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Bisphenol-A (BPA) and caffeine, which classified as endocrine disrupting compounds (EDCs), pose risks the human health and environmental safety through their improper removal and failure of treatment by the conventional water treatment facilities. Although membrane technologies such as reverse osmosis and nanofiltration, have been extensively used to remove EDC from water bodies, it still falls short in several aspects, particularly the water flux-rejection trade off and high membrane fouling tendency. The modification of bioinspired nanomaterials such as liposome is expected to address these issues. The objective of this study is to develop 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) liposomes-coated nanofiltration thin film nanocomposite (NF TFN) membranes and to assess the impact of DOPC liposomes coating on the water permeability and EDCs rejection. DOPC liposomes with different concentrations were coated onto the polyamide thin film composite (PA TFC) membrane. The filtration studies were carried out by using 10 ppm of synthetic BPA and caffeine feed solution to assess the filtration performances of the neat TFC membrane and all DOPC liposomes-coated NF TFN membranes. The results showed that DOPC liposome coating greatly enhanced the membranes’ surface hydrophilicity, as supported by the characterizations. The 0.05TFN membrane, with 0.05 mg/mL of DOPC liposomes coated onto the PA TFC membrane had the greatest water permeability, measuring 6.64 L m−2h−1bar−1, 32% improvement from that of the neat membrane. The 0.05 TFN membrane achieved rejections of 75.5% and 83.5% for BPA and caffeine, accordingly. Additionally, this membrane also demonstrated a high flux recovery ratio (FRR) of 96.53% during BPA filtration while 97.56% for caffeine filtration, suggesting its potential to minimize fouling issue. Through this facile coating, the DOPC liposomes-coated NF TFN membranes enhanced the water permeability without compromising the ability to remove EDCs. Thus, it is concluded that liposomes-modified TFN membranes can serve as an interesting candidate for EDCs treatment.

This work investigated the performances of ZIF-8 membranes coated on a low-cost ceramic hollow fiber (CHF) support developed from quarry dust (QD). The ceramic hollow fiber (CHF) was first fabricated using phase inversion and sintering techniques. The effects of the bore fluid flow rate (6–10 ml·min− 1) and sintering temperature (1050–1150 °C) on the morphology and mechanical strength of the final CHF were systematically evaluated. A larger finger-like macrovoid structure was observed when a longer air gap distance was used. A higher sintering temperature enhances the mechanical properties of CHFs due to pore densification, but it also leads to a less porous CHF, which can affect their permeation flux. The relatively low sintering temperature needed for QD-based CHF (< 1150 °C) leads to a reduction in energy consumption, which is economically attractive for future commercialization. By controlling the ZIF-8 loading (0.4–1.6 wt%) in the coating solution, a uniform and well-coated ZIF-8 selective layer was coated to form a quarry dust ceramic hollow fiber membrane (QD-CHFM). A single gas permeation study was conducted at 2–6 bar, and it was observed that the permeability of gases was greater when the ZIF-8 loading was lower, particularly for CO2(1.19 × 10− 4cm3(STP)·cm·cm− 2·s− 1·cm− 1·Hg− 1). A further increase in the ZIF-8 concentration in the coating solution caused agglomeration, which simultaneously increased the path tortuosity. Therefore, the gas diffusion rate across the membrane decreased. The performances of ZIF-8/QD-CHFM were observed to be similar to those of other ceramic membranes available in the literature. This work indicated that ZIF-8 loading could significantly affect gas separation performance. In addition, reutilizing QDs as a raw material for ceramic membrane fabrication can help reduce disposal issues and reduce the overall cost of ceramic membranes for future development.

The water issue has emerged as a significant concern in the current century, mostly attributed to the exponential rise of the worldwide population and the process of globalization. Nanoscience and nanotechnology have emerged as crucial tools in effectively tackling a diverse array of water pollution challenges through the implementation of innovative and efficacious remedies. There has been a significant amount of attention given to the identification and management of new chemical pollutants in recent times. Consequently, it is desired to have dependable and expeditious analytical instruments that possess the capability to conduct sample analysis with heightened sensitivity, extensive selectivity, desirable durability, and less sample manipulation for the identification, breakdown, and elimination of perilous pollutants. This review examines the several gold–carbon nanocomposites-based systems that have been established to date. This paper examines the chemical functionalization of gold-carbon nanocomposites, focusing on its role in providing stable platforms, enabling different applications, and facilitating effective monitoring of water contaminants. The present study discusses the challenges faced in previous research and the potential future utilization of gold-carbon nanocomposites in prognostic sampling for real-time assessment of water quality. This approach offers a promising avenue for addressing the global water issue.

