Progress and perspectives for synthesis of sustainable antifouling composite membranes containing in situ generated nanoparticles

Integrated In Situ Fabrication of CuO Nanorod-Decorated Polymer Membranes for the Catalytic Flow-Through Reduction of p-Nitrophenol

We developed a novel method to fabricate copper nanorods in situ in a poly(ether sulfone) (15 wt %) casting solution by a sonochemical reduction of Cu2+ ions with NaBH4. The main twist is the addition of ethanol to remove excess NaBH4 through Cu(0) catalyzed ethanolysis. This enabled the direct use of the resulting copper-containing casting dispersions for membrane preparation by liquid nonsolvent-induced phase separation and led to full utilization of the copper source, generating zero metal waste. We characterized the copper nanorods as presented in the membranes via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV/vis spectroscopy. We could demonstrate that the rapid immobilization from reducing conditions led to the membrane incorporation of copper nanorods in a state of high reactivity, which also promoted the complete oxidation to CuO after fabrication. We further observed a large aspect ratio and crystal straining of the nanorods, likely resulting from growth around the matrix polymer. The entanglement with poly(ether sulfone) further facilitated a selective presentation at the pore surface of the final CuO-decorated membranes. The membranes also exhibit high water permeances of up to 2800 L/m2hbar. Our catalytic membranes achieved exceptionally high activities in the aqueous flow-through reduction of p-nitrophenol (p-NP), with turnover frequencies of up to 115 h-1, even surpassing those of other state-of-the-art catalytic membranes that incorporate Pd or Ag. Additionally, we demonstrated that catalytic hydrolysis of the reducing agent in water can lead to hydrogen gas formation and blocking of active sites during continuous catalytic p-NP hydrogenation. We illustrated that the accompanying conversion loss can be mitigated by facilitated gas transport in the water-filled pores, which is dependent on the orientation of the pore size gradient and the flow direction.

A PEGylated PVDF Antifouling Membrane Prepared by Grafting of Methoxypolyethylene Glycol Acrylate in Gama-Irradiated Homogeneous Solution

In this study, methoxypolyethylene glycol acrylate (mPEGA) served as a PEGylated monomer and was grafted onto polyvinylidene fluoride (PVDF) through homogeneous solution gamma irradiation. The grafting process was confirmed using several techniques, including infrared spectroscopy (FTIR), thermodynamic stability assessments, and rotational viscosity measurements. The degree of grafting (DG) was determined via the gravimetric method. By varying the monomer concentration, a range of DGs was achieved in the PVDF-g-mPEGA copolymers. Investigations into water contact angles and scanning electron microscopy (SEM) images indicated a direct correlation between increased hydrophilicity, membrane porosity, and higher DG levels in the PVDF-g-mPEGA membrane. Filtration tests demonstrated that enhanced DGs resulted in more permeable PVDF-g-mPEGA membranes, eliminating the need for pore-forming agents. Antifouling tests revealed that membranes with a lower DG maintained a high flux recovery rate, indicating that the innate properties of PVDF could be largely preserved.

Enhancing the water permeability of composite NF membranes through the incorporation of organic ions in the aqueous phase

Composite nanofiltration (NF) membranes prepared using interfacial polymerization (IP) have gained significant attention in the field of wastewater treatment. In this study, sodium camphor sulfonate (CSA-Na) and tetraethylammonium chloride (TEAC) were employed as aqueous phase additives to regulate the diffusion of piperazine (PIP) molecules through electrostatic interactions. The dissociated CSA-Na and TEAC in the aqueous solution formed an organic structure at a certain concentration, restricting the interfacial transport behavior of PIP monomers. The results show that when the content of CSA-Na is 2% w/v, TEAC is 3.9% w/v, that is, the material dosage ratio is 1 : 3, and the NF membrane shows the best performance, with a water flux of 55.61 L m-2 h-1 (test pressure is 0.5 MPa), and MgSO4 rejection rate of more than 98%.

