Graphene Oxide

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Applications of Polymer, Composite, and Coating Materials

Robust Covalently Crosslinked Polybenzimidazole/Graphene Oxide Membranes for High-Flux Organic Solvent Nanofiltration Fan Fei, Levente Cseri, Gyorgy Szekely, and Christopher Francis Blanford ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.8b03591 • Publication Date (Web): 19 Apr 2018 Downloaded from http://pubs.acs.org on April 19, 2018

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ACS Applied Materials & Interfaces

Robust Covalently Crosslinked Polybenzimidazole/Graphene Oxide Membranes for High-Flux Organic Solvent Nanofiltration Fan Fei,a,b Levente Cseri,c Gyorgy Szekely,*,c Christopher F. Blanford*,a,b a

School of Materials, University of Manchester, Oxford Road, Manchester, M13 9PL, United Kingdom b Manchester Institute of Biotechnology, University of Manchester, 131 Princess Street, Manchester, M1 7DN, United Kingdom c School of Chemical Engineering and Analytical Science, University of Manchester, The Mill, Sackville Street, Manchester, M1 3BB, United Kingdom * Corresponding authors: Tel.: +44 161 306 8915, email: [email protected]; Tel.: +44 161 306 4366, email: [email protected]

Keywords composite membrane, graphene sieve, mixed matrix membrane, surface modification, crosslinking

Abstract Robust, readily scalable, high-flux graphene oxide (GO) mixed matrix composite membranes were developed for organic solvent nanofiltration. Hydroxylated polybenzimidazole was synthesized by N-benzylation of polybenzimidazole with 4-(chloromethyl)benzyl alcohol, which was confirmed by FTIR and NMR spectroscopy. Flat sheet composite membranes comprising of polybenzimidazoles and 1 or 2 wt% GO were fabricated via conventional blade coating and phase inversion. Subsequently, GO was covalently anchored to the hydroxyl groups of the polymer using a diisocyanate crosslinking agent. The even distribution of GO in the membranes was mapped by visible-light microscopy. Hydroxylation and incorporation of GO in the polymer matrix increased the permeance up to 45.2±1.6 L m–2 h–1 bar–1 in acetone, nearly 5 times higher than the unmodified benchmark membrane. The enhancement in permeance from the addition of GO did not compromise the solute rejection. The composite membranes were found to be tight in seven organic solvents, having molecular weight cut-offs (MWCO) as low as 140 g mol–1. Permeance increased with increasing solvent polarity, while rejection of a 420 g mol–1 pharmaceutical remained over 93%. The covalent anchoring resulted in robust composite membranes that maintained constant performance over 14 days in a continuous cross-flow configuration.

Abbreviations GO: graphene oxide; MWCO: molecular weight cut-off; OSN: organic solvent nanofiltration; PBI: polybenzimidazole; PBI-OH: hydroxylated polybenzimidazole; TDI: toluene 2,4-diisocyanate; DMAc: N,N-dimethylacetamide; DMF: N,N-Dimethylformamide; THF: tetrahydrofuran; DCM: dichloromethane; MeOH: methanol; MeCN: acetonitrile

