Membrane Fouling Resistance Research Articles

High-Performance Novel MoS2@Zeolite X Nanocomposite-Modified Thin-Film Nanocomposite Forward Osmosis Membranes: A Study of Desalination and Antifouling Performance.

Novel thin-film nanocomposite (TFN) membranes modified by the MoS2@Zeolite X nanocomposite were made and studied for desalination by the forward osmosis (FO) method. Herein, MoS2@Zeolite X nanocomposite (MoS2@Z) and zeolite X particles are integrated into the polyamide (PA) selective layer of the TFN membranes, separately. The aim of this study is the synthesis of nanocomposites containing hydrophilic zeolite X particles with a modified surface and pore and improvement of their effective properties on desalination and antifouling performance. For this purpose, MoS2 nanosheets with a high hydrophilicity were selected. The existence of polymer-matrix-compatible MoS2@Z inside the PA active layer caused the formation of a defect-free smooth surface with further channels within this layer that could increase the water flux and fouling resistance of the TFN membranes. The TFN-MZ2 membrane (containing 0.01 wt % MoS2@Z) showed the top desalination performance in the FO process. In contrast to the pristine thin-film composite (TFC) and TFN-Z2 membrane (containing 0.025 wt % zeolite X, the most optimal membrane among the zeolite-modified membranes), its water flux has increased by 2.6 and 1.8 times, respectively. Furthermore, in the fouling test, this optimal TFN-MZ2 membrane with a flux decrement of 19.6% revealed an ∼2.2- and 1.8-fold enhancement in antifouling tendency compared to the TFC and TFN-Z2, respectively. Also, based on the antibiofouling test, the water flux drop of 48.6% for the TFC membrane has reached 36.9% for the optimal membrane. Hence, this high-performance TFN-MZ2 membrane shows good capability for commercial employment in FO desalination application.

Efficient removal of perfluorinated compounds with the polyamide nanofiltration membrane and membrane fouling resistance analysis

Abstract Perfluorinated compounds (PFCs) are significant pollutants known for their high toxicity and resistance to natural degradation, posing a severe threat to both the global environment and human health. In this study, a polyamide (PA) membrane with an intermediate layer structure of MXene-TiO2 (referred to as MXT-NFM) was utilized for the removal of PFCs. Experimental results confirm that MXT-NFM exhibited remarkable capacity in intercepting PFCs, accompanied by the high water flux. To gain insights into the mechanisms governing membrane fouling induced by PFCs, inorganic ions, and organics, a series of fouling tests were conducted using MXT-NFM under diverse conditions. Additionally, the XDLVO theory was employed to provide a theoretical perspective on the interactions occurring during the fouling process. The findings suggest that the MXene-TiO2 intermediate layer contributed to the exceptional hydrophilicity and rough surface properties, enabling multiple functionalities. These include alleviating membrane pore plugging, improving the physical configuration of the PA layer, and effectively mitigating fouling phenomena in coexisting systems during practical applications. Moreover, the particle size of pollutant colloids and the acid–base interaction were identified as decisive factors influencing the development of membrane fouling.

Development of a novel hydrophilic SiO2/PVDF Janus membrane via different modification methods for robust antiwetting and antifouling membrane distillation

The development of novel membrane distillation (MD) membranes with high resistance to wetting and fouling has a great importance for the treatment of surfactant or oil-containing wastewater. In this study, superwettable Janus membranes were produced using hydrophilic silica nanoparticles (SiO2 NPs) via blending phase inversion (M1), delayed phase inversion (M2), and spray coating (M3) methods. Scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM/EDS) and Fourier transform infrared spectrometry (FTIR) analysis showed that SiO2 NPs were successfully deposited on the top layers of the membranes, while no SiO2 NPs were detected on the bottom layers. Furthermore, underwater superoleophobic properties were achieved for M2 and M3 membranes, while M1 membrane showed a satisfactory underwater oleophobicity. In MD filtration tests, the M2 membrane exhibited the highest membrane wetting and fouling resistance, followed by the M1 membrane. However, the sprayed SiO2 NPs coating layer on the M3 membrane did not remain stable, resulting in a similar permeate water flux and rejection profiles to the pristine membrane after a short time. This study indicates that Janus membranes fabricated by blending and delayed phase inversion methods could be a strong candidate in MD for the treatment of complex wastewater containing surfactants and oil.