Reactive membranes for groundwater remediation of chlorinated aliphatic hydrocarbons: competitive dechlorination and cost aspects

A nanocomposite membrane incorporating reactive Pd-Fe nanoparticles (NPs) was developed to remediate chlorinated aliphatic hydrocarbons (CAHs) from groundwater. Other than recapturing the produced Fen+ for in-situ regeneration, the functionalized polyanions prevented NPs agglomeration and resulting in a spherical Fe0 core (55 nm, O/Fe = 0.05) and an oxidized shell (4 nm, O/Fe = 1.38). The reactive membranes degraded 92% of target CAHs with a residence time of 1.7 seconds. After long-term treatment and regeneration, reusability was confirmed through recovered reactivity, recurrence of Fe0 in X-ray photoelectron spectroscopy, and >96% remaining of Fe and Pd. The total cost (adjusted present value for 20 years) was estimated to be 13.9% lower than the granular activated carbon system, following an EPA work breakdown structure-based cost model. However, non-target CAHs from groundwater can compete for active sites, leading to decreased surface-area normalized dechlorination rate ( k sa ) by 28.2-79.9%. A hybrid nanofiltration (NF)/reactive membrane was proposed to selectively intercept larger competitors, leading to 54% increased dechlorination efficiency and 1.3 to 1.9-fold enlarged k sa . Overall, the practical viability of the developed reactive membranes was demonstrated by the stability, reusability, and cost advantages, while the optional NF strategy could alleviate competitive degradation towards complex water chemistry.

Closed-loop recyclable membranes enabled by covalent adaptable networks for water purification

In the state-of-the-art membrane industry, membranes have linear life cycles and are commonly disposed of by landfill or incineration, sacrificing their sustainability. To date, little or no thought is given in the design phase to the end-of-life management of membranes. For the first time, we have innovated high-performance sustainable membranes, which can be closed-loop recycled after long-term usage for water purification. By synergizing membrane technology and dynamic covalent chemistry, covalent adaptable networks (CANs) with thermally reversible Diels-Alder (DA) adducts were synthesized and employed to fabricate integrally skinned asymmetric membranes via the nonsolvent-induced phase separation technique. Due to the stable and reversible features of CAN, the closed-loop recyclable membranes exhibit excellent mechanical properties and thermal and chemical stabilities as well as separation performance, which are comparable to or even higher than the state-of-the-art nonrecyclable membranes. Moreover, the used membranes can be closed-loop recycled with consistent properties and separation performance by depolymerization to remove contaminants, followed by refabrication into new membranes through the dissociation and reformation of DA adducts. This study may fill in the gaps in closed-loop recycling of membranes and inspire the advancement of sustainable membranes for a green membrane industry.

Recent Advances on the Fabrication of Antifouling Phase-Inversion Membranes by Physical Blending Modification Method

Membrane technology is an essential tool for water treatment and biomedical applications. Despite their extensive use in these fields, polymeric-based membranes still face several challenges, including instability, low mechanical strength, and propensity to fouling. The latter point has attracted the attention of numerous teams worldwide developing antifouling materials for membranes and interfaces. A convenient method to prepare antifouling membranes is via physical blending (or simply blending), which is a one-step method that consists of mixing the main matrix polymer and the antifouling material prior to casting and film formation by a phase inversion process. This review focuses on the recent development (past 10 years) of antifouling membranes via this method and uses different phase-inversion processes including liquid-induced phase separation, vapor induced phase separation, and thermally induced phase separation. Antifouling materials used in these recent studies including polymers, metals, ceramics, and carbon-based and porous nanomaterials are also surveyed. Furthermore, the assessment of antifouling properties and performances are extensively summarized. Finally, we conclude this review with a list of technical and scientific challenges that still need to be overcome to improve the functional properties and widen the range of applications of antifouling membranes prepared by blending modification.

