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Carbon dioxide (CO 2 ) is the main culprit of greenhouse gases produced mainly via the combustion of fossil fuel. This paper reviewed the performance of emerging dual-layer hollow fiber membrane, its fabrication via co-extrusion process, improvement, challenges, spinning parameters, advantages and disadvantages in comparison to single-layer hollow fiber membrane for natural gas purification. Development of delamination-free dual-layer hollow fibers via co-extrusion and phase inversion technology is one of the potential solutions for the use of expensive and brittle polymers for the outer selective layer and low cost polymers with high thermal and mechanical properties for the porous inner layer. [ABSTRACT FROM AUTHOR]

Polyphenylsulfone (PPSU) based asymmetric hollow fiber membranes were prepared by the addition of different percentages of ZSM-5 particles by diffusion induced phase separation method. Polyvinylpyrrolidone (PVP) was used as a pore forming agent. The fabricated membranes were characterized by Field Emission scanning electron microscopy (FESEM), Energy Dispersive Spectroscopy (EDS), contact angle, water permeability, water uptake and by porosity measurements. Membranes filtration study was performed using different proteins namely bovine serum albumin (BSA), egg albumin (EA) and hazardous dyes like Reactive black 5 (RB-5), Reactive orange 16 (RO-16) in aqueous solutions. It was found that, addition of ZSM-5 in membrane matrix showed better dye removal capacity because of its hydrophilic and adsorptive nature. The membrane (PZ-3) with higher loading of additive exhibited rejection percentages of 100% for BSA, 95.23% for EA proteins and with reactive dyes 90.81% for RB-5 and 82.84% for RO-16 as compared to the pristine HF membrane. [ABSTRACT FROM AUTHOR]

A simple, efficient and scalable approach was developed for the fabrication of highly fouling resistance nanocomposite hollow fiber membranes with the aim of effective removal of environmentally detrimental reactive dyes. The naturally occurring halloysite nanotubes were functionalized via facile self-polymerization of m -aminophenol in mild acidic condition and employed as a hydrophilic additive. The chemical modification was confirmed by FTIR, TEM and energy dispersed X-ray (EDX) analysis. The hybrid nanocomposite membrane was prepared by dry–wet spin technique with different additive dosage. The resultant membrane was characterized in terms of contact angle, surface energy, porosity, zeta potential, elemental mapping and morphology. The permeation experiments illustrated superior water flux of 104.9 Lm −1 h −1 and 9.6% of irreversible fouling with more than 90.3% of flux recovery by the simple hydraulic cleaning. Most importantly, prepared membrane was subjected for hazardous reactive dye removal application with different experimental parameters. The hybrid membrane with 2 wt. % of additive concentration showed more than 97% and 94% for the Reactive Red 102 and Reactive Black 5 dyes respectively. This approach may also be very useful in developing high flux, fouling resistant ultrafiltration hollow fiber membranes for the other similar type applications such as hemodialysis membranes. [ABSTRACT FROM AUTHOR]

Porous hydrophobic polyvinylidene fluoride (PVDF) composite hollow fiber membranes were fabricated via phase inversion method by embedding different amounts of hydrophobic calcium carbonate (CaCO 3 ) nano-particles in the polymer matrix. The effects of nano-particle loadings on the morphology, structure and performance of the spun membranes in gas–liquid contactors were investigated. The incorporation of hydrophobic nano-particles into the polymer network enabled the formation of more abundant and narrower finger-like pores in the composite membranes compared to plain PVDF membrane. Moreover, the addition of nano-particles enhanced the surface roughness, permeation rate, porosity and wettability resistance of the composite membranes. CO 2 absorption performance of the fabricated membranes was evaluated via a gas–liquid membrane contactor system. The CO 2 flux was improved to some extent by increasing the mixing ratio of CaCO 3 . Peak absorption performance of 1.52 × 10 −3 mol m −2 s −1 at 300 ml/min absorbent flow rate was achieved when 20/100 weight ratio of CaCO 3 /PVDF was employed. However, further increase of the ratio resulted in a composite membrane with lower absorption performance than the other composite membranes. Moreover, a long-term stability study of the composite membrane with the best CO 2 absorption flux showed no decline in performance in the initial 210 h of operation, indicating that the membrane possesses high potential for gas–liquid contactor applications. [ABSTRACT FROM AUTHOR]

The surface hydrophobicity of membrane is a key factor in contactor applications where the penetration of liquid into membrane pores has negative effect on the contactor performance. Therefore, different methods have been proposed for surface modification. Blending hydrophobic polymers such as surface modifying macromolecules (SMM) has been investigated in our earlier researches. In this study, the effect of polyvinylidene fluoride (PVDF) blending on the surface and bulk morphology of polyetherimide (PEI) hollow fiber membrane and its performance in membrane gas absorption process was studied. It was found that the pore size increased from 112 nm to 210 nm from the neat PEI membrane to the PEI membrane spun from the solution blended with 0.25 wt% PVDF. At the same time, the contact angle increased from 78.3 and 84.3. Furthermore, the absorption flux of PVDF blended membrane enhanced by 13% compared to the neat PEI membrane. [ABSTRACT FROM AUTHOR]

Asymmetric PEI hollow fiber mixed matrix membranes (MMMs) with improved structure and wetting resistance were fabricated via wet phase inversion method. The effects of incorporating hydrophobic MMT into polymer matrix in different loadings on the membrane properties were investigated. The membranes were characterized in terms of scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX), gas permeation test, hydrophobicity, wetting resistance and mechanical stability. All membranes possessed finger-like structures differing in skin layer thickness which increased with clay loading. The results revealed that the MMMs have significantly smaller pore size, higher porosity, hydrophobicity, LEPw and mechanical stability than plain PEI membrane. The membranes were further characterized by CO 2 absorption test via contactor system using distilled water as absorbent and pure CO 2 as solute gas. The results showed that the CO 2 absorption performance increased with addition of MMT nano-clay. The membrane containing 1 wt% MMT recorded the highest absorption flux of 2.35 × 10 −3 mol m −2 s −1 at the liquid velocity of 3 m s −1 , almost 135% higher than the flux of plain membrane at the same velocity. Comparatively, the flux of MMM was superior to several in-house made and commercial membranes. [ABSTRACT FROM AUTHOR]

Porous polyetherimide (PEI) and polyethersulfone (PES) hollow fiber membranes were spun under the same spinning conditions and the fabricated membranes were characterized using various analytical methods. The membranes were then subjected to gas–liquid contactor experiments. While the PEI casing solution was thermodynamically less stable, the PES casting solution was less viscous which resulted in a more porous membrane structure. The mean pore size and effective surface porosity obtained by the gas permeation test showed superior properties of the PES membrane. Both PEI and PES membranes had sufficiently high LEPw values even though both polymers were known to be relatively hydrophilic, most likely due to their small pore sizes. The absorption flux of the PES membrane was 4.4×10 −3 mol m −2 s −1 at the liquid flow velocity V liquid of 1.8 m s −1 , which was 267% higher than that of the PEI membrane (1.2×10 −3 mol m −2 s −1 ) due to the larger pore size and smaller tortuosity of the PES membrane. [ABSTRACT FROM AUTHOR]

