Long-term stable metal organic framework (MOF) based mixed matrix membranes for ultrafiltration

Removal of Heavy Metals from Wastewaters and Other Aqueous Streams by Pressure-Driven Membrane Technologies: An Outlook on Reverse Osmosis, Nanofiltration, Ultrafiltration and Microfiltration Potential from a Bibliometric Analysis

A bibliometric study to analyze the scientific documents released until 2024 in the database Scopus related to the use of pressure-driven membrane technologies (microfiltration, ultrafiltration, nanofiltration and reverse osmosis) for heavy metal removal was conducted. The work aimed to assess the primary quantitative attributes of the research in this field during the specified period. A total of 2205 documents were identified, and the corresponding analysis indicated an exponential growth in the number of publications over time. The contribution of the three most productive countries (China, India and USA) accounts for more than 47.1% of the total number of publications, with Chinese institutions appearing as the most productive ones. Environmental Science was the most frequent knowledge category (51.9% contribution), followed by Chemistry and Chemical Engineering. The relative frequency of the keywords and a complete bibliometric network analysis allowed the conclusion that the low-pressure technologies (microfiltration and ultrafiltration) have been more deeply investigated than the high-pressure technologies (nanofiltration and reverse osmosis). Although porous low-pressure membranes are not adequate for the removal of dissolved heavy metals in ionic forms, the incorporation of embedded adsorbents within the membrane structure and the use of auxiliary chemicals to form metallic complexes or micelles that can be retained by this type of membrane are promising approaches. High-pressure membranes can achieve rejection percentages above 90% (99% in the case of reverse osmosis), but they imply lower permeate productivity and higher costs due to the required pressure gradients.

Performance improvement of polyethersulfone membranes with Ti3AlCN MAX phase in the treatment of organic and inorganic pollutants

In this work, the hydrophobic polyethersulfone (PES) membrane was modified by incorporating Ti3AlCN MAX phase. Synthesis of Ti3AlCN MAX phase was performed using the reactive sintering method. The scanning electron microscopy (SEM) images showed a 3D compressed layered morphology for the synthesized MAX phase. The Ti3AlCN MAX phase was added to the casting solution, and the mixed-matrix membranes were fabricated by the non-solvent induced phase inversion method. The performance and antifouling features of bare and modified membranes were explored by pure water flux, flux recovery ratio (FRR), and fouling resistance parameters. Through the modification of membranes by introducing the Ti3AlCN MAX phase, the enhancement of these features was observed, in which the membrane containing 1 wt% of MAX phase showed 17.7 L/m2.h.bar of permeability and 98.6% for FRR. Also, the separation efficiency of all membranes was evaluated by rejecting organic and inorganic pollutants. The Ti3AlCN MAX membranes could reject 96%, 95%, and 88% of reactive blue 50, Rose Bengal, and azithromycin antibiotics, respectively, as well as 98%, 80%, 86%, and 36% of Pb2+, As5+, Na2SO4, and NaCl, respectively. Finally, the outcomes indicated the Ti3AlCN MAX phase was an excellent and efficient novel additive for modifying the PES membrane.

Synthesis of MOF-5/polyethersulfone (PES) mixed matrix membranes for enhancing membrane filtration performance in polyphenol purification

