Gas separation performance of polyethersulfone/multi-walled carbon nanotubes mixed matrix membranes

Carbon nanotubes buckypapers: A new frontier in wastewater treatment technology

Occurrence of contaminants in water is one of the major global concerns humanity is still facing today: most of them are extremely toxic and dangerous for human health, obliging their removal for a proper and correct process of sanitation. Among wastewater treatment technologies, in the view of development of sustainable and environmentally friendly processes, membrane adsorption has proved to be a fast and simple method in the removal of pollutants, offering great contaminants recovery percentages, fast adsorbent regeneration and recycle, and easy scale-up. Due to their large surface area and tunable chemistry, carbon nanotubes (CNTs)-based materials revealed to be extraordinary adsorbents, exceeding by far performances of ordinary organic and inorganic membranes such as polyethersulfone, polyvinylidene fluoride, polytetrafluoroethylene, ceramics, currently employed in membrane technologies for wastewater treatment. In consideration of this, the review aims to summarize recent developments in the field of carbon nanotubes-based materials for pollutants recovery from water through adsorption processes. After a brief introduction concerning what adsorption phenomenon is and how it is performed and governed by using carbon nanotubes-based materials, the review discusses into detail the employment of three common typologies of CNTs-based materials (CNTs powders, CNTs-doped polymeric membranes and CNTs membranes) in adsorption process for the removal of water pollutants. Particularly focus will be devoted on the emergent category of self-standing CNTs membranes (buckypapers), made entirely of carbon nanotubes, exhibiting superior performances than CNTs and CNTs-doped polymeric membranes in terms of preparation strategy, recovery percentages of pollutants and regeneration possibilities. The extremely encouraging results presented in this review aim to support and pave the way to the introduction of alternative and more efficient pathways in wastewater treatment technologies to contrast the problem of water pollution.

Development of blend PEG-PES/NMP-DMF mixed matrix membrane for CO2/N2 separation

The carbon dioxide (CO2) separation technology has become a focus recently, and a developed example is the membrane technology. It is an alternative form of enhanced gas separation performance above the Robeson upper bound line resulting in the idea of mixed matrix membranes (MMMs). With attention given to membrane technologies, the MMMs were fabricated to have the most desirable gas separation performance. In this work, blend MMMs were synthesised by using two polymers, namely, poly(ether sulfone) (PES) and poly (ethylene glycol) (PEG). These polymers were dissolved in blend N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF) solvents with the functionalised multi-walled carbon nanotubes (MWCNTs-F) fillers by using the mixing solution method. The embedding of the pristine MWCNTs and MWCNTs-F within the new synthesised MMM was then studied towards CO2/N2 separation. In addition, the optimisation of the loading of MWCNTs-F for blend MMM for CO2/N2 separation was also studied. The experimental results showed that the functionalised MWCNTs (MWCNTs-F) were a better choice at enhancing gas separation compared to the pristine MWCNTs (MWCNTs-P). Additionally, the effects of MWCNTs-F at loadings 0.01 to 0.05% were studied along with the polymer compositions for PES:PEG of 10:20, 20:20 and 30:10. Both these parameters of study affect the manner of gas separation performance in the blend MMMs. Overall, the best performing membrane showed a selectivity value of 1.01 + 0.05 for a blend MMM (MMM-0.03F) fabricated with 20 wt% of PES, 20 wt% of PEG and 0.03 wt% of MWCNTs-F. The MMM-0.03F was able to withstand a pressure of 2 bar, illustrating its mechanical strength and ability to be used in the post combustion carbon capture application industries where the flue gas pressure is at 1.01 bar.

Dimensional Transformation of Percolation Structure in Mixed-Matrix Membranes (MMMs)

A large number of studies of mixed-matrix membranes (MMMs) have confirmed the possibility of obtaining new materials with unique transport properties, including for solving specific problems in the separation of mixtures of liquids and gases. The choice of particles with a given affinity for the matrix and separable components allows researchers to adjust the selective properties of MMMs in a wide range, which changes the properties of MMMs in a wide range. However, even within the framework of the most complex percolation mechanism of the formation of the MMM structure, it is possible to explain only some of the observed effects. In particular, questions about the required particle concentration and fluctuation of properties in various MMM samples are still the subject of research. The results of the numerical modeling of such structures presented in this paper determined the possible causes of the observed deviations of the experimental results, for example, particle size dispersion, agglomeration, and interaction with the matrix. According to our research, the key factor that qualitatively changes the parameters of percolation structures is the ratio of the geometric dimensions of the system. We have confirmed in a wide range a significant change in the conditions of cluster formation and its power at different particle diameters and lengths (traditional parameters in percolation studies). But in our work, we additionally studied the effect on the cluster parameters of the interfacial layer and the anisotropy of the matrix (the transition from the cube to the film). The results obtained show that changing the parameters of the matrix-particle interaction affects agglomeration, and the degradation of the percolation structure is possible. That is, with an increase in concentration, the parameters of the percolation cluster, its power, and the probability of formation, may decrease. But even more negative changes in percolation structures are observed during the transition from a volumetric matrix to films. The anisotropy of space leads to the formation of percolation through the film in certain areas at low concentrations of particles. At the same time, in a significant part of the matrix, percolation between the film surfaces will be absent, and the effect of changing the properties of MMMs in the matrix as a whole decreases. Our study explains the observed instability of MMM properties at fixed concentrations and parameters of embedded particles, including the effect of reducing the influence of particles with increasing concentration.

