Surface enriched sulfonated polyarylene ether benzonitrile (SPEB) that enhances heavy metal removal from polyacrylonitrile (PAN) thin-film composite nanofiltration membranes

Heavy Metal Rejection Performance and Mechanical Performance of Cellulose-Nanofibril-Reinforced Cellulose Acetate Membranes

In this research, cellulose acetate (CA) and CA nanocomposite membranes, reinforced with mass fractions of cellulose nanofibrils (CNF), are prepared using the phase separation technique. The membranes are extensively characterized using several techniques: Fourier Transform Infrared (FTIR) spectroscopy confirms the chemical structures, while Scanning Electron Microscopy (SEM) reveals their surface morphology. Mechanical characterization is conducted to explore the mechanical behavior of the membranes under wet and dry conditions through tensile testing. The mechanical properties of CA and CA-CNF membranes are also estimated using the Mori-Tanaka mean-field homogenization method and compared to experimental findings. The flux performance for pure and dam water, assessed at 3 bar, demonstrates that CNF reinforcement notably enhances the CA membrane's performance, particularly in flux rate and fouling resistance. The CA membrane shows high efficiency in removing Fe2+, Ba2+, and Al3+ from dam water, while CA-CNF membranes exhibit a varied range of removal efficiencies for the same ions, with the 0.5 wt % CNF variant showing superior resistance to surface fouling. Additionally, while CNF increases tensile strength and stiffness, it leads to earlier failure under smaller deformations, especially at higher concentrations. This research provides a detailed assessment of CA and CA-CNF membranes, examining their chemical, structural, and mechanical properties alongside their effectiveness in water treatment applications.

Material Design Strategies for Recovery of Critical Resources from Water

Population growth, urbanization, and decarbonization efforts are collectively straining the supply of limited resources that are necessary to produce batteries, electronics, chemicals, fertilizers, and other important products. Securing the supply chains of these critical resources via the development of separation technologies for their recovery represents a major global challenge to ensure stability and security. Surface water, groundwater, and wastewater are emerging as potential new sources to bolster these supply chains. Recently, a variety of material-based technologies have been developed and employed for separations and resource recovery in water. Judicious selection and design of these materials to tune their properties for targeting specific solutes is central to realizing the potential of water as a source for critical resources. Here, the materials that are developed for membranes, sorbents, catalysts, electrodes, and interfacial solar steam generators that demonstrate promise for applications in critical resource recovery are reviewed. In addition, a critical perspective is offered on the grand challenges and key research directions that need to be addressed to improve their practical viability.

A PEI/TMC membrane modified with an ionic liquid with enhanced permeability and antibacterial properties for the removal of heavy metal ions

Heavy metal ions in drinking water severely threaten public health in various places worldwide. Nanofiltration (NF) membrane technology is an attractive option for heavy metal ions removal; however, improving NF membrane filtration performance is required to make their industrial application viable. In this study, a positively charged THPC/PEI-TMC NF membrane was designed via simple one-step incorporation of Tetrakis (hydroxymethyl) phosphonium chloride (THPC) biocide on the surface of PEI-TMC membranes, significantly optimizing surface morphology, roughness, hydrophilicity, and zeta potential of PEI-TMC membranes. It was found that the pure water permeability (11.6 Lm^-2h^-1bar^-1) of the THPC modified membrane was three times larger than that of the original PEI-TMC membrane (3.4 Lm^-2h^-1bar^-1) while maintaining a high level of ion rejections (around 95% for Zn²⁺, Cd²⁺, Ni²⁺, Cu²⁺ and about 90% for Pb²⁺). Additionally, the incorporation of the THPC on the original PEI-TMC membrane surface also conferred good antibacterial properties, which protect the organic membrane from bacterial growth and prolong the lifespan of the membrane.