Next-generation graphene oxide additives composite membranes for emerging organic micropollutants removal: Separation, adsorption and degradation

In the past two decades, membrane technology has attracted considerable interest as a viable and promising method for water purification. Emerging organic micropollutants (EOMPs) in wastewater have trace, persistent, highly variable quantities and types, develop hazardous intermediates and are diffusible. These primary issues affect EOMPs polluted wastewater on an industrial scale differently than in a lab, challenging membranes-based EOMP removal. Graphene oxide (GO) promises state-of-the-art membrane synthesis technologies and use in EOMPs removal systems due to its superior physicochemical, mechanical, and electrical qualities and high oxygen content. This critical review highlights the recent advancements in the synthesis of next-generation GO membranes with diverse membrane substrates such as ceramic, polyethersulfone (PES), and polyvinylidene fluoride (PVDF). The EOMPs removal efficiencies of GO membranes in filtration, adsorption (incorporated with metal, nanomaterial in biodegradable polymer and biomimetic membranes), and degradation (in catalytic, photo-Fenton, photocatalytic and electrocatalytic membranes) and corresponding removal mechanisms of different EOMPs are also depicted. GO-assisted water treatment strategies were further assessed by various influencing factors, including applied water flow mode and membrane properties (e.g., permeability, hydrophily, mechanical stability, and fouling). GO additive membranes showed better permeability, hydrophilicity, high water flux, and fouling resistance than pristine membranes. Likewise, degradation combined with filtration is two times more effective than alone, while crossflow mode improves the photocatalytic degradation performance of the system. GO integration in polymer membranes enhances their stability, facilitates photocatalytic processes, and gravity-driven GO membranes enable filtration of pollutants at low pressure, making membrane filtration more inexpensive. However, simultaneous removal of multiple contaminants with contrasting characteristics and variable efficiencies in different systems demands further optimization in GO-mediated membranes. This review concludes with identifying future critical research directions to promote research for determining the GO-assisted OMPs removal membrane technology nexus and maximizing this technique for industrial application.

Recent Advances in Responsive Membrane Functionalization Approaches and Applications

In recent years, significant advances have been made in the field of functionalized membranes. With the functionalization using various materials, such as polymers and enzymes, membranes can exhibit property changes in response to an environmental stimulation, such as heat, light, ionic strength, or pH. The resulting responsive nature allows for an increased breadth of membrane uses, due to the developed functionalization properties, such as smart-gating filtration for size-selective water contaminant removal, self-cleaning antifouling surfaces, increased scalability options, and highly sensitive molecular detection. In this review, new advances in both fabrication and applications of functionalized membranes are reported and summarized, including temperature-responsive, pH-responsive, light-responsive, enzyme-functionalized, and two-dimensional material-functionalized membranes. Specific emphasis was given to the most recent technological improvements, current limitations, advances in characterization techniques, and future directions for the field of functionalized membranes.

A passive-active combined strategy for ultrafiltration membrane fouling control in continuous oily wastewater purification

Membrane-based technology has been confirmed as an effective way to treat emulsified oily wastewater, however, membrane fouling is still one of practical challenges in long-term operation. Herein, a novel passive-active combined strategy was proposed to control membrane fouling in continuous oily wastewater purification, where the δ-MnO₂ decoration layer helped to reduce the total fouling ratio (passive strategy for fouling mitigation) and the catalytic cleaning effectively removed the irreversible oil fouling (active strategy for fouling removal). The functional membrane was prepared via in-situ modification, referred to as δ-MnO₂@TA-PES. The morphology, crystalline phase, chemical structure and surface properties of the membranes were systematically characterized. Compared with PES, the δ-MnO₂@TA-PES possessed superhydrophilicity, enhanced electronegativity and narrowed pore size. The δ-MnO₂@TA-PES achieved high water permeation flux of 723.9 L·m ^- 2·h ^- 1·bar^-1, excellent oil rejection with separation efficiency above 98.5% for various emulsions, and durable anti-oil-fouling performance with FRR_b of 98.0%. Notably, the oil cake layer fouling on δ-MnO₂@TA-PES was greatly alleviated owing to its enhanced surface properties. In addition, δ-MnO₂@TA-PES showed high cleaning efficiency in the peroxymonosulfate (PMS) cleaning process, where the radical and nonradical pathways occurred simultaneously. And the active substances generated in the nonradical process (especially ¹O₂) were considered as the main contributor to the reduction of irreversible fouling. Overall, the novel strategy of fouling control ensured the efficient operation of ultrafiltration membranes for the continuous oily wastewater purification.