Material and Process Tests of Heterogeneous Membranes Containing ZIF-8, SiO2 and POSS-Ph

Heterogeneous membranes made of a polymer matrix and containing nano-metric fillers in their structure may present improved physicochemical and process properties compared to homogeneous membranes made only of polymer materials. Membranes made of a PEBAX^®2533 block copolymer were tested with fillers such as ZIF-8, SiO₂ and POSS-Ph being dosed to them. The material analysis and process tests indicate that these nanomaterials can be used as fillers for heterogeneous membranes. Chemometric analyses determined the influence of individual fillers on selected physicochemical properties of the materials which were used to produce the membranes. For specific concentrations of these fillers, improvement in the permeability and selectivity of the membranes, or at least in one of these parameters, was achieved. The greatest increase in permeability against the homogeneous membrane was obtained for membranes containing 10 wt% ZIF-8 (for CO₂, an increase of 2.07 times; for CH₄, 2.36 times; for N₂, 3.08 times). In turn, the greatest increase in selectivity was obtained for the CO₂/CH₄ mixture for the membrane containing 5 wt% SiO₂ (1.15 times), and for the CO₂/N₂ mixture for the membrane containing 2 wt% POSS-Ph (1.21 times).

Doubly modified MWCNTs embedded in polyethersulfone (PES) ultrafiltration membrane and its anti-fouling performance

Multiwall carbon nanotubes (MWCNTs) are often used to modify polymer membranes as additives, however, MWCNTs are easy to agglomerate and entangle in polymer matrix due to their own strong van der Waals force. MWCNTs were doubly modified by bonding octadecylamine (ODA) and SiO2 through the respective amidation and esterification reactions to prepare SiO2-MWCNT-ODA nanocomposites. The amino groups on ODA were amidated with the carboxyl groups on MWCNT-COOH. Then the hydroxyl groups on SiO2 were bonded to MWCNT-COOH through esterification to obtain SiO2-MWCNT-ODA nanocomposites. PES/SiO2-MWCNT-ODA composite ultrafiltration (UF) membrane was prepared by non-solvent induced phase separation (NIPS) method. SiO2-MWCNT-ODA nanocomposites and PES/SiO2-MWCNT-ODA membrane were characterized by FTIR, XRD, TGA, and SEM, etc. The results showed that PES/SiO2-MWCNT-ODA membrane had significantly improved permeability, rejection, and antifouling properties for comparison with PES membrane. The pure water flux of PES/Nano.2-0.5 reached 212.5 L m−2 h−1, which was approximately 2.6 times than that of PES membrane, and the rejection of BSA protein for composite membrane was as high as 94.2%. PES/SiO2-MWCNT-ODA composite membrane had excellent antifouling performance and the flux recovery rate (FRR) of PES/Nano.2-0.5 membrane could still maintain at higher value of 84.82% after two cycles in the antifouling test.

Incorporating Carbon Nanotubes in Nanocomposite Mixed-Matrix Membranes for Gas Separation: A Review

Carbon nanotube (CNT) is a prominent material for gas separation due to its inherent smoothness of walls, allowing rapid transport of gases compared to other inorganic fillers. It also possesses high mechanical strength, enabling membranes to operate at high pressure. Although it has superior properties compared to other inorganic fillers, preparation of CNTs into a polymer matrix remains challenging due to the strong van der Waals forces of CNTs, which lead to agglomeration of CNTs. To utilize the full potential of CNTs, proper dispersion of CNTs must be addressed. In this paper, methods to improve the dispersion of CNTs using functionalization methods were discussed. Fabrication techniques for CNT mixed-matrix membrane (MMM) nanocomposites and their impact on gas separation performance were compared. This paper also reviewed the applications and potential of CNT MMMs in gas separation.

