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The unique characteristics of polyether ether ketone (PEEK) including low elastic modulus, high mechanical strength, and biocompatibility have made it an attractive alternative for the metallic biomaterials. However, its bioinert property is always the main concern, which could lead to poor osseointegration and subsequent clinical failure of the implant. Changing the surface structure to porous structure and mixing it with bioactive hydroxyapatite (HA) are the common methods, which could be used to enhance the properties of the PEEK-based implants. In this study, friction stir processing was utilized for the fabrication of porous HA/PEEK surface nanocomposite. Scanning electron microscopic image of the nanocomposite surface showed nano-scale roughness of the porous structure. Water contact angle test confirmed the increase in the wettability of the treated specimens. In vitro bioactivity test via simulated body fluid solution, initial cell adhesion, cell proliferation, and cell differentiation assay also confirmed the enhancement in bioactivity of the treated surface in comparison to the bare PEEK. This surface modification method requires no special equipment and would not damage the heat-sensitive PEEK substrate due to the low temperature used during the fabrication process.

Polyamide (PA) Thin-Film Composite (TFC) membranes are widely used for large-scale water and wastewater treatment processes worldwide owing to their good balance between water permeability and dissolved solutes separation rate. The physicochemical properties of the cross-linked PA layer are the main criteria determining the filtration performance of the resultant TFC membrane, and this selective layer can be created through Interfacial Polymerization (IP) between two immiscible active monomers, i.e., amine monomer in aqueous solution and acyl chloride monomer in organic solution. This patent review article intends to provide insights to researchers in fabricating improved properties of TFC membranes through the utilization of secondary monomers during IP process. To the best of our knowledge, this is the first review that gives a state-of-the-art account of the subject matter by emphasizing the impacts of secondary monomers (both amine and acyl chloride monomers) on the properties of conventional TFC membranes for nanofiltration and reverse osmosis applications. Our review indicated that the introduction of secondary monomers into either aqueous or organic solution could alter the physical and chemical properties of PA layer, which led to variations in membrane filtration performance. Nevertheless, more research is still required, as most of the secondary monomers reported in the literature did not overcome the membrane trade-off effect between permeability and selectivity. The subject of improved PA layer development is a multi-disciplinary study that requires researchers with different backgrounds (e.g., materials science, chemistry, physics and engineering) to work together.

In this study, two different methods were used to introduce functionalized graphene oxide (GO) onto the surface of nanofiltration (NF) membrane to improve its performance for heavy metal removal. The first method was based on coating in which the surface of NF membrane was coated with cross-linked GO, while the second method was introducing GO into monomer solution during interfacial polymerization. The efficiency of different methods was then compared by characterizing membrane physiochemical properties, as well as separation performance. With regard to performances, the water flux of TFN-i2 membrane (with GOs incorporated into thin layer) was reported to be 95 L/m2 h compared to 75 L/m2 h found in the TFN-c2 membrane (with GOs coated on the surface) at 8 bar. Both modified membranes exhibited higher water flux than the control membrane without GO incorporation (40 L/m2 h). Although the water flux of TFN-c2 membrane was lower, it achieved higher cobalt removal (97%) than that of TFN-i2 membrane (73%) due to its higher negative surface charge that improved separation via the Donnan exclusion effect.

Ammonium is known to be one of the most significant pollutants in water bodies. The presence of ammonium in water is mainly originated from agricultural activities, domestic sewage and industrial effluent. This study evaluates the performance of two commercial thin film composite (TFC) membranes, i.e., NF270 and XLE from FilmTec™ for ammonium removal using synthetic wastewater and domestic sewage. The filtration experiment was conducted at different feed ammonium concentrations, humic acid concentrations, pHs and pressure. Results showed that the membrane rejection against ammonium increased dramatically with increasing ammonium concentration. However, the membrane flux was slightly compromised at higher ammonium concentration. With respect to pH, highest ammonium removal rate was able to be achieved at an optimum pH of 10. Besides, the permeation flux increased gradually with increasing feed pressure. From the results, the XLE membrane outperformed the NF270 membrane in terms of ammonium rejection. The retentate of XLE membrane filtration process was found to be useful as liquid fertiliser for plant growth. The results indicated that the TFC membrane process is not only able to produce permeate with an ammonium concentration below the acceptable limit of 10 mg/L but also able to produce retentate with enriched ammonium for plant growth.

This work aims to investigate the polyamide (PA) morphology on polysulfone (PSf) membrane supports with different morphologies. It was achieved by systematically varying the N-Methyl-2-Pyrrolidone (NMP) and Dimethylformamide (DMF) solvent composition ratios in dope solution as adapted in Tiraferri et al. The PSf membrane support was firstly synthesized via phase separation technique. Next, the PA layer of the thin film composite (TFC) membrane was synthesized via consistent interfacial polymerization parameters on the PSf membrane support. The PA layer over the resulting array of membrane supports was investigated on their surface wettability, top and cross-sectional morphologies, and performances. Result shows that with more NMP content in the dope solution produces thin and dense sponge-like top skin layer with intense extended finger-like macrovoids sublayer. Meanwhile, more DMF content in the dope solution produces thicker and dense sponge-like morphology on the top skin with finger-like pores underneath. A layer of smaller and loosen ridge-and-valley PA structures is formed on the thicker and dense sponge-like morphology. TFC membrane over support made of NMP to DMF (40:60) was observed had the highest hydrophilicity with the lowest contact angle measurement of 61.9 ± 3.1°. It also performed the highest water permeability of 4.06 LMH/bar, moderate salt rejection of 95.65% with salt permeability of 1.9 gMH.

A green hybrid nanocomposite of rGO/ZIF-8 was successfully synthesised via multi-recycling approach by reusing unreacted reagents in mother liquor. This eco-friendly approach allows for minimal addition of fresh chemicals and thus reduces the synthesis cost. The one-pot synthesised rGO/ZIF-8 powder was recovered by filtration, and the mother liquor filtrate was reused for the next cycle of synthesis. The product yield from each cycle was evaluated by quantifying the product’s mass. Detailed characterisation studies were carried out by using XRD, TGA, FTIR, BET, SEM, and TEM. ZIF-8 nanoparticles anchored well on the surfaces of rGO without sacrificing the product yield. This approach minimises the use of organic linker and its waste product, leading to low-cost and environmentally friendly synthesis process for rGO/ZIF-8.