Dual regulation of graphene oxide membrane by crosslinker and hydrophilic promoter for dye separation

Graphene oxide (GO)-based membranes have shown considerable promise in the field of water treatment. However, the structural swelling of GO membranes in water has hindered their further development. A single regulatory approach seems difficult to simultaneously improve permeability, selectivity, and stability. In this study, we present a dual regulation strategy for GO membranes employing the 1,4-Diaminobutane crosslinker to prevent swelling and maintain an interlayer spacing of 1.34 nm, resulting in effective dye rejection, and employing the hydrophilic EMT-type zeolite promoter to improve the membrane's water permeability. The obtained NH2-GO/10EMT composite membrane exhibited enhanced pure water flux (from 9.0 to 20.8 L/m2 h bar) and anionic dye rejection (from 87.2% to 97.6%) with promising structure stability (at least 20 h), while greatly improving the membrane's fouling resistance (the water recovery ratio increased from 46.5% to 86.2%). Our findings provide a straightforward and efficient approach to the development of high-performance GO membranes for selective water separation.

Controlling ultrafiltration membrane fouling in surface water treatment via combined pretreatment of O3 and PAC: Mechanism investigation on impacts of technological sequence

In this research, the effects of combined powdered activated carbon (PAC)-ozone (O3) pretreatment on ultrafiltration (UF) performance were comprehensively examined and compared with the conventional O3-PAC pretreatment. The performance of pretreatments on mitigating membrane fouling caused by Songhua River water (SHR) was evaluated by specific flux, membrane fouling resistance distribution, and membrane fouling index. Moreover, the degradation of natural organic matter in SHR was investigated by UV absorbance at 254 nm (UV254), dissolved organic carbon (DOC), and fluorescent organic matter. Results showed that the 100PAC-5O3 process was the most effective in improving the specific flux, with 82.89 % and 58.17 % reductions in the reversible fouling resistance and irreversible fouling resistance respectively. Additionally, the irreversible membrane fouling index was reduced by 20 % relative to 5O3-100PAC. The PAC-O3 process also exhibited superior performance in the degradation of UV254, DOC, three fluorescent components, and three micropollutants in the SHR system compared to O3-PAC pretreatment. The O3 stage played a major role in mitigating membrane fouling, while PAC pretreatment enhanced the oxidation in the subsequent O3 stage during the PAC-O3 process. Furthermore, the Extended Derjaguin-Landau-Verwey-Overbeek theory and pore blocking-cake layer filtration model fitting analysis were employed to explain the mechanisms of membrane fouling mitigation and fouling patterns transformation. It was found that PAC-O3 significantly increased the repulsive interactions between the foulants and the membrane, which restrained the formation of the cake layer filtration stage. Overall, this study evidenced the potential of PAC-O3 pretreatment in surface water treatment applications, providing new insights into the mechanism of controlling membrane fouling and improving the permeate quality.

Enhancing fouling resistance and separation performance of polyethersulfone membrane through surface grafting with copolymerized thermo-responsive polymer and copper oxide nanoparticles

Surface modification is a critical aspect for improving the efficiency of membranes and reducing the risk of fouling in applications such as wastewater treatment and oil/water separation. The objective of this study is to minimize membrane fouling and maximize its rejection rate through surface modification. Here, for the first time, we developed a dual-functionalized PES membrane using a two-step process, involving grafting with a thermo-responsive polymer (P(NIPAm-co-AAm)) and subsequent functionalization with copper oxide nanoparticles. The membranes were evaluated for any changes in their chemical composition, structural properties, porosity, surface charge, and wetting characteristics. The hydrophilicity of all the modified membranes increased as indicated by a noticeable reduction in the water contact angle. The modified membranes displayed a change in their receding water contact angle based on changes in water temperature, confirming the thermo-responsive nature of PNIPAm. The receding contact angle for the PES membrane grafted with P(NIPAm-co-AAm) was significantly low (∼13°) below 33 °C but increased to 28° when the temperature exceeded 40 °C, indicating the dependence of the surface wettability of the treated PES membranes on temperature. The dual-functionalized membrane outperformed the pristine PES membrane, with a 13% increase in flux and 26% rise in flux recovery ratio. Additionally, the CuO@PES-g-P(NIPAm-co-AAm) membrane showed significant improvements in contaminant rejection and antifouling ability, with > 98% rejection rate for both oil-water emulsion and bovine serum albumin (BSA). The achieved separation and antifouling properties make the dual-functionalized membrane an excellent candidate for water treatment and demonstrate the efficacy of our simple modification process.