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1. Introduction Conventional separation processes account for up to 70% of the total capital and operational cost of chemical plants, and consequently remain an obstacle to sustainable manufacturing.1 Membranebased technologies provide more economic and sustainable alternatives to conventional separation processes.2 Organic solvent nanofiltration (OSN) is a pressure-driven separation technique that uses semi-permeable membranes that can selectively distinguish solutes between 50 and 2,000 g mol–1.3 OSN has found applications mainly in petrochemical and pharmaceutical industries, being used for solvent exchange and recycling, product purification and concentration, and catalyst recovery. Membrane materials are core parts of any membrane-based technologies, and consequently the prime focus of the current membrane research lies in developing new materials to improve stability, permeance, rejection and robustness in general. State-of-the-art OSN membranes provide long-term stability in organic media, low molecular weight cut-off (MWCO) values — the molecular weight of the compound that is 90% rejected — and a trade-off between selectivity and ultra-high permeance to minimize the processing time and membrane area.4-7 Recent research suggests the potential of advanced materials such as metal-organic frameworks,8 carbon nanosheets,9 and graphene,10 for the fabrication of more efficient membranes. Graphene oxide (GO), a chemical derivative of graphite in the family of graphene nanomaterials, comprises of carbon sheets decorated with oxygen-containing functionalities on the edges (hydroxyl, carbonyl and carboxyl groups) and on the surface (hydroxyl and epoxide groups). GO is a versatile starting material due to its ready dispersibility and reactivity in both organic and aqueous media. GO can be used as a membrane either on its own as a laminate,11 or mixed with polymers to fabricate mixed matrix membranes.12 A series of different techniques such as vacuum filtration,11 drop casting,13 dip-coating,14 spin-coating,15 spray-evaporation,16 layer-by-layer assembly17 and shear alignment 18 have been used to prepare GO membranes. GO membranes have been mainly developed for desalination19 and gas separation.20 However, efforts aiming at molecular separation are emerging with promising results in the field of OSN.21-23 Incorporation of GO into a polypyrrole matrix significantly enhanced solvent permeance without compromising solvent rejection.21 In contrast, GO-embedded polyethyleneimine membranes displayed enhanced solute rejection and adequate solvent flux.22 These studies were carried out in a limited number of mild solvents (acetone and alcohols), in a dead-end configuration with limited volume of test solutions, hindering long-term performance studies. The adhesion between the components of a mixed matrix membrane plays an important role in the performance and long-term stability.24 Therefore, not only the individual characteristics but the interaction of the phases should be considered when designing mixed matrix membranes. The distribution of GO flakes in polymer matrix is an important aspect for composite filtration membranes; aggregation of GO was attributed for the membrane permeance decline in previous reports.25 Herein, we report the fabrication, characterization, performance and long-term stability of mixed matrix membranes comprised of polybenzimidazole (PBI) and GO. PBI was selected as polymer matrix due to its outstanding ability to withstand extreme thermal, chemical and mechanical conditions.26 PBI-based OSN membranes have been recently developed by the Livingston group,27-28 and they have been successfully used for solvent exchange29 and solvent recovery.30


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2. Experimental 2.1. Materials and reagents Polybenzimidazole dope solution (PBI, 26 wt% in DMAc) was purchased from PBI Performance Products, Inc. (Charlotte, USA). Graphene oxide (flake) was purchased from William Blythe Ltd (Accrington, UK). Potassium tert-butoxide (tBuOK) and analytical grade organic solvents were purchased from Fisher Scientific. 4-(Chloromethyl)benzyl alcohol, toluene 2,4-diisocyanate (TDI), methyl styrene dimer and mepenzolate bromide (N,N-dimethyl-3-piperidiniobenzylate bromide) were purchased from Sigma-Aldrich. Novatexx 2471 polypropylene non-woven backing was purchased from Freudenberg Filtration Technologies (Crewe, UK). Polystyrene markers for solute rejection evaluation were purchased from Agilent Technologies. Microscope slides and dialysis tubing (SnakeSkin MWCO 10K 35mm diameter) were purchased from Thermo Scientific. Si/SiOx (silicon surface with a silica layer of approximately 290 nm) wafer was purchased from IDB Technologies Ltd. All materials and solvents were used as received without further purification. All solutions were prepared using water with a resistivity of 18.2 MΩ cm at 25°C (Milli-Q).

2.2. Synthesis of hydroxylated polybenzimidazole Hydroxylated polybenzimidazole (PBI-OH) was synthesized through N-benzylation of polybenzimidazole (Figure 1). In a typical synthesis, 26 wt% PBI dope solution (4.46 g) was diluted with DMAc (45 mL) stirred at room temperature for 0.5 h, followed by the addition of tBuOK (0.886 g, 7.91mmol, 2.1 eq. per repeating unit). The color of the reaction mixture turned from brown to red indicating the deprotonation of the amine groups of the polymer. The mixture was stirred at room temperature for 3 h in order to ensure completion of deprotonation. 4-(Chloromethyl)benzyl alcohol (1.182 g, 7.53 mmol, 2 eq. per repeating unit) was added in one portion and the reaction was stirred at room temperature for 3 days. The product was precipitated in 1 L H2O/ethanol (1:1 v/v) mixture, and then filtered. The filter cake was dialyzed in water and freeze-dried to obtain the final product as yellow powder.

Figure 1. Reaction scheme showing the N-benzylation of polybenzimidazole and the diisocyanate-based (A) crosslinking of hydroxylated polybenzimidazole chains, (B) anchoring of GO sheets, and (C) crosslinking of GO sheets.


