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The recycling of depleted high global warming mixtures of fluorinated gases (F-gases) with close-boiling or azeotropic behavior requires advanced separation processes to obtain effectively the pure components. Herein, several types of PIM-1 membranes were tested for the first time towards the separation of hydrofluorocarbons and hydrofluoroolefins, showing extraordinarily high permeability coefficients for the value-added difluoromethane (R-32), up to 4100 barrer, coupled with high selectivity for the F-gas pairs of interest. Additionally, the solubility of selected F-gases in PIM-1 was measured and fitted to the dual-mode and Guggenheim, Anderson and de Boer sorption models. The separation performance of the standard PIM-1 and a highly branched PIM-1 was examined with the mixture R-410A (containing R-32 and pentafluoroethane R-125) to assess the influence of the membrane topology on the mixed-gas permeation properties over time (physical aging). Considering that the branched PIM-1 membrane was the least impacted by the aging phenomena, it was used to recover high purity R-32 (concentration in the permeate side as high as 98.9 vol % was achieved) from refrigerant gas mixtures R-410A and R-454B (mixture of R-32 and R-1234yf) in continuous long-term experiments. Results showed the great potential of PIM-1 membranes for the separation of R-32 from refrigerant mixtures collected from end-of-life equipment. This research is supported by project PID2019-105827RB-I00 funded by MCIN/AEI/10.13039/501100011033. F.P. and S.V.G.H. acknowledge the support of the Spanish State Research Agency and the Spanish Ministry of Science and Innovation (grants IJC2020-043134-I and PRE2020-093568, respectively). A.B.F and P.M.B acknowledge EPSRC Grant ep/v047078/1 (SynHiSel). P.G. is supported by Grant RYC2019-027060-I funded by MCIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”.

With the continuous growth of the world population, the demand for fresh water is ever increasing. Water desalination is a means of producing fresh water from saline water, and one of the proposed solutions in the scientific community for solving the current global freshwater shortage. Adsorption is foreseen as a promising technology for desalination due to its relatively low energy requirements, low environmental impact, low cost and high salt removal efficiency. More importantly, chemicals are not required in adsorption processes. Active carbons, zeolites, carbon nanostructures, graphene and coordination framework materials are amongst the most investigated adsorbents for adsorption desalination, which show different performances regarding adsorption rate, adsorption capacity, stability and recyclability. In this review, the latest adsorbent materials with their features are assessed (using metrics) and commented critically, and the current trend for their development is discussed. The adsorption mode is also reviewed, which can provide guidance for the design of adsorbents from the engineering application point of view., Patricia Gorgojo is grateful to the Spanish Ministerio de Economía y Competitividad and the European Social Fund for her Ramon y Cajal Fellowship (RYC2019-027060-I/AEI/10.13039/501100011033). B.Q. thanks the China Scholarship Council (202006240076)-University of Manchester joint studentship for supporting her PhD research.

The next generation of gas separation membranes requires from novel membrane materials with superior performance, sufficient mechanical stability, and long-term stability under harsh operation conditions. Two-dimensional (2D) materials offer several advantages over conventionally used polymeric materials. However, gas separation membranes containing 2D materials have not reached commercialization yet, despite having been discovered almost two decades ago. Difficulties in membrane scalability and high costs associated with the manufacturing processes are the main challenges. This review focuses on the current state and prospects of the technology and highlights novel 2D materials and strategies to fabricate ultrathin membranes that have been developed during the last three years. A multidisciplinary approach, covering the fields of physics, chemistry, and chemical engineering, needs to be taken to achieve the preparation of robust, large-scale, and economically affordable (2D material)-based membranes capable of breaking into the gas separation market., J.M. Luque-Alled acknowledges the Spanish Ministerio de Economía y Competitividad and the European Social Fund for funding through the Margarita Salas programme. C. Moreno and P. Gorgojo are supported by Grant RYC2019-028110-I and RYC2019-027060-I funded by the Spanish Ministerio de Ciencia e Innovación/Agencia Estatal de Investigación MICIN/AEI/10.13039/501100011033 and by the European Social Fund “ESF Investing in your future”. This research was supported by the Spanish Ministerio de Ciencia e Innovación- Agencia Estatal de Investigación —, under Contract no. PID2019-107338RB-C65 and by the FLAG-ERA grant LEGOCHIP, under Grant agreement no. PCI2019-111890-2.

PIM-1/holey graphene oxide (GO) mixed matrix membranes (MMMs) have been prepared and their gas separation performance for CO2/CH4 mixtures assessed. Nanopores have been created in the basal plane of gas-impermeable GO by chemical etching reactions, and the resulting holey flakes have been further chemically functionalized, either with octadecylamine (ODA) or with PIM-1 moieties, to aid their dispersion in PIM-1. It is found that nanopores barely promote gas transport through the graphene-like nanofiller for fresh membranes (tested right after preparation); however, the prepared hybrid PIM-1/holey GO membranes exhibit higher CO2 permeability and CO2/CH4 selectivity than the pure polymer membrane 150 days after preparation and 13 and 15% higher CO2 permeability for filler contents of 0.1% of octadecylamine-functionalized holey GO and 1% of (PIM-1)-functionalized holey GO, respectively. The most significant improvement is observed for the mitigation of physical aging, as MMMs using 10% of (PIM-1)-functionalized holey GO nanofillers are capable of maintaining up to 70% of their initial CO2 permeability after 150 days, whereas only 53% is kept for pure PIM-1 after the same period. The gas permeability of the nanofiller has been rationalized with the aid of the Maxwell–Wagner–Sillars equation., The authors are grateful to EPSRC for funding under grant numbers EP/K016946/1 and EP/M01486X/1. J. M. Luque-Alled is grateful to the Department of Chemical Engineering and Analytical Science─The University of Manchester for funding his Ph.D. studies. P. Gorgojo acknowledges the Spanish Ministry of Economy and Competitiveness and the European Social Fund through the Ramon y Cajal programme (RYC2019-027060-I/AEI/10.13039/501100011033).

The polymer of intrinsic microporosity PIM-1 was synthesized with different topologies and negligible network content. A more rapid heating rate from room temperature yielded a predominantly di-substituted PIM-1 (D-PIM-1), whereas a marginally lower heating rate produced a more branched structure (B-PIM-1). Both polymers were acid-hydrolyzed to give carboxylic acid functionalization (cPIM-1), as indicated by FT-IR, 1H NMR, and elemental analysis. Both PIM-1 and cPIM-1 were processed into self-supported membranes and into thin film composite (TFC) membranes on a polyacrylonitrile support. For a 70% hydrolysed polymer (D-cPIM-1-70%), the initial CO2 permeance reached 7700 GPU, with ideal selectivity of 56 for CO2/N2 and 37 for CO2/CH4. D-PIM-1 and D-cPIM-1-70% showed 85% and 52% CO2 permeance drop after 60 days’ aging, respectively. B-PIM-1, with initial CO2 permeance of 3100 GPU and ideal selectivity of 19 for CO2/N2 and 11 for CO2/CH4, showed only a 65% decrease. Polymer that was both branched and hydrolysed (B-cPIM-1-73&81%), with CO2 permeance of 3200 GPU and selectivity of 64 for CO2/N2 and 45 for CO2/CH4, showed no decrease of CO2 permeance after 60 days. The branched structure is crucial for reducing membrane aging. Plasticization gave rise to reduced selectivity in mixed gas experiments, but nevertheless TFC membranes prepared from B-cPIM-1-81% were able to concentrate CO2 to 38% from a 10% CO2/90% N2 mixture at 4.8 bar.