Recently, a thermally-driven membrane process known as membrane distillation (MD) has emerged as an alternative to the high-pressure membrane process for contaminants removal from water. The driving force for MD is a vapor pressure gradient produced by a temperature differential across a hydrophobic porous membrane, which results in the transfer of water vapor from hot to cold side. However, the feasibility of MD for industry adoption is hampered by several issues such as temperature polarisation effects, low permeate flux, membrane wetting, and fouling. The membrane properties are known to have a significant role in controlling the final performances of MD. This review first looks into the feature of ideal MD membrane properties. Then, the use of graphene-based materials for the development of high performances MD membrane is discussed. Besides enhancing the water permeability and selectivity of MD, the incorporation of graphene offers additional properties such as anti-fouling, antibacterial, and photodegradation. The future direction of using graphene-based photothermal material in MD for heat generation under solar irradiation is also reviewed. It is found that the localised heating at membrane surfaces by photothermal material can minimise temperature polarisation effects and subsequently enhance the driving force for effective vapour transport. Thus, a more energy-efficient MD system can be developed.

In this research, reduced graphene oxide (rGO) and zeolitic imidazole framework-8 (ZIF-8) were used to functionalise molybdenum disulphide (MoS2). They were deposited as a thin-film composite membrane onto alumina support for oily water separation. The functionalisation of MoS2aimed to control fouling activities on the membrane surface and enhance the permeation flux and oil rejection rate. Besides the physicochemical characterisation of MoS2–rGO and MoS2–ZIF-8 powder using FTIR and XRD, the surface morphology of the coated membrane was also investigated using contact angle analysis, mercury intrusion porosimeter, AFM, and FESEM. The impacts of operating parameters such as transmembrane pressure (TMP, 1–2 bar) and oil concentration in the feed water (Coil, 100–1000 ppm) were investigated in terms of permeate flux and oil removal efficiency using a dead-end permeation setup. The MoS2–rGO and MoS2–ZIF-8 deposition significantly increased the properties of the membranes and hold promise for oil/water separation due to the excellent permeation flux and oil rejection rate. A high permeation flux of 102.3 L·m−2·h−1and 92.5% oil rejection were obtained at 2 bar and 100 ppm of feed concentration using MoS2–rGO/alumina membrane. This might be due to its hydrophilic properties and nanoporous multilayer 2D MoS2–rGO structure, which helped increase the permeate transport rate across the membrane and sieved the oil from entering the permeate stream. This work indicates that the coated alumina nanofiltration membrane has a high potential for oily wastewater treatment only if the operating conditions are optimised.

The conventional interfacial polymerization (CIP) technique used for preparing thin-film composite (TFC) nanofiltration membranes typically requires a large amount of monomers during polyamide (PA) synthesis where most of the monomers are discarded after cross-linking. Thus, a new fabrication concept is proposed in this work to synthesize a PA layer via a mist-based interfacial polymerization (MIP) technique where only a small amount of aqueous solution is dispersed as mist. This approach also eliminates the rubber-rolling step in CIP. In addition to forming a thinner and looser PA structure, the piperazine solution required in the IP reaction is significantly reduced, that is, 17 times lower than that of CIP. The microdroplet dispersion approach in MIP could form a higher cross-linked PA due to the high polymerization interface besides forming a higher free-volume selective layer due to the disruption in the PA repeat structure. Our findings revealed that the newly developed mist-based TFC membrane could achieve 9.08 L/m2·h·bar pure water permeability and 97.2% Na2SO4rejection coupled with a complete flux recovery rate. As a comparison, the conventional TFC membrane only attained 2.84 L/m2·h·bar and 95.7%, respectively. The MIP technique could also be potentially considered for developing a nanofiller-incorporated TFC membrane due to the absence of the rubber-rolling step.