Fabrication and dialysis performance of functionalized multiwall carbon nanotubes integrated cellulose acetate/poly(vinylpyrrolidone) membranes

Mixed matrix membranes (MMMs) of cellulose acetate/poly(vinylpyrrolidone) (CA/PVP) infused with acid functionalized multiwall carbon nanotubes (f-MWCNTs) were fabricated by an immersion phase separation technique for hemodialysis application. Membranes were characterized using FTIR, water uptake, contact angle, TGA, DMA and SEM analysis. The FTIR was used to confirm the bonding interaction between CA/PVP membrane matrix and f-MWCNTs. Upon addition of f-MWCNTs, TGA thermograms and glass transition temperature indicated improved thermal stability of MMMs. The surface morphological analysis demonstrated revealed uniform distribution of f-MWCNTs and asymmetric membrane structure. The water uptake and contact angle confirmed that hydrophilicity was increased after incorporation of f-MWCNTs. The membranes demonstrated enhancement in water permeate flux, bovine serum albumin (BSA) rejection with the infusion of f-MWCNTs; whereas BSA based anti-fouling analysis using flux recovery ratio test shown up to 8.4% improvement. The urea and creatinine clearance performance of MMMs were evaluated by dialysis experiment. It has been found that f-MWCNTs integrated membranes demonstrated the higher urea and creatinine clearance with increase of 12.6% and 10.5% in comparison to the neat CA/PVP membrane. Thus, the prepared CA/PVP membranes embedded with f-MWCNTs can be employed for wide range of dialysis applications.

A review on chitosan-based membranes for sustainable CO2 separation applications: Mechanism, issues, and the way forward

Effective carbon dioxide (CO₂) separation by nominal energy utilization is the factual attempt in the present era of energy scarcity and environmental calamity. In this perspective, the membrane- based gas separation technology is a budding endeavour owing to its cost -effectiveness, ease of operational maintenance and compact modular design. Among various membrane materials, bio-based polymers are of interest as they are abundant and can be obtained from renewable resources, and can also reduce our dependency on exhaustible fossil fuel-based sources. In this review, the structure-property relationship of chitosan and some of its film-forming derivatives has been critically studied for the first time in view of the fundamental properties required for gas separation applications. Various factors affecting the gas permeation performance of chitosan-based membranes have been highlighted along with prospects and propositions for the design of a few novel bio-based membranes based on the exhaustive analyses.

A Prospective Concept on the Fabrication of Blend PES/PEG/DMF/NMP Mixed Matrix Membranes with Functionalised Carbon Nanotubes for CO2/N2 Separation

With an ever-increasing global population, the combustion of fossil fuels has risen immensely to meet the demand for electricity, resulting in significant increase in carbon dioxide (CO₂) emissions. In recent years, CO₂ separation technology, such as membrane technology, has become highly desirable. Fabricated mixed matrix membranes (MMMs) have the most desirable gas separation performances, as these membranes have the ability to overcome the trade-off limitations. In this paper, blended MMMs are reviewed along with two polymers, namely polyether sulfone (PES) and polyethylene glycol (PEG). Both polymers can efficiently separate CO₂ because of their chemical properties. In addition, blended N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF) solvents were also reviewed to understand the impact of blended MMMs’ morphology on separation of CO₂. However, the fabricated MMMs had challenges, such as filler agglomeration and void formation. To combat this, functionalised multi-walled carbon nanotube (MWCNTs-F) fillers were utilised to aid gas separation performance and polymer compatibility issues. Additionally, a summary of the different fabrication techniques was identified to further optimise the fabrication methodology. Thus, a blended MMM fabricated using PES, PEG, NMP, DMF and MWCNTs-F is believed to improve CO₂/nitrogen separation.

Review: Mixed-Matrix Membranes with CNT for CO2 Separation Processes

The membranes' role is of supreme importance in the separation of compounds under different phases of matter. The topic addressed here is based on the use of membranes on the gases separation, specifically the advantages of mixed-matrix membranes (MMMs) when using carbon nanotubes as fillers to separate carbon dioxide (CO₂) from other carrier gas. MMMs consist of a polymer support with additive fillers to improve their efficiency by increasing both selectivity and permeability. The most promising fillers in the MMM development are nanostructured molecules. Due to the good prospects of carbon nanotubes (CNTs) as MMM fillers, this article aims to concentrate the advances and developments of CNT-MMM to separate gases, such as CO₂. The influence of functionalized CNT or mixtures of CNT with additional materials such as zeolites, hydrogel and, graphene sheets on membranes performance is highlighted in the present work.