There is increasing interest in the use of polyether ether ketone (PEEK) for orthopedic and dental implant applications due to its elastic modulus (close to that of bone), biocompatibility and radiolucent properties. However, PEEK is still categorized as bioinert owing to its low integration with surrounding tissues. Methods such as depositing hydroxyapatite (HA) onto the PEEK surface could increase its bioactivity. However, depositing HA without damaging the PEEK substrate is still required further investigation. Friction stir processing is a solid-state processing method that is widely used for composite substrate fabrication. In this study, a pinless tool was used to fabricate a HA/PEEK surface nanocomposite for orthopedic and dental applications. Microscopical images of the modified substrate confirmed homogenous distribution of the HA on the surface of the PEEK. The resultant HA/PEEK surface nanocomposites demonstrated improved surface hydrophilicity coupled with better apatite formation capacity (as shown in the simulated body fluid) in comparison to the pristine PEEK, making the newly developed material more suitable for biomedical application. This surface deposition method that is carried out at low temperature would not damage the PEEK substrate and thus could be a good alternative for existing commercial methods for PEEK surface modification.

The discharge of industrial effluent containing heavy metal ions would cause water pollution if such effluent is not properly treated. In this work, the performance of emerging nanofiltration (NF) like-forward osmosis (FO) membrane was evaluated for its efficiency to remove copper ion from water. Conventionally, copper ion is removed from aqueous solution via adsorption and/or ion-exchange method. The engineered osmosis method as proposed in this work considered four commercial NF membranes (i.e., NF90, DK, NDX and PFO) where their separation performances were accessed using synthetic water sample containing 100 mg·L−1 copper ion under FO and pressure retarded osmosis (PRO) orientation. The findings indicated that all membranes could achieve almost complete removal of copper regardless of membrane orientation without applying external driving force. The high removal rates were in good agreement with the outcomes of the membranes tested under pressure-driven mode at 1MPa. The use of appropriate salts as draw solutes enabled the NF membranes to be employed in engineered osmosis process, achieving a relatively low reverse solute flux. The findings showed that the best performing membrane is PFO membrane in which it achieved > 99.4% copper rejection with very minimum reverse solute flux of

This paper evaluated the effectiveness of polyester (PS)/poly(vinyl alcohol) (PVA) dynamic membrane (DM) incorporating photocatalytic zeolite/TiO2 for oil-in-water (O/W) emulsion separation. The photocatalytic zeolite/TiO2 was established onto the membrane surface via self-forming and pre-coating method with the aims of reducing membrane fouling during O/W emulsion treatment. The results obtained showed that the pre-coated composite DM could decrease support membrane fouling by improving flux recovery rate by 5.8%, while the use of the self-forming composite DM exhibited lower flux recovery rate after three filtration cycles in O/W emulsion treatment. The results were confirmed by cleaning and oil removal efficiency. The cleaning efficiency of composite DM was further enhanced by substitution of deionized water with sodium dodecyl sulfate as a cleaning agent in the treatment of O/W emulsion. Using sodium dodecyl sulfate, the pre-coated composite DM showed higher flux recovery rate (81%) than the self-forming composite DM. In addition, the photocatalytic effects of zeolite/TiO2 on the DM with respect to flux recovery rate and oil rejection under UV light source were investigated. It was found that by combining cleaning process and UV irradiation, the fouling of DM was further decreased, recording high flux recovery rate (up to 83.6%) without compromising oil rejection rate (85.3%).

In this study, the capability of a mixed matrix composite membrane (MMCM) fabricated using polyether block amide polymer PEBAX MH1657 from Arkema and in lab synthesized aminated partially reduced graphene oxide (A-prGO) nanofiller as a selective layer has been studied for gas separation. Moreover, the effects of nanofiller addition on membrane structure properties and performance were examined. The PEBAX/A-prGO membrane was fabricated as a selective layer on top of a supporting substrate layer of polysulfone 1700. MMCM was prepared in five different loadings of A-prGO nanofiller (0, 0.05, 0.1, 0.2, 0.6 (w/w)%) of the used PEBAX amount. The synthesized nanofiller and fabricated MMCM were characterized using different characterization tests (XRD, FTIR, EDX, and SEM). The optimum separation of the membrane was found when the loading of A-prGO was 0.1%. The permeability of the membrane for CO2, N2 and CH4 gases were 47.5 Barrer for CO2, 0.45 Barrer for N2 & 2 Barrer for CH4 while the selectivity of CO2/N2 and CO2/CH4 are 105.6 and 23.75, respectively. Surprisingly, the fabricated membrane performance found to be above the Robeson 2008 upper bound of permeability- selectivity relation for CO2/N2 gases separation.

This paper reports the synthesis and characterization of novel ultrafiltration (UF) electrospun nanofibrous membranes (ENMs) incorporated with iron oxide (Fe3O4) nanoparticles (NPs) for effective oily solution treatment. Three strategies were employed to improve the physiochemical properties of the resultant ENMs. Firstly, n-methyl-pyrrolidinone (NMP) was added to dimethylformamide (DMF) wherein the solvent stimulated fusion of the inter-fiber junctions was enhanced. Secondly, Fe3O4 NPs were introduced into the ENMs to improve their hydrophilicity and anti-fouling resistance against oil molecules. Thirdly, hot pressed technique was adopted to strengthen the electrospun mat, avoiding delamination of the ENMs layer during liquid filtration processes. The findings indicated that the developed Fe3O4 NPs incorporated ENMs exhibited outstanding oil elimination (94.01%) and excellent water flux recovery (79.50%) when tested with synthetic oil solution (12,000 ppm). Water productivity of over 3200 L/m2 h was achieved without forfeiting the rate of oil removal under gravity. Extraordinarily low flux declination disclosed by the proposed ENMs was attributed to their tailored surface resistance mediated oil anti-fouling character. The enhanced mechanical and oil anti-fouling traits of the prepared ENMs were established to be potential for the treatment of diverse oily effluents (especially emulsions of oil–water) in the industries.