Efficient recovery of ammonia from digestate by membrane distillation: Nano-FeOOH re-entry structure modification, anti-fouling, and anti-wetting performance

The recovery of resources from wastewater has drawn worldwide attention, and digestate has the potential to produce amino fertilizers as an ammonia-rich carrier. Membrane distillation (MD) is an effective process to recover ammonia from digestate, but membrane fouling and wetting are identified as major challenges faced. However, the research to enhance membrane fouling resistance and ammonia transfer efficiency through membrane modification has seldom been explored. Herein, we fabricated FeOOH grafted membranes with superior resistance to wetting by simple hydrothermal synthesis and fluorination. The grafted re-entrant FeOOH nanoparticles and fluorosilanes were confirmed by SEM, EDS, FTIR, and XRD. The superior hydrophobicity of the modified film was confirmed by contact angle (CA = 152.9 ± 2.8°) analysis. The fouling growth behavior of the membrane surface was monitored in situ by optical coherence tomography (OCT), and the anti-fouling performance was proved to be superior to that of commercial polyvinylidene fluoride membrane (PVDF) (no fouling accumulation was detected for 6 h). The modified membrane achieved ammonia recovery flux of 3.89 ± 0.18 g/m2 h and high ammonia recovery of 95.2 ± 2.3% without wetting occurrence. Our research illustrates that the grafting of nano-FeOOH re-entrant structures facilitates the recovery of ammonia from highly concentrated ammonia wastewater without wetting and fouling, revealing its promising prospect in MD resource recovery.

Integration of antibacterial and photocatalysis onto polyethersulfone membrane for fouling mitigation and contaminant degradation

Biofouling is a significant constraint in the development of membrane filtration technology. In this study, Ag nanoparticles (AgNPs) were synthesized homogeneously in situ on the polyethersulfone (PES) membrane surface, and titanium dioxide (TiO2) photocatalytic agent was subsequently coated through the functional polydopamine intermediate layer. The Ag-TiO2-PDA/PES membrane presented enhanced hydrophilicity, attractive antibacterial ability, and photocatalytic performance. The AgNPs modification achieved 96% bacterial inactivation by using the E.coli DH5α as the model microorganism, and TiO2 provided a photocatalytic degradation ability to the membrane. The improved flux recovery of the Ag-TiO2-PDA/PES membrane, which was approximately 95% in the third cyclical filtration, revealed the efficient antifouling ability through AgNPs and TiO2 modification. The Ag-TiO2-PDA/PES membrane inhibited biofouling in dynamic filtration by AgNPs and degraded the irreversible fouling by TiO2 during the cleaning procedure. The combined modification of the PES membrane by AgNPs and TiO2 exhibited a synergistic effect on the improvement of antifouling properties. This study provides a multifunctional membrane design strategy by combining antibacterial and photocatalysis to improve membrane fouling resistance.

Separation Performance of Membranes Containing Ultrathin Surface Coating of Metal-Polyphenol Network.

Metal-polyphenol networks (MPNs) are being used as versatile coatings for regulating membrane surface chemistry and for the formation of thin separation layers. The intrinsic nature of plant polyphenols and their coordination with transition metal ions provide a green synthesis procedure of thin films, which enhance membrane hydrophilicity and fouling resistance. MPNs have been used to fabricate tailorable coating layers for high-performance membranes desirable for a wide range of applications. Here, we present the recent progress of the use of MPNs in membrane materials and processes with a special focus on the important roles of tannic acid-metal ion (TA-Mn+) coordination for thin film formation. This review introduces the most recent advances in the fabrication techniques and the application areas of TA-Mn+ containing membranes. In addition, this paper outlines the latest research progress of the TA-metal ion containing membranes and summarizes the role of MPNs in membrane performance. The impact of fabrication parameters, as well as the stability of the synthesized films, is discussed. Finally, the remaining challenges that the field still faces and potential future opportunities are illustrated.