Polyvinylidene fluoride (PVDF) membranes containing hydrophobic graphene nanofillers were prepared and tested for membrane distillation applications. The nanofillers were obtained by a two-step process: 1st) chemical grafting of hydrophobic molecules, either octylamine (OA) or perfluoroctylamine (PFOA), to graphene oxide (GO) nanosheets, and 2nd) chemical reduction of functionalized GO (rGO) to remove unreacted oxygen-containing functional groups. This resulted in OA-functionalized reduced GO (OA-rGO) and PFOA-functionalized rGO (PFOA-rGO). The addition of these nanomaterials to PVDF membranes prepared by the phase inversion process led to an increase in the membrane contact angle, and therefore higher hydrophobicity, as well as an increase in the membrane porosity. When comparing both nanofillers, OA-rGO and PFOA-rGO, the latter was more efficient in achieving higher contact angles due to the presence of fluorine atoms, whereas OA-rGO led to a greater enhancement in membrane porosity as compared to PFOA-rGO. MMMs containing 0.7 wt% nanofiller loadings of OA-rGO and PFOA-rGO achieved the highest water fluxes of 9.1 and 8.8 L m−2 h−1, respectively and salt rejection above 99.9%, which was monitored for at least 162 h of operation for the former. In comparison with pure PVDF (flux of 5 L m−2 h−1), the addition of OA-rGO and PFOA-rGO nanofillers results in a flux increment of 82% and 76%, respectively.

This work demonstrates very high removal rates (below the detection limit of 0.045 ppb) of inorganic arsenic from water using electrospun polyvinylidene difluoride (PVDF) membranes enhanced by the addition of functionalized graphene oxide in membrane distillation. This shows potential for applications in the many parts of the world suffering from arsenic-contaminated groundwater. These membranes were enhanced by the addition of reduced graphene oxide functionalized with superhydrophobic polyhedral oligomeric silsesquioxane molecules (POSS-rGO) into the spinning solutions. The flux of the best-performing rGO-enhanced membrane (containing 2 wt % POSS-rGO) was 21.5% higher than that of the pure PVDF membrane and almost double that of a commercial polytetrafluoroethylene (PTFE) membrane after 24 h of testing, with rejection values exceeding 99.9%. Furthermore, the flux of this membrane was stable over 5 days (∼28 L m-2 h-1) of continuous testing and was more stable than those of the PTFE and control membranes when treating a concentrated fouling solution of calcium carbonate and iron(III) sulfate heptahydrate. It also achieved higher permeate quality in these conditions. The Young's modulus and ultimate tensile strength of the best-performing membrane increased by 38 and 271%, respectively, compared to the pure polymer membrane, while both had similar porosities of ∼91%.

Physical aging is currently a major obstacle for the commercialization of PIM-1 membranes for gas separation applications. A well-known approach to reversing physical aging effects of PIM-1 membranes at laboratory scale is soaking them in lower alcohols, such as methanol and ethanol. However, this procedure does not seem applicable at industrial level, and other strategies must be investigated. In this work, a regeneration method with alcohol vapors (ethanol or methanol) was developed to recover permeability of aged PIM-1 membranes, in comparison with the conventional soaking-in-liquid approach. The gas permeability and separation performance, before and post the regeneration methods, were assessed using a binary mixture of CO2 and CH4 (1:1, v:v). Our results show that an 8-hour methanol vapor treatment was sufficient to recover the original gas permeability, reaching a CO2 permeability > 7000 barrer.

Membrane distillation (MD) is a thermal-based separation technique with the potential to treat a wide range of water types for various applications and industries. Certain challenges remain however, which prevent it from becoming commercially widespread including moderate permeate flux, decline in separation performance over time due to pore wetting and high thermal energy requirements. Nevertheless, its attractive characteristics such as high rejection (ca. 100%) of nonvolatile species, its ability to treat highly saline solutions under low operating pressures (typically atmospheric) as well as its ability to operate at low temperatures, enabling waste-heat integration, continue to drive research interests globally. Of particular interest is the class of carbon-based nanomaterials which includes graphene and carbon nanotubes, whose wide range of properties have been exploited in an attempt to overcome the technical challenges that MD faces. These low dimensional materials exhibit properties such as high specific surface area, high strength, tuneable hydrophobicity, enhanced vapour transport, high thermal and electrical conductivity and others. Their use in MD has resulted in improved membrane performance characteristics like increased permeability and reduced fouling propensity. They have also enabled novel membrane capabilities such as in-situ fouling detection and localised heat generation. In this review we provide a brief introduction to MD and describe key membrane characteristics and fabrication methods. We then give an account of the various uses of carbon nanomaterials for MD applications, focussing on polymeric membrane systems. Future research directions based on the findings are also suggested.

Studies of blends of topologically distinct samples of the polymer of intrinsic microporosity PIM-1 demonstrate, for the CO2/N2 gas pair, the ability to vary dramatically the selectivity and aging behaviour of thin film composite (TFC) membranes. Polymerizations carried out in the absence of nitrogen gas produced polymers with higher degrees of branching, which formed further into loops and at higher temperatures into significant amounts of colloidal network PIM-1 (

The synthesis of PIM-1 is reported from step growth polymerizations of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindane (TTSBI) with the commercially cheaper monomer, tetrachloroterephthalonitrile (TCTPN). Nitrogen purged polymerizations (100 - 160 C) were quenched after a monitored increase in viscosity. A combination of multiple detector SEC, NMR, MALDI TOF, DLS and elemental analysis was used to elucidate significant structural differences (cyclic, branched, tadpole, extended and network topologies) in the polymers produced under different conditions. A significant proportion of the apparent surface area (up to 200 m2 g-1) associated with PIM-1 can be attributable to whether its contorted polymer chains in fact link to form cyclic or other non-linear structures. Membranes cast from solutions of polymer samples containing higher branching and network content exhibited higher gas pair selectivities (CO2 / CH4 and CO2 / N2), above the Robeson 2008 upper bound. A toolbox approach to the characterization and production of topologically different PIM-1 samples has been developed which can be used to tune membrane performance for gas separation and other applications.

PIM-1 mixed matrix membranes (MMMs) were fabricated with polyhedral oligomeric silsesquioxane (POSS) and graphene oxide (GO) functionalized with POSS (GO-POSS), and tested for CO2/N2 (single gas) and CO2/CH4 (1:1, v:v gas mixture). The CO2 permeability of the best performing fresh MMM (containing 0.05 wt% GO-POSS) was ∼ 12000 Barrer, which is 69% higher than that of the neat PIM-1 membrane, with about the same selectivity (CO2/CH4 selectivity ∼ 12 and CO2/N2 selectivity ∼ 20). In both cases, the gas separation data surpass the 2008 Robeson upper bound. In addition to the initial CO2 permeability enhancement, the use of GO-POSS is an efficient strategy to slow down physical aging. The MMM at a filler loading of 0.75 wt% showed less than half of the reduction in CO2 permeability than the neat PIM-1 membrane 160 days after preparation (26% for the MMM vs 58% for the purely polymeric one)., S. Mohsenpour thanks the University of Manchester for funding his Ph.D. studies. P. Gorgojo acknowledges the Spanish Ministry of Economy and Competitiveness and the European Social Fund through the Ramon y Cajal programme (RYC2019-027060-I/AEI/10.13039/501100011033).