In this study, a quantitative performance of three commercial polyamide nanofiltration (NF) membranes (i.e., NF, NF90, and NF270) for phosphorus removal under different feed conditions was investigated. The experiments were conducted at different feed phosphorus concentrations (2.5, 5, 10, and 15 mg·L−1) and elevated pHs (pH 1.5, 5, 10, and 13.5) at a constant feed pressure of 1 MPa using a dead-end filtration cell. Membrane rejection against total phosphorus generally increased with increasing phosphorus concentration regardless of membrane type. In contrast, the permeate flux for all the membranes only decreased slightly with increasing phosphorus concentration. The results also showed that the phosphorus rejections improved while water flux remained almost unchanged with increasing feed solution pH. When the three membranes were exposed to strong pHs (pH 1.5 and 13.5) for a longer duration (up to 6 weeks), it was found that the rejection capability and water flux of the membranes remained very similar throughout the duration, except for NF membrane with marginal decrement in phosphorus rejection. Adsorption study also revealed that more phosphorus was adsorbed onto the membrane structure at alkaline conditions (pH 10 and 13.5) compared to the same membranes tested at lower pHs (pH 1.5 and 5). In conclusion, NF270 membrane outperformed NF and NF90 membranes owing to its desirable performance of water flux and phosphorus rejection particularly under strong alkali solution. The NF270 membrane achieved 14.0 L·m−2·h−1 and 96.5% rejection against 10 mg·L−1 phosphorus solution with a pH value of 13.5 at the applied pressure of 1 MPa.

Novel thin film nanocomposite (TFN) nanofiltration membrane with tunable physico-chemical properties and separation performances was fabricated by incorporating the copper benzene-1,3,5-tricarboxylate (CuBTC) nanoparticles with different concentrations (ranging from 0 to 0.75 wt.%) in the polysulfone (PSf) substrates, followed by the interfacial polymerization process of trimesoyl chloride (TMC) and piperazine (PIP) to establish top selective layer. Charaterization results show that both chemical and physical properties of poly(piperazineamide) selective layer was altered when PSf substrate was modified by CuBTC. The introduction of CuBTC nanoparticles improved the hydrophilicity of the TFN membranes (from 70.25° to 59.02°) and promoted formation of more linear structure of poly(piperazineamide) entangled with −COOH pendant groups. By incorporating 0.25 wt.% of CuBTC into the PSf substrate, the resultant membrane flux was enhanced by 22% with MgSO4 rejection remained at 97.31%. Furthermore, a notable increment of rejection against NaCl could be attained by increasing the CuBTC content in the substrate. This could be explained by the Donnan potential effect occurred on the more linear structures of poly(piperazineamide) surfaces, which results in an increase in the selectivity of monovalent salts. Moreover, the incorporation of CuBTC rendered the TFN membranes to exhibit good anti-fouling property against bovine serum albumin.

In this study, polyethersulfone (PES) hollow fibre membranes incorporated with different loadings of coupled zinc–iron oxide (ZIO) (0–2 wt%) nanoparticle were fabricated and used to remove the colour of aerobically treated palm oil mill effluent (AT-POME). The ZIO nanoparticles were synthesized via solution combustion method and characterized for their physicochemical properties. A specific amount of ZIO nanoparticles was then added into the PES dope solution followed by dry/wet-jet spinning technique to produce hollow fibre membrane of negatively charge surface properties. The membranes were characterized with respect to their cross-sectional morphology, hydrophilicity, tensile strength and surface charge. The separation performance of the membranes was then evaluated using pure water and AT-POME as feed solution. Results show that the membrane incorporated with 0.5 wt% ZIO was the best performing membrane, showing pure water flux and AT-POME flux of 2.46 and 2.0 L/m2 h, respectively, when tested at 1 bar. Furthermore, this membrane also showed reasonably good rejection against colour (76.2% reduction) and improved antifouling resistance.

In this work, a new type of ultrafiltration (UF) electrospun nanofibrous membranes (ENMs) incorporating hydrous manganese dioxide (HMO) nanoparticles was fabricated with the objective of improving properties of polyethersulfone (PES)-based membrane for synthetic oily solution treatment. Two treatments were carried out to improve the mechanical property and hydrophilicity of the PES-based membrane without compromising its porosity and water permeance. The first treatment involved the use of mixed solvents – dimethylformamide and n-methyl-pyrrolidinone (DMF/NMP) in which NMP is a high vapor pressure component that could enhance the mechanical properties of the nanofibrous by improving solvent-induced fusion of inter-fiber junction points. The second treatment involved the incorporation of specific amount of HMO nanoparticles in PES dope solution to enhance membrane hydrophilicity. Heat treatment was also adopted as an effective approach to strengthen and prevent delamination of the nanofibrous mat during UF process. The HMO-incorporated ENMs exhibited an excellent oil rejection (97.98% and 94.04%) and a promising water flux recovery (89.29% and 71.10%) when used to treat a synthetic oily solution containing 5000 or 10,000 ppm oil, respectively. The best promising HMO-incorporated ENM exhibited much higher magnitude of water productivity (>7000 L/m2h) without sacrificing oil removal rate. Most importantly, this nanofillers-incorporated membrane showed significantly lower degree of flux decline as a result of improved surface resistance against oil fouling and is of potential for long-term operation with extended lifespan. The promising mechanical and anti-fouling properties of the ENMs is potentially applicable in the efficient industrial oily effluents treatment when challenged with oil-in-water emulsions.