Prospects of Polymeric Nanocomposite Membranes for Water Purification and Scalability and their Health and Environmental Impacts: A Review

Water shortage is a major worldwide issue. Filtration using genuine polymeric membranes demonstrates excellent pollutant separation capabilities; however, polymeric membranes have restricted uses. Nanocomposite membranes, which are produced by integrating nanofillers into polymeric membrane matrices, may increase filtration. Carbon-based nanoparticles and metal/metal oxide nanoparticles have received the greatest attention. We evaluate the antifouling and permeability performance of nanocomposite membranes and their physical and chemical characteristics and compare nanocomposite membranes to bare membranes. Because of the antibacterial characteristics of nanoparticles and the decreased roughness of the membrane, nanocomposite membranes often have greater antifouling properties. They also have better permeability because of the increased porosity and narrower pore size distribution caused by nanofillers. The concentration of nanofillers affects membrane performance, and the appropriate concentration is determined by both the nanoparticles' characteristics and the membrane's composition. Higher nanofiller concentrations than the recommended value result in deficient performance owing to nanoparticle aggregation. Despite substantial studies into nanocomposite membrane manufacturing, most past efforts have been restricted to the laboratory scale, and the long-term membrane durability after nanofiller leakage has not been thoroughly examined.

Advances in plasmonic-based MOF composites, their bio-applications and perspectives in this field

INTRODUCTION

Nanomaterials have been used for bio-applications since the late 20st century. In an attempt to tailor and optimize their properties, and by extension their efficiency, composites have attracted considerable attention. In this regard, recent studies on plasmonic nanoparticles and metal-organic framework (NP@MOF) composites suggested these materials show great promise in this field.

AREAS COVERED

This review focused on the more recent scientific advances in the synthetic strategies to optimize plasmonic MOF nanocomposites currently available, as well as their bio-application, particularly as biosensors and therapy.

EXPERT OPINION

Plasmonic MOF nanocomposites have shown great potential as they combine the properties of both materials with proven efficiency in bio-application. On the one hand, nanoMOFs have proven their potential particularly as drug nanocarriers, owing to their exceptional porosity and tunability. On the other hand, plasmonic nanoparticles have been an asset for imaging and phototherapy. Different strategies have been reported to develop these nanocomposites, mainly including core-shell, encapsulation, and in situ reduction. In addition, advanced composite structures should be considered, such as mixed metal nanoparticles, hollow structures or the combination of several approaches. Specifically, plasmonic MOF nanocomposites prove to be attractive stimuli responsive drug delivery systems, phototherapeutic agents as well as highly sensitive biosensors.

Incorporating Ag@RF core-shell nanomaterials into the thin film nanocomposite membrane to improve permeability and long-term antibacterial properties for nanofiltration