Adsorption of Sodium Diclofenac in Functionalized Palygoskite Clays

The effects of acid and organo-functionalizations on the surface of Brazilian palygorskite clay was investigated, evaluating its potential in the adsorptive capacity of the drug sodium diclofenac present in wastewaters. The modifications on the clay structure were investigated by X-ray diffraction, X-ray fluorescence, thermogravimetric, differential thermal analysis, Fourier transform infrared spectroscopy, surface area by N₂ adsorption (77.5 K) and Zeta potential. The experimental design was carried out to find the best conditions for the adsorption tests, in which concentration, mass and pH were significant. In the kinetic study, the pseudo-second-order model better described the adsorption process for acid and organo-functionalized samples. Such results indicate that the adsorption behavior probably occurs due to the phenomenon of chemisorption. Regarding the adsorption isotherms, the Langmuir model was the one that best adjusted both the experimental data of acid and the organo-functionalized samples, whose maximum adsorption capacity were 179.88 and 253.34 mg/g, respectively. This model also indicates that the sodium diclofenac is adsorbed to monolayers homogeneously through chemisorption. In general, the studied clays proved to be suitable adsorbents for the removal of sodium diclofenac.

High-performance photocatalytic membranes for water purification in relation to environmental and operational parameters

Growing technologies, increasing population and environmental pollution lead to severe contamination of water and require advanced water treatment technologies. These aspects lead to the need to purify water with advanced smart materials. This paper reviews the recent advances (during the last 5 years) in photocatalytic composite membranes used for water treatment. For this purpose, the authors have reviewed the main materials used in the development of (photocatalytic membranes) PMs, environmental and operational factors affecting the performance of photocatalytic membranes, and the latest developments and applications of PMs in water purifications. The composite photocatalytic membranes show good performance in the removal and degradation of pollutants from water.

Fabrication of an antifouling PES ultrafiltration membrane via blending SPSF

Sulfonated polysulfone (SPSF) with different sulfonation degrees (10%, 30%, and 50%) was added to polyethersulfone (PES) to improve the separation and antifouling performance of polyethersulfone ultrafiltration membranes. The PES/SPSF blend ultrafiltration membrane was prepared by the non-solvent induced phase inversion method (NIPS), and the effect of sulfonation degree on the ultrafiltration performance was studied. The compatibility of SPSF and PES was calculated by the group contribution method, and confirmed by differential scanning calorimetry (DSC). The morphology and surface roughness of the membrane were characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), the chemical composition of the membrane was analyzed by X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (FTIR), and the permeability and anti-fouling performance of the blend membrane were studied through filtration experiments. The research shows that the flux and anti-fouling performance of the blend membrane have been improved after adding SPSF. When the sulfonation degree of the SPSF is 30%, the pure water flux of the blend membrane can reach 530 L m⁻² h⁻¹, the rejection rate of humic acid (HA) is 93%, the flux recovery rate of HA increases from 69.23% to 79.17%, and the flux recovery rate of BSA increases from 72.56% to 83%.

The chemical structures of (a) PES and (b) SPSF.

Fabrication of a hybrid ultrafiltration membrane based on MoS2 modified with dopamine and polyethyleneimine

The hydrophobicity of ultrafiltration membranes is the main cause of membrane fouling and reduced permeability, so it is necessary to improve the hydrophilicity and anti-fouling performance of ultrafiltration membrane materials. MoS₂ nanoparticles that were modified with polydopamine (PDA) and polyethyleneimine (PEI), named MoS₂-PDA-PEI, were added to fabricate a polyethersulfone ultrafiltration membrane (PES/MoS₂-PDA-PEI) for the first time. The effects of modified MoS₂ nanoparticles on membrane performance were clarified. The results indicated that the permeability, rejection, and anti-fouling capability of the hybrid PES/MoS₂-PDA-PEI membrane have been improved compared with the pristine PES membrane. When the content of MoS₂-PDA-PEI nanoparticles in the membrane is 0.5%, the pure water flux of the hybrid membrane reaches 364.03 L m⁻² h⁻¹, and the rejection rate of bovine serum albumin (BSA) and humic acid (HA) is 96.5% and 93.2% respectively. The flux recovery rate of HA reached 97.06%. As expected, the addition of MoS₂-PDA-PEI nanoparticles promotes the formation of the porous structure and improves the hydrophilicity of the membrane, thereby improving its antifouling performance.