PIM-1-based freestanding mixed matrix membranes (MMMs) and thin film nanocomposites (TFNs) were prepared by incorporating porous silica nanosheets (SN) and exfoliated SN (E-SN) derived from natural vermiculite (Verm) in the PIM-1 polymer matrix. In addition, SN were functionalized by sulfonic acid and amine groups (S-SN and N-SN, respectively) and were also used as fillers for the preparation of MMMs. The gas separation performance was evaluated using CO2/CH4 and CO2/N2 (1:1, v:v) binary gas mixtures. Among freestanding membranes, fresh ones (i.e. tested right after preparation) containing 0.05 wt% functionalized SN and E-SN outperformed the neat PIM-1, surpassing the 2008 Robeson upper bound. At the same filler concentration, fresh MMMs with sulfonic acid-functionalized SN (S-SN) exhibited 40% higher CO2 permeability, 20% higher CO2/N2 selectivity and almost the same CO2/CH4 selectivity as neat PIM-1 membranes. Moreover, after 150 days of aging, these membranes were capable of maintaining up to 68% of their initial CO2 permeability (compared to 37% for neat PIM-1). When prepared as TFN membranes, the incorporation of 0.05 wt% of S-SN led to 35% higher initial CO2 permeance and five times higher CO2 permeance after 28 days., S. Mohsenpour thanks the University of Manchester for funding his Ph.D. studies. P. Gorgojo acknowledges the Spanish Ministry of Economy and Competitiveness and the European Social Fund through the Ramon y Cajal programme (RYC2019-027060-I/AEI/10.13039/501100011033). Stuart M. Holmes thanks the EPSRC grant EP/009050.

Supported liquid membranes (SLMs) containing novel green solvents are proposed as a sustainable alternative separation process in the recovery of biomolecules. In this work, succinic acid has been successfully extracted from model fermentation broths through a stripping phase-facilitated transport mechanism with four different green supported liquid membranes: two eutectic solvents (DL-menthol:OctA and N4444Cl:OctA), the bio-based solvent eucalyptol and the ionic liquid [C4pyrr][Tf2N]. A permeability activity-based model that takes into account for the first time solute-phase affinities has been developed using the quantum chemical COSMO-RS method; the model corrects the mass transfer driving force and allows extraction predictions beyond the concentration equilibrium. The best recovery has been achieved experimentally for the eucalyptol-based SLM (concentration factor of 1.4) using an alkaline aqueous solution (0.5 M NaOH) as the stripping phase. A countercurrent cascade extraction process design is proposed, and a graphical method to determine the stage number, interstage concentrations as well as mass transfer area requirements is presented. This new tool, the Permeability Activity-Based Linear Operation (PABLO) method, will substantially enhance the process design of SLMs technology for the biorefinery industry., This work was funded by the CONICYT PFCHA/DOCTORADO BECAS CHILE/2017 – 72180306. P. Gorgojo acknowledges the Spanish Ministry of Economy and Competitiveness and the European Social Fund through the Ramon y Cajal programme (RYC2019-027060-I/AEI/10.13039/501100011033). M. González-Miquel acknowledges Madrid Government (Comunidad de Madrid-Spain) for funding through the Multiannual Agreement with Universidad Politécnica de Madrid under the Excellence Programme for University Professors, in the context of the V PRICIT (Regional Programme of Research and Technological Innovation).

This article is part of the themed collection: Recent Open Access Articles., Loss of free volume over time (i.e. aging) is the main hurdle towards the commercial use of super glassy polymers for gas separation membranes. Aging takes place at a much faster rate in polymeric thin films, with permeability reductions of over 50% in only a few days. In this work 2D reduced holey graphene oxide (rHGO) nanosheets containing amine groups were added into thin films of the super-glassy polymer of intrinsic microporosity PIM-1. At filler loadings of 1 wt% of rHGO-tris(4-aminophenyl)amine, the CO2 permeance after 1 year of physical aging was 846 ± 37 GPU, which remained very close to that of the fresh membrane tested right after preparation (1050 ± 70 GPU), and was double that of 1 year-aged purely PIM-1 thin film composite membranes (432 ± 4 GPU). Membranes with lower filler concentrations of 0.1 wt% showed CO2 permeance values of 604 ± 34 GPU after 1 year of aging, but they aged quite rapidly; the initial CO2 permeance values of the fresh thin film nanocomposite (TFN) membrane at filler loading of 0.1 wt% was 3351 ± 662 GPU. The aging behaviour was also investigated in several tens of micrometres thick membranes (up to 2 years) for filler loadings of 0.1 wt% and the gas separation performance showed similar tendencies to that of thin films; leading to higher CO2 permeability without sacrificing CO2/CH4 selectivity., F. Almansour is grateful to the Department of Research & Development, Saudi Aramco for funding and supporting his PhD studies. M. Alberto is grateful to EPSRC for funding under the research grant number EP/S032258/1. A. B. Foster acknowledges the EPSRC for the grant number EP/v047078/1 “SynHiSel”. P. Gorgojo acknowledges the Spanish Ministry of Economy and Competitiveness and the European Social Fund through the Ramon y Cajal programme (RYC2019-027060-I/AEI/10.13039/501100011033).

The solubility and involved energies of organic acids in green solvents are relevant to the design of sustainable biorefinery downstream processes. In this work, the solubility of two important bio-based organic acids such as succinic acid and fumaric acid, in water and four bio-based solvents (i.e., ethyl acetate, 1,8-cineole, cyclopentyl methyl ether, and 2-methyl tetrahydrofuran) were measured within a temperature range of [283 – 313] K. A gravimetric methodology was adopted, previously validated using the organic acid aqueous solubilities available in the literature. The reported data present an average estimated uncertainty of measurement, with a level of confidence of 95%, of 5.2·10-4 mol·mol−1. Experimental results were correlated with the van’t Hoff equation, and the Buchowski–Ksiazaczak λh model, where the root mean squared deviations were, This work was funded by the CONICYT PFCHA/DOCTORADO BECAS CHILE/2017 – 72180306. P. Gorgojo acknowledges her Ramón y Cajal fellowship RYC2019-027060-I funded by MICIN/AEI/10.13039/501100011033 and by “ESF Investing in your future”. M. González-Miquel also acknowledges Comunidad Autónoma de Madrid (Spain) for funding through “Programa de Excelencia para el Profesorado Universitario”.

