Novel nanocomposite pervaporation membranes composed of poly(vinyl alcohol) and chitosan-wrapped carbon nanotube

Research Progress of Natural Rubber Wet Mixing Technology

The performance of natural rubber (NR), a naturally occurring and sustainable material, can be greatly enhanced by adding different fillers to the NR matrix. The homogeneous dispersion of fillers in the NR matrix is a key factor in their ability to reinforce. As a novel method, wet mixing technology may effectively provide good filler dispersion in the NR matrix while overcoming the drawbacks of conventional dry mixing. This study examines the literature on wet mixing fillers, such as graphene, carbon nanotubes, silica, carbon black, and others, to prepare natural rubber composites. It also focuses on the wet preparation techniques and key characteristics of these fillers. Furthermore, the mechanism of filler reinforcement is also examined. To give guidance for the future development of wet mixing technology, this study also highlights the shortcomings of the current system and the urgent need to address them.

Innovative strategies for enhancing gas separation: Ionic liquid-coated PES membranes for improved CO2/N2 selectivity and permeance

As a cost-effective advancement in membrane technology, this study investigates the impact of PEG additive and CBT on the structural, stability, and gas permeance properties of PES-coated membranes, utilizing 1-dodecyl-3-methylimidazolium chloride ionic liquid ([DDMI][Cl] IL) as a carrier liquid. BET and FT-IR analyses highlight the significant enhancement in performance through the immobilization of pores with [DDMIM][Cl] IL. The investigation focuses on PES-M5-coated membranes, revealing excellent stability in finger-like pore structures prepared through direct immersion and nitrogen pressure immobilization. PES-M5-coated membranes with [DDMIM][Cl] IL via direct immersion experience lower weight loss than those coated using nitrogen pressure, with critical pressures at 1.4 and 1.25 bar, respectively. The study identifies PES-coated membranes, particularly PES-M25 (20.88 GPU) with macro-void pores and PES-M5 (29 GPU) with finger-like pores, exhibiting the highest CO2 permeance and CO2/N2 selectivity. As a cost-effective advancement in membrane technology, ionic liquids are employed in support membranes to enhance gas separation. Employing pure PES membranes with varying pore structures, created through the NIPS method, the study immobilizes [DDMI][Cl] IL in membrane pores through nitrogen pressure and direct immersion. Results underscore the successful application of porous support materials coated with ionic liquids for continuous CO2 and sulfur compound separation, showcasing competitive permeability and selectivity compared to traditional polymer membranes.

Surface Segregation Methods toward Molecular Separation Membranes

As a highly promising approach to solving the issues of energy and environment, membrane technology has gained increasing attention in various fields including water treatment, liquid separations, and gas separations, owing to its high energy efficiency and eco-friendliness. Surface segregation, a phenomenon widely found in nature, exhibits irreplaceable advantages in membrane fabrication since it is an in situ method for synchronous modification of membrane and pore surfaces during the membrane forming process. Meanwhile, combined with the development of synthesis chemistry and nanomaterial, the group has developed surface segregation as a versatile membrane fabrication method using diverse surface segregation agents. In this review, the recent breakthroughs in surface segregation methods and their applications in membrane fabrication are first briefly introduced. Then, the surface segregation phenomena and the classification of surface segregation agents are discussed. As the major part of this review, the authors focus on surface segregation methods including free surface segregation, forced surface segregation, synergistic surface segregation, and reaction-enhanced surface segregation. The strategies for regulating the physical and chemical microenvironments of membrane and pore surfaces through the surface segregation method are emphasized. The representative applications of surface segregation membranes are presented. Finally, the current challenges and future perspectives are highlighted.