The hydrophobicity of ultrafiltration membranes is the main cause of membrane fouling and reduced permeability, so it is necessary to improve the hydrophilicity and anti-fouling performance of ultrafiltration membrane materials.

Thin-film nanocomposite NF membrane with GO on macroporous hollow fiber ceramic substrate for efficient heavy metals removal

The ceramic membrane has been widely used in the wastewater treatment based on the chemical resistance and superior separation performance. A robust and defect-free thin-film nanocomposite (TFN) nanofiltration (NF) membrane on the macroporous hollow fiber ceramic (HFC) substrate was novelly developed for heavy metals removal. Before interfacial polymerization (IP), the aqueous solution of graphene oxide (GO) grafted with ethylenediamine (EDA) was deposited on the HFC substrate by vacuum filtration. Then, a thin polyamide (PA) film was fabricated by EDA and 1,3,5-trimesoyl chloride (TMC), followed by heat treatment. The effects of GO content and EDA concentration on the performance of the NF membrane have been systematically investigated. The results showed that when the GO content was 0.015 mg·mL^-1 and the EDA concentration was 0.75 wt.%, the as-prepared eGO₃/PA-HFC membrane had a rejection rate of 94.12% for MgCl₂ and a pure water flux of 18.03 L·m^-2·h^-1. Additionally, the removal ability of eGO₃/PA-HFC membranes for heavy metal ions was satisfactory (93.33%, 92.73%, 90.45% and 88.35% for Zn²⁺, Cu²⁺, Ni²⁺ and Pb²⁺, respectively). The study explored further that it was efficient and stable for heavy metal ions removal during 30 h in the simulated tap water and mining wastewater, which indicated that the eGO/PA-HFC membrane has great application potential in wastewater treatment.

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.

Pressure-Driven Membrane Process: A Review of Advanced Technique for Heavy Metals Remediation

Pressure-driven processes have come a long way since they were introduced. These processes, namely Ultra-Filtration (UF), Nano-Filtration (NF), and Reverse-Osmosis (RO), aim to enhance the efficiency of wastewater treatment, thereby aiming at a cleaner production. Membranes may be polymeric, ceramic, metallic, or organo-mineral, and the filtration techniques differ in pore size from dense to porous membrane. The applied pressure varies according to the method used. These are being utilized in many exciting applications in, for example, the food industry, the pharmaceutical industry, and wastewater treatment. This paper attempts to comprehensively review the principle behind the different pressure-driven membrane technologies and their use in the removal of heavy metals from wastewater. The transport mechanism has been elaborated, which helps in the predictive modeling of the membrane system. Fouling of the membrane is perhaps the only barrier to the emergence of membrane technology and its full acceptance. However, with the use of innovative techniques of fabrication, this can be overcome. This review is concluded with perspective recommendations that can be incorporated by researchers worldwide as a new problem statement for their work.

In Situ Synthesis of Silver Nanoparticles on Amino-Grafted Polyacrylonitrile Fiber and Its Antibacterial Activity

In this study, amino hyperbranched polymers (HBP)-grafted polyacrylonitrile (PAN) fiber was prepared through an amidation reaction in an autoclave. The prepared PAN-G-HBP fiber can complex Ag⁺ through amino groups of amino HBP, and in a hot steaming condition, Ag⁺ can be converted to Ag0 through the reducibility of HBP. PAN-G-HBP and Ag nanoparticles (NPs)-coated fibers were then characterized through FTIR, UV-VIS DRS, FE-SEM, EDS, XPS and antibacterial measurement. FTIR results confirmed HBP was grafted on the surface of PAN fiber. FE-SEM showed that after grafting with HBP, the average diameter of PAN fibers was amplified. EDS, XPS, and UV-VIS DRS method indicated that under hot steaming condition and with the reducibility of HBP, Ag NPs uniform coating on the PAN-G-HBP. Ag NPs-coated fibers exhibits excellent antibacterial property against Escherichia coli and Staphylococcus aureus. Even under 20 times home washing conditions, the antibacterial reduction of Ag NPs-coated PAN fiber can achieved more than 98.94%.