The various apple products industries produce a large amount of apple residue, which is easily fermented, causes environmental pollution, and its disposal cost is high, but is rich in nutrients, such as polyphenols. Polyphenols can be purified to realize high-value deep processing of apple pomace and to promote energy reuse of food waste. In this study, the highly selective purification of polyphenols was achieved by membrane filtration using prepared Metal-organic framework (MOF)-5/PES mixed matrix membranes with apple peels as raw material. The polyethersulfone mixed matrix membrane was loaded with MOF-5 by the phase inversion method, and their structural and physicochemical properties were characterized by scanning electron microscopy (SEM), and X-ray diffraction (XRD). Zeta potential and specific surface area of MOF-5 particles were measured, as well as the water contact angle and anti-fouling properties of the mixed matrix membrane were analyzed. It was confirmed that the membrane loaded with MOF-5 showed better hydrophilicity and mechanical properties compared with the pristine polyether sulfone membrane. Under practical conditions, the increased hydrophilicity could enhance the anti-fouling properties of membranes, which would improve the flux recovery ratio of membranes. In addition, the prepared MOF-5/PES mixed matrix membrane was applied to the purification of polyphenols, showing excellent purification performance of polyphenols. In particular, the purity of polyphenol after membrane filtration could reach 70.45% when the additional amount of MOF-5 was 10%. This research provides a method to prepare MOF-5/PES mixed matrix membranes, which effectively solves the problem of unstable and unsatisfactory purification effect of commercially available membranes, promotes the development of new materials in membrane science, and realizes high-value deep processing and comprehensive resource development of food waste using membrane filtration.

Zeolite Imidazolate Frameworks-8@SiO2-ZrO2 Crystal-Amorphous Hybrid Core-Shell Structure as a Building Block for Water Purification Membranes

Metal-organic frameworks (MOFs) are emerging as promising materials for water purification membranes, owing to their uniform microporous structures and chemical functionalities. Here, we report a simple procedure for depositing MOF-based nanofiltration membranes on commercial TiO2 ceramic tubular supports, completely avoiding the use of dispersants or binders. Zeolite imidazolate frameworks-8 (ZIF-8) nanocrystals were synthesized in methanol at room temperature and subsequently coated with an amorphous SiO2-ZrO2 gel to generate a dispersion of ZIF-8@SiO2-ZrO2 core-shell nanoparticles. The amorphous SiO2-ZrO2 gel served as a binding agent for the ZIF-8 nanocrystals, thus forming a defect-free continuous membrane layer. After repeating the coating twice, the active layer had a thickness of 0.96 μm, presenting a rejection rate >90% for the total organic carbon in an aquaculture effluent and in a wastewater treatment plant, while reducing the concentration of trimethoprim, here used as a target pollutant. Moreover, the oxide gel provided the MOF-based active layer with good adhesion to the support and enhanced its hydrophilicity, resulting in a membrane with excellent mechanical stability and resistance to fouling during the crossflow filtration of the real wastewater samples. These results implied the high potential of the MOF-based nanocomposite membrane for effective treatment of actual wastewater streams.

Durable and recyclable MOF@polycaprolactone mixed-matrix membranes with hierarchical porosity for wastewater treatment

With the fast-growing global water crisis, the development of novel technologies for water remediation and reuse is crucial. Industrial wastewater especially contains various toxic pollutants that pose an additional threat to the environment; thus, efficient removal of such contaminants can ensure safe reprocessing of industrial wastewater, thereby alleviating the demand for fresh water. Herein, we describe a novel and efficient approach for preparing porous polycaprolactone (PCL) membranes with a hierarchical architecture via a simple solvent/non-solvent methodology. A mixed-matrix membrane (MMM) was further constructed utilizing an amine-functionalized metal-organic framework as the sorbent filler nanoparticles and PCL as the polymer support matrix (MOF@PCL) for wastewater treatment applications. The MOF@PCL MMM demonstrated homogeneous morphology as well as exceptional performance towards the removal of both cationic (methylene blue, MB) and anionic (methyl orange, MO) organic dyes, where the maximum adsorption capacities reached 309 mg g-1 and 208 mg g-1, respectively. Kinetic and thermodynamic investigations revealed that the adsorption process was endothermic with a fast intraparticle diffusion rate constant. The MOF@PCL MMM also displayed excellent mechanical stability and recyclability, where the removal efficiency was maintained after 10 cycles.