In this work, two types of thin film nanocomposite (TFN) membranes were developed (by incorporating either 0.05 wt/v% surface-modified nanoporous titanium oxide (f-nTiO2) or titanate nanotube (f-TNT) in the polyamide selective layer) to investigate the impacts of nanomaterial structures (i.e., sizes and shapes) on membrane properties and desalination performances. The filtration results revealed that the incorporation of f-nTiO2 yielded membrane of better filtration performances than the one incorporated with f-TNT. Compared to the TFN-f-TNT membrane, the TFN-f-nTiO2 membrane possessed greater water flux (4.26 vs. 3.36 L/m2 h bar) and higher NaCl (98.04 vs. 97.28%) and boron rejection (54.82 vs. 48.86%). It was also found that surface coating of TFN membranes with hydrophilic polyvinyl alcohol could further improve membrane solute rejection (up to 9%) with slight reduction in water flux.

Oxygen enriched air (OEA) is widely applied in various areas such as chemical and medical applications. Currently, cryogenic distillation and pressure swing adsorption are the two common technologies that being commercially used for i the production of OEA. However, these two techniques are not economically favorable due to required intensive energy and large built-up area. With the advancement of membrane technology in separation process, it garners the interest from both industrial and academic to explore the feasibility of membrane in gas separation. In this study, polysulfone (PSF) hollow fiber membranes with poly(ether block amide) (PEBAX) coating were used for the separation of O2/N2 gas. The hollow fiber membranes used in this work were fabricated by phase inversion spinning process using PSF pellet, along with N,N-dimetyhlacetamide (DMAc) and ethanol (EtOH) as solvent and co-solvent, whereas tetrahydrofuran (THF) as additive. The fabricated membrane exhibited dense structure in the inner layer whereas finger like layer at the outer surface. The formation of this structure was attributed by rapid phase inversion of the solution arose from strong solvent used. The EDX surface mapping analysis confirmed the formation of PEBAX coating on the membrane surface. Gas permeation study in this work illustrated that the pristine PSF membrane exhibited better gas separation performance relative to the PEBAX coated membrane with 20% higher in terms of permeance. The results obtained from this work suggested that the PEBAX coating enhanced the membrane surface but not certain to improve the gas separation performance. Further study on the PEBAX materials for the membrane coating is essential to polish its potential in gas separation.

Mixed matrix membranes (MMMs) were successfully fabricated by incorporating reduced graphene oxide (rGO) and zeolitic imidazole framework-8 (ZIF-8) nanofillers into the polyethersulfone (PES) matrix. The synthesized nanofillers were characterized using XRD, FTIR, TGA and BET before being embedded into PES-based membranes. Their effects on the membrane morphology and gas separation performances at various operating pressure were studied. It was found that the addition of nanofillers led to a significant enhancement in gas permeabilities, particularly when a combination of rGO-ZIF-8 nanofillers was used. However, the CO2 and CH4 permeabilities for 2.0rGO-ZIF-8 MMMs were observed to decrease with increasing operating pressure. This work suggests that the formation of interface voids and membrane defects in the MMMs might lead to the high gas permeabilities and low gas selectivity. The membranes were then coated with polyether block amide (PEBAX) and the O2/N2 and CO2/CH4 selectivities were observed to improve significantly.

The conventional interfacial polymerization (IP) technique that requires a rubber roller in removing amine aqueous solution is likely to cause uneven distribution of nanomaterials on microporous substrate during thin film nanocomposite (TFN) membrane fabrication. A novel IP technique was developed in this work to pre-coat the substrate with graphene oxide (GO) nanosheets followed by vacuum filtration of amine aqueous solution through the substrate before initiating polyamide cross-linking process. This novel technique was also employed to fabricate a composite membrane that contained no nanomaterials. The results showed that the GO-incorporated TFN membrane exhibited 71.7% and 129.4% higher pure water flux compared to the composite membranes without GO incorporation that were synthesized using conventional and filtration IP technique, respectively. The water enhancement of the TFN membrane could be attributed to the existence of hydrophilic GO that was distributed evenly throughout the substrate surface coupled with the formation of porous selective layer that reduced water transport resistance. Besides exhibiting promising rejection against divalent ions, the newly developed TFN membrane also showed significantly lower water flux deterioration in filtrating bovine serum albumin and Reactive Black 5 solution. The enhanced membrane antifouling resistance was mainly due to the improved membrane surface properties that minimize deposition and adsorption of foulants on the TFN membrane surface.

The structural (S) parameter of a medium is used to represent the mass transport resistance of an asymmetric membrane. In this study, we aimed to fabricate a membrane sublayer using a novel composition to improve the S parameter for enhanced forward osmosis (FO). Thin film composite (TFC) membranes using polyamide (PA) as an active layer and different polysulfone:polyethersulfone (PSf:PES) supports as sublayers were prepared via the phase inversion technique, followed by interfacial polymerization. The membrane made with a PSf:PES ratio of 2:3 was observed to have the lowest contact angle (CA) with the highest overall porosity. It also had the highest water permeability (A, 3.79 ± 1.06 L m−2 h−1 bar−1) and salt permeability (B, 8.42 ± 2.34 g m−2 h−1), as well as a good NaCl rejection rate of 74%. An increase in porosity at elevated temperatures from 30 to 40 °C decreased Sint from 184 ± 4 to 159 ± 2 μm. At elevated temperatures, significant increases in the water flux from 13.81 to 42.86 L m−2 h−1 and reverse salt flux (RSF) from 12.74 to 460 g m−2 h−1 occur, reducing Seff from 152 ± 26 to 120 ± 14 μm. Sint is a temperature-dependent parameter, whereas Seff can only be reduced in a high-water- permeability membrane at elevated temperatures.

NOx (NO and NO2) are air toxins that endanger life and represent a hazard to the environment, such as photochemical smog, global warming, acid rain, ozone depletion, and the occurrence of respiratory infections. Some technological strategies to diminish NOx emissions to meet regulations depend on two techniques: the dry process and the wet process. This study applies polyvinylidene fluoride (PVDF) hollow fiber membrane modules as a medium to remove NOx from solutions containing several absorbents such as hydrogen peroxide and nitric acid (H2O2-HNO3) solutions, sodium chlorite and sodium hydroxide (NaClO2-NaOH) solutions, and sodium chlorate and sodium hydroxide (NaClO3-NaOH) solutions. The experimental results showed that the oxidant’s strength influences NOx removal efficiency, where the absorbent solutions containing hydrogen peroxide had the highest removal efficiency as hydrogen peroxide is the most potent oxidant, followed by sodium chlorite and sodium chlorate. The three pairs of absorbents also gave a high NOx removal efficiency (above 90%), which means that all the absorbents used in the study are very potential to be used to diminish NOx via the wet process. NOx removal efficiency at the same feed gas flow rate increased as the number of fiber and absorbent concentrations is increased. However, NOx removal efficiency is reduced as the feed gas flow rate is increased at the same membrane module and absorbent concentration.