Several efforts to produce mechanically robust polymeric hollow fiber membranes have led to the use of polyethylene terephthalate (PET) hollow braided tubes, which offer rigidity to hollow fiber membranes. However, a compensation of flux exists with increased filtration pathway occasioned by braid substrate and thick polymer coating. It is often difficult to control the fabrication parameters to achieve uniformly coated and thin separation layer. In this work, we report a modification of the erstwhile dry-jet wet spinning process for braided hollow fiber by introducing a loop-system to increase resident time in the coagulation bath for effective solvent exchange and leaching of pore former additive. A combination of air gap (5, 15 and 25 cm), polymer concentration (15%, 17% and 19%) and take-up speed (1.2, 2.4 and 3.6 m/min) were varied to produce membranes with optimum filtration performance against crude oil emulsion feed. BRP-HM8 spun with 15 wt% PVDF, 15 cm air gap and take-up speed of 2 rpm exhibited thin and uniform coating outside of braid, well-developed pore structure resulting in high flux up to 620 L/m2h, good hydrophilic/oleophobic characteristics with > 98% rejection of crude oil as well high mechanical properties against harsh feed and elevated pressure. [Display omitted] • Loop-system for improved spinning of braided hollow fiber membranes. • Thin and uniform polymer coating reducing filtration pathway with well-developed finger-like pores. • Excellent rejection properties occasioned by good underwater oleophobicity. • High-strength reusable membranes with simple flushing. [ABSTRACT FROM AUTHOR]

In this study, thin-film composite (TFC) hollow fibers (HFs) were fabricated by an in-situ coating of polyamide layer on the lumen side of PVC/PC blend substrates for desalination by forward osmosis (FO). Particularly, the substrate HFs were spun at two air gap distances of 2 and 6 cm, to investigate the effect of the air-gap distance on the FO performance. The substrate HFs were characterized by pure water flux measurement, FESEM, and gas permeability test. The Interfacial polymerization (IP) method was then utilized for coating polyamide (PA) layer on the lumen surface of the substrate to fabricate TFC HFs. The TFC HFs so fabricated were also characterized by FESEM, before their FO performance was tested. Furthermore, the effect of HF length on the FO flux was investigated. The results showed that the novel TFC HFs exhibited good FO performance. The longer the air gap distance, the better becomes the FO performance in terms of simultaneous water flux and alginate fouling resistance, while the effect of the HF length remains a controversial issue. • Higher surface porosity resulted defect free active layer. • Higher surface porosity enhanced mass transfer coefficient, by reducing CP. • Irreversible fouling is suppressed when HF spun with longer air gap distance. • Water flux decreased with the fiber length, contrary to the model simulation. • In high flux mode increasing number of the fibers can increase productivity. [ABSTRACT FROM AUTHOR]

Highlights: [•] Formation of finger-like macrovoids enhanced by the addition of clay nanoparticles. [•] Wetting resistance, surface hydrophobicity and roughness increased with MMT loading. [•] CO2 flux of fabricated MMMs superior to several commercial and in-house membranes. [•] 350h of constant CO2 absorption flux confirmed high reliability of fabricated membrane. [ABSTRACT FROM AUTHOR]

Highlights: [•] Blending SMM resulted in higher hydrophobicity and gas permeability. [•] The modified membrane showed higher wetting resistance at 24cm air gap. [•] The membrane showed less mass transfer resistance by removing inner skin. [•] Increasing air gap and SMM concentration resulted in higher CO2 flux. [•] A long-term stable operation was achieved by developing PVDF membranes. [ABSTRACT FROM AUTHOR]

In this study, hollow fiber PVC/ZnO-nanocomposite in an MBR was investigated for municipal wastewater treatment. The following parameter were evaluated: BOD, COD, TSS, NTU, TP, TKN. ZnO nanoparticles caused to decrease the contact angle from 78° to 67° for the neat PVC and 0.5 wt% ZNO-nanocomposite membrane, respectively. The majority of the neat membrane resistance was due to irreversible resistance. Because of the antibacterial properties of zinc oxide nanoparticles, with increasing nanoparticles loading, the resistance of irreversible part compared to the reversible resistance experienced a significant decrease. This confirm that the fabricated nanocomposite membranes did not show affinity toward adsorption of the sludge inside the pores hence substantially limited the membrane fouling. The FTIR results showed the reduction of proteins and polysaccharides onto the surface of the nanoparticle-incorporated membranes, approaching the clean PVC membrane. This was most likely due to the antibacterial properties of ZnO NPs. Nitrogen and phosphor removal for PVC0.5 membrane was 99% and 79% and TSS removal up to 100% was achieved. The findings of this study showed that modification of PVC polymer using ZnO nanoparticles with the presence of ferric chloride coagulant is a very effective technique for municipal wastewater treatment to meet the well-known standard levels. [Display omitted] [ABSTRACT FROM AUTHOR]

• Membrane heat treatment is a simple method to improve MC stripping performance. • There was a direct correlation between the temperature and the performance. • The best performance was observed at the shortest heat exposure time. The scope of this study was to investigate the effect of the heat treatment process on the performance of the PEI hollow fiber membrane contactor for CO 2 stripping process. The membranes were fabricated via a wet spinning technique into water as a non-solvent bath. Then, the membranes were heat treated by exposing them to various temperatures of 80,120 and 160 °C for the time intervals of 5, 15 and 30 min under a hot air atmosphere. The observations revealed that the most pronounced enhancement belonged to the membranes with the lowest heat treatment temperature preferentially at the shorter exposure times. It was shown that the absorbent velocity and temperature had substantial influence on the CO 2 stripping flux, however the temperature exhibited a stronger influence. In fact the dual functionality of temperature on the system i.e. (i) thermodynamics (by decrease in CO 2 solubility) and (ii) kinetics (by increase in CO 2 diffusivity) led to the enhancement in CO 2 stripping flux. Also, it was revealed that by increasing the heat treatment temperature, more tendency toward the pore wetting will be observed. There was a meaningful correlation between the wetting ratio and the CO 2 stripping flux. Also experimentally it was revealed that, a marginal progress in the wetting ratio, surprisingly caused to a dramatic decline in the stripping flux. [ABSTRACT FROM AUTHOR]