ZIF-67 Incorporated Sulfonated Poly (Aryl Ether Sulfone) Mixed Matrix Membranes for Pervaporation Separation of Methanol/Methyl Tert-Butyl Ether Mixture

Mixed matrix membranes (MMMs) with nano-fillers dispersed in polymer matrix have been proposed as alternative pervaporation membrane materials. They possess both promising selectivity benefiting from the fillers and economical processing capabilities of polymers. ZIF-67 was synthesized and incorporated into the sulfonated poly (aryl ether sulfone) (SPES) matrix to prepare SPES/ZIF-67 mixed matrix membranes with different ZIF-67 mass fractions. The as-prepared membranes were used for pervaporation separation of methanol/methyl tert-butyl ether mixtures. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and laser particle size analysis results show that ZIF-67 is successfully synthesized, and the particle size is mainly between 280 nm and 400 nm. The membranes were characterized by SEM, atomic force microscope (AFM), water contact angle, thermogravimetric analysis (TGA), mechanical property testing and positron annihilation technique (PAT), sorption and swelling experiments, and the pervaporation performance was also investigated. The results reveal that ZIF-67 particles disperse uniformly in the SPES matrix. The roughness and hydrophilicity are enhanced by ZIF-67 exposed on the membrane surface. The mixed matrix membrane has good thermal stability and mechanical properties, which can meet the requirements of pervaporation operation. The introduction of ZIF-67 effectively regulates the free volume parameters of the mixed matrix membrane. With increasing ZIF-67 mass fraction, the cavity radius and free volume fraction increase gradually. When the operating temperature is 40 °C, the flow rate is 50 L·h^-1 and the mass fraction of methanol in feed is 15%, the mixed matrix membrane with ZIF-67 mass fraction of 20% shows the best comprehensive pervaporation performance. The total flux and separation factor reach 0.297 kg·m^-2·h^-1 and 2123, respectively.

Biological MWCNT/chitosan composite coating with outstanding anti-corrosion property for implants

Biocompatible coatings that can protect metal implants have great potential in tissue engineering. In this work, MWCNT/chitosan composite coatings with hydrophobic-hydrophilic asymmetric wettability were facilely prepared by one-step in situ electrodeposition. The resultant composite coating exhibits excellent thermal stability and mechanical strength (0.76 MPa), benefiting from the compact internal structure. The thickness of the coating can be controlled precisely by the amounts of transferred charges. The MWCNT/chitosan composite coating demonstrates a lower corrosion rate due to its hydrophobicity and compact internal structure. Compared with exposed 316 L stainless steel, its corrosion rate is reduced by two orders of magnitude from 3.004 × 10^-1 mm/yr to 5.361 × 10^-3 mm/yr. The content of iron released from 316 L stainless steel into the simulated body fluid drops to 0.1 mg/L under the protection of the composite coating. In addition, the composite coating enables efficient calcium enrichment from simulated body fluids and promotes the formation of bioapatite layers on the coating surface. This study contributes to furthering the practical application of chitosan-based coatings in implant anticorrosion.

Effect of Nanofillers on Properties and Pervaporation Performance of Nanocomposite Membranes: A Review

In recent years, a well-known membrane-based process called pervaporation (PV), has attracted remarkable attention due to its advantages for selective separation of a wide variety of liquid mixtures. However, some restrictions of polymeric membranes have led to research studies on developing membranes for efficient separation in the PV process. Recent studies have focused on preparation of nanocomposite membranes as an effective method to improve both selectivity and permeability of polymeric membranes. The present study provides a review of PV nanocomposite membranes for various applications. In this review, recent developments in the field of nanocomposite membranes, including the fabrication methods, characterization, and PV performance, are summarized.

Effect of Phase Heterogeneity on the Properties of Poly(vinyl alcohol)-Based Composite Pervaporation Membranes

The structure, thermophysical characteristics, and pervaporation properties of composite membranes based on poly(vinyl alcohol) (PVA) are studied in dependence of the film preparation conditions. It is shown that the nature of the supramolecular organization of the composite polymer film determines which of the components of the separated mixtures of toluene and heptane predominantly penetrate through the corresponding pervaporation membrane. The observed structural effects can become more pronounced if the second component of a polymer mixture is purposefully selected (in this case, poly(N,N-dimethylaminoethyl methacrylate) instead of poly(acrylic acid)) or a nano-sized filler that can be well dispersed in the polymer matrix is introduced. Multi-wall carbon nanotubes are introduced into binary PVA-containing polymer blends. The influence of these fillers on the structure and transport properties of the obtained membranes is studied.