Thin film composite (TFC) membranes of the prototypical polymer of intrinsic microporosity (PIM-1) have been prepared by dip-coating on a highly porous electrospun polyvinylidene fluoride (PVDF) nanofibrous support. Prior to coating, the support was impregnated in a non-solvent to avoid the penetration of PIM-1 inside the PVDF network. Different non-solvents were considered and the results were compared with those of the dry support. When applied for the separation of n-butanol/water mixtures by pervaporation (PV), the developed membranes exhibited very high permeate fluxes, in the range of 16.1–35.4 kg m–2 h–1, with an acceptable n-butanol/water separation factor of about 8. The PV separation index (PSI) of the prepared membranes is around 115, which is among the highest PSI values that have been reported so far. Hybrid PV-distillation systems have been designed and modeled in Aspen HYSYS using Aspen Custom Modeler for setting up the PIM-1 TFC and commercial PDMS membranes as a benchmark. The butanol recovery cost for the hybrid systems is compared with a conventional stand-alone distillation process used for n-butanol/water separation, and a 10% reduction in recovery cost was obtained., J.C.-M. is thankful for the grant received from the Spanish Ministry of Economy and Competitiveness and the European Social Fund. M.K., C.G.-P., and J.C.-M. appreciate the financial support from Spanish Ministry of Economy and Competitiveness through its project CTM2015-65348-C2-2-R and the Spanish Ministry of Science, Innovation, and Universities through its project RTI2018-096042-B-C22. S.M. thanks The University of Manchester for funding his Ph.D. studies. P.G. acknowledges the Spanish Ministry of Economy and Competitiveness and the European Social Fund through the Ramon y Cajal program (RYC2019-027060-I/AEI/10.13039/501100011033).

In this work, thin film nanocomposite (TFN) membranes of super-glassy polymer PIM-1 containing zeolitic imidazolate framework-8 (ZIF-8)/graphene oxide (GO) composites (ZG) have been prepared by dip-coating onto water pre-impregnated polyvinylidene fluoride (PVDF) substrates. Higher flux and improved separation factors as compared to bare PIM-1 thin film composite (TFC) membranes have been achieved in organophilic pervaporation; for an aqueous feed solution with 5 wt% of butanol at 65 °C, a total permeate flux of 7.9 ± 0.69 kg m−2h−1 and a separation factor (βBtOH/H2O) of 29.9 ± 1.99 have been obtained with a TFC membrane containing 0.5 wt% of ZG filler. The pervaporation separation index (PSI) of this membrane (228 kg m−2h−1) is amongst the highest values reported in the literature. This excellent performance is attributed to the formation of a defect-free PIM-1 active layer (, Patricia Gorgojo is grateful to the Spanish Ministerio de Economía y Competitividad and the European Social Fund for her Ramon y Cajal Fellowship (RYC2019-027060-I/AEI/10.13039/501100011033). Boya Qiu would like to acknowledge the China Scholarship Council (CSC, file no. 202006240076)and the University of Manchester for the joint PhD studentship to support her research.

Wastewater from textile dyeing plants contains a complex mixture of dyes, salts, surfactants and other additives which make it challenging to treat and harmful to release directly into the water system. Current treatment technologies are composed of many steps, increasing the cost and complexity of water management. Air gap membrane distillation (AGMD) is a versatile water treatment process which has potential to reduce the complexity of textile dyeing wastewater but has not yet been investigated for this application. In this work, we used commercial polytetrafluoroethylene (PTFE) membranes in AGMD to recover pure water from simulated textile wastewater containing NaCl and either sunset yellow (SY) or rose bengal (RB) dyes and sodium dodecyle sulfate (SDS) surfactant. 100% salt and colour removal was achieved for binary feed solutions (NaCl + SY or RB) over 20 h of testing, whilst maintaining stable fluxes between 11.7 and 12.6 L m−2 h−1 (LMH) throughout. After 24 h of continuous testing of the ternary feed solution (NaCl + RB + SDS) the flux was as high as 11 LMH with permeate conductivity less than 50 µS cm−1. However after 70 h these had reached ∼3 LMH and 421.8 µS cm−1, respectively indicating a need for cleaning or back-flushing between batches. Parallel direct contact membrane distillation (DCMD) tests achieved lower colour and total carbon removal after just 8 h of testing with the ternary feed solution. Comparisons between our tests and those found in the literature are made and indicate that AGMD may be the most suitable configuration for this application due to reduced flux decline and potentially higher thermal efficiency.

High free volume glassy polymers or polymers of intrinsic microporosity such as poly[1-trimethylsilyl-1-propyne] (PTMSP) and polybenzodioxane (PIM-1) are extra high gas permeability membrane materials. One of their major drawbacks is low gas selectivity. In this study, thin film composite (TFC) membranes have been developed with high CO2 permeance and superior CO2/N2 selectivity due to a strong synergistic effect. The TFC membranes, comprising a thin layer (0.29–0.42 μm) of PIM-1 atop a cross-linked PTMSP gutter layer (2.07–3.44 μm) on a porous backing material, were fabricated by coating PIM-1 solution on the cross-linked PTMSP support. A key element is that for coating PIM-1 a mixed solvent of chloroform and trichloroethylene (1 : 1) was successfully implemented for the first time. All membrane samples demonstrated a strong synergistic enhancement of CO2/N2 selectivity (α = 35.8–55.7) compared to PIM-1 (α = 18.5) and cross-linked PTMSP (α = 3.7). SEM, TEM and laser interferometry studies revealed that the synergistic enhancement of gas selectivity in the TFC membranes is most likely due to the creation of a very thin boundary layer between PIM-1 and the cross-linked PTMSP gutter layer. The aged TFC membranes (after three months) showed a severe drop in gas permeance while keeping nearly the same high selectivity. Thus, future success in the prevention of polymer physical aging, together with the synergy effect in selectivity reported for the first time in this work, will give new opportunities for application of polymers of intrinsic microporosity.

We investigated the drying dynamics and resulting salt deposition patterns from evaporating saline droplets on fabricated graphene oxide (GO) and reduced graphene oxide (rGO) membranes. As evaporation proceeds, the salt concentration increases until it exceeds substantially the solubility limit which results in the formation of salt crystals. Scanning electron microscopy imaging enabled us to investigate how the properties of the fabricated membranes influence the salt deposition patterns and crystal morphology, providing us with an opportunity to control salt deposition patterns on the surface. The observation from the drying of saline droplets on fabricated GO and rGO membranes leads us to conclude that combined effects of the membrane roughness, interlayer spacing, and nanochannel connectivity determines the drying dynamics and the final salt deposition patterns. Our results extend the understanding of the interaction between surface properties and salt deposition patterns, which is relevant information for various engineering processes such as coating of marine vessels and in water remediation technologies.

A strategy to reduce the physical aging in PIM-1 membranes by incorporating novel functionalized graphene oxide (GO) fillers is reported. PIM-1 was covalently attached both to as-synthesized GO and to GO reacted with (3-aminopropyl)triethoxysilane (APTS-GO), leading to homogeneous dispersion of the nanofillers in the mixed matrix membranes (MMMs). It was found that the aging rate decreases with increasing content of (PIM-1)-functionalized GO, as evidenced by the smaller decrease in gas permeability over time. The best performance was achieved by a membrane containing 10 wt% of (PIM-1)-functionalized APTS-GO. This membrane maintains 85% of the initial CO2 permeability after 150 days (drop of only 310 Barrer), which represents about nine-fold less CO2 permeability drop as compared to pure PIM-1.