Comparison studies in suspension and hybrid photocatalytic membrane reactor (HPMR) system was investigated by using Reactive Black 5 (RB5) as target pollutant under UVA light irradiation. To achieve this aim, hybrid TiO 2 /clinoptilolite (TCP) photocatalyst powder was prepared by solid-state dispersion (SSD) methods and embedded at the outer layer of dual layer hollow fiber (DLHF) membranes fabricated via single step co-spinning process. TiO 2 and CP photocatalyst were also used as control samples. The samples were characterized by Scanning Electron Microscopy (SEM), Energy Dispersion of X-ray (EDX), X-ray diffraction (XRD) and Brunauer–Emmett–Teller (BET) analyses. The result shows that TCP was actively functioned as photocatalyst in suspension system and 86% of RB5 photocatalytic degradation achieved within 60 min; however the additional step is required to separate the catalyst with treated water. In the HPMR system, even though the RB5 photocatalytic degradation exhibits lower efficiency however the rejection of RB5 was achieved up to 95% under UV irradiation due to the properties of photocatalytic membranes. The well dispersed of TCP at the outer layer of DLHF membrane have improved the surface affinity of DL-TCP membrane towards water, exhibit the highest pure water flux of 41.72 L/m2.h compared to DL-TiO 2 membrane. In general, CP can help on improving photocatalytic activity of TiO 2 in suspension, increased the RB5 removal and the permeability of DLHF membrane in HPMR system as well. • The work aims to study effect of TiO 2 /clinoptilolite composites in dual layer hollow fiber membranes. • The effect of TiO 2 /clinoptilolite composites prepared by solid state dispersion methods. • TCP actively functioned as photocatalyst and achieved 86% degradation in hybrid system. • The removal of RB5 after filtration process in HPMR system was achieved around 95%. • The well dispersed of TCP at the outer layer of DLHF membrane also have improved the surface affinity. [ABSTRACT FROM AUTHOR]

A novel method, Thermally Modified Non-Solvent Induced Phase Separation (T-NIPS) has been developed to fabricate translucent hollow fiber (THF) photocatalytic membrane for membrane's photodegradation efficiency enhancement. The process involves two-step temperature treatment that attacks crystalline property of polyvinylidene fluoride (PVDF). Graphitic carbon nitride in a modified morphological structure (hollow nanofiber) was used as photocatalyst to investigate the effect of translucency on membrane's photodegradation efficiency. UV-Vis analysis coupled with FTIR highlighted different crystalline phase appearance and membrane's translucency. The membranes showed high translucency, ranging from 60.0% to 93.9%, with THF-PVDF/PVP-GCN (2.0) exhibiting the highest. The filtration experiment showed that membrane with GCN photocatalyst had high PWF (1200 L/m2h) and rejection (90%) OPW compared to neat THF-PVDFs. In suspended mode, GCN demonstrated an impressive photodegradation efficiency of 99.98%. When immobilized in opaque PVDF membrane, the photodegradation has decreased substantially to 49.40%. However, when immobilized in a translucent PVDF membrane, the photodegradation efficiency of HN-GCN significantly improved compared to the opaque PVDF membrane, reaching 95%. Translucent membrane was subjected to five cycle regeneration test and showed 90% recovery even after the fifth cycle. The 10% reduction in the recovery was investigated using FESEM analysis revealed that there is a cake layer formation on the membrane surface. Therefore, this study proved that translucency of membrane has significant effect on immobilized photocatalyst's photocatalytic efficiency. [Display omitted] • Novel T-NIPS method to produce THFM is developed. • HN-GCN successfully immobilized in THFM. • HN-GCN immobilized THFM showed increased degradation efficiency of OPW. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • A low cost kaolin was utilized in fabrication of ceramic hollow fibre membrane. • Surface modification with fluoralkylsilane agent was applied. • Modified membrane has a contact angle value of 145 and average pore size of 0.32 µm. • Excellent performance of 100% arsenic removal was achieved. Abstract In this work, a low cost hydrophobic kaolin hollow fiber membranes (h-KHFM) was successfully prepared by phase inversion/sintering technique followed by a modification via grafting with fluoroalkylsilane (FAS) molecules. The influence of sintering temperature varied from 1200 to 1500 °C on the hydrophobization and separation performance of kaolin hollow fiber membrane (KHFM) was investigated through direct contact membrane distillation (DCMD) system towards synthetic arsenic wastewater. The results reveal that h-KHFM prepared at a sintering temperature of 1300° °C induced a high contact angle value of 145°, an excellent LEPw value of 2 bar, and an average pore size of 0.32 µm. As a consequence, a high permeate flux of 28 kg/m2 h for As(III) and 25 kg/m2 h for As(V) with 100% arsenic rejection was obtained at a feed temperature of 60 °C and has met the required standard of maximum contaminant level (MCL) of 10 ppb. In addition, arsenic concentrations of up to 1000 ppm with various pH values of arsenic were also investigated using h-KHFM sintered at 1300 °C and there was no arsenic detected in the permeate. [ABSTRACT FROM AUTHOR]

This study involves the preparation of a double-skinned thin film composite (TFC) and thin film nanocomposite (TFN) hollow fiber (HF) membrane for forward osmosis (FO) applications. The porous substrate consisted of a Polyvinyl chloride (PVC) / Polycarbonate (PC) blend HF membrane. Interfacial polymerization (IP) was then applied to coat a polyamide (PA) layer on the lumen surface and the porous substrate's outer surface. In addition, the impact of the outer PA active layer and the addition of nanoparticles to the outer selective layer on the FO flux and internal concentration polarization (ICP) were studied. By adding the second active layer to the substrate, water flux, reverse salt flux and ICP decreased. Also, the decline of water flux decreased over time due to the fouling agent. To compensate for the decrease in water flux in the double-skinned membrane, graphene oxide (GO) nanoparticles with 0.05% and 0.1%wt were added to the outer active layer. Addition of 0.1%wt graphene oxide nanoparticle to the outer active layer can help to improve water flux about 78% without spoiling the reverse salt flux. Moreover, the performance of double-skinned membranes against osmotic dilution process for oily wastewater treatment was investigated. The findings of this study demonstrated that the novel double-skinned TFN HF membrane exhibited high FO performance with low ICP and fouling. [Display omitted] • Inclusion of a second active layer without reducing the reverse salt flux and fouling. • To improve fouling resistance of membrane, GO was added to second active layer. • By adding GO to outer active layer, reverse salt flux and fouling was reduced. • The Hermia model showed intermediate blocking in neat membrane. • The predominant fouling in double-skin membranes is cake formation. [ABSTRACT FROM AUTHOR]

The aim of this work was to investigate the effects of heat treatment applying hot air at different temperatures and durations on the morphology and the performance of polyetherimide (PEI) hollow fiber membrane contactors for CO 2 separation. The membranes were fabricated via a wet spinning into non solvent bath technique. Then, the membranes were heat treated by exposing them at 80,120 and 160 °C for all time intervals of 5, 15 and 30 min under a hot air atmosphere. To study the influence of the hot air on the membranes structural parameters and the performance of the membranes they were characterized by: gas permeation test, membrane overall porosity measurement, critical entry pressure of water (CEPw) and gas absorption via a membrane contacting process. The experimental results revealed that, the greatest effect on the membranes structure was observed in the shortest time duration and the lowest temperature i.e. 5 min and 80 °C, which exhibited a pore size of 49 (nm), a maximum effective surface porosity of 26.8 (1/m) and a CEPw of 3.4 bar. Also, for all the time periods and the temperatures tested, the density of the fibers reduced and the CEPws along with the overall porosities increased. In conclusion, applying heat treatment technique on PEI hollow fiber membranes is a simple and easy approach to improve the performance of hollow fiber membrane contactors for CO 2 removal. [ABSTRACT FROM AUTHOR]