Percolation Effects in Mixed Matrix Membranes with Embedded Carbon Nanotubes

Polymeric membranes with embedded nanoparticles, e.g., nanotubes, show a significant increase in permeability of the target component while maintaining selectivity. However, the question of the reasons for this behavior of the composite membrane has not been unequivocally answered to date. In the present work, based on experimental data on the permeability of polymer membranes based on Poly(vinyl trimethylsilane) (PVTMS) with embedded CNTs, an approach to explain the abnormal behavior of such composite membranes is proposed. The presented model considered the mass transfer of gases and liquids through polymeric membranes with embedded CNTs as a parallel transport of gases through the polymeric matrix and a "percolation" cluster-bound regions around the embedded CNTs. The proposed algorithm for modeling parameters of a percolation cluster of embedded tubular particles takes into account an agglomeration and makes it possible to describe the threshold increase and subsequent decrease permeability with increasing concentration of embedded particles. The numerical simulation of such structures showed: an increase in the particle length leads to a decrease in the percolation concentration in a matrix of finite size, the power of the percolation cluster decreases significantly, but the combination of these effects leads to a decrease in the influence of the introduced particles on the properties of the matrix in the vicinity of the percolation threshold; an increase in the concentration of embedded particles leads to an increase in the probability of the formation of agglomerates and the characteristic size of the elements that make up the percolation cluster, the influence of individual particles decreases and the characteristics of the percolation transition determine the ratio of the sizes of agglomerates and matrix; and an increase in the lateral linear dimensions of the matrix leads to a nonlinear decrease in the proportion of the matrix, which is affected by the introduced particles, and the transport characteristics of such MMMs deteriorate.

Fabrication of a Novel (PVDF/MWCNT/Polypyrrole) Antifouling High Flux Ultrafiltration Membrane for Crude Oil Wastewater Treatment

The present work deals with the fabrication of novel poly(vinylidene fluoride) (PVDF)/Multi-wall Carbon Nanotubes (MWCNT)/Polypyrrole (PPy) ultrafiltration membrane by phase inversion technique for the removal of crude oil from refinery wastewater. In situ polymerization of pyrrole with different concentrations of MWCNT ranging from 0.025 wt.% to 0.3 wt.% in PVDF prepared solutions. Measurement of permeability, porosity, contact angle, tensile strength, zeta potential, rejection studies and morphological characterization by scanning electron microscopy (SEM) were conducted. The results showed that membrane with (0.05% MWCNT) concentration had the highest permeability flux (850 LMH/bar), about 17 folds improvement of permeability compared to pristine PVDF membrane. Moreover, membrane rejection of crude oil reached about 99.9%. The excellent performance of this nanocomposite membrane suggests that novel PVDF modification with polypyrrole had a considerable effect on permeability with high potential for use in the treatment of oily wastewater in the refinery industry.

Fabrication and Characterization of Poly (Vinyl Alcohol)-Chitosan-Capped Silver Nanoparticle Hybrid Membranes for Pervaporation Dehydration of Ethanol

Chitosan-capped silver nanoparticle (CS-capped AgNPs)-incorporated Poly(vinyl alcohol) (PVA) hybrid membranes were prepared by a solution-casting technique for ethanol dehydration via pervaporation. The incorporation of CS-capped AgNPs into the PVA membrane and its influence on membrane properties and pervaporation-separation process of azeotropic water/ethanol mixture was studied. The addition of CS-capped AgNPs into the PVA membrane reduced the crystallinity, thereby increasing the hydrophilicity and swelling degree of the hybrid membrane, supported by contact angle (CA) analyzer and swelling degree experiments, respectively. Fourier transform infrared spectroscopy (FTIR) demonstrated the formation of polymeric matrix between PVA and CS and also the binding of AgNPs onto the functional group of CS and PVA, which was also reflected in the microstructure images demonstrated by scanning electron microscopy (SEM) and by 2θ angle of wide-angle X-ray diffraction (WAXD). The effect of CS-capped AgNPs on the thermal stability of the hybrid membrane was demonstrated by differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA). These characteristics of the hybrid membrane positively impact the efficiency of the dehydration of ethanol, as indicated by pervaporation experiments. The best performances in total flux (12.40 ± 0.20 × 10⁻² kg/m² h) and selectivity (3612.33 ± 6.03) at 30 °C were shown for CS-capped AgNPs PVA hybrid membrane containing 2 wt.% CS-capped AgNPs (M-4). This confirms that the developed hybrid membranes can be efficiently used to separate water from azeotropic aqueous ethanol.