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2.3. Membrane fabrication Dope solutions containing PBI, PBI-OH and GO were prepared. The total solid content in all dope solutions was 20 wt% by adding suitable amount of DMAc as solvent. The percentage of PBI, PBI-OH and GO in the solid content for each membrane is shown in Table 1. Homogeneous dope solutions were realized by mechanical stirring of the components at 50 rpm and room temperature for 6 h, followed by degassing under argon in an incubator shaker at 400 rpm and 30 °C for 12 h. Membranes were cast onto non-woven polypropylene support using an Elcometer 4340 film applicator with a casting knife set to a thickness of 250 μm and casting speed of 5 cm s–1. The membranes were formed by the precipitation of the film in a coagulation bath containing deionized water (15.0 MΩ cm) at 20 °C. The A4-size membrane sheets were cut into 9 cm diameter discs. The membranes were washed and soaked in acetonitrile prior to crosslinking to remove the water. The GO sheets were anchored to the polymer matrix and the polymer chains were simultaneously crosslinked using TDI (Figure 1), which was previously reported for crosslinking Pebax membranes.31 Crosslinking was performed by immersing the membrane discs in 2 wt% TDI in acetonitrile for 30 minutes followed by washing with 3x40 mL acetonitrile. Covalent crosslinking is often used to lower the MWCO and improve the stability of membranes. In this particular work, the GO is also crosslinked to the polymer matrix in order to prevent it leaching out of the membrane over time. Table 1. Abbreviations and compositions of membranes. The total solid content in all dope solutions were 20 wt%. The table shows the percentage of PBI, PBI-OH and GO in the solid content. Composite membranes having 3 wt% GO were prepared but were found to be unsuitable for testing due to their brittleness. Membrane designation M1 M2 M3 M4 M5 M6 M7

PBI (wt%)

PBI-OH (wt%)

GO (wt%)

100 90 90 89 89 88 88

0 10 10 10 10 10 10

0 0 0 1 1 2 2

TDI crosslinking reaction No No Yes No Yes No Yes

2.4. Characterization NMR analyses were performed on a B500 Bruker Avance II+ 500 MHz instrument using DMSO-d6 as a solvent. The solvent peak was used as an internal chemical shift reference. Solid state NMR spectra were recorded on a Bruker Avance III 400 MHz solid state NMR spectrometer with cross-polarization (CP) pulse and magic angle spinning (MAS) using adamantane as an external 13C chemical shift reference. Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) spectra of powder and membrane samples were acquired using a Bruker Alpha-P run in air, mounting on a zinc– selenium/diamond plate. The spectra were recorded at a resolution of 4 cm-1 as an average of 16 scans. Raman analysis of the PBI-containing materials was not possible because of the intrinsic fluorescence of the polymer. Optical microscope images were obtained by Keyence VHX-5000 digital microscope. Samples were prepared by sticking the dried membranes on glass slides using double-sided tape. Membrane surface and cross-sectional microstructure was determined by scanning electron microscopy (SEM) using a Hitachi S-3000N with a tungsten hairpin filament emission gun at an accelerating voltage of 5 kV. Samples were prepared by sticking the membranes on a conductive


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carbon tab and sputter coated with gold/palladium under an argon atmosphere using a Quorum Q150TES in order to make the samples conductive. Atomic force microscopy (AFM) images were acquired in tapping mode in air using a Digital Instruments Dimension 3100 with Bruker TESPA-V2 probe with a nominal spring constant of 37 N m-1 and a nominal tip apex radius of 7nm. Samples were prepared by sticking the membranes on a glass slide using double-sided tape. For roughness calculations, three membranes of each type with an area of 25 μm2 were scanned and analyzed with the NanoScope Analysis software. Thermogravimetric analysis (TGA) was determined using a TA Instruments Q500 in N2 atmosphere with the ramp rate of 10 °C min–1.

2.5. Membrane performance tests Membrane performance was tested in a typical stainless steel cross-flow nanofiltration apparatus at 10 bar (Figure S9, Supporting Information). Two independently prepared membrane discs of each type were tested, and the reported results are the mean values of these measurements. The effective area (A) of each membrane was 52.8 cm2. The permeance was calculated as given in Equation 1. J V Permeance [L m–2 h–1 bar–1] = ∆P = ∆PAt

(1)

The permeance of each membrane was calculated by dividing the solvent flux through the membrane (J) by the transmembrane pressure (∆P). The flux was obtained by measuring the volume of solvent (V) that permeates through the membrane per membrane area (A) per time (t). The model system for the MWCO curve determination comprised of a mixture of 1 g L–1 PS580 and PS1300 polystyrene markers and 0.1 g L–1 of divinylbenzene (130 g mol–1) and 0.1 g L–1 methyl styrene dimer (236 g mol–1) solutions.3, 32-33 Due to its versatile solubility, mepenzolate bromide (420 g mol–1) at 0.1 g L–1 was used for solute rejection determinations in various solvents. The rejection (R) of solutes was determined as the ratio of its measured concentration in the permeate (Cp) and the feed (Cf) as defined in Equation 2. Cp R [%] = 1 – C  · 100  f