A photocatalytic reactor based on novel dual-layer hollow fibre membranes with immobilized titanium dioxide (TiO 2 ) nanoparticles was proposed in this study and tested for the degradation of highly recalcitrant endocrine disrupting compound of nonylphenol (NP). The presence of TiO 2 on the outer surface of dual-layer hollow fibres was confirmed by scanning electron microscopy (SEM), energy dispersion of X-ray (EDAX), and atomic force microscopy (AFM). The effect of TiO 2 loading, where the mass fraction TiO 2 /PVDF was varied from 0 to 1, on the degradation of toxic NP was evaluated by high-performance liquid chromatography (HPLC). The addition of TiO 2 nanoparticles showed a significant effect on the membrane pore size and NP degradation rate. The presence of TiO 2 on the outer layer of dual-layer hollow fibre membranes actively functioned as a photocatalyst, with the hollow fibre of TiO 2 /PVDF ratio of 1 possessed the highest NP degradation rate. [ABSTRACT FROM AUTHOR]

In this work a novel method to evaluate the partial pore wetting of gas absorption membranes is proposed. The method consists of two approaches, one by energy-dispersive X-ray spectrometry (EDX), and the other by calculating the mass transfer resistances from the gas and liquid phase in the pore, using the parameter obtained by He gas permeation experiments. For this purpose, hollow fibers were spun from polyetherimide (PEI) and polyethersulfone (PES). As well, the lumen of a PEI hollow fiber was coated with silicone rubber. The hollow fibers were then characterized by He gas permeation experiments, critical entry pressure of water (CEPw), contact angle, scanning electron microscopy (SEM) and EDX. The hollow fibers were then subjected to CO 2 gas absorption using aqueous NaCl solution as absorbent. After drying the hollow fiber was subjected to the EDX analysis. The cross-sectional profile of Na and Cl content in the hollow fiber revealed that the pores of the PES hollow fibers were partially wetted, particularly at the pore inlet. Calculation of mass transfer resistances, on the other hand, revealed that the resistance came from gas phase in most hollow fibers, except for the PES hollow fiber where the liquid phase contribution was significant. Silicone rubber coating of the PEI hollow fiber increased the surface hydrophobicity and reduced the pore wetting considerably. Thus, it was concluded that the proposed method can be used as a powerful tool to investigate the pore wetting for many membrane contactor applications. [ABSTRACT FROM AUTHOR]

Over recent years, there has been an explosive growth of interest in the development of alternative approaches for crude palm oil (CPO) refining. During a typical refinery process, free fatty acid (FFA) is one of the key objectionable impurities that need to be reduced if not completely removed from CPO in order to minimize their detrimental effects on the oil quality. Polyvinylidene fluoride (PVDF) membrane shows great potential in removing FFA from CPO owing to its hydrophobic properties, high mechanical strength and good thermal stability. However, low concentration of FFA in CPO, which is normally ranging from 3% to 5%, has hindered the capability of the membranes to separate the trace amount of FFA from the bulk. Thus, modification of PVDF membrane is essential to enhance the interaction between the membrane surface and FFA molecules, facilitating efficient FFA removal. In order to achieve this purpose in the present study, the outer surface of PVDF hollow fiber membranes was crosslinked with polyvinyl alcohol (PVA). Glutaraldehyde (GA) was used as a crosslinking agent to avoid the PVA dissolution. Despite the negligible morphological change observed in the resultant membranes upon PVA crosslinking, the contact angle has been significantly reduced in proportional to the concentration of PVA used for the crosslinking, suggesting the decrease in membrane hydrophobicity. Additionally, the average roughness of the crosslinked PVDF membranes increased with the increasing PVA concentration. The results obtained suggested that the PVDF hollow fiber crosslinked with 100 ppm PVA exhibited the highest FFA rejection of 5.93% after 3 h of operation. In addition, the membrane also showed good result in reducing the content of phosphorus in the permeate and partial reduction of its color intensity. This study served as the first attempt of CPO deacidification through UF membrane system without the addition of any chemical during the filtration process. [ABSTRACT FROM AUTHOR]

Dual-layer hollow fiber (DLHF) membranes prepared via a phase inversion based co-extrusion technique offer a number of advantages, such as self-supporting structure, high active surface area to volume ratio, easy fabrication and ability to withstand high operating pressure. This paper reports novel DLHF membranes fabricated via a single step co-extrusion technique with immobilized titanium dioxide (TiO 2 ) nanoparticles embedded in their outer layer. In this work, the DLHF membranes were prepared by extruding two different dope solutions simultaneously, in which the inner layer consisted of poly(vinylidene fluoride) (PVDF) and solvent N,N-dimethylacetamide (DMAc) while the outer layer was a mixture of PVDF, TiO 2 and DMAc. The effect of TiO 2 loading, where the mass fraction of TiO 2 /PVDF was varied from 0 to 1, on the morphologies and properties of the DLHF membranes were investigated using scanning electron microscopy (SEM), contact angle goniometer, surface roughness and filtration experiments. The SEM results showed that DLHF membranes have a good interfacial adhesion between layers with no delamination found. The structure of the membranes characterized by the length of their finger-like voids was significantly affected by the TiO 2 addition. The void lengths were elongated by the rise of the TiO 2 loading up to certain fraction of TiO 2 /PVDF. Based on all the findings, it can be concluded that the proposed method of producing the DLHF membranes could provide good layer–layer interfacial adhesion and well-dispersed TiO 2 in their outer layer. [ABSTRACT FROM AUTHOR]