High Proton Conductivity of the UiO-66-NH2-SPES Composite Membrane Prepared by Covalent Cross-Linking

A sulfonated poly(ethersulfone) (SPES)-metal-organic framework (MOF) film with excellent proton conductivity was synthesized by anchoring UiO-66-NH₂ to the main chain of the aromatic polymer through the Hinsberg reaction. The chemical bond was formed between the amino group in MOFs and the -SO₂Cl group in chlorosulfonated poly(ethersulfones) to conduct protons in the proton channel of the membrane, making the membrane have excellent proton conductivity. UiO-66-NH₂ is successfully prepared as a result of the consistency of the experimental and simulated powder X-ray diffraction (PXRD) patterns of MOFs. The existence of absorption peaks of characteristic functional groups in Fourier transform infrared (FTIR) spectra proved the successful preparation of SPES, PES-SO₂Cl, and a composite film. The results of the AC impedance test indicate that the composite film with a 3% mass fraction has the best proton conductivity of 0.215 S·cm^-1, which is 6.2 times higher than that of the blended film without a chemical bond at 98% RH and 353 K. To our knowledge, there are rarely any reports on the preparation of a composite membrane by directly linking MOFs and the membrane matrix with chemical bonds. This work provides a good way to synthesize the highly conductive proton exchange film.

The recent advance of precisely designed membranes for sieving

Developing new membranes with both high selectivity and permeability is critical in membrane science since conventional membranes are often limited by the trade-off between selectivity and permeability. In recent years, the emergence of advanced materials with accurate structures at atomic or molecular scale, such as metal organic framework, covalent organic framework, graphene, has accelerated the development of membranes, which benefits the precision of membrane structures. In this review, current state-of-the-art membranes are first reviewed and classified into three different types according to the structures of their building blocks, including laminar structured membranes, framework structured membranes and channel structured membranes, followed by the performance and applications for representative separations (liquid separation and gas separation) of these precisely designed membranes. Last, the challenges and opportunities of these advanced membranes are also discussed.

Incorporation of 2D-biotene to polyethersulfone ultrafiltration membrane with superhydrophilicity and antifouling properties for removal of organic pollutants

Here, for the first time, one or few-layer exfoliated 2D-Biotene (E-BIT) was prepared by a cost-effective liquid-phase exfoliation of economical and accessible bulk biotite (B-BIT). The successful preparation of E-BIT was further verified by different characterization methods. XRD pattern demonstrated that B-BIT's basal spacing was increased from 10.07 Å to 11.02 Å. Also, the transparency of the E-BIT to the electron beam showed its small thickness after exfoliation, which was confirmed by AFM results, too. This natural material was utilized as an efficient nano-additive to improve the properties of polyethersulfone (PES) polymeric membrane. E-BIT blended membranes with various quantities (0-2 wt%) were prepared via the non-solvent induced phase inversion method. Small holes at the up layer, coarse finger-like holes and macro-voids at the sublayer were seen in asymmetric prepared membranes. Modification caused the improvement of the membranes' hydrophilicity, which the contact angle was reduced from 69.3 to 53.4 for bare PES and 1 wt% E-BIT blended membranes, respectively. 1 wt% E-BIT blended membrane illustrated flux enhancement of 198.8 L/m² h, and high elimination efficiency of bovine serum albumin (99%), reactive red 195 (97.8%), reactive green 9 (93.5%), and reactive blue 19 (88.4%), with improved flux recovery ratio of 73%.

Fabrication and Investigation of Acid Functionalized CNT Blended Nanocomposite Hollow Fiber Membrane for High Filtration and Antifouling Performance in Ultrafiltration Process

In this study, we fabricated a nanocomposite polyethersulfone (PES) HF membrane by blending acid functionalized carbon nanotubes (FCNT) to address the issue of reduced membrane life, increased energy consumption, and operating costs due to low permeability and membrane fouling in the ultrafiltration process. Additionally, we investigated the effect of FCNT blending on the membrane in terms of the physicochemical properties of the membrane and the filtration and antifouling performance. The FCNT/PES nanocomposite HF membrane exhibited increased water permeance from 110.1 to 194.3 LMH/bar without sacrificing rejection performance and increased the flux recovery ratio from 89.0 to 95.4%, compared to a pristine PES HF membrane. This study successfully developed a high filtration and antifouling polymer-based HF membrane by blending FCNT. Furthermore, it was validated that blending FCNT into the membrane enhances the filtration and antifouling performance in the ultrafiltration process.