(2)

3. Results and discussion 3.1. Polymer and membrane characterization The N-benzylation of PBI was confirmed by IR and 1H NMR spectroscopy. In the IR spectrum (Figure 2A), PBI-OH exhibits two additional peaks compared to PBI, which can be assigned to alkane C–H stretch bonds of methylene (2867 cm–1) and alcohol C–O stretch bonds (1015 cm–1). The N-benzylation causes two red shifts in the spectrum: C=N stretching vibrations shifted from 1612 cm–1 to 1619 cm–1 due to the electronic effects of N-substitution, and the out-of-plane bending of C–H groups in the imidazole ring shifted from 687 cm–1 to 700 cm–1.34 The 1H NMR spectrum (Figure 2B) is also in good agreement with the expectations. In the case of PBI-OH, five additional signals were observed compared with PBI. Two significant peaks in the upfield aromatic region, at 7.21 and 7.02 ppm, are attributed to the protons of the para-substituted


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benzene ring. Two peaks of methylene protons were identified at 5.69 ppm (N–CH2–φ) and 4.40 ppm (φ–CH2–O) while the peak at 5.13 ppm belongs to OH protons. The relative peak areas of these five signals are 2:2:2:2:1 in agreement with the expected structure. A peak at 13.24 ppm in the spectrum of PBI-OH, identified as NH protons, shows that the N-benzylation was not complete. The degree of benzylation was calculated to be 70% based on the ratio between aromatic backbone protons and the methylene protons found at 4.40 ppm. The incomplete N-benzylation can be attributed to the steric crowding around the polymeric backbone. Furthermore, a significant change can be observed in the structure of aromatic protons compared with PBI. The phenylene protons at 9.19 and 8.36 ppm significantly downshifted due to the extra shielding provided by the introduced benzyl groups. Moreover, their signals are split up as a result of the incomplete modification.

Figure 2. (A) ATR-FTIR spectra of PBI and PBI-OH powders. The additional C–H and C–O peaks in the PBI-OH spectrum arise 1 from the presence of hydroxymethyl groups. (B) H NMR spectra of PBI and PBI-OH. In the spectrum of PBI-OH, the five new peaks between 7.5 and 4.0 ppm, and the change of the signal structure in the aromatic region confirm the N-benzylation.

Membranes were characterized by FTIR and TGA analysis. The crosslinking was verified by two characteristic signals of urethane bond in the IR spectrum (Figure 3). In the crosslinked membranes, the peaks of the C=O stretch (1665 cm–1) and C–N stretch (1225 cm–1) were observed. Owing to the small GO content (1–2 wt%), it has no characteristic peak in the FTIR spectra.


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Figure 3. FTIR spectra of GO flake and membranes of different compositions. The crosslinked membranes exhibit two characteristic peaks which confirm the presence of the urethane groups formed during the crosslinking. GO peaks could not be identified in the membrane spectra due to the low GO content.

The chemical composition of membranes was characterized by suspension and solid-state 13C NMR spectroscopy (Figure 4). Both techniques provided similar results; however the solid-state NMR showed higher sensitivity, while the suspension NMR had higher resolution. The PBI signals were the most prominent in the spectra with aromatic signals between 110–140 ppm, and the imidazole carbon at 151 ppm (δ). Weak signals of benzyl carbons originating from PBI-OH (β and γ) were identified in the solid state spectra of M6 and M7. The spectra of M7 contain the characteristic methyl carbon of the crosslinker at 17 ppm (α). Furthermore, the two additional aromatic signals of the crosslinker can be observed in the suspension NMR spectra at 130 and 138 ppm. The appearance of urethane carbons at 153 ppm (ε) indicated successful diisocyanate crosslinking, which was also confirmed with TGA analysis (Figure S12, Supporting Information).


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Figure 4. C NMR analysis of polymers PBI and PBI-OH, and membranes M6 and M7. Characteristic signals are indicated by Greek letters, and they are assigned to carbons showed in Figure 1. An asterisk (*) is used to mark the solvent (DMSO-d6) in liquid state spectra. ls: liquid state NMR (homogeneous); ls-s: liquid state NMR (suspension); ss: CP-MAS solid state NMR.