Studies on mixed matrix membrane (MMM) have been sprouting rapidly since the last few decades, but mostly fabricated in the form of dense, flat films. In this work, hollow fiber Polysulfone (PSF)-Cloisite®15A (C15A) MMM were produced using our in-house hollow fiber spinning machine. Various spinning parameters are at play in order to ensure the formation of defect-free high performance hollow fiber. Spinning process parameters such as dry gap height, force convection rate, dope extrusion rate, and take-up speed have been systematically studied in order to identify the optimum fabrication conditions. Extensive characterizations on the membrane morphology, membrane surface properties, polymer d -spacing and gas separation performance were conducted using SEM, AFM, XRD, and pure gas permeation experiment. The appropriate balance between dry-gap residence time and force convective rate is essential to yield membrane with good permeability–selectivity combinations. CO 2 permeance was increased from 17.39 to 56.25 × 10 − 6 cm 3 (STP)/cm 2 s cmHg when the dope extrusion rate was increased from 1.5 cm 3 /min to the optimum extrusion rate of 2.5 cm 3 /min. Membranes spun at high collection speed (up to 35 m/min) exhibited practically attractive fiber geometry comparable to commercial hollow fibers (∼300 μm diameter) but the permeation properties were rather disappointing which might be caused by excessive deformation of polymer chain due to stretching. Hollow fiber MMM containing layered organoclay has exhibited excellent CO 2 /CH 4 pure gas selectivity of 40.26%, 46% higher than that of pristine hollow fiber fabricated under the same optimized conditions without compromising the CO 2 flux. The MMM was also found to be more thermally and mechanically robust in comparison to its neat counterpart. [ABSTRACT FROM AUTHOR]

Novel polyphenylsulfone (PPSU)/nano tin oxide (SnO 2) mixed matrix hollow fiber membranes (HFMs) were fabricated by dry-wet spinning via phase separation method. In the current research, reported the contrast between neat PPSU membrane and nanocomposite membranes (PPSU/SnO 2), to determine the toxic reactive dyes namely, reactive black-5 (RB-5) and reactive orange-16 (RO-16) removal ability from the aqueous media. Scanning electron microscopy (SEM) was used to observe the HFMs cross-sectional morphological changes and surface roughness parameters of membranes were analyzed using atomic force microscopy (AFM). The surface wettability ability of HFMs was examined with a contact angle, water uptake, and porosity measurements. The cross-flow filter unit was engaged to quantify the water permeability, anti-fouling ability as well as the dye rejection ability of fabricated membranes. With increasing the SnO 2 NPs wt% in PPSU polymer matrix the membrane performance was enhanced continuously, it became evident that the incorporated SnO 2 NPs plays main role in membrane performance. Added, water-soluble poly (vinylpyrrolidone) (PVP) can also impact the pore morphology in membranes. At the end, PS-3 membrane exhibited lower contact angle (63.7 0), higher water uptake (74.8%), porosity (84.1%), pure water flux 362.9 L/m2 h, and high potential for dyes rejection application, of about >94% for RB-5, and >73% for RO-16 dye, respectively. From the preliminary results, it can be stated that the usage of SnO 2 NPs in membrane technology become effective towards wastewater treatment. Unlabelled Image • Novel PPSU/nano SnO 2 mixed hollow fiber membranes were fabricated by dry-wet spinning via phase separation process. • The cross-flow filter unit was engaged to check the permeability and rejection efficacy of the membranes. • The nanocomposite membranes showed better outcomes. • The PS-3 membrane displayed dyes rejection above 94% and 73% for RB-5 and RO-16 dyes, respectively. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Graphitic carbon nitride (GCN) photocatalyst was incorporated in nanofibers. • Photocatalytic nanofibers were electrospun on alumina hollow fiber membranes. • Cross-flow microfiltration demonstrated purification of oilfield produced water. • Hydrophilic, highly-porous nanofiber coating exhibited excellent fouling resistance. • Photodegradation ability of GCN offered cleaning performance of robust membranes. Abstract Cost-effective purification technology of oilfield produced water (OPW) is becoming a global challenge for future petroleum exploration and production industry. Energy-efficient operation of membrane separation is potentially promising. However, severe fouling problem of oil droplets demands new robust and fouling-resistant membranes with high permeability and rejection efficiency. Here, we propose a photocatalytic nanofiber-coated inorganic hollow fiber membrane suitable for OPW treatment. The membrane was fabricated by coating polyacrylonitrile (PAN) nanofiber incorporated with graphitic carbon nitride (GCN) photocatalyst on an alumina (Al 2 O 3) hollow fiber membrane. While the highly porous coating made of smooth hydrophilic nanofibers facilitated water permeation, the coating effectively captured oil droplets in its opening, resulting in a better rejection efficiency of oil contaminants. Its sparse mesh morphology prevented oil contaminants to form dense fouling film on the membrane surface and maintained high permeate flux even after 180 min filtration. The best permeate flux of 640 L·m−2·h−1 and oil rejection percentage of 99% were recorded for 180 min crossflow filtration of OPW at 2 bar along with the highest pure water flux of 816 L·m−2·h−1. The photocatalytic activity of GCN enabled the coating to degrade the captured oil contaminants under UV irradiation, demonstrating permeate flux of 577 L·m−2·h−1 and oil rejection of 97% after three cycles of 180 min filtration. The excellent fouling resistance and cleaning performances of the membrane are considerably beneficial for a long-term repeated filtration operation. This work will motivate researchers to develop nanofiber-coated hollow fiber membranes for future membrane separation technology. [ABSTRACT FROM AUTHOR]

• Fabrication of natural zeolite based ceramic membrane for ammonia removal. • Effect of sintering temperature on HFCM's properties and performance was studied. • Sintering temperature of 1050 °C has produced the best HFCM. • Ammonia removal using the fabricated HFCM gave nearly 90% rejection. • Synergism between adsorption and separation resulted to the high ammonia removal. The excessive presence of ammonia has led to serious potable water scarceness worldwide. This work aims to fabricate natural zeolite based hollow fibre ceramic membrane (HFCM) via phase inversion and sintering techniques for the ammonia removal in wastewater. The physical properties of the fabricated HFCM were investigated through morphologies, mechanical strength, dope suspension viscosity and pure water permeation also the performance test using synthetic wastewater. It was found that 5 cm, 15 mL/min and 1050 °C were the best fabrication conditions for the air – gap distance, bore fluid flow rate and sintering temperature, respectively. The membrane also revealed desired asymmetric structure, sufficient mechanical strength (50.92 MPa) and excellent pure water permeation flux (249.57 L/m2 h). Additionally, the ammonia removal gave an outstanding performance of 90% rejection. These findings show that natural zeolite based HFCM has a great potential to be developed as a single – step ammonia removal in wastewater. [ABSTRACT FROM AUTHOR]

In this work, green silica-based ceramic hollow fiber membranes (CHFMs) derived from rice husk ash waste were successfully prepared via phase inversion and sintering technique. Prior to the fabrication, rice husk waste was converted into amorphous and crystalline silica-based rice husk ash (ARHA and CRHA). The surface of CHFMs could be easily modified to become hydrophobic by grafting with a fluoroalkylsilane (FAS) agent. The CHFMs were characterized before and after grafting using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), measurement of contact angle and liquid entry pressure of water (LEPw), and three-point bending test. The pore size and the porosity of the membrane surface were also evaluated using mercury intrusion porosimetry (MIP). Lotus-leaf structure formed at the surface of HFMs by grafting, leading to a high contact angle of >150°. Direct contact membrane distillation (DCMD) performance of membrane after grafting was conducted for 200 h using the synthetic seawater of various NaCl concentrations at different feed temperatures. The experimental results show that the permeate flux decreased with the increasing feed concentration, whereas it was enhanced with the increasing feed temperature. A high water flux of 38.2 kg/m 2 h and salt rejection up to 99.9% were obtained by CHFM prepared from CRHA (CHFM/CRHA). [ABSTRACT FROM AUTHOR]