Graphene and its derivatives have shown fascinating potential in biomedical applications. However, the biocompatibility of graphene with vascular smooth muscle cells (VSMCs) and applications to vascular engineering have not been explored extensively. Using a rat aortic smooth muscle cell line, A7r5, as a VSMC model, we have explored the effects of graphene oxide (GO) on the growth and behaviours of VSMCs. Results demonstrated that GO had no obvious toxicity to VSMCs. Cells cultured on GO retained the expression of smooth muscle cell-specific markers CNN1, ACTA2 and SMTN, on both mRNA and protein levels. A wound healing assay demonstrated no effect of GO on cell migration. We also found that small-flaked GO favoured the proliferation of VSMCs, suggesting a potential of using surface chemistry or physical properties of GO to influence cell growth behaviour. These results provide insight into the suitability of GO as a scaffold for vascular tissue engineering.

A low cross-link density (LCD) network-PIM-1, which offers high compatibility with the polymer of intrinsic microporosity PIM-1, is synthesized by a modified PIM-1 polycondensation that combines both a tetrafluoro- and an octafluoro-monomer. To maximize the advantages of utilizing such cross-linked PIM-1 fillers in PIM-1-based mixed matrix membranes (MMMs), a grafting route is used to decorate the LCD-network-PIM-1 (dispersed phase) with PIM-1 chains, to further enhance compatibility with the PIM-1 matrix. Mixed-gas CO2/CH4 (1:1, v/v) separation results over 160 days of membrane aging confirm the success of a relatively short (24 h) grafting reaction in improving the initial CO2 separation performance, as well as hindering the aging of PIM-1/grafted-LCD-network-PIM-1 MMMs. For MMMs based on a 24 h grafting route, all the gas separation data surpass the 2008 Robeson upper bound by a significant margin, and the 160-day aged membranes show only 29% reduction from the initial CO2 permeability, which is substantially less than the equivalent losses of nearly 70% and 48% for PIM-1 and traditionally fabricated MMMs counterparts, respectively. These results demonstrate the potential of network-PIM components for obtaining much more stable gas separation performance over extended periods of time.

Bio-based organic acids constitute an important group of building block chemicals that can be produced from renewable resources, becoming a sustainable alternative to conventional petrochemical-derived commodities. However, due to the growing number of green solvents emerging as extraction media, the proper solvent selection for biomolecule separation from fermentation broths has become a key challenge in the bio-refinery industry. The overall aim of this work is to develop a roadmap to select and design green solvents for sustainable downstream processing of bio-based organic acids. To this end, a wide range of neoteric solvents (ionic liquids, eutectic solvents and bio-based solvents) were systematically evaluated for the recovery of relevant bio-organic acids through combination of experimental and COSMO-RS molecular simulation methods. Comprehensive thermodynamic analyses evaluating the organic acid partition coefficients, excess enthalpy contributions, solvent-water affinity, and process spontaneity were performed to elucidate the main mechanism driving the separation process and to provide essential guidelines for further solvent development. Based on these findings, a rational screening approach was established to identify suitable solvents for the recovery of structurally different bio-organic acids. Ultimately, this paper provides a green solvent selection guide to design sustainable separation processes of bio-based organic acids, as valuable platform chemicals transitioning towards a bio-based economy.

This work deals with the use of octadecylamine (ODA)-functionalized reduced graphene oxide (rGO) for thin film nanocomposite (TFN) membranes. The functionalization of rGO with ODA leads to graphene-based nanofillers, more hydrophobic than GO, and thus to the easier dispersion in the organic phase of the interfacial polymerization (IP) reaction carried out to produce polyamide (PA) TFN membranes. The performance of the new TFN membranes is evaluated by organic solvent nanofiltration (OSN) of alcoholic solutions containing dyes Acridine Orange (AO, MW 265 g·mol−1), Sunset Yellow (SY, MW 452 g·mol−1) and Rose Bengal (RB, MW 974 g·mol−1). The functionalized nature of the nanoparticles introduced into the hydrophilic PA layer allows an increase of the ethanol permeance from 2.8, 3.4 and 3.7 L·m−2·h−1·bar−1 for AO, SY and RB, respectively, corresponding to the bare thin film composite membrane (without rGO-ODA particles), to 4.3, 4.6 and 6.0 L·m−2·h−1·bar−1 for AO, SY and RB, respectively, for the rGO-ODA based TFN membrane. In fact, we hypothesize that the increase of the ethanol flux achieved with the use of rGO-ODA as a filler in TFN membranes is owing to a combination of the simultaneous presence of polar and non-polar groups from rGO-ODA nanosheets and the creation of still selective narrow gaps between these particles and the polyamide (PA)., Financial support from the Research Project MAT2016-77290-R (MINECO/AEI/FEDER, UE) is gratefully acknowledged. The Aragón Government (T43-17R) and the ESF is also gratefully acknowledged. Lorena Paseta would like to express her gratitude to the Spanish MINECO for the predoctoral grant (BES-2014-068287) awarded.

Adsorptive separation is a promising alternative to the energy-intensive cryogenic distillation process for separating the ethane/ethylene (C2H6/C2H4) mixtures. Herein, two pillared-layer metal-organic frameworks (MOFs), Ni(HBTC)(bipy) and Ni2(HBTC)2(bipy)0.6(dabco)1.4, are prepared as the C2H6-selective adsorbents for C2H4 purification from C2H6/C2H4 mixtures. The effect of the type of pillars on the framework structure, thermal and moisture stability, as well as the C2H6 and C2H4 adsorption propertiy, of the MOFs was studied. The use of the longer pillars (i.e. bipy versus dabco) to scafolld the Ni(HBTC) improved the pore size (5.5 A versus 5.3 A), specific surface area (1474 m2/g versus 1070 m2/g) and moisture stability in the relative humidity range of 0–90%, but compromised the thermal stability (267 °C versus 278 °C). Both MOFs were C2H6-selective, which was evidencd by the single component adsorption experiments using C2H6 and C2H4. The ideal adsorbed solution theory (IAST) selectivity for C2H6/C2H4 mixtures (1:1 and 1:15, v/v) is in the range of 1.4–1.7 at 25–50 °C and 0–1 bar. The preferential adsorption towards C2H6 over C2H4 on both MOFs is then explained by the isosteric heat of adsorption. Additionally, Ni(HBTC)(bipy) also shows the best capacity of up to 6.6 mmol/g for C2H6 adsorption in comparison with other C2H6-selective MOFs at 25 °C and 1 bar. Both MOFs showed the excellent recyclability, with the negligible reduction in the gas uptake observed during four cycles of adsorption/desorption tests. Besides, breakthrough experiments demonstrated that both MOFs can achieve efficient separation of an equimolar C2H6/C2H4 mixture. The findings suggest that Ni(HBTC)(bipy) and Ni2(HBTC)2(bipy)0.6(dabco)1.4 can be further considered as C2H6-trapping adsorbents for the C2H6/C2H4 separation applications in practice.