This study focuses on the development of flat sheet thin film nanocomposite (TFN) pressure retarded osmosis (PRO) membranes for the enhancement of osmotic power generation by the incorporation of laboratory-synthesised graphene oxide (GO) into the polysulfone (PSf) polymer matrix. A series of membranes containing different weight percent of GO (0, 0.1, 0.25, 0.5 and 1.0 wt%) were fabricated via a phase inversion method with polyethylene glycol (PEG) as the pore forming agent. The results show that the TFN-0.25GO membrane has excellent water flux, salt reverse flux, high porosity and an enhanced microvoids morphology compared to the control membrane. The highest power density was achieved when TFN-0.25GO was used is 8.36 Wm&minus, 2 at pressure &gt, 15 bar. It was found that the incorporation of GO into the polymer matrix has significantly improved the intrinsic and mechanical properties of the membrane.

One of the most critical issues encountered by polymeric membranes for the gas separation process is the trade-off effect between gas permeability and selectivity. The aim of this work is to develop a simple yet effective coating technique to modify the surface properties of commonly used polysulfone (PSF) hollow fiber membranes to address the trade-off effect for CO2/CH4 and O2/N2 separation. In this study, multilayer coated PSF hollow fibers were fabricated by incorporating a graphene oxide (GO) nanosheet into the selective coating layer made of polyether block amide (Pebax). In order to prevent the penetration of Pebax coating solution into the membrane substrate, a gutter layer of polydimethylsiloxane (PDMS) was formed between the substrate and Pebax layer. The impacts of GO loadings (0.0&ndash, 1.0 wt%) on the Pebax layer properties and the membrane performances were then investigated. XPS data clearly showed the existence of GO in the membrane selective layer, and the higher the amount of GO incorporated the greater the sp2 hybridization state of carbon detected. In terms of coating layer morphology, increasing the GO amount only affected the membrane surface roughness without altering the entire coating layer thickness. Our findings indicated that the addition of 0.8 wt% GO into the Pebax coating layer could produce the best performing multilayer coated membrane, showing 56.1% and 20.9% enhancements in the CO2/CH4 and O2/N2 gas pair selectivities, respectively, in comparison to the membrane without GO incorporation. The improvement is due to the increased tortuous path in the selective layer, which created a higher resistance to the larger gas molecules (CH4 and N2) compared to the smaller gas molecules (CO2 and O2). The best performing membrane also demonstrated a lower degree of plasticization and a very stable performance over the entire 50-h operation, recording CO2/CH4 and O2/N2 gas pair selectivities of 52.57 (CO2 permeance: 28.08 GPU) and 8.05 (O2 permeance: 5.32 GPU), respectively.

Membrane technology for industrial gas separation was begun in the 1980s and has shown significant advantages over conventional techniques such as cryogenic distillation and solvent absorption in terms of energy consumption and operational cost. The main objective of this work is to develop a simple yet effective coating technique to modify the surface properties of polysulfone (PSF) hollow fiber membranes for enhanced separation of CO2/CH4 and O2/N2. The hollow fiber membranes made of different polymer concentration (15–35 wt%) were coated with different materials (polydimethylsiloxane (PDMS) or polyether-block-amide (Pebax) or PDMS followed by Pebax) through a simple dip-coating method before subjecting to pure gases testing and instrumental characterization. Results showed that the multilayer coated membranes exhibited better performance compared to the single-layer PDMS-coated and single-layer Pebax-coated membranes. It is also found that the Pebax concentration could affect the performance of the multilayer coated membranes in which the gas permeance decreased while its selectivity decreased with increasing Pebax concentration from 1 to 3 wt.%. Further increase in Pebax concentration from 3 to 9 wt% however negatively affected selectivities as high Pebax concentration tended to cover the membrane surface with tighter polymer chain packing which led to lower free volume. Experimental results also showed that the optimized multilayer coated membrane (3 wt.% Pebax) could achieve the highest gas pair selectivity, recording 34.28 and 6.65 for CO2/CH4 and O2/N2 separation, respectively. As a comparison, the membrane coated with 1 wt% Pebax only showed selectivity of 29.47 and 6.07, respectively. The findings of this work demonstrated that multilayered coating could be performed on the outer layer of hollow fiber membranes and is not limited to the flat sheet membranes as previously reported in the literature, provided a good combination of two coating solutions were used.

Photocatalysis is regarded as a promising technology that can be used for the elimination of any recalcitrant organic contaminants that lie in the wastewater treatment plant. The concept of photocatalysis is originally adapted from advanced oxidation processes (AOPs) by the generation of hydroxyl radicals that are highly reactive species that in turn could mineralize the organic contaminants into harmless products such as CO2 and water. Since the discovery of TiO2 as a viable photocatalyst (PC) in 1972 by Fujishima and Honda, much fundamental progress has been made in developing novel semiconductor PCs that are particularly visible light-response catalyst for efficient utilization of solar energy. Recently, perovskite-based PC is discovered to be an efficient PC due to its ability to initiate photocatalytic activity with visible light irradiation. There are different types of perovskite that have been further explored, such as titanite perovskite, tantalite perovskite, vanadium-based perovskite, and ferrite perovskite. Perovskite oxides have great importance because it exhibits wide range of beneficial properties, which includes high proton and oxygen ion conductivity, magnetic and dielectric properties. In this chapter, several criteria for selecting high desired physicochemical properties of perovskite PCs such as particle morphology, surface area, crystallinity effect, and bandgap have been discussed in detail. Other than that, this chapter also discussed in detail the factors that affected the properties of the perovskite PCs such as synthesis method, chelating agents, and calcination temperature. The proposed mechanisms of chelating based on previous studies were explained in detail. Lastly, the chapter discussed the fundamental basics of operational parameter for photocatalytic degradation of organic pollutants, including the effect of catalyst loading, initial concentration, and presence of scavengers that have influenced on the process of the photocatalysis.