• Increasing MPD and TMC concentrations enhance water vapor flux and membrane H 2 O/N 2 selectivity. • Increasing interfacial polymerization time controls the selectivity decline rate at high pressures. • Disregarding very low concentration of water vapor, it shows a great plasticizing impact on the gas permeance. • H 2 O-induced plasticization impact on nitrogen permeance is more intense than on water vapor. • Both the Henry and Langmuir models control the water adsorption while only the Henry controls N 2. Separation of moisture from gaseous mixtures, such as natural gas, humid air in food and goods storage warehouses or in sports halls and so on is of great importance. In this article, the separation of water from a wet gas stream is carried out by a TFC membrane made by interfacial polymerization on the sublayer of porous polyetherimide hollow fibers. Then the key-parameters affecting membrane efficiency is studied. The outcomes show that increasing the concentration of MPD has a substantial effect on enhancing the membrane water vapor flux. Moreover, it is disclose that increasing the concentration of TMC has the greatest effect on reducing nitrogen gas permeability and increasing the selectivity. Our findings reveals that disregarding the very low concentration of water vapor in the feed, shows a great impact on the permeance of each component compared to the pure state. Also, based on the modelling, it is obvious that for nitrogen gas in the entire pressure range, the adsorption mechanism is almost completely controlled by the Henry model, while the Langmuir adsorption mechanism is controlling for water vapor at low pressures, although at high pressures, the Henry mechanism has absolute superiority. Surprisingly, the H 2 O-induced plasticization impact on nitrogen permeance is more intense than on water vapor permeance. According to the modeling outputs, it is revealed that because D N2 is one to two order of magnitude lower than D H2O , water vapor permeance is much higher than that of nitrogen. [ABSTRACT FROM AUTHOR]

In this study, a novel polyvinylidene fluoride (PVDF) hollow fiber nanocomposite ultrafiltration (UF) hollow fiber membrane was fabricated by introducing titanate nanotubes (TNTs) into the membrane matrix. Prior to membrane fabrication, the properties of TNTs were characterized using TEM, XRD and BET. The effect of TNTs loading (0–1.0%) on the properties of PVDF membrane such as cross section morphology, permeation and rejection capabilities were studied. Characterizations in term of membrane cross section morphology, contact angle and porosity were conducted. PVDF-TNT 0.5% nanocomposite membrane exhibited the most promising results, with colour removal of 58.9%, based on the American Manufacturers Dye Index (ADMI) value. Furthermore, these membranes were able to maintain flux values of 35.8 L/m 2 h for the duration of 240 min, showing very minimal signs of fouling. Analysis on flux recovery after simple pure water washing of the membranes also showed TNT loaded membranes are resistant towards fouling with 90% flux recovery and >95% rejection recovery rate when membranes were filtered for 5 continuous cycles. [ABSTRACT FROM AUTHOR]

A new application of green ceramic hollow fiber membrane (CHFM) derived from rice husk ash (RHA) for efficient heavy metals removal has been developed. A common and advanced fabrication method, i.e. combined phase inversion and sintering technique was used to produce the membrane with high flux. Thereby, the membrane can effectively act, as both adsorbent and separator for heavy metals in single-step process with high separation efficiency up to 99% removal of zinc [Zn(II)], lead [Pb(II)] and nickel [Ni(II)]. The kinetic data of these heavy metals show the best fit for pseudo-first order for Ni (II) [R 2 =0.981] and intraparticle diffusion kinetic model for Zn (II) [R 2 =0.913] and Pb (II) [R 2 =0.914]. Thus, this study convinced that the ceramic membrane from waste rice husk ash proved to be an attractive, effective and environmentally friendly both adsorbent and separator for heavy metals removal from aqueous solution. [ABSTRACT FROM AUTHOR]

The objective of this study is to produce superhydrophilic, low cost kaolin-based ceramic hollow fibre membrane (KHFM) for efficient oily-wastewater separation. The asymmetric KHFMs with short finger-like voids were successfully prepared via a combined phase inversion and sintering technique. It was observed that the increase in sintering temperature enhanced membrane mechanical strength and promoted significant changes on membrane morphology. The combination of hydrophilic characteristic (contact angle of 33°) and small pore size (0.35 μm) of the kaolin KHFM sintered at 1500 °C resulted in excellent oily wastewater separation, with a 100% success rate, thus indicating that KHFM is able to repel most of the oil and allow only water to pass through its pores. In conclusion, the developed KHFM can be regarded as a promising medium for oily wastewater separation. [ABSTRACT FROM AUTHOR]

Ceramic hollow fibre membranes (CHFMs) are known to have superior characteristics including excellent thermal, mechanical, and chemical stability. Major limitations include their high cost and brittleness, traits which have hindered the commercial adoption of this technology. This paper studies the effects of three main fabrication parameters, i.e. ceramic content, bore fluid flowrate, and sintering temperature, on morphology and mechanical strength of low-cost CHFM from a well-known material in producing high strength concrete, i.e. metakaolin. The novel CHFM from metakaolin was prepared via a combined phase inversion and sintering technique. Scanning electron microscopy (SEM) and three-point bending strength were employed to examine the hollow fibre's morphology and mechanical strength. Response surface methodology (RSM) based on historical data design (HDD) was used to further verify experimental and predicted values for mechanical strength in terms of the three operating parameters mentioned above. The highest mechanical strength of 225.8 MPa was obtained with 37.5 wt% metakaolin content and 3 mL/min of BF flowrate at a sintering temperature of 1500 °C. The desirability of this work is 0.985, indicating that RSM is a suitable approach to validate the effects of fabrication parameters on the mechanical strength of metakaolin-based CHFM. [ABSTRACT FROM AUTHOR]

Asymmetric alumina hollow fiber membranes were prepared using the phase inversion technique followed by the sintering process at high temperatures. The ceramic suspensions were formulated by mixing alumina powder with polyethersulfone (PESf), polyethylene glycol-30-dipolyhydroxystearate and N-methyl-2-pyrrolidone (NMP) as the polymer binder, dispersant and solvent, respectively. The objectives of this study were (i) to investigate the effects of spinning parameters, namely, ceramic loading, ceramic to polymer binder ratio, different internal coagulant temperatures and air gap variation on asymmetric structure formation and (ii) to study the self-cleaning properties of alumina hollow fiber membranes. The ceramic hollow fiber membrane was characterized in terms of its viscosity, structural morphology and mechanical strength using a scanning electron microscope (SEM). The results showed that the finger-like structures in alumina hollow fiber membranes could be formed but their patterns were influenced by the ceramic suspension and spinning parameters. Variations in their morphology resulted in significant effects on the mechanical properties and permeability of ceramic hollow fiber membranes. A CuO/CeO 2 catalyst was deposited onto the alumina membrane support with the catalyst distribution determined by SEM/EDX. Self-cleaning properties were examined by comparing normal cleaning and self-cleaning properties with irradiation of UV for protein rejection. The result of self-cleaning by UV showed higher bovine serum albumin (BSA) permeation due to super-hydrophilicity of the CuO/CeO 2 catalyst. [ABSTRACT FROM AUTHOR]