Polyamide thin film composite (TFC) membranes have been the gold standard of various industrial water and wastewater treatments since the 1980 s. The excellent performance compared to the asymmetric membranes is due to its extremely thin cross-linked selective layer formed over a microporous substrate. Over the past decade, commercial TFC membranes have substantially advanced, e.g., water flux improvement without compromising salt rejection, enhanced anti-scaling resistance and greater boron rejection during desalination. Findings from numerous research studies indicate that the performance of TFC membranes could be further enhanced via the incorporation of 2D graphene oxide (GO) into the membrane matrix. Different strategies have been developed to address the inherent limitations of both selective and substrate layers of the membrane, promising to further augment membrane surface characteristics and thereby treatment efficiencies. Given the importance of TFC membranes for water/wastewater treatment, this article aims to provide a state-of-the-art review on the development of GO-incorporated polyamide TFC membranes, with an emphasis on the incorporation techniques of GO, and the corresponding roles in improving the properties of the selective and substrate layers. This review offers guidance in designing TFC membranes embedded with GO for higher performance.

Thin film composite (TFC) membrane performance is often restricted by permeability and selectivity trade-off effect, even with the modification of nanoparticles. Graphene oxide-poly(2-(dimethylamino)ethyl methacrylate) (GO-PDMAEMA) with brush structure has abundant hydrophilic oxygen-containing functional groups and amine groups. It was synthesized via the atom transfer radical polymerization method and incorporated into TFC polyamide layer using interfacial polymerization. The GO-PDMAEMA-modified thin film nanocomposite membranes (TFNG-P) with Turing structure and higher surface hydrophilicity enhanced water permeability by 40.7–55%, with relatively low nanoparticle loading (0.005–0.02 wt%). Besides, TFNG-P2 (0.01 wt% GO-PDMAEMA) has the highest Na2SO4rejection (97.8%), 4.4% higher than TFC. The PDMAEMA brushes on GO with additional amine groups promoted the amide linkage and increased the PA layer cross-linking by 16.2%. The higher cross-linking did not negatively affect the membrane flux, as the better hydrophilicity offset this effect. The utilization of the modified membranes in the treatment of palm oil mill effluent demonstrated enhanced resistance to fouling with TFNG-P2, which exhibited the highest flux recovery rate, reaching 89.4%. Thus, this study showed GO modification by grafting PDMAEMA brushes had enhanced the membrane properties, resulting in TFNG-P with higher permeability, promising separation and antifouling performance.

Physical damage on the membrane is the common issues that cause the loss of membrane performance. Pinpointing the precise damage location is almost impossible, sparking increased interest among researchers to tackle this demanding task. Polyelectrolytes polyethyleneimine (PEI) and poly(acrylic acid) (PAA) have demonstrated successful healing ability in various applications, but their healing ability in membrane technology is still unclear. Herein, this research fabricates a water-responsive self-healing membrane by modifying polyethersulfone (PES) substrate surface using PEI and PAA via layer-by-layer (LbL) method. Surface functional groups, morphology analysis and elemental compositions of the fabricated membrane were examined. From the results, the best-performing membrane exhibited its highest self-healing effectiveness at 75.9% based on pure water flux (PWF) when employing a concentration of 5.0mg/mL of PEI and PAA solutions, with a ratio of 1:1 in a single-bilayer configuration. Besides, the tartrazine rejection of the healed membrane at the aforementioned configuration successfully improved by 95.6% compared to the pristine PES membrane. These findings revealed the capability of PEI and PAA as potential healing agents in membrane technology for water filtration. However, further studies are suggested to improve the membrane performance and self-healing efficiency of the fabricated membrane by investigating various modifications.

Polymeric membranes were initially introduced for commercial water treatment applications in the 1960s. Over the years, membrane manufacturers and scientists have made significant strides in enhancing these membranes, focusing on improving water permeance (while maintaining solute rejection) and increasing resistance to both organic and inorganic fouling. These advancements have produced more efficient membranes with reduced system footprints for water treatment processes. However, the demands of harsh filtration environments, including extreme pH conditions, elevated temperatures, high operating pressures and the presence of oxidative agents, have necessitated further improvements in membrane technology. In this paper, we embark on a comprehensive review of the advancements achieved in various types of polymeric membranes customized for use in these demanding environments. Our exploration of research efforts aimed at enhancing membrane properties for water filtration in challenging conditions can be broadly categorized into four primary areas, i.e., chlorine/oxidative resistance, acid/alkali stability, thermal resistance and compaction resistance. To facilitate a comprehensive understanding of these advancements, we categorize the strategies employed by researchers into several methods, i.e., surface modification of asymmetric membranes, bulk modification of asymmetric membranes (a.k.a.mixed matrix membrane) and surface modification of polyimide thin film composite membranes. By thoroughly reviewing the progress and strategies in these areas, this article aims to offer valuable insights into developing polymeric membranes with enhanced properties for challenging environments in water filtration applications.