Membrane morphology was characterized by optical microscopy, SEM and AFM. None of the techniques revealed any difference between non-crosslinked membranes and their crosslinked counterparts. The images of crosslinked membranes (M3, M5 and M7) can be found in the supporting information. Visible-light images of the membranes are shown in Figure 5A. Images of GO containing membranes (M4 and M6) revealed shiny flakes which are similar in shape and size to the pristine GO (Figure S1, Supporting Information). The flakes were evenly distributed on the membrane surfaces. ImageJ analysis (Figure S8, Supporting Information) revealed the mean apparent area of GO flakes in the top layers of M4 and M6 to be 0.39 μm2 and 0.37 μm2, and the coverage are 1.5% and 2.0%, respectively.


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Figure 5. Images of membranes cast from pure PBI (M1), PBI + 10 wt% PBI-OH (M2), PBI + 10wt% PBI-OH and 1 wt% GO (M4) and PBI + 10wt% PBI-OH and 2 wt% GO. (A) Visible-light microscope reflection images (frame size: 100μm×100μm), (B) surface and (C) cross-sectional SEM images (Scale bar: 10μm; see Figure S6 for active layer thickness), (D) AFM height images (scan size: 25μm×25μm) of membranes.

SEM surface and cross-sectional images of the membranes are shown in Figure 5B and Figure 5C, respectively. All the membranes show typical structure of integrally skinned asymmetric polymer membranes formed via phase inversion, with dense top layers, spongy support structures in the middle of the membrane and macroscopic voids at the bottom of the membranes. AFM height images (Figure 5D) revealed similar surface morphology with cavities in a few micrometers for all membranes. The incorporation of PBI-OH reduces the root mean square (RMS) roughness. However, there is no trend for the influence of the incorporation of GO and crosslinking towards surface roughness (Table S1, Supporting Information).

3.2. Membrane performance As shown in Figure 6A, the 10 wt% addition of PBI-OH (M2) increased the initial permeance by almost two and half times compared to the pristine PBI membrane (M1), which could be attributed to the hydrophilicity (Figure S11, Supporting Information),35 and lower packing density of PBI-OH.36 Nonetheless, the M2 membrane showed considerable compaction over time, which resulted in a 33% permeance decline in 14 days. Having crosslinked the membrane (M3), the decline in permeance was found to be only 11%, which is less prominent than for the non-crosslinked membrane (M2). The incorporation of GO increased both the permeance and the long-term stability of the membranes (M4–M7). The decrease of membrane top layer thickness (Figure S6, Supporting Information) can contribute to the increase of the permeance. Moreover, it is speculated that the presence of GO inhibits compaction of the polymer matrix, subsequently the permeance is


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maintained over 14 days of continuous operation. The highest flux of 45.2±1.6 L m–2 h–1 bar–1 was demonstrated by M6, which is around 18 times higher than commercial OSN membranes (2.5 L m–2 h–1 bar–1).3, 37 The increase from 1 wt% to 2 wt% GO content improved the permeance, but further increase to 3 wt% GO resulted in a fragile membrane not suitable for filtration.

Figure 6. Comparison of membrane performance in acetone: (A) permeance of acetone over time, and (B) solute rejection. Error bars represent standard deviations derived from two independently prepared membranes cast from separately prepared dope solutions. The effect of solvent on membrane performance: (C) permeance of various solvents, and (D) –1 rejection values for mepenzolate (420 g mol ). Error bars represent standard deviations derived from two experiments using independently prepared membranes.

The benchmark M1 membrane showed the highest MWCO of 485 g mol–1 (Figure 6B). Based on the cut-off curves, the rest of the membranes formed two distinguished clusters. Cluster 1 consists of the non-crosslinked membranes (M2, M4, M6) with MWCO of about 277±7 g mol–1, and cluster 2 consists of the crosslinked membranes (M3, M5, M7) with MWCO of about 137±15 g mol–1. The results show that the TDI crosslinking tightened the membranes via decreasing the permeance (Figure 6A) and increasing the solute rejection and the MWCO values (Figure 6B). Interestingly, the GO-induced increase in permeance does not compromise the cut-off profile. The reported OSN performances of GO-based membranes are compared with this work in Table 2. The MWCO values for M4–M7 show comparable, or even tighter membranes than previously reported GO/polymer mixed matrix membranes.21-22 Moreover, the permeance obtained for M6 is one order of magnitude higher than the others. Our work outperforms the GO laminate membrane38 in permeance, although the latter has an unprecedented ultra-sharp sieving cut-off. Such