This work describes the preparation of yttria-stabilized zirconia (YSZ) hollow fibre membranes using the phase inversion and sintering process. The study aims to provide generic information on the effects of membrane preparation on the morphology and mechanical properties of YSZ hollow fibre membranes. In this work, ceramic suspensions were prepared by mixing YSZ particles, dispersant, polymer binder and organic solvent using a planetary ball milling machine. This process was followed by extrusion into a coagulation bath via an air gap, drying and sintering process at temperatures ranging from 1250 °C to 1400 °C. The results show that by varying the YSZ loading and YSZ/PESf ratio, different morphologies of ceramic hollow fiber membranes can be obtained due to variations in the viscosities of ceramic suspensions. Similarly, air-gap length between the spinneret and coagulant surface was found to affect the growth of the finger-like structures and sponge-like regions. Varying these parameters also gave significant effects on the mechanical strength of the ceramic membrane due to the change in membrane thickness and compactness. The sintering process had insignificant effects on the membrane morphology but the process can be used to enhance the mechanical strength of ceramic hollow fiber membranes. The optimum temperature of the sintering process was identified. It was found that increasing the sintering temperature further caused a reduction in the mechanical strength due to crack formation in the ceramic hollow fiber membrane. The preliminary performance tests showed that the ceramic hollow fiber membrane sintered at 1300 °C has a pure water flux of 118.4 L/m 2 h. It also has a high PEG rejection with molecular weight cut off (MWCO) of 60 kDa. [ABSTRACT FROM AUTHOR]

This study presents an alternative approach to improve the gas separation performance of conventional asymmetric membranes. For the first time, multicomponent composite/hybrid asymmetric membrane was prepared by unifying two prominent concepts in gas separation membranes: (1) sealing or caulking asymmetric membrane imperfections by means of coating a highly permeable polymer layer, and (2) the incorporation of selective inorganic particle in polymer matrix generally known as the mixed matrix membrane. Asymmetric hollow fiber membranes (polysulfone (PSF)) was externally coated by polydimethylsiloxane (PDMS) solution containing suspended Cu 3 (BTC) 2 metal organic framework (MOF) by dip-coating technique. FESEM–EDS mapping confirmed the increase in Cu 3 (BTC) 2 adherence with increasing number of coating. The pure gas permeation experiment with CO 2 , N 2 and CH 4 corroborated the contribution of Cu 3 (BTC) 2 particle to the overall composite/hybrid membrane performance. The gas permeation rates were increased with increasing number of PDMS–Cu 3 (BTC) 2 coating applied. CO 2 permeance increased from 69.7 to 109.2 × 10 −6 cm 3 (STP)/cm 2 s cmHg after 5 consecutive coatings. In addition, the CO 2 /CH 4 and CO 2 /N 2 selectivities were found to be increased as well. Cu 3 (BTC) 2 contributed to higher affinity toward CO 2 due to the coordinatively unsaturated copper sites in its crystal network, which provide exceptionally high adsorptive capability for polar molecules, hence resulted in the increase of the overall selectivities and gas permeation rates across the membrane. Further development based on this study will create vast opportunities for future improvement on any commercially available gas separation membranes by implementing the method described herein. [ABSTRACT FROM AUTHOR]

Surface modified polysulfone (PSf) hollow fiber membranes (HFMs) using surface modifying macromolecules (SMM) were spun with air-gaps of 0–50 cm. Morphological analysis of the prepared fibers were carried out using scanning electron microscopy (SEM) and atomic force microscopy (AFM). The wetting resistances of the membranes were determined by critical water entry pressure (CEPw) and contact angle (CA) measurements. The HMFs were further subjected to CO 2 capture by membrane contactor (MC) where water was used as absorbent. The test results indicated that both CEPw and CA showed a maximum value at 15 cm air-gap distance. The maximum He permeation was also achieved at 15 cm air-gap. The CO 2 flux of prepared membranes showed a maximum of 4.79 × 10 −3 mol/m 2 s at the absorbent flow rate of 300 ml/min. It was deduced that both He permeation and CO 2 absorption flux were governed by the HFM surface porosity. The long-term stability test revealed the reduction of 25% in CO 2 flux during the first 55 h of operation for the PSf membrane prepared at 15 cm air-gap. This study indicated that the surface modified HFMs prepared using an appropriate air-gap could be a promising option to increase membrane performance in MC systems. [ABSTRACT FROM AUTHOR]

[Display omitted] • Boron doped TNT immobilized on the outer layer of a dual layered PVDF hollow fiber membrane. • A finger-like structure on both outer and inner layer, sandwiching a dense interlayer. • PVDF-L2% exhibited a maximum flux of 39.62L/m2h and colour removal of 79.42%. • Membrane recovered more than 95% of performance after 4 filtration cycles, exhibiting antifouling propensity. • Long term study confirms membrane usability over 20 days. The emergence of hybrid photocatalytic membranes has provided a new direction in search of efficient technologies to separate and degrade pollutants present in wastewaters. Colour pigments originated from different sources including agricultural waste pose serious threats towards water bodies as their presence will lead to multiple environmental problems. This study investigated the potential of a photocatalytic dual layered hollow fiber membrane (DLHFM) incorporated with boron doped titania nanotubes (TNT-B) photocatalyst for the photodegradation and removal of colour pigment molecules present in aerobically treated palm oil mill effluent (AT-POME). The colour removal efficiencies and separation performance of the DLHFM were evaluated through a submerged membrane photo reactor (SMPR) system driven by visible light. Polyvinylidene fluoride-based DLHFM loaded with 2% of photocatalyst (PVDF-L2%) exhibited the best membrane performance with a flux of 39.62 L/m2h and colour removal efficiency of 79.42%. The controlled distribution of photocatalysts as well as the synergistic combination of membrane filtration and photodegradation concertedly contributed to the improvement in membrane's performance. 95% of flux and colour removal efficiency were sustained after four filtration cycles. The membrane exhibited efficient performance in terms of consistent flux and colour removal efficiency after 20 days of continuous photocatalytic filtration, implying their high long-term stability. This study highlights the efficiency and potential of visible light photocatalytic membranes in treating colour laden wastewaters. [ABSTRACT FROM AUTHOR]