Membrane morphology of integrally skinned asymmetric membranes made by phase inversion can be tailored by precise control of the thermodynamic properties of the casting solution. In this work, the morphology of polyethersulfone (PES) and polyvinylidene fluoride (PVDF) membranes containing graphene oxide (GO) and their phase separation behavior have been studied. The Flory-Huggins theory and the Hansen solubility parameters have been used to construct theoretical binodal lines for ternary and quaternary systems, which have been validated by conducting cloud titration experiments. Moreover, the effect of different solvents on the morphology of PES membranes is discussed through the thermodynamic and kinetic properties of the casting solutions. Nontoxic solvents dimethyl sulfoxide (DMSO) and dihydrolevoglucosenone (Cyrene™) induce PES/GO membranes with finger-like pores and cellular voids, respectively. The addition of GO in the PES and the PVDF casting solutions increases their thermodynamic instability, leading to thinner selective top layers and higher porosities, up to a point where the high viscosity of the GO-containing solutions hinders the solvent-nonsolvent demixing. The highest porosity and pure water flux (PWF) occurs at 0.1 wt% GO for PES/GO/DMSO and at a loading of 0.3 wt% GO for systems PES/GO/Cyrene and PVDF/GO., S. Mohsenpour and J. Shokri thank the University of Manchester for funding their Ph.D studies. P. Gorgojo acknowledges the Spanish Ministry of Economy and Competitiveness and the European Social Fund through the Ramon y Cajal programme (RYC2019-027060-I/AEI/10.13039/501100011033). The authors are also grateful to the EPSRC for funding under the grant number EP/S032258/1.

Physical aging of polymer of intrinsic microporosity PIM-1 is one of the major obstacles for its application as a commercial membrane material for gas separation. In this work, physical aging of PIM-1 and matrices of this same polymer containing graphene-like materials were studied. Graphene-like fillers resulted from the functionalization of graphene oxide (GO) with two alkyl chains of different lengths, using octylamine (OA) and octadecylamine (ODA), and further chemical reduction. Extents of membrane aging were evaluated through changes in gas permeability over time; the separation of gas mixtures comprising carbon dioxide and methane, which are of great interest for industrial applications such as the production of biogas or the purification of natural gas, was carried out. 50:50 vol% CO 2 /CH 4 mixtures were used as feed and separation performance analysed for fresh membranes and at intervals of approximately a month up to 155 days. At the end of this testing period, aged PIM-1 membranes showed a CO 2 permeability of (2.0 ± 0.7) × 10 3 Barrer, which corresponds to a CO 2 permeability reduction of 68% from the value obtained right after their fabrication. The addition of alkyl-functionalized GO is shown to be an efficient strategy to retard the physical aging of PIM-1 membranes; filler loadings as low as 0.05 wt% of reduced octyl-functionalized GO showed a CO 2 permeability of (3.5 ± 0.6) × 10 3 Barrer after 5 months, which is almost three quarters higher than that of pure PIM-1 membrane aged for the same time period and represents a reduction of just 39% from its initial value. Moreover, the addition of graphene-like materials to PIM-1 does not affect its mechanical properties.

Air gap membrane distillation (AGMD) is an emerging desalination technology with the potential to meet the challenge of global water scarcity due to its low cost and high thermal efficiency compared to other processes. However, despite the potential of AGMD, a lack of appropriate membranes limits its commercial application. Therefore, this study was focussed on the fabrication of high flux, robust membranes for the purification of artificial sea water by incorporating graphene oxide functionalized with 3-(aminopropyl)triethoxysilane (APTS) into PVDF polymer solutions. Successful functionalisation of GO with APTS was confirmed with XPS and FTIR. It was shown that the addition of GO and GO-APTS enhanced the permeate flux by 52% and 86%, respectively, compared to pure PVDF. The best performing membrane contained 0.3 wt% GO-APTS (with respect to PVDF) and had a flux of 6.2 LMH (L m−2 h−1) whilst maintaining perfect salt rejection (>99.9%). These improvements were attributed to increased surface and bulk porosity, larger mean pore size and hydrophilic interactions owing to the functional groups of GO and GO-APTS. These membranes are evidence of the potential that GO and related materials have as nanocomposite fillers in high performance desalination membranes.

Physical aging represents one of the major obstacles towards adoption of polymer of intrinsic microporosity (PIM) membranes for gas separation applications. In this work, mixed matrix membranes (MMMs) of 2D boron nitride nanosheets (BNNS) and PIM-1 were prepared and applied in the separation of a CO2/CH4 (1:1, v:v) binary gas mixture. The membranes were tested over a period of more than one year to evaluate their anti-aging properties as compared to neat PIM-1. The results show that introducing BNNS into PIM-1 leads to a significant reduction in the physical aging of PIM-1, as demonstrated by the values of reduction in CO2 permeability after 414 days (22% for the MMMs as compared to 58% for neat PIM-1). This work paves the way to using PIM-based membranes in industry.

Membrane distillation (MD) is an emerging thermal-based membrane technology that has the capacity to treat a wide range of feed waters, including high salinity brines and wastewater. Compared with pressure-driven processes, MD has the following advantages: low electrical energy consumption, complete removal of non-volatile solutes and ambient operating pressures. On the other hand, membrane fouling and pore wetting remain a challenge holding back its wider industrial implementation. To manage this issue, effective pretreatment and cleaning strategies are essential, as with other membrane processes. Despite the importance of these aspects for achieving a stable and reliable water treatment process, far too little attention has been paid to them in the MD literature. Evidence of this is that a comprehensive review on both membrane cleaning and pretreatment in MD is still lacking, despite the large and growing number of publications related to the technology. In this work, we first provide an overview of the three main types of fouling present in MD: inorganic, organic and biological fouling. After this we review, in detail, the use of pretreatment protocols in a range of MD applications, highlighting their efficacy in preventing fouling and ensuring stable performance. Next, we review the use of state-of-the-art chemical and physical cleaning strategies and discuss the development of ‘self-cleaning’ membranes that are superhydrophobic or omniphobic. Finally, future research directions are suggested, with the aim of helping researchers working in this field to develop membrane distillation technology towards wider commercial implementation.

Membranes that enable the recovery of organic compounds from dilute aqueous solution are desired for applications such as biobutanol production. The polymer of intrinsic microporosity PIM-1 shows promise for organophilic separations and here it is incorporated into thin film composite (TFC) membranes in order to increase the flux of permeate. Asymmetric polyvinylidene fluoride (PVDF) supports were prepared with pore sizes at the surface in the size range 25–55 nm and fractional surface porosities in the range 0.38–0.69, as determined by atomic force microscopy (AFM). The addition of phosphoric acid to the PVDF dope solution helped to control the pore size and porosity. Supports were coated with PIM-1 to form TFC membranes with active layer thicknesses in the range 1.0–2.9 µm. Membranes were tested for the pervaporation of a 1-butanol/water mixture (5 wt%). At 65 °C, values of total flux up to 9 kg m −2 h −1 were obtained, with separation factors up to 18.5 and values of pervaporation separation index (PSI) up to 112 kg m −2 h −1 .

Microporous polymer nanosheets with thicknesses in the range 3–5 nm and with high apparent surface area (Brunauer–Emmett–Teller surface area 940 m2 g−1) are formed when the effectively bifunctional (tetrafluoro) monomer used in the preparation of the prototypical polymer of intrinsic microporosity PIM-1 is replaced with an effectively tetrafunctional (octafluoro) monomer to give a tightly crosslinked network structure. When employed as a filler in mixed-matrix membranes based on PIM-1, a low loading of 0.5 wt% network-PIM-1 nanosheets gives rise to enhanced CO2 permeability and CO2/CH4 selectivity, compared to pure PIM-1.