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Loose nanofiltration membranes (LNMs) have attracted increasing attention due to their applications in sustainable management of high salinity textile wastewater. Remained challenges include achieving efficient dye/salt fractionation and mitigating high biofouling tendencies. In this work, Ag-loaded UiO-66-NH2(Ag@UiO-66-NH2) nanoparticles were prepared by a simple method of stirring, and subsequently used to blend with cellulose acetoacetate (CAA) to obtain antibacterial Ag@UiO-66-NH2@CAA (MOF@CAA) LNMs. Water contact angle (WCA), scanning electron microscopy (SEM), and X-ray photoelectron spectrometer (XPS) were used to characterize the MOF@CAA membranes. In addition, the antibacterial properties, pure water flux and dye/salt fractionation properties of the membrane were studied in detail. MOF@CAA LNMs has a porous surface and a sponge-like cross-sectional structure. The membrane has a reasonable water permeability (65.3 L/m2h), a rejection of 99.2 % for Congo red (CR) and almost zero rejection to inorganic salts (CR concentration: 100 mg/L, inorganic salts concentration: 1000 mg/L, operating pressure: 0.2 MPa). In addition, the MOF@CAA LNMs reduced 99.70 % of E. coli and 99.69 % of S. aureus in the bacterial suspensions. It is also found that the release of Ag+ion from the MOF@CAA LNMs is stably maintained at 0.1 μg L−1day−1for a period of 30 days. As the Ag nanoparticals (NPs) presented in the membrane were stably wrapped in UiO-66-NH2, its release could be maintained at a very slow rate continuously to achieve the purpose of controlled release and long-term sterilization.

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 NFand 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−1and 96.5% rejection against 10 mg·L−1phosphorus solution with a pH value of 13.5 at the applied pressure of 1 MPa.

Researchers worldwide have extensively studied metal organic framework (MOF) for its adsorption capabilities. Despite its potential, challenges such as particle agglomeration, low porosity and low surface area persist. This study aims to enhance the performance of MIL-100(Fe) for As(V) adsorption using a feasible and straightforward technique. To achieve this, benzoic acid was introduced as a modulator for ligand exchange, creating vacancy defects within the MIL-100(Fe) structure, resulting in defective MIL-100(Fe)-BA1. Through TEM imaging, visible deformations were observed on the surface of the adsorbent, with an average particle size of approximately 200 nm. XRD spectrum analysis revealed a reduction in peak intensity at 2–5°, indicating reduced crystallinity in the MIL-100(Fe) due to the presence of defects. Meanwhile, BET analysis demonstrated a significantly larger surface area for defective MIL-100(Fe) at 1081.09 m2/g, compared to the pristine MIL-100(Fe) with a surface area of 844.00 m2/g. Regarding adsorptive performance, the defective MIL-100(Fe) exhibited higher As(V) adsorption capacity (173.82 mg/g at pH8) than the pristine form (70 mg/g). This improvement can be attributed to the larger pore size of the particles and the exceptional affinity of As(V) anions towards the bulk Lewis Acid sites present on the surface of defective MIL-100(Fe). However, it is important to note that for effective As(V) adsorption by defective MIL-100(Fe)-BA1, it is crucial to eliminate competing compounds such as carbonate and phosphate anions from the water sources. Addressing these challenges will further enhance the efficacy of the adsorption process

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.

•The preparation and characterization of graphene oxide- magnetic iron oxide nanoparticles (GO-MNP) have been outlined.•The use of GO-MNP as high efficient adsorbent for removal of methylene blue dye from polluted water.•Adsorption kinetics and equilibrium isotherm models for MB dye were reviewed.