Ag@resorcinol-formaldehyde resin (Ag@RF) core-shell nanomaterials were prepared by Stöber method, and introduced into polyamide (PA) selective layer of thin-film nanocomposite (TFN) membranes through the interfacial polymerization (IP) process. Due to the abundant hydroxyl groups on the surface and suitable particle size, Ag@RF nanoparticles (Ag@RFs) could be uniformly dispersed in the piperazine aqueous solution and participate in the IP process to precisely regulate the microstructure of the PA selective layer. The resulting "crater structure" and irregular granular structure enlarged the permeable area and contributed to the surface hydrophilicity. For the nanofiltration application, the water flux of TFN membrane modified by Ag@RFs to Na₂SO₄ solution reached 150 L·m^-2·h^-1 which was 87.5% greater than TFC, and salt rejection was maintained. The antibacterial efficiency of the prepared TFN membrane on E. coli reached 99.6% in the antibacterial experiment. In addition, due to the special structure of Ag@RFs, the TFN membrane also showed an expected slow-release capability of Ag⁺, allowing for long-term anti-biofouling properties. This work demonstrates that Ag@RF core-shell nanoparticles with high compatibility of organic nanoparticles and antibacterial properties of Ag nanoparticles could be used as promising nanofillers for designing functional nanofiltration TFN membranes.

Different metal-doped ZnS quantum dots photocatalysts for enhancing the permeability and antifouling performances of polysulfone membranes with and without UV irradiation

In this study, the effect of three different transition metal ion dopants (Mn²⁺, Fe^2+, and Co²⁺) on the characteristics of zinc sulfide (ZnS) quantum dots (QDs) was investigated and the obtained QDs photocatalysts were applied for the modification of polysulfone (PSf) mixed matrix membranes to reduce membrane fouling. The synthesized QDs and fabricated membranes were fully identified with SEM, TEM, AFM, FTIR analyses, and also underwent porosity and contact angle tests. Flux recovery ratios (FRR) significantly increased from 69.8% (bare) to 85.0% (1% Fe-doped ZnS QDs) after modification of membranes with metal-doped QDs. The contact angles of the prepared membranes decreased with doping of dissimilar metals, therefore hydrophilicity increased, and reversible/non-reversible blockages were improved. Besides, the use of UV irradiation during the washing of the membranes increased the FRR of the photocatalytic activated membranes to 91.2%. Compared to the bare PSf membrane in dye solution filtration, 1% Fe-doped ZnS QDs membrane yielded twice as much flux and 15% higher FRR results. Therefore, the results proved that metal-doped QDs can be used in the modification of PSf membranes with high efficiency.

Applications of Polymeric Membranes with Carbon Nanotubes: A Review

Nanomaterials have been commonly employed to enhance the performance of polymeric membrane materials that are used in several industrial applications. Carbon nanotubes (CNTs) have gained notable attention over the years for use in membrane technology due to their anti-biofouling properties, salt rejection capability, exceptional electrical conductivity, and mechanical properties. This paper aims to discuss some of the recent applications of CNTs in membrane technology and their effect on a larger scale. The paper reviews successful case studies of incorporation of CNTs in membranes and their impact on water purification, desalination, gas separations, and energy storage, in an effort to provide a better understanding of their capabilities. Regarding the future trends of this technology, this review emphasizes improving the large-scale production processes and addressing environmental and health-related hazards of CNTs during production and usage.

Carbon-based low-pressure filtration membrane for the dynamic disruption of bacteria from contaminated water

Carbon-based materials, especially graphene oxide (GO) and carbon dots possessing antibacterial properties, are widely used for various applications. Recently, we reported the antibacterial and antioxidant properties of carbonized nanogels (CNGs) for the treatment of bacterial keratitis, and as a virostatic agent against infectious bronchitis virus. In this work, we demonstrate the use of CNGs/GO nanocomposite (GO@CNGs) membrane for the efficient removal of Gram-negative (E. coli) and Gram-positive (S. aureus) bacteria from contaminated water. The GO@CNGs composite membrane with an optimized ratio of GO to CNGs could achieve more than 99% removal efficiency toward E. coli and S. aureus. Various strains of bacteria interact differently with the membrane, and hence the membrane shows different removal rate, which can be optimized by controlling the interaction time through regulating the water flux. The GO@CNGs membrane with an active area of 2.83 cm² achieved > 99% bacterial removal efficiency at a water flux of 400 mL min^-1 m^-2. The dynamic disruption of bacteria by GO@CNGs plays a crucial role in eliminating the bacteria. Rather than filtering out the bacteria, GO@CNGs membrane allows them to pass through it, interact with the bacteria and rupture the bacterial cell membranes. Our GO@CNGs membrane shows great potential as a filter to remove bacteria from contaminated water samples, operating under tap water pressure without any extra power consumption.