Polyethersulfone/polyamide thin-film nanocomposite membrane decorated by WS2-Cys-UiO-66-(CO2H)2 nanocomposites for forward osmosis

The fabrication of some new high-performance WS2-Cys-MOF-incorporated thin-film nanocomposite (TFN) forward osmosis (FO) membranes for use in desalination applications is reported. Herein, WS2-Cys-MOF nanosheets are synthesized through UiO-66-(CO2H)2 grafting on WS2-Cys and integrated into the PA selective layer of TFN membranes. The nanofillers content in the MPD aqueous solution was varied from 0 to 0.25 wt% to acquire the optimal loading and the best FO performance. The presence of polymer-matrix compatible WS2-Cys-MOF in the PA selective layer led to the formation of a defect-free smooth surface with additional channels within this layer, which can boost water flux and fouling resistance of TFN membranes. The TFN-0.1 membrane containing 0.1 wt% WS2-Cys-MOF results in the best FO desalination performance. Compared to the virgin TFC membrane, its water fluxes are almost doubled with a slight increase in the selectivity ∼18% evaluated under AL-FS orientation using 1 M NaCl as the draw solution and deionized water as the feed solution. Moreover, in the fouling test, this optimum TFN-0.1 membrane with a flux decline of 7.63% revealed a ∼1.4-fold enhancement in anti-fouling tendency. Hence, these high-performance WS2-Cys-MOF-incorporated TFN membranes show excellent potential for commercial utilization in the FO-desalination application.

Cobalt oxide decorated activated carbon/peroxymonosulfate pretreatment for ultrafiltration membrane fouling control in secondary effluent treatment: Insights into interfacial interaction and fouling model transformation

To control the ultrafiltration (UF) membrane fouling caused by the secondary effluent, cobalt oxide loaded activated carbon (CoOx-PAC) activating peroxymonosulfate (PMS) was applied as a pretreatment. The degradation of natural organic matter (NOM) and membrane fouling mitigation performance for the CoOx-PAC/PMS pretreatment were comprehensively investigated. The dissolved organic carbon (DOC), fluorescent organics, and phenol in the secondary effluent system were utilized to evaluate the removal effect of the CoOx-PAC/PMS process on the organic matter. Results showed that 100 mg/L 0.5 %CoOx-PAC combined with 2 mM PMS (0.5 %CoOx-PAC/PMS) had an excellent degradation on NOM, removing 84.92 % of DOC, and above 97 % of fluorescent organics within 120 min. The catalytic activity of phenol in this process was even superior to that of homogeneous catalysis (Co2+/PMS). Moreover, the normalized specific flux and membrane fouling resistance were employed to verify the influences of the CoOx-PAC/PMS on membrane fouling. The 0.5 %CoOx-PAC/PMS system significantly improved the specific flux, with a 94.26 % decline in reversible membrane fouling resistance and a 53.05 % reduction in irreversible fouling resistance. O2•− and 1O2 were involved in the reaction as crucial reactive oxide species according to electron paramagnetic resonance and quenching tests. They changed the physicochemical properties of NOM, which decomposed the high molecular weight organics into low molecular weight hydrophilic fractions, thereby delaying the formation of cake layers and alleviating membrane fouling. The Extended Derjaguin-Landau-Verwey-Overbeek theory was used to assess the interaction between the foulants and the UF membranes. The transformation of fouling models was analyzed and found that the intricate membrane fouling filtration mechanisms were transformed into a single standard blocking mode after 0.5 %CoOx-PAC/PMS pretreatment.

Efficient oily wastewater treatment by a novel electroflotation-membrane separation system consisting a Ni-Cu-P membrane prepared by electroless nickel plating

Electroflotation-membrane separation system with a conductive membrane has recently emerged as a promising technology for oily wastewater treatment. However, the conductive membrane prepared by electroless plating often suffers the problems of low stability and high activation cost. To solve these problems, this work proposed a new strategy regarding surface metallization of polymeric membrane by surface nickel-catalyzed electroless nickel plating of nickel‑copper‑phosphorus alloys for the first time. It was found that, addition of copper source remarkably enhanced the membranes' hydrophilicity, corrosion resistance and fouling resistance. The Ni-Cu-P membrane had an underwater oil contact angle of up to 140°, and simultaneously possessed rejection rate > 98 % with rather high flux of 65,663.0 L·m−2·h−1 and excellent cycling stability when separating n-hexane/water mixtures under gravity drive. The permeability is higher than the state-of-the-art membranes for oil/water separation. The Ni-Cu-P membrane as the cathode can be assembled into an electroflotation-membrane separation system, allowing to separate oil-in-water emulsion with 99 % rejection. Meanwhile, the applied electric field significantly improved membrane flux and fouling resistance (flux recovery up to 91 %) when separate kaolin suspensions. Polarization curve and Nyquist curve analysis further confirmed that addition of Cu element obviously enhanced corrosion resistance of the Ni modified membrane. This work provided a novel strategy to make up high-efficiency membranes for oily wastewater treatment.