In this work, the surface of a PVDF-based hollow fiber membrane was modified by coating MoS2-TiO2to improve the performance of membrane distillation (MD). The MoS2-TiO2was first synthesized at different ratios using a one-step hydrothermal process. Then, the PVDF-based hollow fiber membrane was spun at various air gaps and PES was also added as an additive. As 5M5T (50 wt% MoS2and 50 wt% TiO2) possessed better physicochemical properties and narrow band gap, the 5M5T was mixed with trichloro(octadecyl)silane in (OTS) at various loading to form a dip-coating solution. The PP20 membrane (PVDF + PES) spun at a 20 cm air gap was used as a support for MD due to its high porosity and low membrane thickness. It was observed that the contact angle of the MoS2-TiO2/PP20 membrane increased significantly to 136.8 ± 2.33° when the membrane was coated with 0.2% of 5M5T MoS2-TiO2. The MD performances were investigated via an in-house MD system. The results revealed that the performances of MoS2-TiO2/PP20 membranes were much higher than previously reported membranes due to their enhanced hydrophobicity and porosity properties. It was observed that a higher operating temperature could elevate the permeate flux up to 23.3 kg·m−2·h−1,but less than 0.1% changes in the rejection rate. The results obtained in this work suggest that the MoS2-TiO2coated on the PVDF-based membrane can overcomes the typical permeability/rejection rate trade-off effect, which can play a significant role in enhancing MD performances.

Hexavalent chromium, Cr(VI), is considered hazardous heavy metal in water bodies that can cause severe effects on human health and the environment. Over the years, myriad attention has been focused on developing photocatalysts to remove Cr(VI) from wastewater. However, broad bandgap energy and the high electron recombination rate of these conventional photocatalysts have limited their photocatalytic ability. Therefore, efficient photocatalytic materials for Cr(VI) removal in wastewater is strongly demanded. In this study, delaminated MXene was successfully synthesised and used to remove Cr(IV) from the aqueous solution. The synthesised delaminated MXene was characterised using XRD, EDX, FTIR, FESEM, nitrogen adsorption-desorption analysis, TGA, UV-Vis-NIR spectroscopy and XPS. Based on the results, the optimum operating conditions for Cr(VI) removal by the synthesised MXene was obtained at pH 4 with photocatalyst loading of 1.5 g/L and Cr(VI) initial concentration of 5 mg/L. The removal efficiency of Cr(VI) via adsorption-assisted photocatalysis over various concentrations was around 3.1–28.9% higher than adsorption, verifying a synergistic effect of adsorption and photocatalysis by the delaminated MXene. The isotherm of Cr(VI) adsorption was fitted by the Langmuir model (R2> 0.9848) and was found better than the Freundlich model (R2> 0.8824). Meanwhile, the time dependence of Cr(VI) adsorption was well fitted to the pseudo-second-order kinetic model with R2> 0.9999. In conclusion, the results obtained suggest that the delaminated MXene possesses excellent properties and the ability to remove Cr(VI) via adsorption-assisted photocatalysis and has great potential to be used for industrial wastewater applications.

The oxygen air production are generally be achieved by pressure swing adsorption (PSA) and cryogenic distillation. Both of the techniques are able to produce high purity oxygen level which is more than 95% with a production volume of 20 – 300 tons per day. These techniques however required high energy consumption and with the rising cost of energy, membrane separation is a good option as it require relatively low energy requirement. Membrane separation technique is an emerging technique which garners the interest from academia and industry from last decade as an alternative method to produce oxygen enriched air. To date, the commercially available and research institution self-fabricated polymeric membrane are unable to produce an economically viable membrane with high permeability and selectivity in a large scale production relative to the conventional method. In this works, the progress of the application of polymeric in O2/N2 separation which including the recent developed of self fabricated polymeric membrane and the aspect of operation parameter is discussed. Finally, the paper also intends to present a brief overview of the development of membrane separation technique in O2/N2 separation in addressing the strategies and improvement in the fulfillment of industrial application interest.

Membrane distillation (MD) is a membrane separation process first introduced in 1963 by Bodell whereby the major driving force is by vapor pressure difference between the feed and permeate induced by temperature gradient. The MD applications mainly focus on seawater desalination and other industry application such as extraction of fruit juice. In this study, hydrophobic polyvinylidene fluoride (PVDF) hollow fiber membranes were fabricated by wet/dry phase inversion method with 1-methyl-2-pyrrolidone (NMP) as solvents and ethylene glycol (EG) as non solvent additives. The effect of the additives on the membrane formation was studied based on the results from membrane morphology investigation through scanning electron microscope (SEM) and porosity calculation based on gravitational method. The SEM image indicated the membrane morphology changed from finger like layer extending from inner to outer surface to a finger like layer separated by microvoid attributed addition of ethylene glycol which might lead to permeate flux enhancement. Furthers, results from the gravitational test reveal that the addition of ethylene glycol demonstrated a positive effect on the porosity of the membrane. Later, the membranes were tested by membrane distillation process in sodium chloride removal varying feed inlet temperature to investigate the permeate flux performance of the membrane.