Natural and recycled materials for sustainable membrane modification: Recent trends and prospects

Despite water being critical for human survival, its uneven distribution, and exposure to countless sources of pollution make water shortages increasingly urgent. Membrane technology offers an efficient solution for alleviating the water shortage impact. The selectivity and permeability of membranes can be improved by incorporating additives of different nature and size scales. However, with the vast debate about the environmental and economic feasibility of the common nanoscale materials in water treatment applications, we can infer that there is a long way before the first industrial nanocomposite membrane is commercialized. This stumbling block has motivated the scientific community to search for alternative modification routes and/or materials with sustainable features. Herein, we present a pragmatic review merging the concept of sustainability, nanotechnology, and membrane technology through the application of natural additives (e.g., Clays, Arabic Gum, zeolite, lignin, Aquaporin), recycled additives (e.g., Biochar, fly ash), and recycled waste (e.g., Polyethylene Terephthalate, recycled polystyrene) for polymeric membrane synthesis and modification. Imparted features on polymeric membranes, induced by the presence of sustainable natural and waste-based materials, are scrutinized. In addition, the strategies harnessed to eliminate the hurdles associated with the application of these nano and micro size additives for composite membranes modification are elaborated. The expanding research efforts devoted recently to membrane sustainability and the prospects for these materials are discussed. The findings of the investigations reported in this work indicate that the application of natural and waste-based additives for composite membrane fabrication/modification is a nascent research area that deserves the attention of both research and industry.

Defective MOFs-based electrocatalytic self-cleaning membrane for wastewater reclamation: Enhanced antibiotics removal, membrane fouling control and mechanisms

In order to resolve the poor antibiotics rejection and serious fouling of ultrafiltration (UF) membrane during municipal wastewater reclamation, a novel anodic membrane (defective UiO-66 (D-UiO-66)/Graphite/Polyvinylidene fluoride (PVDF)) with high pure water flux (596.1 L•h ^- 1•m ^- 2•bar^-1) was fabricated by incorporating defective zirconium based metal-organic framework (D-UiO-66) and conductive graphite particles into PVDF matrix and applied in the coupling of electro-oxidation and membrane filtration process. Compared to the other anodic membranes (i.e., Graphite/PVDF and UiO-66/Graphite/PVDF), D-UiO-66/Graphite/PVDF possesses superior anti-fouling and self-cleaning abilities (flux recovery=100%, model foulant: bovine serum albumin) in both intermittent and continuous supply of electric field under current density of 0.01 mA/cm²; moreover, efficient antibiotics (tetracycline, norfloxacin, tylosin and sulfamethoxazole) removal (> 96.6%) and bactericidal efficiency against E. coli and S. aureus (100%) were achieved simultaneously without the addition of chemical reagents due to the higher electrocatalytic activity of anodic membrane for oxidation of pollutants by •OH and •O₂^- free radicals. Three degradation pathways of antibiotics were proposed and the self-cleaning mechanism of membrane was dominated by the synergy of the partial mineralization and the reduced fouling potential of foulants after oxidation as revealed by the increase in hydrophilicity, and decrease in negative charge and molecular weight. The fabricated membrane also presents excellent electrochemical stability, separation and self-cleaning performance for treatment of municipal secondary effluent during long-term filtration with low electric energy consumption, which is promising in wastewater reclamation.