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improvement comes with the requirement for excessive GO quantity as 100% GO is used for the membrane fabrication, which hinders scale-up due to currently limited GO availability and high cost. Table 2. Graphene oxide membranes for molecular separations in organic solvents. Only this work includes GO crosslinking Polymer matrix

GO (wt%)

Maximum permeance (L m–2 h–1 bar–1)

MWCO (g mol–1)

Solvents

Continuous stability test (days)

Process configuration

Ding et al.22

polyethyleneimine

1–4

5 (acetone)

200-400

acetone, ethanol

—

Dead-end cell (batch)

Shao et al.21

polypyrrole

0.05

3 (2-propanol)

93% for 420 g mol–1) in both polar and non-polar solvents. Owing to the high permeance and rejection, the desalination potential of these membranes will be further studied.

Supporting Information The Supporting Information is available: Characterization of commercial GO flakes by visible-light microscopy, SEM, AFM and Raman spectroscopy; viscosity values for the dope solutions; AFM, SEM and visible-light microscope images of membranes; thermogravimetric and nanoindentation analyses of membranes; nanofiltration process scheme; permeance and rejection data in eight solvents; NMR and IR spectra of membranes. In accordance with the University of Manchester’s guidelines, the data are openly available from Mendeley Data (doi:10.17632/tnh4sgrspy.1); the DOI will be activated after acceptance. The draft version of the data for reviewers, is available at https://data.mendeley.com/datasets/tnh4sgrspy/draft?a=f8a17231-c49a-46ad-8619-0e3c5146d125

Conflicts of interest The authors declare no conflict of interest.

Acknowledgements The authors thank the experimental support from Dr Ben Spencer (AFM), Mr Andrew Forrest (nanoindentation), Mr Michael Faulkner (SEM), and Mr Martin Jennings (TGA). This work was supported by the UK’s Biotechnology and Biological Sciences Research Council (BBSRC) and Engineering and Physical Sciences Research Council (EPSRC) through an award from the BioProNET Network in Industrial Biotechnology and Bioenergy (BB/L013770/1). FF acknowledges the financial support from his family for his doctoral studies.

References (1) Adler, S.; Beaver, E.; Bryan, P.; Robinson, S.; Watson, J. Vision 2020: 2000 separations roadmap; EERE Publication and Product Library: 2000. (2) Szekely, G.; Jimenez-Solomon, M. F.; Marchetti, P.; Kim, J. F.; Livingston, A. G. Sustainability assessment of organic solvent nanofiltration: from fabrication to application. Green Chemistry 2014, 16 (10), 4440-4473. (3) Marchetti, P.; Jimenez Solomon, M. F.; Szekely, G.; Livingston, A. G. Molecular separation with organic solvent nanofiltration: a critical review. Chemical Reviews 2014, 114 (21), 1073510806. (4) Shi, B.; Marchetti, P.; Peshev, D.; Zhang, S.; Livingston, A. G. Will ultra-high permeance membranes lead to ultra-efficient processes? Challenges for molecular separations in liquid systems. Journal of Membrane Science 2017, 525, 35-47. (5) Hennessy, J.; Livingston, A.; Baker, R. Membranes from academia to industry. Nature Materials 2017, 16 (3), 280-282.