Titanium dioxide nanofibers with diameter ranging to several nanometers were synthesized via electrospinning technique. The precursor solution was prepared by mixing the polyvinylpyrrolidone, PVP (MW~1,300,000) in ethanol, meanwhile titanium tetraisopropoxide, TTIP in acetic acid was slowly added into the solution under a vigorous stirring. The precursor solutions were then used in the electrospinning process under high voltage supply. As-spun nanofibers were heat-treated under different temperature 400°C and 500°C. The TiO2 nanofibers were characterized by using scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) and X-ray diffraction (XRD). The results indicated that the heat treated TiO2 nanofibers consist of anatase and rutile phases. As the calcination temperature increased (400-500°C), the anatase phases are greater than rutile phase and specific surface area are decreases while the calcination process influenced the nanofibers diameter.

AbstractPoly(piperazine-amide) thin film composite (TFC) nanofiltration (NF) membranes were prepared via interfacial polymerization (IP) of trimesoyl chloride (TMC) in cyclohexane and piperazine (PIP) in water. The effect of polymerization time on the physicochemical characteristics of poly(piperazine-amide) layers and the final membrane performance was studied in detail. The morphological structures of prepared membranes were investigated using atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), by contrast, was used to determine the chemical characteristics of the membranes. It is evident that the surface roughness increased with increasing polymerization time due to the formation of a supergranule-like structure over the interfacially synthesized poly(piperazine-amide) layer. Moreover, increasing the polymerization time led to a dramatic reduction of water permeability due to the significant increase of crosslinking poly(piperazine-amide) barrier layers. Experimentally determined data showed that the TFC NF membrane prepared at 10 s of polymerization time experienced 51.2 l/m2.h of water permeability with 97.02% of Na2SO4salt rejection at an operating pressure of 0.6 MPa.

The discharge of pharmaceutical wastewater is an adversity to the nature. Some of the pharmaceutical product (PP) wastes are highly resistant towards bio-degradation hence physical-based separation technology such as forward osmosis (FO) has been introduced for the treatment. Despite exhibiting high water flux, commercial FO membrane often suffers from fouling and unsatisfactory solute rejection. In this study, carbon nanotubes (CNT) which has high self-bundling tendency was functionalized with tert-butylamine (TBA), a bulky tertiary amine. The agglomeration of the aminated CNT was suppressed via steric hindrance and surface charge repulsion. The nanofillers was then incorporated into the polyamide (PA) layer of thin film nanocomposite (TFN) during interfacial polymerization process to provide the required hydrophilicity and surface charges. Using synthetic paracetamol (PCT) solution as the feed solution (FS), the experimental outcome showed that the incorporation of amino-functionalized CNT (ACNT) successfully enhanced the hydrophilicity and flux stability of the FO membranes. Compared to the control thin film composite (TFC) membrane, ACNT-TFN membrane exhibited an improved water flux from 3.58 L.m−2.h−1to 9.01 L.m−2.h−1, without sacrificing the PCT rejection (99.7 %). This study improves the understanding on the superior benefits of FO for enhancing the pharmaceutical waste removal and stimulates insight for more nanofillers-induced modification on the FO membrane, in order to make it truly useful for more water separation applications in the future.

Membrane contactor as a high-performance and cost-effective separation technology has attracted considerable attentions for environmental protection. It offers promising advantages as it can combine with absorption, desorption, extraction and even distillation in one equipment. In this article, the membrane contactor processes are briefly introduced followed by comprehensive review on the latest progresses for environmental applications. Greenhouse gas capture by membrane gas absorption and the membrane development are critically reviewed. In addition, water and wastewater treatments through various membrane contactor processes are discussed for applications such as oil and dye removal, heavy metal ions and radioactive materials separation, ammonia recovery as well as degasification. This article also highlights the current status and future direction of the technology to provide indications for industrial implementation. Although there are not many pilot/full-scale plants using membrane contactor technology in operation, an increasing interest is expected in near future due to strong potential of the technology for environmental applications.