Ag@BiOBr/PVDF photocatalytic membrane for remarkable BSA anti-fouling performance and insight of mechanism

Membrane technologies offer great potential in desalination and wastewater treatment. However, the serious issue of membrane fouling results in the unsatisfactory sustainability and reusability for treating wastewater containing high level of organic foulants. In this work, a photocatalytic membrane reactor system combining Ag@BiOBr photocatalyst and polyvinylidene fluoride (PVDF) ultrafiltration with remarkable anti-fouling property was constructed. The integrated Ag@BiOBr/PVDF photocatalytic ultrafiltration membranes were prepared by blending Ag@BiOBr nanoparticles (NPs) into PVDF membrane via phase inversion method. The membrane separation performance and fouling resistance were studied in a cross-flow ultrafiltration system using bovine serum albumin (BSA) as the model foulants. Compared with the pristine PVDF membrane, the hydrophilicity and surface smoothness of composite membranes were promoted by photocatalyst-incorporation, the Ag@BiOBr/PVDF membrane with the optimal Ag@BiOBr blending content of 2.0 wt% achieved both enhanced water flux and higher BSA rejection efficiency. More importantly, the mechanism of anti-fouling and self-cleaning performances were further studied, the photocatalysis process based on Ag@BiOBr/PVDF membrane effectively decomposed the BSA foulant into broken protein with induced change of carbonyl, ionic bond and hydrogen bond contents in BSA foulants via the active radicals, weakened the intermolecular force of BSA foulants to prevent membrane pore blockage. Meanwhile, the broken protein peptide chains with more negative charges could result in the strength of electrostatic repulsive forces between BSA molecules and membrane. As a result, the BSA foulant could be stably removed in the Ag@BiOBr/PVDF photocatalytic ultrafiltration system under visible light irradiation, achieving the excellent anti-fouling performance by preventing the membrane pore blockage and foulant adhesion. We believe the Ag@BiOBr/PVDF photocatalytic membrane presented in this study will be one example among many photocatalyst-membrane combinations that can be further pursued for organic pollutants removal. In particular, we expect the theoretical support can present a great opportunity to design novel photocatalytic membranes with sustainable anti-fouling performance.

Interaction between MIL-101(Cr) and natural organic matter in an integrated MOF-UF system

As an emerging metal organic framework (MOF) material, MIL-101(Cr) has a large specific surface area and good hydraulic stability, making it ideal in applications before ultrafiltration (UF). However, the unclear interaction between MIL-101(Cr) and natural organic matter (NOM) was identified as the main limitation to understand membrane fouling. To reveal the working mechanisms of NOM removal using MIL-101(Cr), an integrated system of MOF and UF was constructed and operated in separation mode (SM) and coating mode (CM). Based on the results, MIL-101(Cr) had a high NOM adsorption capacity of 68.454 mg/g for HA and 174.725 mg/g for BSA at saturation. Permeate quality improvement occurred in both modes over a 37.7% UV254 removal rate and a 15% fluorescence intensity decrease, and permeation performance of the hybrid system was simultaneously enhanced. We found that MIL-101(Cr) influenced membrane fouling behaviors and models because of the foulant transformation in SM and dispersed NOM in the MIL-101(Cr) layer in CM. Furthermore, MIL-101(Cr) played a dual role in the integrated system. It could remove NOM by adsorption, leading to membrane fouling reduction, but also caused additional filtration resistance. Notably, MIL-101(Cr) showed the overall positive effects due to its open hollow structure and good hydrophilicity. The π-π interactions and salt-bridges between MIL-101(Cr) and NOM played a dominant role in adsorption. Whilst SM was more efficient in membrane fouling mitigation due to reduced membrane fouling resistance and a normalized flux increase above 15%, CM could achieve the same permeate quality with less MIL-101(Cr) usage and reaction time. This study reveals the interaction between MIL-101(Cr) and NOM and their effects on UF, providing a scientific basis for the widespread application of MOFs.