Studies on sorption kinetics and sorption isotherm for pervaporative separation of benzene from model pyrolysis gasoline using insitu nano silver/polyvinyl alcohol membrane

Pyrolysis gasoline (Py gas) is used as an octane enhancer of gasoline as it is rich in aromatics. However, removal of carcinogenic benzene from Py gas before blending with gasoline is important to meet the fuel specifications. The main focus of this present study is to determine the sorption kinetics and sorption isotherm of a fabricated insitu nano silver/polyvinyl alcohol (insitu nano Ag/PVA) membrane for pervaporative separation of benzene from model Py gas [mixture of benzene (aromatic) and 1-octene (aliphatic)]. The thickness, surface morphological structure (Atomic Force Microscopy) and degree of swelling of the fabricated membrane were determined. The highest pervaporation separation index achieved for the selected system was 14.259 kg/m²/h at 303 K, with 30 volume% benzene in model Py gas using a downstream pressure of 1 mm of Hg. The sorption kinetics of benzene in insitu nano Ag/PVA membrane obeyed the Elovich model while the Temkin isotherm model fitted the experimental data of the chosen system most accurately.

Highly-efficient PVDF adsorptive membrane filtration based on chitosan@CNTs-COOH simultaneous removal of anionic and cationic dyes

An adsorptive membrane filtration based on polyvinylidene fluoride (PVDF) with chitosan (CS) and carboxylated carbon nanotubes (CNTs-COOH) is prepared by method of phase conversion, and the PVDF-CS@CNTs-COOH membranes can effectively separate anionic and cationic dye wastewater. Compared to pure PVDF membranes, PVDF-CS@CNTs-COOH increases pure water flux from 36.39 (L·m^-2·h^-1) to 85.25 (L·m^-2·h^-1), an increase of nearly 230%. The membrane exhibits excellent rejection performance in the filtration of six types of dye wastewater. The modified membranes also performed well in terms of rejection of mixed anionic and cationic dyes and also have a high performance in recycling, with a flux of over 94% for both anionic and cationic dyes. In addition, the adsorption curve fitting results showed that the adsorption process was more consistent with the pseudo-second-order adsorption kinetic model and Langmuir mode.

Self-assembly in biobased nanocomposites for multifunctionality and improved performance

Concerns of petroleum dependence and environmental pollution prompt an urgent need for new sustainable approaches in developing polymeric products. Biobased polymers provide a potential solution, and biobased nanocomposites further enhance the performance and functionality of biobased polymers. Here we summarize the unique challenges and review recent progress in this field with an emphasis on self-assembly of inorganic nanoparticles. The conventional wisdom is to fully disperse nanoparticles in the polymer matrix to optimize the performance. However, self-assembly of the nanoparticles into clusters, networks, and layered structures provides an opportunity to address performance challenges and create new functionality in biobased polymers. We introduce basic assembly principles through both blending and in situ synthesis, and identify key technologies that benefit from the nanoparticle assembly in the polymer matrix. The fundamental forces and biobased polymer conformations are discussed in detail to correlate the nanoscale interactions and morphology with the macroscale properties. Different types of nanoparticles, their assembly structures and corresponding applications are surveyed. Through this review we hope to inspire the community to consider utilizing self-assembly to elevate functionality and performance of biobased materials. Development in this area sets the foundation for a new era of designing sustainable polymers in many applications including packaging, construction chemicals, adhesives, foams, coatings, personal care products, and advanced manufacturing.

Separation of Benzene/Cyclohexane Mixtures by Pervaporation Using Poly (Ethylene-Co-Vinylalcohol) and Carbon Nanotube-Filled Poly (Vinyl Alcohol-Co-Ethylene) Membranes