This study aimed at evaluating the concomitant electrochemical reduction and separation of organic and inorganic model contaminants from water. A highly conductive (40,000 S/m) support free carbon nanotube (CNT) membrane was used as a cathode in a three-electrode electrochemical crossflow membrane filtration system. Diatrizoate (DTZ), a recalcitrant iodinated contrast media; resazurin (RZ), a redox indicator; and hexavalent chromium ion (Cr(VI)), a ‘gold’ standard for characterization of reducing systems, were tested as model contaminants. Voltages of −0.6 to −1.0 V were enough to remove between 90% and 95% of the three model contaminants tested. Removal of Cr(VI) proceeded by reduction to Cr(III) followed by adsorption onto the cathode, which could be efficiently regenerated (up to 95%) applying reversal (anodic) potential. Preliminary findings applying AC current (0.6–1.5 V, 10 Hz-1 kHz) suggest that it could be a feasible approach for detoxification with minimization of membrane clogging. Resazurin was immediately transformed into resorufin to near completion which was in turn further reduced to dihydroresorufin. The reductive transformation of DTZ resulted in almost complete deiodination, leading to the accumulation of 3,5-diacetamidobenzoic acid as the main end-product. Although other five secondary transformation products were detected, four of them were fully deiodinated. Concluding, the proposed electrochemical filtration cell equipped with a highly conductive CNT-cathodic membrane can be regarded as a potential technique for water decontamination and effective dehalogenation of organic compounds.

In recent years, the amount of agricultural and industrial wastes being generated is increasing rapidly. This leads to numerous disposals, governance, and environmental issues. Therefore, the re-utilisation of these wastes into value-added products such as mesoporous silica nanoparticles (MSNs) has attracted great attention. MSNs have garnered immense attention in various applications owing to their tuneable pore dimensions, high surface areas, and tailorable structure, suitable for different post-functionalisation. In this review, recent progress on the synthesis of MSNs from waste using a chemical synthesis route is presented. This route offers the possibility to control silica structure, phase, morphology, and sizes by fine tuning the reaction parameters/conditions. The characteristics and applications of the MSNs produced are also analysed to examine the potential of using agricultural and industrial waste as the silica precursor. Although the use of inexpensive waste-derived materials seems promising for both waste reduction and value-added products synthesis, further research is still needed to boost the production of silica especially at a larger scale.

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 ~106° to 120–135°) 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.

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 KMnO4during 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.

The polyamide layer of reverse osmosis (RO) membrane is susceptible to chlorination degradation. Guidelines for validation and integrity monitoring of the low pressure RO (LERO) membrane morphology and performance upon chlorination is still rarely reported. In this study, we selected three commercial LERO membranes (i.e., LP, ULP and LCLE) to study their structure and separation performance change for exposing to chlorine under both pressurized and static chlorination conditions, with different active chlorine concentrations and pH. At the pressurized testing, the membrane water flux increased at the initial stage due to the decrease of water passage restriction by the destroy of the hydrogen bond in the polyamide, and then the water flux sharply decreased and gradually leveled off, which should be resulted from the destroy of chemical structure of polyamide and membrane compaction under high pressure. The salt rejection slightly changed, presumably due to the combination of tightening effect, compactness and defect plugging by foulants. As for the static chlorination test, active chlorine concentration and chlorination time were not unequivocalness at the same chlorination intensity. Higher active chlorine concentration could cause more serious chlorination degradation. Based on the water flux change at neutral pH and under static chlorination conditions, a flux reduction equation with active chlorine concentration was fitted by y = axb(1＜x＜1000), which could help us to predict the water flux under a specific chlorine concentration and time.

Photocatalytic dual layer hollow fiber membrane (DLHFM) is advantageous over its single layer counterpart due to a better photocatalyst dispersion on the outer layer to maximize the potential of the photocatalyst in improving the overall membrane performance. In this study, a polyvinylidene fluoride (PVDF) dual-layer hollow fiber membrane with antibiofouling properties was successfully synthesized via dry-wet spinning phase inversion method, where the Ag-TNT was incorporated onto the outer layer membrane for photocatalytic degradation of AT-POME pigments in a submerged membrane photoreactor (SMPR). The results revealed that the incorporation of Ag-TNT into the PVDF matrix increased pure water flux from 16.20 L/m2h for pristine PVDF membrane to 37.12 L/m2h. The synergistic advantages of photocatalysis and membrane filtration was exhibited by the photocatalytic Ag-TNT membrane which showed the highest AT-POME color removal efficiency of 84.0% compared to the other membranes prepared in this work. With the presence of silver nanoparticles, the modified membrane exhibited antibacterial efficiency of 95.8% with a 1.73 mm inhibition zone around the membrane against P. aeruginosa.Based on the results obtained, the photocatalytic PVDF Ag-TNT membrane showed immense potential as an innovative technology for water reclamation in the palm oil industry.