New insights into interfacial interaction and nanoconfinement effect in synergistic oxidation-filtration via CoFe2O4-ceramic membrane activated peroxymonosulfate

Ceramic membranes incorporating CoFe2O4 (CoFeCM) were synthesized to activate peroxymonosulfate (PMS), and the performance and mechanisms of its oxidation-filtration were comprehensively investigated. The catalytic filtration performance of CoFeCM/PMS was evaluated by degradation of organic pollutants and the mitigation of membrane fouling. Results indicated that CoFeCM/PMS effectively removed toxic micropollutants, including phenol (82.56%), atrazine (93.42%), and carbamazepine (87.40%), ensuring the permeate quality and safety. Also, this synergistic process notably improved the degradation of natural organic matter (NOM) in the secondary effluent and Songhua River water. CoFeCM/PMS filtration effectively mitigated membrane fouling caused by three typical model organics, reducing their irreversible membrane fouling resistance by 70.85–83.62%, and increasing the normalized flux to 48.74–82.61%. The membrane fouling derived from two actual water systems was also greatly alleviated by CoFeCM/PMS. Based on the Extended Derjaguin-Landau-Verwey-Overbeek theory analysis, NOM was oxidized by reactive oxide species into hydrophilic small molecular fractions, resulting in remarkably increased repulsive interaction between NOM and CoFeCM surface. Density functional theory calculation results confirmed the nanoconfinement effect in CoFeCM pores, which can slow down the growth of foulants in pores and effectively alleviate irreversible membrane fouling. Consequently, standard blocking transformed into the dominant membrane fouling pattern due to the synergistic effects of nanoconfinement catalysis (in membrane pores) and repulsive interactions (on membrane surface) during oxidation-filtration.

Synergistic effects of silica derived granite dust and MoS2 on oil-water separation performances of mixed matrix PES membrane

Membrane separation technology has been widely examined for the treatment of oily wastewater owing to its numerous advantages, including high efficiency, energy saving, compact structure, and ease of operation. However, the overall performance of membrane separation highly depends on the membrane properties such as hydrophilicity and morphology structure. Nanoparticles (NPs) have been widely used to increase membrane hydrophilicity and fouling resistance. In this work, silica derived from granite dust (GD) via the sol–gel method was hydrothermally treated with molybdenum disulfide (MoS2) and used for the fabrication of MoS2-silica-PES mixed matrix membranes (MMMs). The synthesis of MoS2-silica composite was first confirmed via XRD analysis. Then, 1.0 wt% of MoS2-silica was blended into the PES casting solution, and the flat sheet membrane was cast by controlling the thickness of about 100 μm. The MoS2-silica-PES MMMs were then subjected to chemical, hydrophilicity and surface morphology studies. It was found that the addition of silica into MoS2 leads to a notable improvement in hydrophilicity and water flux as compared to bare PES and MoS2-PES membranes. The performance of MoS2-silica-PES membrane was then evaluated for oil–water separation using 1000 ppm oil concentrations at 1 bar and room temperature. The membrane was first compacted for 2 h at 2 bar before the oil–water separation test to maintain a stable flux. It was found that there was a substantial increase in the oil–water flux of the composite membranes (from 3.25 LMH to 41.68 LMH) when silica was added. This was due to the enhancement in membrane properties and morphology structure. Generally, the oil rejection of the MoS2-silica-PES MMMs fabricated in this work was maintained above 95 %. This study indicates that the fabricated MoS2-silica-PES MMMs have excellent potential for commercial applications. Using silica-derived granite dust offers an opportunity to lower the cost of the membrane.