Poly(ethylene-co-vinylalcohol) (E-VOH) and carbon nanotube-filled poly (vinyl alcohol-co-ethylene) (E-VOH/CNT) were used as membranes to separate benzene/cyclohexane mixtures by pervaporation technique. To reach this goal, E-VOH and E-VOH/CNT membranes were prepared by solvent casting method and characterized by differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The swelling tests were used to study the mass transfer of the benzene/cyclohexane mixture and their pure components. The separation by pervaporation process was carried out at 25 °C in which the effect of CNTs incorporated into E-VOH matrix and the initial concentration of benzene in the feed on the permeate flux, j, and separation factor, β, performance was investigated. The results obtained were very promising, in which the integration of CNTs through E-VOH chains increased the absorption area and raised the flux to 740 g/m2∙h. The separation factor increased to 9.03 and the pervaporation separation reached an index of 5942.2 g/m2∙h for the azeotropic mixture during 3 h of the separation process. In contrast, for the unfilled E-VOH membrane, it was found that these parameters were a rise of 280 g∙m−2∙h−1, separation factor of 12.90 and pervaporation separation index of 3332.0 g/m2∙h, under the same conditions. Likewise, the calculation of the performance of the E-VOH/CNT membrane with regard to that of the unfilled membrane indicated 2.64 for the total flux and 0.70 for the separation factor. It was also revealed that the best compromise of the filled membrane in terms of total cumulative flux and separation factor is obtained for the feed containing the azeotropic mixture.

Dimensional Nanofillers in Mixed Matrix Membranes for Pervaporation Separations: A Review

Pervaporation (PV) has been an intriguing membrane technology for separating liquid mixtures since its commercialization in the 1980s. The design of highly permselective materials used in this respect has made significant improvements in separation properties, such as selectivity, permeability, and long-term stability. Mixed-matrix membranes (MMMs), featuring inorganic fillers dispersed in a polymer matrix to form an organic-inorganic hybrid, have opened up a new avenue to facilely obtain high-performance PV membranes. The combination of inorganic fillers in a polymer matrix endows high flexibility in designing the required separation properties of the membranes, in which various fillers provide specific functions correlated to the separation process. This review discusses recent advances in the use of nanofillers in PV MMMs categorized by dimensions including zero-, one-, two- and three-dimensional nanomaterials. Furthermore, the impact of the nanofillers on the polymer matrix is described to provide in-depth understanding of the structure-performance relationship. Finally, the applications of nanofillers in MMMs for PV separation are summarized.

Novel fabrication of PSSAMA_Na capped silver nanoparticle embedded sodium alginate membranes for pervaporative dehydration of bioethanol

Polystyrene-4-sulfonic acid co maleic acid sodium salt (PSSAMA_Na) capped silver nanoparticle (Ag_Np) embedded sodium alginate (Na-Alg) nanocomposite membranes have been developed to improve the pervaporation (PV) dehydration of bioethanol. The effect of PSSAMA_Na capped Ag_Nps on the micro-morphology, physicochemical properties and separation performance of the derived membranes was analyzed as a function of temperature at the azeotropic composition of the bioethanol–water mixture. WAXD analysis shows a decrease in crystalline domains with the increase in PSSAMA_Na capped Ag_Nps content and confirms the presence of Ag_Nps. DSC analysis demonstrated that the hydrophilic nature enhances as the PSSAMA_Na capped Ag_Nps content increases in the membrane matrix. Further, both total permeation flux and separation selectivity were increased with an increase in PSSAMA_Na capped Ag_Nps content. The results revealed that the membrane with 3 mass% of PSSAMA_Na capped Ag_Nps exhibited the highest permeation flux (13.40 × 10⁻² kg m⁻² h⁻¹) and separation selectivity (11 406) at 30 °C which indicate its better PV performance. The total permeation flux and permeation flux of water values were close to each other, which confirms that the membranes can be efficiently used to remove the water from azeotropic aqueous bioethanol.

Polystyrene-4-sulfonic acid co maleic acid sodium salt (PSSAMA_Na) capped silver nanoparticle (Ag_Np) embedded sodium alginate (Na-Alg) nanocomposite membranes have been developed to improve the pervaporation (PV) dehydration of bioethanol.