[Display omitted] • ZIF-8, SiO 2 /ZIF-8 and amine modified (A@SiO 2 /ZIF-8) nanofillers were synthesised. • Synthesised nanofillers incorporated polysulfone hollow fiber MMMs were fabricated. • Investigated the gas permeation and selectivity of MMMs for CO 2 , CH 4 and N 2 gases. • A@SiO 2 /ZIF-8 contributed 89 and 61% increase in CO 2 /N 2 and CO 2 /CH 4 selectivities. High tunable properties of metal–organic frameworks (MOFs) allows different modifications to be used for distinct applications. Zeolitic imidazolate frameworks-8 or ZIF-8 are hybrid organic–inorganic porous materials that have shown great potential in membrane-based gas separations. In our study, SiO 2 /ZIF-8 (S/ZIF-8) nanofiller was synthesized via a facile one-step strategy. Furthermore, the S/ZIF-8 nanofiller was subjected to amine modification using an ammonium hydroxide solution. X-ray photoelectron spectroscopy (XPS) analysis confirms the strong binding of amine and SiO 2 on ZIF-8 nanofillers. The synthesized ZIF-8, S/ZIF-8 , and amine-modified S/ZIF-8 (A@S/ZIF-8) of 0.5 wt% were incorporated into the polysulfone (PSf) matrix, and the hollow fiber mixed matrix membranes (MMMs) were fabricated using dry–wet phase inversion technique. The inclusion of an amine group in the S/ZIF-8 nanofillers enhances the interaction between the nanofillers and PSf matrices, thus improving the CO 2 /CH 4 and CO 2 /N 2 separation performances. The fabricated membranes were morphologically characterized by Scanning electron microscope (SEM), Brunauer–Emmett–Teller (BET) surface area, and the pore size distribution. It is noteworthy that the BET surface area was enhanced with nanofillers addition and significantly increased gas separation performance. The fabricated asymmetric hollow fiber MMMs were further studied for gas permeation experiments for CO 2 , N 2 , and CH 4. PSf with A@S/ZIF-8 MMMs showed the best performance as observed from the Robeson upper bound limit, CO 2 permeability of 4.25 barrer with the improvements in CO 2 /N 2 and CO 2 /CH 4 selectivities of 89.75 and 61.46% respectively, compared with neat PSf membrane. The enhanced permselectivity of PSf–A@S/ZIF-8 membranes is explained by CO 2 -facilitated transport, where the high CO 2 affinity of the amine group allows the selective transport of CO 2 rather than CH 4 and N 2. [ABSTRACT FROM AUTHOR]

Recently, forward osmosis (FO) has attracted a great deal of attention in desalination and wastewater treatment. Nevertheless, there are several critical challenges such as the need for new advances in designing membranes that must be met to enhance the water flux in FO processes, control the reverse salt flux, concentration polarization and fouling. Therefore, designing a suitable membrane with a high-water flux, low reverse salt flux, low fouling, and controlled concentration polarization seems to be essential. Thin film composite (TFC) membranes are the most widely used membranes in the FO field. Extensive research has been performed to fabricate and design high performance TFC membranes which can be exclusively used in FO processes. This paper aims to review three types of TFC membranes i.e. TFC's with polyamide active layer (TFC-A), thin film nanocomposites (TFC-N) and double-skinned TFC membranes (TFC-D) in flat sheet and hollow fiber configuration. Finally, an attempt is made to generate a general performance curve based on the water flux and reverse salt flux of these three TFC FO types and the future direction of the R and D on the FO membrane are discussed. • A general performance curve for TFC-FO membranes was generated. • Active layer modified TFNs and double-skinned membranes possess very high potential for FO. • More researches should be performed on the less considered conditions of FO. [ABSTRACT FROM AUTHOR]

Mixed matrix membranes (MMMs) have received worldwide attention for natural gas purification due to their superior performance in terms of permeability and selectivity. The zeolitic imidazole framework-8 (ZIF-8) blended polysulfone (PSf) membranes have been fabricated for natural gas purification. ZIF-8 was selected due to its low cost, remarkable thermal and chemical stabilities, and tunable microporous structure. The neat PSf hollow fiber membrane and mixed matrix hollow fiber membranes incorporated with the various ZIF-8 loadings up to 1.25% were fabricated. The prepared membranes were evaluated using field emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), and gas separation performance. The low loading of ZIF-8 nanoparticles to the MMM improved thermal stability and glass transition temperature and yielded low surface roughness. MMMs were tested using pure gases with a significant improvement of 36% in CO 2 permeability and 28% in CO 2 /CH 4 selectivity compared to the neat membrane. However, the high ZIF-8 loading reduced the separation performances. Moreover, CO 2 /CH 4 selectivity decreased at elevated pressure (8 and 10 bar) due to CO 2 -induced plasticization. Previously, the incorporation of ZIF-8 particles has primarily been subjected to the fabrication of flat sheet membranes, whereas this work focused on hollow fiber membranes which are rarely investigated. Hence, the promising results obtained at low feed pressure in this study demonstrated the potential of ZIF-8 based hollow fiber membrane for natural gas purification. • MMMs give significant improvement of CO 2 permeability and CO 2 /CH 4 selectivity using pure gases. • MMMs were investigated and characterized at various loadings of ZIF-8. • The CO 2 -induced plasticization occurred at elevated pressure. [ABSTRACT FROM AUTHOR]

• Successful coating of HPMA thin film on PVDF membranes in low temperature. • Characterizations indicated successful growth of HPMA thin film on PVDF membrane. • Coating greatly enhanced membrane hydrophilicity and reduce surface roughness. • Enhanced membrane permeation and rejection performance. • Easy coating in highly controlled environment. Thin films of hydroxypropyl methacrylate (HPMA) were grown on polyvinylidene fluoride (PVDF) hollow fiber membranes via initiated chemical vapor deposition (iCVD), utilising di- tert -butyl peroxide as radical initiator. This method was able to completely coat PVDF membranes, producing uniform deposition of hydrophilic HPMA of 50 nm and 100 nm thickness on the membrane surface. The deposition of HPMA layer has been evidenced from the microscopy images and Fourier transform infra-red spectra. The HPMA coated membranes exhibited significantly improved surface hydrophilicity as reflective from the reduction in water contact angle from 78.1° to 23.6° meanwhile the membrane surface roughness was reduced with the thin film coating. The separation performance of HPMA-PVDF membranes was evaluated in the treatment of in-house prepared synthetic aerobically-treated palm oil mill effluent (AT-POME), which consists of lignin and tannic acid (TA). 100HPMA-PVDF membranes exhibited improved membrane flux and rejection of 50.8L/m2h and 83.1%, respectively. Additionally, 100HPMA-PVDF membrane maintained stable high permeation and rejection properties after four filtration cycles, due to its greatly improved surface hydrophilicity and reduced surface roughness. The studies open possibilities for highly controlled surface modification of membranes using low temperature iCVD methods to tailor the membrane selective layer. [ABSTRACT FROM AUTHOR]