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(6) Park, H. B.; Kamcev, J.; Robeson, L. M.; Elimelech, M.; Freeman, B. D. Maximizing the right stuff: The trade-off between membrane permeability and selectivity. Science 2017, 356 (6343), eaab0530. (7) Marchetti, P.; Peeva, L.; Livingston, A. The Selectivity Challenge in Organic Solvent Nanofiltration: Membrane and Process Solutions. Annual Review of Chemical and Biomolecular Engineering 2017, 8 (0), 473-497. (8) Campbell, J.; Davies, R. P.; Braddock, D. C.; Livingston, A. G. Improving the permeance of hybrid polymer/metal–organic framework (MOF) membranes for organic solvent nanofiltration (OSN)–development of MOF thin films via interfacial synthesis. Journal of Materials Chemistry A 2015, 3 (18), 9668-9674. (9) Karan, S.; Samitsu, S.; Peng, X.; Kurashima, K.; Ichinose, I. Ultrafast viscous permeation of organic solvents through diamond-like carbon nanosheets. Science 2012, 335 (6067), 444-447. (10) Joshi, R. K.; Carbone, P.; Wang, F.-C.; Kravets, V. G.; Su, Y.; Grigorieva, I. V.; Wu, H. A.; Geim, A. K.; Nair, R. R. Precise and ultrafast molecular sieving through graphene oxide membranes. Science 2014, 343 (6172), 752-754. (11) Huang, L.; Li, Y.; Zhou, Q.; Yuan, W.; Shi, G. Graphene oxide membranes with tunable semipermeability in organic solvents. Advanced Materials 2015, 27 (25), 3797-3802. (12) Zinadini, S.; Zinatizadeh, A. A.; Rahimi, M.; Vatanpour, V.; Zangeneh, H. Preparation of a novel antifouling mixed matrix PES membrane by embedding graphene oxide nanoplates. Journal of Membrane Science 2014, 453, 292-301. (13) Sun, P.; Zhu, M.; Wang, K.; Zhong, M.; Wei, J.; Wu, D.; Xu, Z.; Zhu, H. Selective ion penetration of graphene oxide membranes. Acs Nano 2012, 7 (1), 428-437. (14) Lou, Y.; Liu, G.; Liu, S.; Shen, J.; Jin, W. A facile way to prepare ceramic-supported graphene oxide composite membrane via silane-graft modification. Applied Surface Science 2014, 307, 631-637. (15) Nair, R.; Wu, H.; Jayaram, P.; Grigorieva, I.; Geim, A. Unimpeded permeation of water through helium-leak–tight graphene-based membranes. Science 2012, 335 (6067), 442-444. (16) Guan, K.; Shen, J.; Liu, G.; Zhao, J.; Zhou, H.; Jin, W. Spray-evaporation assembled graphene oxide membranes for selective hydrogen transport. Separation and Purification Technology 2017, 174, 126-135. (17) Nan, Q.; Li, P.; Cao, B. Fabrication of positively charged nanofiltration membrane via the layerby-layer assembly of graphene oxide and polyethylenimine for desalination. Applied Surface Science 2016, 387, 521-528. (18) Akbari, A.; Sheath, P.; Martin, S. T.; Shinde, D. B.; Shaibani, M.; Banerjee, P. C.; Tkacz, R.; Bhattacharyya, D.; Majumder, M. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide. Nature Communications 2016, 7, 10891. (19) Abraham, J.; Vasu, K. S.; Williams, C. D.; Gopinadhan, K.; Su, Y.; Cherian, C. T.; Dix, J.; Prestat, E.; Haigh, S. J.; Grigorieva, I. V.; Carbone, P.; Geim, A. K.; Nair, R. R. Tunable sieving of ions using graphene oxide membranes. Nature Nanotechnology 2017, 12 (6), 546-550. (20) Kim, H. W.; Yoon, H. W.; Yoon, S.-M.; Yoo, B. M.; Ahn, B. K.; Cho, Y. H.; Shin, H. J.; Yang, H.; Paik, U.; Kwon, S.; Choi, J.-Y.; Park, H. B. Selective gas transport through few-layered graphene and graphene oxide membranes. Science 2013, 342 (6154), 91-95. (21) Shao, L.; Cheng, X.; Wang, Z.; Ma, J.; Guo, Z. Tuning the performance of polypyrrole-based solvent-resistant composite nanofiltration membranes by optimizing polymerization conditions and incorporating graphene oxide. Journal of Membrane Science 2014, 452, 82-89. (22) Ding, R.; Zhang, H.; Li, Y.; Wang, J.; Shi, B.; Mao, H.; Dang, J.; Liu, J. Graphene oxide-embedded nanocomposite membrane for solvent resistant nanofiltration with enhanced rejection ability. Chemical Engineering Science 2015, 138, 227-238.