The incorporation of microporous mixed-matrix membranes (MMMs) with inorganic nanomaterials has created an opportunity for developing new types of polymeric-based membranes with improved physicochemical properties and filtration performance for water applications. This chapter will review the latest developments of MMMs being incorporated into a wide range of nanomaterials for water and wastewater treatment processes. More specifically, it will provide an overview of the effects of various functionalized nanomaterials (i.e., titanium-based nanomaterials, carbon-based nanoparticles, binary metal oxides, silicon dioxide, and metal-organic framework) on the properties of MMMs with respect to hydrophilicity, morphology, water flux, solute rejection, antifouling, and antibacterial resistances. The potential for using functionalized nanomaterials in adsorptive MMMs fabrication for heavy-metal ions removal process will also be reviewed and discussed.

This chapter discusses the prospect of the membrane technology in oxygen gas separation to cater to the rising global demand of oxygen gas. The chapter starts with a brief introduction of the historical development of the membrane technology in gas separation followed by the recent review of oxygen gas demand in liquefied natural gas and oxy-fuel combustion sector. The chapter later deliberates the conventional techniques in oxygen production, limitation of membrane technology in oxygen gas separation with the in-depth discussion of governing equations and Robeson upper bound. Lastly, the chapter provides a comprehensive evaluation of latest development in the nanocomposite membrane and a review of the literature reporting performance of oxygen/nitrogen gas separation performance using nanocomposite membrane.

Although the commercial polyurethane (PU) foams are hydrophobic in nature, they generally show low degree of reusability for oil and organic solvent absorption. In this work, we proposed a solvent-free and rapid surface functionalization approach based on chemical vapor deposition (CVD) process to improve the surface characteristics of PU foam, increasing not only its reusability but also its absorption capacity. Among the monomers used to functionalize the surface of foam, our results showed that only hexamethyldisiloxane (HMDSO) and 2,2,3,4,4,4-hexafluorobutyl acrylate (HFBA) were promising to increase the absorption performance of the control PU foam, owing to the enhanced foam’s surface hydrophobicity (with contact angle increased from ~106o to 120–135o) without altering the foam’s porosity. These promising features are attributed to the formation of ultrathin highly hydrophobic yet uniform layer on the foam surface. Further investigation indicated that the modified foams outperformed the control foam for the multicycle cyclohexane and crude oil absorption (up to 10 cycles) by showing significantly higher absorption capacity. The reusability of the modified foams could be further improved when ethanol was employed to rinse the saturated foam after each absorption cycle. Such solvent rinsing help in maintaining the foam absorption capacity. In conclusion, the proposed greener surface modification method clearly demonstrated its effectiveness in functionalizing the PU foam, leading to higher absorption capacity against cyclohexane and crude oil as well as higher degree of reusability.

In this study, thin film nanocomposite (TFN) membranes were fabricated by incorporating highly hydrophilic halloysite nanotubes (HNTs) and self-synthesized graphitic carbon nitride (g-C3N4) nanoparticles into polysulfone-based substrate and interfacially polymerized polyamide top layer, respectively. The TFN membranes were evaluated for their performance in forward osmosis (FO) applications. The XRD, ATR-FTIR, FESEM and TEM results confirmed the successful synthesis of g-C3N4 nanoparticles. The effects of nanomaterials incorporation were investigated in terms of membrane surface morphology, hydrophilicity and separation performance. When 0.05 wt/v% of g-C3N4 was added to the polyamide layer, the membrane surface contact angle was significantly reduced from 68° in the control membrane (TFN0.0) to

Support layer of thin film composite (TFC) membrane plays an important role in forward osmosis (FO) performance. A new type of support layer or nanocomposite substrate was developed by incorporating titanium dioxide (TiO2)/graphene oxide (GO) into polysulfone (PSF) matrix. Prior to performance evaluation, the developed substrates were characterized with respect to surface chemistry, roughness and cross-sectional morphology. The results showed that both surface hydrophilicity and roughness of PSF-based substrates were increased upon incorporation of nanomaterials. Substrates with long finger-like voids extended from the top to the bottom could be developed upon incorporation of TiO2 (SubstrateTiO2) or TiO2/GO mixture (SubstrateTiO2/GO). The improved surface hydrophilicity and favorable structure formed are the main factors leading to higher water flux of nanocomposite substrate. Moreover, the water flux of FO using TFC membranes could be enhanced using this nanocomposite substrate. Comparing to the control TFC membrane, the TFC membranes made of SubstrateTiO2 and SubstrateTiO2/GO exhibited greater water flux with minimum increase in reverse draw solute flux. Based on the results obtained, it can be concluded that the incorporation of TiO2 and/or GO nanoparticles into PSF substrate could potentially improve the TFC membrane performance during FO applications. Keywords: Nanocomposite substrate, TFC membrane, TiO2, Graphene oxide, Forward osmosis

In this paper, the synthesis of LaFeO3 based on the gel combustion method has been improved by using citric acid (CA) as a secondary chelating agent on glucose. The synthesized samples were calcined at 600 °C and further characterized using X-ray diffraction (XRD), Fourier transform infrared, field-emission scanning electron microscopy (FESEM), scanning electron microscopy, energy-dispersive X-ray spectrophotometry, N2 adsorption–desorption analyses, thermogravimetric analysis, and UV–vis–near-IR spectroscopy. The XRD data revealed that the pure orthorhombic perovskite phase LaFeO3 was obtained when CA was added on glucose. From FESEM and Brunauer–Emmett–Teller analysis, LaFeO3 synthesized using the addition of CA on glucose potentially showed well-uniform spherical particles and a high specific surface area of 40.77 m2/g with a particle size of 70 nm compared to glucose, which only showed 15.68 m2/g with a particle size of 100–300 nm. The photocatalytic activity of LaFeO3 was evaluated by the degradation...