Recent advances in hydrophilic modification and performance of polyethersulfone (PES) membrane via additive blending

The blending of additives in the polyethersulfone (PES) matrix is an important approach in the membrane industry to reduce membrane hydrophobicity and improve the performance (flux, solute rejection, and reduction of fouling). Several (hydrophilic) modifications of the PES membrane have been developed. Given the importance of the hydrophilic modification methods for PES membranes and their applications, we decided to dedicate this review solely to this topic. The types of additives embedded into the PES matrix can be divided into two main categories: (i) polymers and (ii) inorganic nanoparticles (NPs). The introduced polymers include polyvinylpyrrolidone, chitosan, polyamide, polyethylene oxide, and polyethylene glycol. The introduced nanoparticles discussed include titanium, iron, aluminum, silver, zirconium, silica, magnesium based NPs, carbon, and halloysite nanotubes. In addition, the applications of hydrophilic PES membranes are also reviewed. Reviewing the research progress in the hydrophilic modification of PES membranes is necessary and imperative to provide more insights for their future development and perhaps to open the door to extend their applications to other more challenging areas.

Polymeric Nanocomposite Membranes for Next Generation Pervaporation Process: Strategies, Challenges and Future Prospects

Pervaporation (PV) has been considered as one of the most active and promising areas in membrane technologies in separating close boiling or azeotropic liquid mixtures, heat sensitive biomaterials, water or organics from its mixtures that are indispensable constituents for various important chemical and bio-separations. In the PV process, the membrane plays the most pivotal role and is of paramount importance in governing the overall efficiency. This article evaluates and collaborates the current research towards the development of next generation nanomaterials (NMs) and embedded polymeric membranes with regard to its synthesis, fabrication and application strategies, challenges and future prospects.

Fabrication of Polyimide Membrane Incorporated with Functional Graphene Oxide for CO2 Separation: The Effects of GO Surface Modification on Membrane Performance

Two kinds of isocyanate were used to modify graphene oxide (GO) samples. Then, polyimide (PI) hybrid membranes containing GO and modified GO were prepared by in situ polymerization. The permeation of CO₂ and N₂ was studied using these novel membranes. The morphology experiments showed that the isocyanate groups were successfully grafted on the surface of GO by replacement of the oxygen-containing functional groups. After modification, the surface polarity of the GO increased, and more defect structures were introduced into the GO surface. This resulted in a good distribution of more modified GO samples in the PI polymer matrix. Thus, the PI hybrid membranes incorporated by modified GO samples showed a high gas permeability and ideal selectivity of membranes. In addition, enhancement of the selectivity due to the solubility of CO₂ played a major role in the increase in the separation performance of the hybrid membranes for CO₂, although the diffusion coefficients for CO₂ also increased. Both the higher condensability and the strong affinity between CO₂ molecules and GO in the polymer matrix caused an enhancement of the solubility selectivity higher than the diffusion selectivity after GO surface modification.

Carbon Nanotube Membranes: Synthesis, Properties, and Future Filtration Applications

Over the course of the past decade, there has been growing interest in the development of different types of membranes composed of carbon nanotubes (CNTs), including buckypapers and composite materials, for an ever-widening range of filtration applications. This article provides an overview of how different types of CNT membranes are prepared and the results obtained from investigations into their suitability for different applications. The latter involve the removal of small particles from air samples, the filtration of aqueous solutions containing organic compounds and/or bacteria, and the separation of individual liquids present in mixtures. A growing number of reports have demonstrated that the incorporation of CNTs into composite membranes confers an improved resistance to fouling caused by biomacromolecules and bacteria. These results are discussed, along with evidence that demonstrates it is possible to further reduce fouling by taking advantage of the inherent conductivity of composite membranes containing CNTs, as well as by using different types of electrochemical stimuli.

Fabrication and Water Treatment Application of Carbon Nanotubes (CNTs)-Based Composite Membranes: A Review

Membrane separation technology is widely explored for various applications, such as water desalination and wastewater treatment, which can alleviate the global issue of fresh water scarcity. Specifically, carbon nanotubes (CNTs)-based composite membranes are increasingly of interest due to the combined merits of CNTs and membrane separation, offering enhanced membrane properties. This article first briefly discusses fabrication and growth mechanisms, characterization and functionalization techniques of CNTs, and then reviews the fabrication methods for CNTs-based composite membranes in detail. The applications of CNTs-based composite membranes in water treatment are comprehensively reviewed, including seawater or brine desalination, oil-water separation, removal of heavy metal ions and emerging pollutants as well as membrane separation coupled with assistant techniques. Furthermore, the future direction and perspective for CNTs-based composite membranes are also briefly outlined.