Immobilization techniques of a photocatalyst into and onto a polymer membrane for photocatalytic activity

This article reviews the various techniques of immobilizing a photocatalyst into and onto the polymer membrane for pollutant removal and as a problem solver in handling suspended photocatalyst issues from the previous literature. A particular focus is given to the preparation of mixed matrix membranes and deposition techniques for photocatalytic degradation in applications for wastewater treatment. Advantages and disadvantages in this application are evaluated. Various operating conditions during the process are presented. About 90 recently published studies (2008–2020) are reviewed. From the literature, it was found that TiO₂ is the most favoured photocatalyst that is frequently used in photocatalytic water treatment. Dry–wet co-spinning and sputtering techniques emerged as the promising technique for immobilizing a uniformly distributed photocatalyst within the polymeric membrane, and exhibited excellence pollutant removal. In general, the technical applicability is the key factor in selecting the best photocatalyst immobilizing technique for water treatment. Finally, the scope of various techniques that have been reviewed may provide potential for future photocatalytic study.

This article reviews the various techniques of immobilizing a photocatalyst into and onto the polymer membrane for pollutant removal and as a problem solver in handling suspended photocatalyst issues from the previous literature.

Selective and efficient removal of Hg (II) from aqueous media by a low-cost dendrimer-grafted polyacrylonitrile fiber: Performance and mechanism

Polyacrylonitrile fiber was successfully modified with triazine-based dendrimer via grafting method as a promising adsorbent for removal of mercury species from aqueous media. The prepared adsorbent was characterized by elemental analysis, scanning electron microscope, Fourier transform infrared spectroscopy, porous structure analysis and X-ray photoelectron spectroscopy, providing the evidence of successful fabrication. The adsorption conditions were found via varying pH, dosage, coexisting substances, contact time, temperature and concentration. Adsorption performance, described better by the pseudo-second-order kinetics with intraparticle diffusion as rate controlling step and Langmuir isotherm model, indicated a chemisorption process with the maximum Langmuir adsorption amount of 227.64 mg g^-1 for mercury ions. Thermodynamically, adsorption of mercury ions was spontaneous and endothermic. Desorption and regeneration experiments demonstrated that it could be reused in five successive adsorption cycles without significant loss of its original performance. Experimental data and density functional theory calculation disclosed the coordination geometries and chelating mechanism between the adsorbent and mercury ions. The proposed study would provide a new prospect for the purification of mercury in aqueous system by functionalizing commercial polyacrylonitrile fiber with dendrimers.

Removal of As(V), Cr(VI) and Cu(II) using novel amine functionalized composite nanofiltration membranes fabricated on ceramic tubular substrate

Novel amine functionalized composite membranes were prepared over tubular ceramic substrate using facile dip-coating and cross-flow filtration approach. The two fabricated membranes, P-60S and P-60S-EDTA with polyethyleneimine (PEI) and EDTA-modified PEI as functional layers respectively, were characterized in terms of EDX, FTIR, XPS, FESEM, AFM and contact angle analyses which confirmed their stable physical and chemical structure for use in high pressure application. Clean water permeability and MWCO study revealed the superior permeability and rejection efficiency of the P-60S-EDTA compared to the P-60S membrane. Incorporation of bulky EDTA molecules in the membrane functional layer simultaneously decreased pore size and increased membrane hydrophilicity. The removal of As(V), Cr(VI) and Cu(II) heavy metals by both membranes were found to be highly pH dependent and overall rejection improved in case of P-60S-EDTA membrane [99.82% for Cu(II), 96.75% for As(V) and 97.22% for Cr(VI)]. Interestingly, rejection of As(V) and Cr(VI) was significantly improved in presence of Cu(II) due to volume resistance provided by EDTA-Cu(II) complex towards the passage of other heavy metal ions. Excellent stability of P-60S-EDTA membrane in continuous operation of 36 h in both ideal and practical water environment suggests its promising application in real field heavy metal contaminated waste water treatment.

