeable area. Composite membranes comprising crumpled nanofilms on alumina supports provided high retention of solutes, with acetonitrile permeances up to 112 liters per square meter per hour per bar. This is more than two orders of magnitude higher than permeances of commercially available membranes with equivalent solute retention.

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Thin-film nanocomposite membranes containing a range of 50-150 nm metal-organic framework (MOF) nanoparticles [ZIF-8, MIL-53(Al), NH2-MIL-53(Al) and MIL-101(Cr)] in a polyamide (PA) thin film layer were synthesized via in situ interfacial polymerization on top of cross-linked polyimide porous supports. MOF nanoparticles were homogeneously dispersed in the organic phase containing trimesoyl chloride prior to the interfacial reaction, and their subsequent presence in the PA layer formed was inferred by a combination of contact angle measurements, FT-IR spectroscopy, SEM, EDX, XPS, and TEM. Membrane performance in organic solvent nanofiltration was evaluated on the basis of methanol (MeOH) and tetrahydrofuran (THF) permeances and rejection of styrene oligomers (PS). The effect of different post-treatments and MOF loadings on the membrane performance was also investigated. MeOH and THF permeance increased when MOFs were embedded into the PA layer, whereas the rejection remained higher than 90% (molecular weight cutoff of less than 232 and 295 g·mol(-1) for MeOH and THF, respectively) in all membranes. Moreover, permeance enhancement increased with increasing pore size and porosity of the MOF used as filler. The incorporation of nanosized MIL-101(Cr), with the largest pore size of 3.4 nm, led to an exceptional increase in permeance, from 1.5 to 3.9 and from 1.7 to 11.1 L·m(-2)·h(-1)·bar(-1) for MeOH/PS and THF/PS, respectively.

Highly permeable and selective membranes are desirable for energy-efficient gas and liquid separations.Microporous organic polymers have attracted significant attention in this respect owing to their high porosity, permeability, and molecular selectivity. However, it remains challenging to fabricate selective polymer membranes with controlled microporosity which are stable in solvents. Here we report a new approach to designing crosslinked, rigid polymer nanofilms with enhanced microporosity by manipulating the molecular structure. Ultra-thin polyarylate nanofilms with thickness down to 20 nm were formed in-situ by interfacial polymerisation. Enhanced microporosity and higher interconnectivity of intermolecular network voids, as rationalised by molecular simulations, are achieved by utilising contorted monomers for the interfacial polymerisation. Composite membranes comprising polyarylate nanofilms with enhanced microporosity fabricated in-situ on crosslinked polyimide ultrafiltration membranes show outstanding separation performance in organic solvents, with up to two orders of magnitude higher solvent permeance than membranes fabricated with nanofilms made from noncontorted planar monomers.Conventional gas and liquid separation processes such as evaporation and distillation are widely used in the oil and gas, energy, chemical, and pharmaceutical industries, but are energy-intensive. An alternative to these processes is membrane separation technology, which typically consumes an order of magnitude less energy. To enable wider deployment of membrane technology, highly permeable membranes are required to process large volumes of gas or solvent using a viable membrane area over a feasible timeframe 1-2 . There are two main strategies being followed to this end. One is to design the polymer structure at the molecular level so as to provide greater interconnected microporosity 3-10 , whilst a second approach is to reduce the thickness of the separating layer to nanometre scale [11][12][13][14][15][16] .Microporous organic materials with well-defined pore structure are excellent candidates for highly permeable and selective membranes 1 , such as metal-organic frameworks (MOFs) and porous coordination polymers (PCPs) [17][18] , covalent organic frameworks (COFs) [19][20] , and porous organic cages 2 (POCs) [21][22][23] . However, the fabrication of these crystalline solids to form defect-free membranes is technically challenging. Recent significant progress includes fabrication of MOFs to form selective membranes by secondary crystal growth 24 , assembly of MOF nanosheets 15 , interfacial synthesis 25 , or mixed matrix membranes 10,26 . By contrast, industrial membranes are dominated by solution processing of polymers and interfacial polymerisation, for example in producing polyamide desalination membranes. Notable examples of microporous polymers are polymers of intrinsic microporosity (PIMs) [6][7][27][28][29][30][31] . Owing to the shape and rigidity of the component monomers, the polymer chains have contorted, ri...

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Thin-film composite membranes comprising a polyamide nanofilm separating layer on a support material are state of the art for desalination by reverse osmosis. Nanofilm thickness is thought to determine the rate of water transport through the membranes; although due to the fast and relatively uncontrolled interfacial polymerization reaction employed to form these nanofilms, they are typically crumpled and the separating layer is reported to be ≈50-200 nm thick. This crumpled structure has confounded exploration of the independent effects of thickness, permeation mechanism, and the support material. Herein, smooth sub-8 nm polyamide nanofilms are fabricated at a free aqueous-organic interface, exhibiting chemical homogeneity at both aqueous and organic facing surfaces. Transfer of these ultrathin nanofilms onto porous supports provides fast water transport through the resulting nanofilm composite membranes. Manipulating the intrinsic nanofilm thickness from ≈15 down to 8 nm reveals that water permeance increases proportionally with the thickness decrease, after which it increases nonlinearly to 2.7 L m h bar as the thickness is further reduced to ≈6 nm.

Can Organic Solvent Nanofiltration (OSN) be considered green? Is OSN greener than other downstream processing technologies? These are the two main questions addressed critically in the present review. Further questions dealt with in the review are as follows: What is the carbon footprint associated with the fabrication and disposal of membrane modules? How much solvent has to be processed by OSN before the environmental burden of OSN is less than the environmental burden of alternative technologies? What are the main challenges for improving the sustainability of OSN? How can the concept of Quality by Design (QbD) improve and assist the progress of the OSN field? Does the scale have an effect on the sustainability of membrane processes? The green aspects of OSN membrane fabrication, processes development and scale-up as well as the supporting concept of QbD, and solvent recovery technologies are critically assessed and future research directions are given, in this review. Gyorgy Szekely Gyorgy received his MSc degree in Chemical Engineering from the Technical University of Budapest, and he earned his PhD degree in Chemistry under Marie Curie Actions from the Technical University of Dortmund. He worked as an Early Stage Researcher in Hovione PharmaScience and an IAESTE Fellow at the University of Tokyo. He is currently a Research Associate in Imperial College London. His multidisciplinary professional background covers supramolecular chemistry, organic and analytical chemistry, molecular recognition, molecular imprinting, process development, nanofiltration and pharmaceutical impurity scavenging. He is the Secretary General of the Marie Curie Fellows Association and a Member of the Royal Society of Chemistry.

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