Improving the Barrier Properties of Packaging Paper by Polyvinyl Alcohol Based Polymer Coating-Effect of the Base Paper and Nanoclay

The poor barrier properties and hygroscopic nature of cellulosic paper impede the wide application of cellulosic paper as a packaging material. Herein, a polyvinyl alcohol (PVA)-based polymer coating was used to improve the barrier performance of paper through its good ability to form a film. Alkyl ketene dimer (AKD) was used to enhance the water resistance. The effect of the absorptive characteristics of the base paper on the barrier properties was explored, and it was shown that surface-sized base paper provides a better barrier performance than unsized base paper. Nanoclay (Cloisite Na⁺) was used in the coating formulation to further enhance the barrier performance. The results show that the coating of PVA/AKD/nanoclay dispersion noticeably improved the barrier performance of the paper. The water vapor transmission rate of the base paper was 533 g/m²·day, and it decreased sharply to 1.3 g/m²·day after the application of a double coating because of the complete coverage of the base paper by the PVA-based polymer coating. The coated paper had excellent water resistance owing to its high water contact angle of around 100°. The grease resistance and mechanical properties of the base paper also improved after coating. This work may provide inspiration for improving the barrier properties of packaging paper through the selection of a suitable base paper and coating formulation.

Composite amine mixed matrix membranes for high-pressure CO2-CH4 separation: synthesis, characterization and performance evaluation

The key challenge in the synthesis of composite mixed matrix membrane (MMMs) is the incompatible membrane fabrication using porous support in the dry-wet phase inversion technique. The key objective of this research is to synthesize thin composite ternary (amine) mixed matrix membranes on microporous support by incorporating 10 wt% of carbon molecular sieve (CMS) and 5-15 wt% of diethanolamine (DEA) in polyethersulfone (PES) dope solution for the separation of carbon dioxide (CO₂) from methane (CH₄) at high-pressure applications. The developed membranes were evaluated for their morphological structure, thermal and mechanical stabilities, functional groups, as well as for CO₂-CH₄ separation performance at high pressure (10-30 bar). The results showed that the developed membranes have asymmetric structure, and they are mechanically strong at 30 bar. This new class of PES/CMS/DEA composite MMMs exhibited improved gas permeance compared to pure PES composite polymeric membrane. CO₂-CH₄ perm-selectivity enhanced from 8.15 to 16.04 at 15 wt% of DEA at 30 bar pressure. The performance of amine composite MMMs is theoretically predicted using a modified Maxwell model. The predictions were in good agreement with experimental data after applying the optimized values with AARE % = ∼less than 2% and R ² = 0.99.

Natural Rubber Composites Filled with Crop Residues as an Alternative to Vulcanizates with Common Fillers

This present study is focused on exploring the possibility of using agricultural waste in the form of cereal straw as an active filler of biocomposites. The effect of lignocellulosic filler addition on the multifunctional properties of natural rubber composites was investigated. The results were compared with the properties of vulcanizates containing commonly used reinforcements in elastomer technology (carbon black, silica, chalk, talc). Rubber mixtures filled with straw showed the highest torque increase during rheometric measurements, which indirectly indicated a high degree of crosslinking and hardness of composites. It was found that the effect of straw addition on vulcanization time of elastomer blends was comparable with the results obtained for other conventional fillers. Moreover, the results confirmed that novel composites based on natural rubber filled with crop residues were attractive materials owing to their capacity for the formation of “structure” in combination with a good impact on reinforcement. Vulcanizates with the addition of straw showed the best barrier properties and resistance to thermo-oxidative aging from all tested samples. Furthermore, straw-based composites demonstrated that cereal straw waste could be used as an alternative, biodegradable and eco-friendly reinforcement of natural rubber composites.

Carbon nanostructures for advanced nanocomposite mixed matrix membranes: a comprehensive overview

The highly progressive membrane separation technology challenges conventional separation processes such as ion exchange, distillation, precipitation, solvent extraction, and adsorption. The integration of many desired properties such as low energy consumption, high removal efficiency, affordable costs, suitable selectivity, acceptable productivity, ease of scale-up, and being environmentally friendly have made the membranes capable of being replaced with other separation technologies. Combination of membrane technology and nanoscience has revolutionized the nano-engineered materials, e.g. nanocomposites applied in advanced membrane processes. Polymer composites containing carbon nanostructures are promising choices for membrane fabrication owing to their enhanced chemistry, morphology, electromagnetic properties, and physicochemical stability. Carbon nanostructures such as carbon nanotubes (CNTs), nano graphene oxides (NGOs), and fullerenes are among the most popular nanofillers that have been successfully applied in modification of polymer membranes. Literature review shows that there is no comprehensive overview reporting the modification of mixed matrix membranes (MMMs) using carbon nanofibers, nano-activated carbons, and carbon nanospheres. The present overview focuses on the applications of carbon nanostructures mainly CNTs and NGOs in the modification of MMMs and emphasizes on the application of CNTs and NGO particles.

Amino-silane-grafted NH2-MIL-53(Al)/polyethersulfone mixed matrix membranes for CO2/CH4 separation

Mixed-matrix membranes (MMMs) are promising candidates for carbon dioxide separation.

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.