Poly(Homopiperazine-Amide) Thin-Film Composite Membrane for Nanofiltration of Heavy Metal Ions

The development of membrane-based technologies for the treatment of wastewater streams and resources containing heavy metal ions is in high demand. Among various technologies, nanofiltration (NF) membranes are attractive choices, and the continuous development of novel materials to improve the state-of-the-art NF membranes is highly desired. Here, we report on the synthesis of poly(homopiperazine-amide) thin-film composite (HTFC)-NF membranes, using homopiperazine (HP) as a monomer. The surface charge, hydrophilicity, morphology, cross-linking density, water permeation, solute rejection, and antifouling properties of the fabricated NF membranes were evaluated. The fabricated HTFC NF membranes demonstrated water permeability of 7.0 ± 0.3 L/(m2 h bar) and rejected Na2SO4, MgSO4, and NaCl with rejection values of 97.0 ± 0.6, 97.4 ± 0.5, and 23.3 ± 0.6%, respectively. The membranes exhibit high rejection values of 98.1 ± 0.3 and 96.3 ± 0.4% for Pb2+ and Cd2+ ions, respectively. The fouling experiment with humic acid followed by cross-flow washing of the membranes indicates that a flux recovery ratio (FRR) of 96.9 ± 0.4% can be obtained.

Assessment of sulfonated homo and co-polyimides incorporated polysulfone ultrafiltration blend membranes for effective removal of heavy metals and proteins

Sulfonated homo and co- polyimide (sPI) were synthesized with new compositional ratios, and used as additives (0.5 wt%, 0.75 wt%, and 1.0 wt%) to prepare blend membranes with polysulfone (PSf). Flat sheet membranes for ultrafiltration (UF) were casted using the phase inversion technique. Surface morphology of the prepared UF membranes were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Surface charge of the membranes were determined by zeta potential, and hydrophilicity was studied by contact angle measurement. The contact angle of the membrane decreased with increasing sPI additive indicates increasing the hydrophilicity of the blend membranes. Filtration studies were conducted for rejection of heavy metals (Pb2+ and Cd2+) and proteins (pepsin and BSA). Blend membranes showed better rejection than pure PSf membrane. Among the blend membranes it was observed that with increasing amount of sPIs enhance the membrane properties and finally, PSf-sPI5 membrane with 1 wt% of sPI5 showed the improved permeability (72.1 L m-2 h-1 bar-1), and the best rejection properties were found for both metal ions (≈98% of Pb2+; ≈92% of Cd2+) and proteins (>98% of BSA; > 86% of Pepsin). Over all, this membrane was having better hydrophilicity, porosity and higher number of sites to attach the metal ions. Its performance was even better than several-reported sulfonic acid based UF membranes. All these intriguing properties directed this new UF membrane for its potential application in wastewater treatment.

A comprehensive review of the structures and properties of ionic polymeric materials

This review focuses on the mechanistic approach, the structure–property relationship and applications of ionic polymeric materials.

Membrane Surface Engineering with Bifunctional Zwitterions for Efficient Oil-Water Separation

Chemical modification provides a solution to the membrane fouling problem in oily water purification. However, complicated synthesis processes and harsh reaction conditions are frequently encountered with this approach. Here we developed two bifunctional zwitterionic materials, i.e., n-aminoethyl piperazine propanesulfonate (P-SO₃-NH₂) and 1,4-bis (3-aminopropyl) piperazine propanesulfonate (P-2SO₃-2NH₂), by a clean method and grafted them onto membrane surface via a fast single-step reaction. These materials endow the resultant membrane a more hydrophilic and smoother surface, significantly improving the water permeability, fouling resistance and recyclability of membrane in forward osmosis oily water reclamation. The water fluxes produced by the P-2SO₃-2NH₂ modified membrane are 47% (from 20.0 to 29.3 LMH) and 60% (from 16.0 to 25.6 LMH) higher than those of the unmodified membrane when DI water and an oily emulsion (1500 ppm) as the respective feeds. A higher water flux recovery is also achieved for the P-2SO₃-2NH₂ modified membrane (94%) than that of the nascent membrane (82%) after a 12-h experiment. These promising findings coupled with a facile and efficient membrane modification approach provide inspiration for both membrane exploration and oily water treatment.