Zwitterionic silica nanogel-modified polysulfone nanoporous membranes formed by in-situ method for water treatment

We report a simple methodology to prepare nano-porous polysulfone membranes using zwitterionic functionalized silica nanogels with high BSA protein rejection and antifouling properties. The zwitterionic silica precursor was prepared by reacting 1,3-propane sultone with 3-aminopropyl triethoxysilane under an inert atmosphere. The precursor was in situ hydrolyzed and condensed in the polysulfone nanoporous membrane network by one-pot acidic phase inversion. The prepared membranes were characterized to establish their physicochemical nature, morphology, and basic membrane properties such as permeation, rejection, and recovery. The zwitterionic membranes showed improved hydrophilicity, membrane water uptake (∼83.5%), water permeation, BSA protein rejection (>95%), and dye rejection (congo red: >52% (∼6-fold increase); methylene blue: ∼15% (∼2-fold increase)) were improved without compromising the membrane flux and fouling resistance. Overall, we report an easy fabrication method of efficient nanocomposite zwitterionic ultrafilter membranes for water treatment with excellent flux, protein separation, filtration efficiency, and antifouling behavior.

Organic Nanobowls Modified Thin Film Composite Membrane for Enhanced Purification Performance toward Different Water Resources

The structure and composition of nanofillers have a significant influence on polyamide nanofiltration (NF) membranes. In this work, an asymmetric organic nanobowl containing a concave cavity was synthesized and incorporated into a polyamide layer to prepare thin film nanocomposite (TFN) membranes via an interfacial polymerization process. Benefiting from the hydrophilicity, hollow cavity and charge property of the compatible organic nanobowls, the separation performance of the developed TFN membrane was significantly improved. The corresponding water fluxes increased to 119.44 ± 5.56, 141.82 ± 3.24 and 130.27 ± 2.05 L/(m²·h) toward Na₂SO₄, MgCl₂ and NaCl solutions, respectively, with higher rejections, compared with the control thin film composite (TFC) and commercial (CM) membranes. Besides this, the modified TFN membrane presented a satisfying purification performance toward tap water, municipal effluent and heavy metal wastewater. More importantly, a better antifouling property of the TFN membrane than TFC and CM membranes was achieved with the assistance of organic nanobowls. These results indicate that the separation performance of the TFN membrane can be elevated by the incorporation of organic nanobowls.

Development of hydrophilic PES membranes using F127 and HKUST-1 based on the RTIPS method: Mitigate the permeability-selectivity trade-off

In this study, to mitigate the permeability-selectivity trade-off effect, Pluronic F127 (F127) and HKUST-1 were employed to construct high-performance membranes based on the reverse thermally induced phase separation (RTIPS) method. F127, as a hydrophilic modifier, was applied to increase permeability and resist polyethersulfone (PES) membrane fouling, while the collapse of HKSUT-1 caused by its instability in pure water improved the permeability and selectivity of the membrane. Characterizations demonstrated the successful synthesis of HKUST-1, together with the successful introduction of HKSUT-1 and F127 in PES membranes. It was observed that the membrane prepared by the RTIPS process possessed a uniformly porous surface and sponge-like cross-section with excellent mechanical properties, higher permeability, and selectivity compared to the dense skin and finger-like cross-section of the membrane prepared by the nonsolvent induced phase separation (NIPS) method. Moreover, the permeation and bovine serum albumin (BSA) rejection rate of the optimal membrane reached 2378 L/m² h and 89.3%, respectively, which were far higher than those of the pure membrane. Hydrophilic F127 and many microvoids formed by the collapse of HKUST-1, played an important role in excellent antifouling properties, high permeability, and selectivity by pure water flux (PWF), flux recovery rate (FRR), BSA flux, and COD removal rate tests. Overall, the membrane with F127 and HKSUT-1 prepared via the RTIPS method not only obtained excellent antifouling properties but also mitigated the permeability-selectivity trade-off.