Hydrophobic polyvinylidene fluoride (PVDF) membranes have been successfully used in membrane distillation (MD) for desalination applications; however, there is still room for performance enhancements both regarding water flux and salt rejection. In this work, reduced graphene oxide (rGO) nanoplatelets with different degrees of reduction (36%, 58%, 65 and 69% removal of oxygen, as characterized by XPS) were incorporated as fillers in PVDF matrices in order to evaluate the effect of the oxygen content of the fillers in the MD performance. UV-Vis and raman spectroscopies were also used to characterize the fabricated rGO. Changes in morphology of the prepared mixed matrix membranes (MMMs) were assessed via scanning electron microscopy (SEM) and were related to the increased hydrophilicity and viscosity of the casting solutions when fillers were added. MMMs containing 0.5 wt% rGO with an optimum degree of reduction of 58% exhibited an improved MD performance, with fluxes of ~7.0 L m-2 h-1 (LMH), representing an enhancement of ~169% in comparison with the plain PVDF membrane, without compromising salt rejection (greater than 99.99%). Continuous testing for up to 96 h showed a stable performance of the developed MMMs, without compromising the quality of the permeate.

Adsorptive separation of ethylene/ethane (C2H4/C2H6) binary mixture has growing interest in petrochemical industries compared to the conventional energy-intensive cryogenic distillation. Development of moisture-stable materials with high selectivity is of great importance to accomplish C2H4/C2H6 separation. Coordination pillared-layer metal-organic framework (CPL-MOF) CPL-2 was synthesised at room temperature, and then modified by silver ions impregnation to enhance the selectivity towards ethylene over ethane. The synthesised CPL-2 and Ag/CPL-2 MOFs have excellent moisture stability which was confirmed by the dynamic water vapour adsorption analysis under 90% relative humidity, showing no significant framework decomposition, even at 50 °C. The calculated selectivity based on gravimetric single-component gas adsorption experiments shows the significantly improved C2H4/C2H6 selectivity from 1.4 to 26.1 after loading 10 wt.% (theoretical) of silver ions on CPL-2. Breakthrough experiments for C2H4/C2H6 (1:1, v/v) mixture suggest that both CPL-2 and 10 wt.% Ag/CPL-2 can achieve the binary mixture separation, and 10 wt.% Ag/CPL-2 shows relatively better dynamic separation performance compared to parent CPL-2. The good adsorption selectivity and moisture stability allow CPL-MOF to be a class of promising porous materials for further exploitation in the separation of C2H4/C2H6 mixtures. Additionally, the method presented here can potentially be extended to other CPLs with different pore sizes for alkene/alkane separations.

The application of three-dimensional (3D) pillared-layer metal-organic frameworks (MOFs) M(bdc) (ted)0.5 (M = Co, Cu, Ni, Zn) in the adsorptive separation of ethane/ethylene (C2H6/C2H4) mixtures was studied. The effect of the type of metals in M(bdc) (ted)0.5 on the framework structure regarding the moisture stability and adsorption performance was investigated. M(bdc) (ted)0.5 MOFs show excellent porous structures with high surface areas of up to 1905 m2/g (M = Ni), as well as being stable under humid conditions (assessed by the dynamic water vapour adsorption tests with maximum 20% relative humidity at 25 °C). M(bdc) (ted)0.5 exhibits the preferential adsorption of C2H6 over C2H4 under all conditions (i.e. 25–50 °C and 0–10 bar), although a reversal in adsorption uptake (i.e. C2H4 adsorption uptake exceeds the amount adsorbed of C2H6) occurs at pressures of >6 bar. The adsorption capacities of C2H6 and C2H4 on M(bdc) (ted)0.5 adsorbents are up to 8.63 and 8.79 mmol/g at 25 °C and 10 bar, respectively. The calculated C2H6/C2H4 selectivity for an equimolar mixture is insensitive to the metal ions in M(bdc) (ted)0.5, which varies between 1.4 and 1.9. Dynamic breakthrough experiments show that C2H6/C2H4 mixture can be separated in a fixed bed packed with Ni(bdc) (ted)0.5. The good adsorption capacity and selectivity, as well as the low isosteric heat of adsorption, make M(bdc) (ted)0.5 MOFs, especially Ni(bdc) (ted)0.5, good candidates to be further developed for the effective separation of C2H6/C2H4 mixtures in the presence of water vapour with a relative humidity lower than 30%.

Growing uncertainty in the future availability of freshwater sources has led to an increase in installations for desalination of seawater. Reverse osmosis (RO), currently the most widely adopted technique, has caused environmental concerns over the high associated greenhouse gas emissions and generation of large amounts of chemicals-containing brine. Significant consumption of electricity for RO desalination is an additional challenge, particularly in remote locations. In this review, forward osmosis (FO), membrane distillation (MD) and capacitive deionisation (CDI) are assessed as potential substitute technologies and the major recent advancements in each field are discussed. These emerging technologies offer significant advantages over RO, such as higher salt rejection (CDI, MD), higher recovery of water (MD), fewer pre-treatment stages (MD, FO) and the ability to use low-grade energy (MD, FO). In their current state, stand-alone technologies cannot compete with RO until certain challenges are addressed, including pore-wetting (MD) and high energy consumption (MD, CDI, FO). Hybrid systems that combine RO and emerging technologies may be useful for feed waters that cannot be treated by RO alone and their benefits may be able to offset the increase in capital costs. These and other aspects, such as operational stability should be considered in larger-scale, long-term studies.

Cu-BTC metal-organic framework (HKUST-1) was evaluated as the model material for CO2 capture from flue gas streams. This paper presents an optimised hydrothermal synthesis of HKUST-1 and an analysis of water stability of HKUST-1. Substantial improvements of the hydrothermal synthesis process of HKUST-1 are shown to increase the quantitative yield up to 89.4% at 100°C. Single-component adsorption experiments were carried out under conditions relevant for flue gases adsorption (45-60°C, 0-1barG) to evaluate the performance of HKUST-1 in terms of adsorption capacity, showing that the amount adsorbed of water can reach up to 21.7mmolg-1, about one order of magnitude higher than CO2 (1.75mmolg-1) and almost two orders of magnitude higher than N2 (0.17mmolg-1). The hydration process of HKUST-1 framework was investigated using dynamic vapour adsorption under the flue gas emitting conditions. HKUST-1 is sensitive to humid streams and dynamic deformation of its porous structure takes place at 40-50°C and various relative humidity values, leading to the irreversible decomposition of HKUST-1 framework and the consequent deterioration in its adsorption capacity. Under humid conditions, water displaces the organic linkers from the copper centres causing the collapse of HKUST-1 framework. These results provide fundamental knowledge to enable future material design for the modification of the hydrophilic nature of copper sites in HKUST-1 to improve its moisture stability.

In this study, graphene oxide (GO) functionalized with 3-aminopropyltriethoxysilane (APTS) was incorporated into polyethersulfone (PES) membranes prepared by non-solvent induced phase inversion (NIPS). This resulted in increased rejections of protein bovine serum albumin (BSA), divalent salts (MgSO4) and low-molecular weight dyes (sunset yellow and acridine orange). The structural properties of the prepared mixed matrix membranes (MMMs) as well as pure PES control membranes were investigated through scanning electron microscopy (SEM), atomic force microscopy (AFM), specific surface area, zeta potential and contact angle. It was found that the introduction of APTS-GO fillers in the polymer matrix made the membranes’ application range move from ultrafiltration (UF) for pure PES membranes to nanofiltration (NF) for MMMs with a molecular weight cut off (MWCO) of ~1000 Da. Furthermore, membranes prepared by using only 0.1 wt% APTS-GO in combination with 1 wt% of pore-forming agent polyvinylpyrrolidone (PVP 40 K) in the casting solution exhibited high water permeance values of 9.9 LMHbar (L m−2 h−1 bar−1) at low operating pressures of 4 bar and rejections of dyes and BSA > 95%. In addition, improved anti-fouling properties and tensile strength values were obtained when incorporating the functionalized GO.