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Page 14 of 16

(23) Huang, L.; Chen, J.; Gao, T.; Zhang, M.; Li, Y.; Dai, L.; Qu, L.; Shi, G. Reduced graphene oxide membranes for ultrafast organic solvent nanofiltration. Advanced Materials 2016, 28 (39), 8669-8674. (24) Wang, Z.; Ren, H.; Zhang, S.; Zhang, F.; Jin, J. Polymers of intrinsic microporosity/metal–organic framework hybrid membranes with improved interfacial interaction for high-performance CO2 separation. Journal of Materials Chemistry A 2017, 5, 10968-10977. (25) Bano, S.; Mahmood, A.; Kim, S.-J.; Lee, K.-H. Graphene oxide modified polyamide nanofiltration membrane with improved flux and antifouling properties. Journal of Materials Chemistry A 2015, 3 (5), 2065-2071. (26) Chung, T.-S. A critical review of polybenzimidazoles: historical development and future R&D. Journal of Macromolecular Science, Part C: Polymer Reviews 1997, 37 (2), 277-301. (27) Valtcheva, I. B.; Kumbharkar, S. C.; Kim, J. F.; Bhole, Y.; Livingston, A. G. Beyond polyimide: crosslinked polybenzimidazole membranes for organic solvent nanofiltration (OSN) in harsh environments. Journal of Membrane Science 2014, 457, 62-72. (28) Valtcheva, I. B.; Marchetti, P.; Livingston, A. G. Crosslinked polybenzimidazole membranes for organic solvent nanofiltration (OSN): Analysis of crosslinking reaction mechanism and effects of reaction parameters. Journal of Membrane Science 2015, 493, 568-579. (29) Peeva, L.; Da Silva Burgal, J.; Heckenast, Z.; Brazy, F.; Cazenave, F.; Livingston, A. Continuous Consecutive Reactions with Inter‐Reaction Solvent Exchange by Membrane Separation. Angewandte Chemie 2016, 128 (43), 13774-13777. (30) Didaskalou, C.; Buyuktiryaki, S.; Kecili, R.; Fonte, C. P.; Szekely, G. Valorisation of agricultural waste with an adsorption/nanofiltration hybrid process: from materials to sustainable process design. Green Chemistry 2017, 19, 3116-3125. (31) Aburabie, J.; Peinemann, K.-V. Crosslinked poly (ether block amide) composite membranes for organic solvent nanofiltration applications. Journal of Membrane Science 2017, 523, 264-272. (32) Toh, Y. S.; Loh, X.; Li, K.; Bismarck, A.; Livingston, A. In search of a standard method for the characterisation of organic solvent nanofiltration membranes. Journal of Membrane Science 2007, 291 (1), 120-125. (33) Campbell, J.; Székely, G.; Davies, R.; Braddock, D. C.; Livingston, A. G. Fabrication of hybrid polymer/metal organic framework membranes: mixed matrix membranes versus in situ growth. Journal of Materials Chemistry A 2014, 2 (24), 9260-9271. (34) Wang, K. Y.; Xiao, Y.; Chung, T.-S. Chemically modified polybenzimidazole nanofiltration membrane for the separation of electrolytes and cephalexin. Chemical Engineering Science 2006, 61 (17), 5807-5817. (35) Eren, E.; Sarihan, A.; Eren, B.; Gumus, H.; Kocak, F. O. Preparation, characterization and performance enhancement of polysulfone ultrafiltration membrane using PBI as hydrophilic modifier. Journal of Membrane Science 2015, 475, 1-8. (36) Jansen, J. C.; Darvishmanesh, S.; Tasselli, F.; Bazzarelli, F.; Bernardo, P.; Tocci, E.; Friess, K.; Randova, A.; Drioli, E.; Van der Bruggen, B. Influence of the blend composition on the properties and separation performance of novel solvent resistant polyphenylsulfone/polyimide nanofiltration membranes. Journal of Membrane Science 2013, 447, 107-118. (37) Vandezande, P.; Gevers, L. E.; Vankelecom, I. F. Solvent resistant nanofiltration: separating on a molecular level. Chemical Society Reviews 2008, 37 (2), 365-405. (38) Yang, Q.; Su, Y.; Chi, C.; Cherian, C.; Huang, K.; Kravets, V.; Wang, F.; Zhang, J.; Pratt, A.; Grigorenko, A. Ultrathin graphene-based membrane with precise molecular sieving and ultrafast solvent permeation. Nature Materials 2017, 16, 1198-1202. (39) Bhanushali, D.; Kloos, S.; Kurth, C.; Bhattacharyya, D. Performance of solvent-resistant membranes for non-aqueous systems: solvent permeation results and modeling. Journal of Membrane Science 2001, 189 (1), 1-21.


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(40) Geens, J.; Van der Bruggen, B.; Vandecasteele, C. Transport model for solvent permeation through nanofiltration membranes. Separation and Purification Technology 2006, 48 (3), 255263. (41) Ramanathan, T.; Abdala, A.; Stankovich, S.; Dikin, D.; Herrera-Alonso, M.; Piner, R.; Adamson, D.; Schniepp, H.; Chen, X.; Ruoff, R. Functionalized graphene sheets for polymer nanocomposites. Nature Nanotechnology 2008, 3 (6), 327. (42) Potts, J. R.; Dreyer, D. R.; Bielawski, C. W.; Ruoff, R. S. Graphene-based polymer nanocomposites. Polymer 2011, 52 (1), 5-25.


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Table of contents and abstract graphical


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Graphene Oxide

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