In this study, polyvinylidene fluoride (PVDF) nanocomposite membranes with different fillers were fabricated using electrospinning technique. The physico-chemical properties of electrospun membranes such as PVDF (NF1), PVDF-polyvinyl pyrrolidone (PVP) (NF2), PVDF-activated carbon (AC) (NF3), PVDF-MnO2 (NF4), PVDF-PVP-AC (NF5), and PVDF-PVP-MnO2 (NF6) were assessed using field emission scanning electron microscopy-energy dispersive X-ray spectroscopy (FESEM-EDX), tensile tester, contact angle measurement, zeta potential, and attenuated total reflection-fourier transform infrared spectroscopy (ATR-FTIR). The Bisphenol A (BPA) removal efficacy of the membranes was assessed using flat sheet membrane filtration unit. The single layer filtration for BPA removal at 30 min was found to be 27%, 100%, 24%, 54%, 100%, and 100% for NF1, NF2, NF3, NF4, NF5, and NF6, respectively. In particular, NF2 and NF6 membranes exhibited maximum removal of BPA with good retention potential for the entire sampling time. In recyclic application, the regenerated NF6 membrane showed better reusability for BPA removal. During the removal process, BPA attached with PVP and MnO2 present in NF6 membrane through hydrogen bonding interaction. The hydrogen bonding length and energies E H were calculated by density functional theory (DFT). Finally, this study suggests that PVP and MnO2 incorporated PVDF membrane might be an effective and reusable membrane for BPA removal from drinking water sources.

In this work, tailor-made graphene oxide (GO) incorporated thin film nanocomposite (TFN) membranes based on novel interfacial polymerization (IP) technique were presented. The embedment of GO nanosheets within ultrathin cross-linked polyamide (PA) layer was successfully achieved without forming particle agglomeration that could affect structural integrity. A total of five composite membranes with different GO loadings (0, 0.01, 0.02, 0.03 and 0.04 g/m2) were fabricated and these membranes were characterized using TEM, FESEM, XPS, ATR-FTIR and contact angle goniometer to evaluate the impact of GO loading on the physicochemical properties of PA selective layer. It is found that with the presence of GO, the TFN membranes exhibited higher surface hydrophilicity due to increment in hydroxyl and carboxyl groups in PA layer, hence, improved the attraction between water molecules and membrane surface. Upon incorporation of 0.02 g/m2 of GO, the resultant TFN membrane achieved 95.8% and 97.7% removal rate for Na2SO4 and MgSO4, respectively along with 31.4% higher water flux than the membrane contained no GO. More importantly, this work demonstrated the broad applicability of novel IP technique in synthesizing TFN membranes with improved antifouling properties independent of the PA chemistry.

In this study, six different types of polysulfone hollow fiber membranes were fabricated from the same polymeric dope solution by manipulating several important parameters during the spinning process, aiming to find the best membrane supports for the coating layer in the gas separation process. The experimental results showed that upon the polydimethylsiloxane (PDMS) coating process, the gas pair selectivities of all six types of membranes were significantly increased with respect to carbon dioxide (CO2)/methane (CH4) and oxygen (O2)/nitrogen (N2) separation. However, the membrane support spun at higher air gap and lower dope extrusion rate was found to be the best support for PDMS coating owing to its good structural integrity that led to a good balance between gas permeance and gas pair selectivity. Further investigation showed that the use of poly(ether block amide) (Pebax) as coating material did not certainly improve both gas permeance and the selectivity of hollow fiber membranes, although Pebax was previously reported to exhibit better performance than PDMS in flat sheet membranes. One of the main reasons is the difficulty of forming a defect-free Pebax coating layer on the outer surface of hollow fibers owing to the stickiness issue among fibers upon coating. More research is still needed to optimize the Pebax coating solution and its drying process in order to achieve the full potential of such coating material for hollow fiber membranes.

Thin film composite (TFC) reverse osmosis (RO) membrane, which has been widely applied for desalination, consists of an ultra-thin polyamide (PA) coating layer that supported on a porous support membrane. The main interest of this work is to perform facile acid modification on the polysulfone (PS) support of TFC and thin film nanocomposite (TFN) membranes. The PS support was acid treated with sulfuric acid (H2SO4) at a concentration ranging from 1 to 2 M for 24–72 h. Response surface methodology (RSM) based on historical data design (HDD) was used to verify the optimum condition of support membrane with respect to NaCl rejection and water permeability. The highest water permeability was achieved at 1.13 L/m2.h.bar when nanoparticles loading of 0.03% was incorporated into the PA layer and PS support treated at 1.5 M H2SO4 for 48 h. The NaCl rejection of all the synthesized membranes was found to be above 96%.

Adsorption is one of the most effective methods for the treatment of wastewater containing dyes owing to its low operating cost, simplicity of process design and smaller amounts of harmful substances. In this work, graphene oxide- magnetic iron oxide nanoparticles (GO-MNP) was synthesized using sonomechanical technique and used as effective adsorbent for synthetic methylene blue (MB) dye removal. Batch adsorption experiments were performed with the variation of initial MB dye concentration, pH solution, adsorbent dosage and contact time. The adsorbent showed significant removal efficiency around 99.6% for MB. It was found that the removal rate of MB dye in the solution was higher when higher pH, larger dosage of adsorbent in solution and longer contact time were used. A regenerative study was carried out and minor reduction in adsorption capacity of the regenerated GO-MNP was observed after 2 cycles. Analysis of adsorption equilibrium revealed that the data is well fitted with Langmuir and Freundlich adsorption isotherm model (R2 > 0.97), indicating multi layer adsorption of dye on the surface of adsorbent. In the case of adsorption kinetics, the GO-MNP adsorbent follows pseudo-second order kinetics model showing R2 > 0.999, whereas for pseudo-first order kinetics model, the value of R2 was significantly lower. The finding of the present work highlights simple fabrication of magnetic GO and its application as efficient and magnetically separable adsorbent for environmental clean-up.