In this work, an environmentally friendly plasma enhanced chemical vapor deposition (PECVD) technique was employed to rapidly alter the surface properties of commercial thin film composite extra-low energy (XLE) reverse osmosis (RO) membrane to improve its fouling resistance and desalination performance. Hereafter, two different hydrophilic precursors, i.e., aniline monomer and oxygen (O2) gas were respectively introduced to the membrane’s polyamide surface at different plasma treatment duration (15 s and 60 s). At 15-s plasma treatment, our results revealed that the O2-modified membrane outperformed the polyaniline (PANI)-modified membrane and unmodified membrane, attributed to the polar functional groups presented on the polyamide surface. Compared to plasma polymerization of aniline, O2plasma etching can lower polyamide densification degree which potentially reduce membrane resistance. Evidently, the O2-modified membrane exhibited higher pure water permeability (6.64 L/m2.h.bar) compared to the PANI-modified membrane (5.57 L/m2.h.bar). The enhanced surface hydrophilicity of O2-modified membrane could be noticed when its water contact angle was reduced from 88.39⁰(unmodified) to 79.46⁰ in just 15-s plasma treatment. Furthermore, this O2-modified membrane achieved an outstanding NaCl and Na2SO4rejection with an increment of 4.2% and 2.6%, respectively compared to the unmodified membrane. However, prolonged gas plasma treatment (60 s) should be avoided as it can damage polyamide selective layer. With respect to fouling resistance, the best O2-modified membrane demonstrated higher flux recovery rate (96%) than that of unmodified membrane (76.5%) after being used to filter 1000-ppm sodium alginate solution. These results highlighted the versatility of O2plasma treatment to improve RO membrane performance.

A sketch showing the cross-flow UF arrangements (the colours have no significance).

In forward osmosis (FO) process, reverse solute flux (RSF) is considered as a major disadvantage that limits the potential of FO. In this study, an innovative approach to reduce RSF was developed by introducing complexing agent into draw solution (DS) containing magnesium chloride (MgCl2). A water-soluble complexing agent namely poly(sodium 4-styrenesulfonate) (PSS) was chosen for this study and its affinity towards complexation with MgCl2was investigated in terms of its loadings (0.1–5.0 w/w%) and pH condition (3.0, 5.0, 7.0 and 9.0). It was found out that the addition of PSS was able to reduce the effect of RSF due to its complexation with MgCl2which enhanced the molecular weight and inhibited the movement of MgCl2across thin film composite (TFC) membrane. Under pH studies, it is demonstrated that the optimum DS condition for complexation affinity was at none-adjusted pH. Compared to RSF value without the PSS addition, reduced RSF value (0.3 g/m2.h) was achieved at 1.0 w/w% PSS. When copper(II) sulphate was used as feed solution, the rejection was maintained at an average value of 95%. Based on these findings, this study promotes the feasibility of polymer-complex DS to be used in FO process for heavy metals removal.

Membrane surface scaling is a major challenge in reverse osmosis (RO) desalination process that could irreversibly deteriorate the membrane filtration efficiency. In this study, a hydrophilic coating layer was introduced onto the polyamide (PA) layer of self-developed thin film nanocomposite (TFN) membrane via plasma enhanced chemical vapour deposition (PECVD) technique to increase the membrane surface energy barrier and hydrophilicity towards silica heterogeneous nucleation. The results revealed that the acrylic acid-coated TFN membrane (AA-TFN) exhibited excellent resistance against silica scaling after subjected to saturated silica concentration (168 ppm at pH 6.7), with much higher flux recovery rate (FRR) (88%) compared to the uncoated TFN (75.5%) and conventional thin film composite (TFC) (72%) membranes. This is attributed to its enhanced surface hydrophilicity (contact angle of 26°) and better surface charge (zeta potential of –47mV at pH 6.7) upon the hydrophilic coating layer deposition which retards the scale deposition. The membrane scaling can be further reduced by increasing the feed pH and at the optimized condition (pH 10), the FRR of coated TFN membrane could reach up to 98.3%, owing to the increased silica solubility at alkaline condition which minimizes the silica aggregation formation on the membrane surface. Our work demonstrated that surface modification of composite membrane using suitable materials and proper feed pH adjustment could offer a great promise in mitigating the scaling for desalination applications. The findings also provide fundamental insights on the importance of membrane surface properties during silica scaling formation.