Preparation of Ni@UiO-66 incorporated polyethersulfone (PES) membrane by magnetic field assisted strategy to improve permeability and photocatalytic self-cleaning ability

Metal-organic frameworks (MOFs) have been considered as promising nanofillers to fabricate mixed matrix membranes for water treatment. However, manipulating distribution of MOFs nanoparticles in the membrane matrix remains a great challenge. In this study, UiO-66 was firstly coated by magnetic Ni via an in-situ reduction reaction, and then incorporated into polyethersulfone (PES) membrane matrix to prepare PES-Ni@UiO-66 membrane. The magnetic Ni allowed to manipulate the distribution of magnetic Ni@UiO-66 in the phase-inversion process by an external magnetic field. The hydrophilic Ni@UiO-66 can be pulled onto membrane surface by the magnetic force, endowing the prepared membrane with rather higher hydrophilicity. The prepared membrane exhibited superior water permeability with a pure water flux of 611.5 ± 19.8 L·m^-2·h^-1 and improved antifouling performance. Moreover, benifiting from photocatalytic activity of the exposed Ni@UiO-66 on membrane surface, the obtained PES-Ni@UiO-66 membrane demonstrated excellent photocatalytic self-cleaning ability with a flux recovery rate (FRR) higher than 95% under UV irradiation. Analyzing by extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory indicated that the improved antifouling performance could be attributed to less attractive or even repulsive interaction between the prepared membrane and pollutants. This work provided valuable guidance for structural regulation and development of high-performance MOFs-based membranes for water treatment.

Metal organic framework UiO-66 incorporated ultrafiltration membranes for simultaneous natural organic matter and heavy metal ions removal

In this work, a new type of UiO-66 incorporated polysulfone (PSf) ultrafiltration (UF) membranes was fabricated to enhance antifouling properties and heavy metal ions removal efficiency. The UF membranes incorporating different loadings of the UiO-66 filler were prepared via the classical phase inversion process. These membranes unveiled enhanced hydrophilicity, porosity, water uptake, zeta potential, mechanical strength, permeability, and HA removal ratios due to the incorporation of hydrophilic UiO-66 fillers. Particularly, HA rejection ratios were observed to be approximately 93% for all the modified membranes, which was attributed to electrostatic repulsion interactions between the hydrophilic groups of HA and UiO-66. Moreover, the antifouling abilities of the modified membranes were evaluated and found to be much better with a high flux recovery ratio (FRR) of about 88% when compared to the blank PSf membrane (only around 34%). Moreover, the UiO-66 incorporated membranes were highly-effective in the removal of contaminants like heavy metal ions (Sr²⁺, Pb²⁺, Cd²⁺, and Cr⁶⁺) and HA at the same time. Overall, the PSf UF membranes incorporating UiO-66 opened up a new avenue to enhance the membrane hydrophilicity, permeability, antifouling properties as well as heavy metal ions removal abilities.

MXene (Ti3C2Tx)/Cellulose Acetate Mixed-Matrix Membrane Enhances Fouling Resistance and Rejection in the Crossflow Filtration Process

Obstacles in the membrane-based separation field are mainly related to membrane fouling. This study involved the synthesis and utilization of covalently crosslinked MXene/cellulose acetate mixed matrix membranes with MXene at different concentrations (CCAM-0% to CCAM-12%) for water purification applications. The membranes’ water flux, dye, and protein rejection performances were compared using dead-end (DE) and crossflow (CF) filtration. The fabricated membranes, especially CCAM-10%, exhibited high hydrophilicity, good surface roughness, significantly high water flux, high water uptake, and high porosity. A significantly higher flux was observed in CF filtration relative to DE filtration. Moreover, in CF filtration, the CCAM-10% membrane exhibited 96.60% and 99.49% rejection of methyl green (MG) and bovine serum albumin (BSA), respectively, while maintaining a flux recovery ratio of 67.30% and an irreversible fouling ratio at (R_ir) of 32.70, indicating good antifouling performance. Hence, this study suggests that covalent modification of cellulose acetate membranes with MXene significantly improves the performance and fouling resistance of membranes for water filtration in CF mode relative to DE mode.