A novel positively charged nanofiltration membrane stimulated by amino-functionalized MXene Ti3C2Tx for high rejection of water hardness ions

The demand to address issues such as drinking water safety and industrial fouling caused by high-hardness ions has still emphasized the development of advanced membrane materials. In this study, through a maneuverable amide-cross-linking strategy, a new positively-charged polyamide (PA) nanofiltration membrane was developed for the first time by incorporating amino-functionalized Ti3C2Tx nanoparticles (Ti3C2Tx-NH2, TN). In addition to the induced electropositivity, the hydrophilicity of the as-obtained PA-TN membrane was also elevated with a maintained nodular structure by tailoring the interfacial polymerization reaction process of piperazine (PIP) with trimesoyl chloride (TMC). Therefore, the newly developed PA-TN membrane exhibited both superhigh rejection of Ca2+ and Mg2+ over 96%, and the flux increased 2–3 times even for the salinity solutions than many similar NF membranes reported in literature. Furthermore, the enhanced long-term stability and fouling resistance of the PA-TN membrane was also validated due to its new organic-inorganic structural coupling and improved hydrophilicity. This work provides a new strategy for the preparation of organic-inorganic hybrid positively charged nanofiltration membranes for water softening treatment.

Enhancing the Permeability and Fouling Resistance of Thin-Film Composite Forward Osmosis Membranes via Poly(ethylene glycol) Diamine as a Comonomer

Enhancing the Permeability and Fouling Resistance of Thin-Film Composite Forward Osmosis Membranes via Poly(ethylene glycol) Diamine as a Comonomer

Improvements of ferrate(VI) pretreatment on membrane flux and membrane rejection using cheap NaClO reagent

Ferrate(VI) pretreatment can effectively alleviate membrane fouling during the ultrafiltration (UF) process, while instability and high expenditure limit its application. This study discovered that the cheap NaClO reagent would improve the performance of ferrate(VI) pretreatment, i.e., establishing Fe(VI)/NaClO (FC) process. 20 μM of Fe(VI) group can increase J/J0 from 0.323 to 0.391, while the optimization process of 20 μM Fe(VI)/4 μM NaClO [FC (5:1)] increased it to 0.491 at the end of cycle 1 filtration. Meanwhile, the reversible and irreversible membrane fouling resistance decreased by 50% and 56% in FC (5:1). This was attributed to the suppression of ferrate(VI) decomposing and in-situ formation of more dispersed ferric nanoparticles in FC process [730.33 nm in Fe(VI) and 606.80 nm in FC (5:1)] by applied NaClO. The rejection ratio of dissolved organic carbon (DOC) increased from 27.18% of Fe(VI) group to 40.34% of FC (5:1) due to the repulsive interaction amplification of acid-base (AB) interaction energy. That was derived from the hydrophilia promotion of the treated sample and the electrical property evolution of in-situ formed ferric nanoparticles by NaClO. It suggested that AB interaction energy, presenting repulsive interaction in membrane-foulants and foulants-foulants, was a major role in Fe(VI) group and FC process. There was no more side effect induced by FC pretreatment, which was confirmed by the result that FC caused no increase in the disinfection by-products (DBPs) formation potential. The present study provided insight into improving the effect of ferrate(VI) pretreatment without inducing side effect, and reduced the costs of ferrate(VI) pretreatment during the process of UF.

High-performance polyethyleneimine based reverse osmosis membrane fabricated via spin-coating technology

Conventional thin-film composite (TFC) reverse osmosis (RO) membranes prepared by ultrafast and uncontrolled interfacial polymerization (IP) generally have unsatisfactory permeability and high fouling propensity, which distinctly impedes their development and wide application. Controllable thickness and roughness offer an opportunity to optimize the permeability and fouling resistance of RO membranes. In this work, we propose spin-coating assisted multilayer interfacial polymerization (SMIP) as a promising approach to fabricating high-performance RO membranes using polyethyleneimine (PEI) and 1, 3, 5-benzoyl chloride (TMC). SMIP integrates the high efficiency and uniformity of spin-coating technology, the nano-level and individual properties control of multilayer interfacial polymerization, and the simplicity of the IP process. Combining the strong hydrophilicity with low diffusion efficiency and positive charge of PEI, a thin, intrinsically hydrophilic, smoother and almost electro-neutral polyamide (PA) nanofilm was obtained. The optimal RO membrane with a controlled thickness of the selective layer (≈61 nm) has a water permeance of 3.12 L m−2 h−1 bar−1 and an acceptable NaCl rejection of 97.5%, while the strong hydrophilicity, minimal surface roughness and almost neutral surface charge afford it excellent fouling resistance. SMIP technology not only provides a new approach to preparing highly permeable and low-fouling RO membranes using macromolecular monomers, but also has great application potential in other separation membranes due to its precise control of the selective layer.