The physicochemical properties and performance of thin film composite (TFC) membranes depend on its synthesis conditions. In this study, TFC membranes were fabricated using interfacial polymerization (IP) method and the effects of heat treatment methods and post-IP rinsing (prior to heat curing step) on the membrane performances were investigated. Keeping the substrate in minimal heat exposure could prevent substrate pore annealing that potentially reduces the membrane water permeability. Evidently, the membranes with only polyamide (PA) layer being heat-treated exhibited > 250% enhancement in pure water flux (PWF) compared to the membranes where both PA and substrate layer were heat-treated. Also, the membranes rinsed with pure n-hexane tended to display higher PWF without significantly decreasing solute rejection, possibly due to the reduced membrane cross-linking following the removal of unreacted monomers and excess solvent from the membrane surface. The membrane performance became practically the same after post-IP rinsing, regardless of the solvent used in the IP reaction, suggesting that the disparity in the membrane performance is mainly caused by the difference in solvent evaporation rate during heat treatment. The variations in solvent surface tension and viscosity during the IP reaction meanwhile did not play a key role affecting PA layer chemistry and performance.

In this work, ultrafiltration (UF) mixed matrix membranes (MMMs) incorporated with hydrophilic hydrous manganese oxide (HMO) nanoparticles were synthesized and used for the treatment process of a highly concentrated oily solution. The MMMs were fabricated via a phase inversion process and were characterized with respect to physiochemical properties and filtration performances. The results showed that the MMMs demonstrated higher water flux and better oil rejection rates compared to the control membrane (without HMO incorporation) when tested at three different oily solutions with oil concentration in the range of 5000–15?000?ppm. The membrane incorporated with the highest amount of HMO (labelled as MMM-2) in particular showed the best results even when subjected to 15?000?ppm oily solution filtration, recording water flux of 32.2 L/m2?·?h?·?bar and oil rejection of 82?%. The enhanced performance can be attributed to improved surface hydrophilicity coupled with better structural integrity and higher porosity that contributed to lower degree of oil molecules deposition and greater water transport rate. It was also reported that with the use of a feed spacer during the filtration process, the degree of flux deterioration of MMMs could be further reduced without compromising rejection. The findings of this work indicated the potential of MMMs for the treatment of highly concentrated oily effluent produced from industries, by producing permeate of high quality at reasonably good water permeability.

This study explores the potential of novel hybrid polyvinylidene fluoride/titanate nanotube (PVDF-TNT) photocatalytic membranes for the colour removal of aerobically treated palm oil mill effluent (AT-POME) in a submerged membrane photo reactor (SMPR). Different loadings (0–1.0 wt%) of TNT photocatalysts were physically mixed into PVDF dope solution prior to the membrane fabrication through dry/wet phase inversion process. The membranes modules were subsequently fitted into a 15 L SMPR tank, with a UV light source placed at the center of the SMPR. The performance analysis indicated that PVDF-TNT0.5 showed the best colour removal of 67.3%. The synergistic effects rendered by both membrane filtration and photocatalysis have remarkably improved the colour removal efficiency compared to filtration alone that barely exhibited colour removal of 34.2%. The operating conditions of the SMPR, such as initial concentration and pH of the feed AT-POME were also investigated. The photocatalytic activity has greatly reduced the fouling susceptibility of PVDF-TNT membranes, where flux loss of only 5.7% was observed after 5 cycles of usage. With its promising performance in terms of colour removal, flux and low membrane fouling susceptibility, this hybrid SMPR holds great potential to be directly applied in the current POME treatment system to improve the effluent quality and reduce freshwater consumption for palm oil extraction process.

Due to the continuing growth of reverse osmosis (RO) water treatment plants worldwide, the amount of discarded end-of-life (EoL) RO membrane modules is expected to increase drastically in coming years. One of the approaches to address this problem is to transform the EoL membranes for other purposes. In this study, a new approach based on sonication was studied to convert the EoL RO membrane from RO properties into microfiltration (MF) properties, offering a transformation process that was much faster (15 min) than that of typical chemical treatment process (ranging from hours to days) using oxidizing agent solution. Our results indicated that with only 15-min ultrasonication, the properties of EoL RO membrane could be significantly altered, reaching pure water permeability of 172.6 L/m2.h.bar (70-fold increment) with NaCl rejection reduced from ~80% to less than 2%. This is attributed to the deterioration of the polyamide thin selective layer atop the EoL RO membrane. As a comparison, the chemical treatment using 5000-ppm potassium permanganate (KMnO4) solution requires at least 168 h to achieve similar membrane properties. It was also found that the presence of KMnO4 during ultrasonication process could accelerate the rate of polymeric degradation, resulting in even higher pure water permeation. As a conclusion, our work demonstrated a rapid and new approach that is capable of transforming the EoL RO membrane for the filtration process of macromolecules, thus offering a practical solution to address the disposal issues of EoL RO membrane modules.

In this work, the polyethyleneimine (PEI)-interlayered thin film nanocomposite (iTFN) membranes were developed by establishing graphene oxide (GO)-incorporated polyamide (PA) layer atop PEI-coated polysulfone (PSf) substrate for reverse osmosis process. The effects of PEI layer sandwiched between selective layer and substrate were studied by varying several main parameters of the PEI coating process, i.e., PEI concentration (0.005–0.2 wt/v%), drying time (0–120 min), and coating layer number (1–3 layers). The positively charged PEI interlayer was found to alter not only the hydrophilicity and pore structure of the substrate but also improve the orientation and distribution of deposited GO through electrostatic interaction. Synergic effects of GO and PEI, including enhanced substrate surface hydrophilicity and increased amine content, eventually formed a rough but thin PA layer. As a result, almost all iTFN membranes exhibited higher NaCl rejection and water permeability than the control TFN membrane (without PEI intermediate layer). This experiment revealed that PSf substrate modified with a single layer of 0.05 wt/v% PEI followed by 60-min drying yielded the TFN membrane (i.e., iTFN-C0.05-T60-L1) with the best desalination performances (96.66% NaCl rejection and 2.24 L/m2·h·bar). The control TFN membrane meanwhile showed lower performance, i.e., 95.61% NaCl rejection and 1.69 L/m2·h·bar.