Interactions between carbon-based nanoparticles and steroid hormone micropollutants in water

The occurrence of micropollutants (MPs) including steroid hormones is a global environmental and health challenge. Carbon-based nanoparticles can be incorporated with water treatment processes to allow MP removal by adsorption. The aim was to compare the suitability of such nanoparticles (graphene, graphene oxide, carbon nanotubes and C₆₀) to adsorb steroid hormones for later incorporation in membrane composites. All nanoparticles displayed fast kinetics; carbon nanotubes and graphene showed high adsorption capacities for hormones undeterminable in isotherm studies (over 10 mg/g). External surface adsorption appears to be the most prominent factor impacting adsorption performance. Structure, conformation, geometry and surface charge of nanoparticles can influence the accessibility of surface area through colloidal instability in aqueous solution. Mechanism inspection shows that adsorption initiates at long ranges (up to 10 nm) through hydrophobic and electrostatic interactions. At relatively short ranges (0.2-0.5 nm), adsorption is enhanced by π/π stacking, XH / π (X = C, O) interactions, van der Waals forces and hydrogen bonding. Both long- and short-range forces transporting hormones from the liquid bulk into the adsorbed phase could control the rate. With relatively short residence time required and high adsorption capacity, carbon nanotubes and graphene are promising for incorporation in a membrane composite.

Evaluation of the formation and antifouling properties of a novel adsorptive homogeneous mixed matrix membrane with in situ generated Zr-based nanoparticles

In situ generation is a powerful technique used to prepare homogenous adsorptive mixed matrix membranes (MMMs) containing functional nanoparticles, although the mechanism of formation of the membranes is not yet clear and there have been few published evaluations of membrane fouling. We therefore used this method to prepare a novel homogeneous adsorptive Zr-based nanoparticle–polyethersulfone (PES) MMM and systematically studied the mechanism of membrane formation at the atomic level. As the amount of ZrOCl₂·8H₂O in the casting solution increased, the phase inversion kinetics changed from instantaneous demixing due to the thermodynamic enhancement effect to a delayed demixing process caused by viscosity hindrance. The in situ generation of nanoparticles in these MMMs can be divided into three stages: the migration stage, the exfoliation stage and the stable stage. Our findings provide a fundamental understanding of the interface chemistry in the development of in situ generated MMMs. M2 showed a higher adsorption of As(v) than the pure PES membrane and could be reused after regeneration. The removal of As(v) from the M2 filtration system mainly took place via adsorption rather than size exclusion, as confirmed by EDS and experimental data. The presence of humic acid slightly inhibited the removal of As(v) during the filtration process as a result of the barrier effect caused by the formation of a filter cake via humic acid fouling. The filtration of a bovine serum albumin solution showed that the MMM with in situ generated nanoparticles had better antifouling properties than the PES membrane alone in multiple applications as a result of the enhanced hydrophilic surface.

A homogeneous in situ generated Zr-based NPs/PES mixed matrix membrane with enhanced adsorptive and antifouling performance was developed.

Influence of Multidimensional Graphene Oxide (GO) Sheets on Anti-Biofouling and Desalination Performance of Thin-Film Composite Membranes: Effects of GO Lateral Sizes and Oxidation Degree