Microwave-assisted synthesis of zirconium (Zr) based metal organic frameworks (MOFs) were performed and the yield and porous property of UiO-67 was optimized by varying the quantity of the modulator (benzoic acid, BenAc and hydrochloric acid, HCl), reaction time and temperature. It was found that (i) an increase in the amount of modulator enhanced the specific surface area and pore volume of UiO-67 due to the promotion of the linker deficiency; and (ii) the presence of the modulator influenced the number of nuclei (and hence the crystal size) and nucleation time (and hence the yield). Optimum amounts of BenAc and HCl for the synthesis of UiO-67 under microwave irradiation were determined as 40 mole equivalent and 185 mole equivalent (to Zr salt), respectively. In comparison to conventional solvothermal synthesis, which normally takes 24 h, microwave methods promoted faster syntheses with a reaction time of 2‒2.5 h (at similar temperatures of 120 °C and 80 °C for BenAc and HCl, respectively). The thermal effect of microwave is believed to contribute to the fast synthesis of UiO-67 in the microwave-assisted synthesis. The reaction mass efficiency and space-time yield show that the microwave heating promoted the simple yet highly efficient preparation of Zr-based MOFs. In addition, UiO-67 MOFs from different synthesis methods (i.e. the microwave-assisted and solvothermal method) were evaluated using single-component (CO2 and CH4) adsorption, showing comparable gas uptakes.

In this work, graphene oxide (GO) was combined with polyethersulfone (PES) to form mixed matrix membranes (MMMs) for ultrafiltration of aqueous solutions. Also, the effect of adding various pore formers (poly(vinylpyrrolidinone (PVP), reverse triblock Pluronic (P31R1), and poloxamine Tetronic (T904)) to the dope solution was investigated. The prepared MMMs were characterised using various techniques, including Fourier-transform infrared spectroscopy, scanning electron microscopy and atomic force microscopy. It was found that the incorporation of 0.5 wt% of GO increased the flux from 2 to 13 L m−2 h−1 (LMH) and the rejection of bovine serum albumin (BSA) from 89.2 to 97% compared to benchmark PES membranes. SEM analysis revealed the increased pore size and porosity of the GO modified membranes, which contributed to the increased flux. The addition of pore formers further increased the flux compared to pure PES and also displayed synergistic effects with GO. The combination of T904 with 0.3 wt% GO increased the water flux significantly from 2 to 245 LMH and increased the rejection of acridine orange (from 40.5 to 48.4%) and BSA (from 89.6 to 93.3%), respectively. Also, fouling properties of the membranes were investigated with the parameters: flux recovery ratio (FRR), total flux decline ratio ( R t ), reversible flux decline ratio ( R r ), and irreversible flux decline ratio ( R ir ), and improved anti-fouling properties were obtained with the addition of GO. This work shows the promise of GO as a performance-enhancing additive in MMMs for wastewater treatment.

Organophilic mixed matrix membranes (MMMs) have been fabricated with the polymer of intrinsic microporosity PIM-1 and graphene oxide (GO) derivatives for the recovery of 1-butanol and ethanol from aqueous solutions via pervaporation (PV). Graphene oxide (GO) has been synthesized in solution through a modified Hummers’ method, functionalized with alkylamines, and further reduced. The use of two alkylamines with chains of different lengths, octylamine (OA) and octadecylamine (ODA) −8 and 18 carbons, respectively - has been evaluated and the functionalized GO materials have been used as fillers in MMMs. The membranes have been prepared by casting-solvent evaporation of PIM-1/GO derivative solutions at room temperature, and a range of characterization techniques have been used to interpret their structure and relate it to their separation performance. Electron microscopy has been carried out to determine the morphology of the membranes and the dispersion of the functionalized GO flakes in the polymer matrix. Moreover, the membranes have been characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), and contact angle. Separation of alcohol from two binary mixtures composed of ethanol (EtOH)/water and butanol (BtOH)/water, containing 5 wt% of alcohol, have been performed. Under these conditions, the incorporation of graphene-like fillers at relatively low concentrations shows an increase in average separation factor for butanol (βBtOH/H2O) from 13.5 for pure PIM-1 membranes to, in some cases, more than double for the MMMs; with the addition of 0.1 wt% of reduced amine-functionalized GO βBtOH/H2O reaches 32.9 and 26.9 for the short-chain (OA) and the long-chain (ODA) alkylamines, respectively.

For thin film composite (TFC) reverse osmosis (RO) membranes, a trade-off is evident between water permeance and salt rejection; and yet to improve their RO performance it is desirable to increase flux without sacrificing selectivity. This paper describes the fabrication of polyamide TCF membranes on highly solvent stable cross-linked polyimide UF supports and the use of an activating solvent as a strategy to increase water flux; and in certain cases, water permeance and salt rejection are increased simultaneously. Performance was evaluated in terms of NaCl rejection and water permeance before and after post-treatment with dimethylformamide (DMF) as the activating solvent. Additionally, the morphology of the TFC membranes was characterized by SEM, their hydrophilicity was determined by contact angle measurements, and zeta (ζ)-potential was obtained by a streaming potential based method. NaCl rejection was found to be improved for TFC membranes with initial NaCl rejections below 90%, reaching a maximum value of 94%. Water permeance was also increased and to greater extent for membranes with low initial permeance values. The biggest improvement was obtained for a TFC membrane with initial permeance value of 0.2 L·m− 2·h− 1·bar− 1, rising to 1.6 L·m− 2·h− 1·bar− 1 with a rejection of 93.8%.

For the development of thin film composite (TFC) OSN membranes the choice of the ultrafiltration (UF) support is as important as the selection of the separating layer. The support should be as smooth as possible (crucial to the formation of a defect free separating layer), and be stable in organic solvents. Other important support parameters that influence the mass transfer through the TFC membrane are porosity, tortuosity, pore size and hydrophilicity. Here, we have studied the impact of the physical–chemical properties of the support membranes on the performance of TFC membranes for OSN applications. Two different polymers; crosslinked polyimide (PI) and poly(ether ether ketone) (PEEK), were selected to prepare UF support membranes for the formation of TFC OSN membranes by interfacial polymerization (IP). UF support membranes were characterized by pure water permeabilities, dextran rejections, water contact angles, mercury porosimetry, N2 adsorption, and AFM. These results confirm that each support has a different skin layer pore morphology and chemistry. It has been previously reported by our group that impregnating the crosslinked polyimide support with polyethylene glycol (PEG) and treating the TFC membranes with an “activating solvent” gives a dramatic increase in solvent flux. In this work, a comparison study of the activating solvent and PEG impregnating effects between these two supports was carried out. Polyamide and modified hydrophobic polyamide TFC membranes were formed on each of the UF supports. The impacts of each support on the overall membrane performance in polar and non-polar solvents were studied and suggest that their hydrophilicity plays an important role in solvent permeation.