The influence of the lateral size and the content of graphene oxide (GO) flakes in specific oxygenate functional groups on the anti-biofouling properties and performance of thin-film composite membrane (TFC) was studied. Three different multidimensional GO samples were prepared with small (500-1200 nm), medium (1200-2300 nm), and large (2300-3600 nm) size distribution, and with different degrees of oxidation (GO3 > GO2 > GO1), varying the concentration of the hydrogen peroxide amount during GO synthesis. GO1 sheets' length have a heterogeneous size distribution containing all size groups, whilst GO2 is contained in a medium-size group, and GO3 is totally contained within a small-size group. Moreover, GO oxygenate groups were controlled. GO2 and GO3 have hydroxyl and epoxy groups at the basal plane of their sheets. Meanwhile, GO1 presented only hydroxyl groups. GO sheets were incorporated into the polyamide (PA) layer of the TFC membrane during the interfacial polymerization reaction. The incorporation of GO1 produced a modified membrane with excellent bactericidal properties and anti-adhesion capacity, as well as superior desalination performance with high water flow (133% as compared with the unmodified membrane). For GO2 and GO3, despite the significant anti-biofouling effect, a detrimental impact on desalination performance was observed. The high content of large sheets in GO2 and small sheet stacking in GO3 produced an unfavorable impact on the water flow. Therefore, the synergistic effect due to the presence of large- and small-sized GO sheets and high content of OH-functional groups (GO1) made it possible to balance the performance of the membrane.

Investigation of Biocidal Effect of Microfiltration Membranes Impregnated with Silver Nanoparticles by Sputtering Technique

Silver nanoparticles were loaded in microfiltration membranes by sputtering technique for the development of biocidal properties and biofouling resistance. This technology allows good adhesion between silver nanoparticles and the membranes, and fast deposition rate. The microfiltration membranes (15 wt.% polyethersulfone and 7.5 wt.% polyvinylpyrrolidone in N,N-dimethylacetamide) were prepared by phase inversion method, and silver nanoparticles were deposited on their surface by the physical technique of vapor deposition in a sputtering chamber. The membranes were characterized by Field Emission Scanning Electron Microscopy, and the presence of silver was investigated by Energy-Dispersive Spectroscopy and X-ray Diffraction. Experiments of silver leaching were carried out through immersion and filtration tests. After 10 months of immersion in water, the membranes still presented ~90% of the initial silver, which confirms the efficiency of the sputtering technique. Moreover, convective experiments indicated that 98.8% of silver remained in the membrane after 24 h of operation. Biocidal analyses (disc diffusion method and biofouling resistance) were performed against Pseudomonas aeruginosa and confirmed the antibacterial activity of these membranes with 0.6 and 0.7 log reduction of viable planktonic and sessile cells, respectively. These results indicate the great potential of these new membranes to reduce biofouling effects.

Fabrication of high performance TFN membrane containing NH2-SWCNTs via interfacial regulation

A high-flux thin film nanocomposite (TFN) nanofiltration (NF) membrane for low pressure operation (3.5 bar) was fabricated by blending purified amino-functionalized single-walled carbon nanotubes (NH₂-SWCNTs) with piperazine (PIP) as aqueous phase monomers through interfacial polymerization (IP). The surface properties and structures of the polyamide (PA) active layer were suitably tailored by introducing different amounts of NH₂-SWCNTs into the PA layer. It was found that the homogeneous incorporation of NH₂-SWCNTs facilitated a more integral PA layer along with improved roughness, hydrophilicity, and surface charge of the modified membranes, which could be validated by membrane characterisation including SEM, AFM, ATR-FTIR, XPS, zeta potential and water contact angle measurements. Based on cross-flow NF tests, the optimized ultra-thin NH₂-SWCNT-TFN membranes with 0.002 wt% of NH₂-SWCNTs exhibited outstanding water permeability of up to 17.8 L m⁻² h⁻¹ bar⁻¹, 71.1% higher than that of the pristine membrane, along with high MgSO₄ rejection of 91.0% and Na₂SO₄ rejection of 96.34%. Meanwhile, NH₂-SWCNT-TFN membranes also showed excellent long-term stability and antifouling ability. This work demonstrates a facile strategy to fabricate a scalable, low-pressure and ultra-thin TFN membrane with excellent performance.

The surface properties and structures of the polyamide (PA) active layer were suitably tailored by introducing different amounts of NH₂-SWCNTs into the PA layer.