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A special issue of Membranes (ISSN 2077-0375). This special issue belongs to the section "Inorganic Membranes".

Deadline for manuscript submissions: closed (30 September 2022) | Viewed by 34044

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Dr. Stephanos Nitodas

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Department of Materials Science and Chemical Engineering, Stony Brook University, Stony Brook, NY 11794, USA
Interests: polymer nanocomposite materials; mixed matrix membranes; carbon nanotubes; mechanical properties; thermal properties; gas permeability
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Special Issue Information

Dear Colleagues,

Membrane technology provides attractive advantages over the “traditional” absorption and adsorption processes, which suffer from drawbacks such as corrosivity, complex process layouts, high installation and operation costs and energy-consuming regeneration processes. Inorganic polycrystalline membranes and organic polymeric membranes are commonly used in numerous separation processes, mainly gas separations. Both membrane systems present many advantages but also limitations. Inorganic membranes possess high thermal, mechanical, and chemical stability combined with notable durability. They are also more permeable and selective than polymeric membranes. On the other hand, their significant brittleness, high cost, and challenges in processability and scale-up potential have held back their commercialization.

In an effort to overcome the aforementioned problems in membrane performance, polymer nanocomposite materials have drawn attention due to the ability to tune their physicochemical properties depending on the application. Different choices of both polymer type and nanofiller, combined with particular processing parameters, can result in new materials with completely different properties—improved or new—that can be used in a wide range of applications, including textiles, packaging, transportation, and the biomedical field.

Membrane technology has embraced the concept of nanocomposite materials by introducing the definition of hybrid membranes. Considerable effort has been dedicated to the synthesis and performance optimization of hybrid membrane materials, mainly polymeric ones, by the incorporation of nanoparticles, such as carbon nanotubes and nanostructured metal oxides. The potential of these hybrid materials lies in the capability of the nanoparticles to improve the membrane’s properties, including increasing the permeability coefficients and selectivity, and enhancing the electrical and/or mechanical properties. These effects are correlated with the change in the degree of crystallinity, polymer chain mobility, and structure of the polymer-free volume, which interacts with nanoparticles. A change in permeation or conductivity is connected with the formation of a percolation threshold in the nanostructured domains at a critical concentration of nanoparticles in the polymeric membrane.

These major breakthroughs are leading the way to greatly enhanced membrane performance and efficiency and many new exciting possibilities. This Special Issue offers a perfect opportunity to document state-of-the-art developments and innovations in nanostructured hybrid membranes. Authors are, therefore, invited to submit their latest results; both original papers and reviews are welcome.

Dr. Stephanos Nitodas
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Membranes is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

Membrane processing
Hybrid membrane materials
Nanotechnology
Membrane property enhancement
Nanostructured carbon
Nano-oxides

Published Papers (11 papers)

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Research

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14 pages, 2955 KiB

Open AccessArticle

Separation Mechanisms and Anti-Fouling Properties of a Microporous Polyvinylidene Fluoride–Polyacrylic Acid–Graphene Oxide (PVDF-PAA-GO) Composite Membrane with Salt and Protein Solutions

by Li-Ting Wang, Yu-Han Chen, Wei-Ting Chang, Selvaraj Rajesh Kumar, Chien-Chang Chen and Shingjiang Jessie Lue

Membranes 2023, 13(1), 40; https://doi.org/10.3390/membranes13010040 - 28 Dec 2022

Cited by 2 | Viewed by 1286

Abstract

This research demonstrates the preparation of composite membranes containing graphene oxide (GO) and investigates the separation mechanisms of various salts and bovine serum albumin (BSA) solutions. A microporous polyvinylidene fluoride–polyacrylic acid–GO (PVDF-PAA-GO) separation layer was fabricated on non-woven support. The GO-incorporating composite resulted in enlarged pore size (0.16 μm) compared with the control membrane (0.12 μm). The zeta potential of the GO composite was reduced to –31 from –19 mV. The resulting membranes with and without GO were examined for water permeability and rejection efficiency with single salt and BSA solutions. Using the non-woven/PVDF-PAA composite, the permeance values were 88–190 kg/m²hMPa, and the salt rejection coefficients were 9–28% for Na₂SO₄, MgCl₂, MgSO₄, and NaCl solutions. These salt removals were based on the Donnan exclusion mechanism considering the ion radii and membrane pore size. Incorporating GO into the separation layer exhibited limited impacts on the filtration of salt solutions, but significantly reduced BSA membrane adhesion and increased permeance. The negatively charged protein reached almost complete removal (98.4%) from the highly negatively charged GO-containing membrane. The GO additive improved the anti-fouling property of the composite membrane and enhanced BSA separation from the salt solution. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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12 pages, 3370 KiB

Open AccessArticle

Long-Chain Modification of the Tips and Inner Walls of MWCNTs and Their Nanocomposite Reverse Osmosis Membranes

by Qing Li, Dengfeng Yang, Qingzhi Liu, Jianhua Wang, Zhun Ma, Dongmei Xu and Jun Gao

Membranes 2022, 12(8), 794; https://doi.org/10.3390/membranes12080794 - 18 Aug 2022

Viewed by 1093

Abstract

Multi-walled carbon nanotubes (MWCNTs) were modified on the tips and inner walls by 12-chloro-12-oxododecanedioic acid-methyl ester groups and then added to the polyamide composite membranes to prepare MWCNT-CH₂OCOC₁₂H₂₃O₂ membranes for desalination. The characterization results of transmission electron microscopy, Fourier transform, infrared transform, and thermogravimetric analysis showed that the 12-chloro-12-oxododecanedioic acid-methyl ester group was successfully grafted to the entrances and inner walls of the MWCNTs. The performance of the MWCNTs’ composite membranes was evaluated by scanning electron microscopy, contact angle, and filtration test. The modified membrane morphology is more uniform, and there is no structural damage. The grafting of carbon nanotubes with methyl 12-chloro-12-oxydodecyldicarboxylate could improve the hydrophilicity of the membrane. Under identical conditions, the water flux of MWCNT-CH₂OCOC₁₂H₂₃O₂ membranes was higher than that of the pristine carbon nanotube’s membrane, and the desalination rate was also slightly improved. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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14 pages, 2104 KiB

Open AccessArticle

Elucidating the Water and Methanol Dynamics in Sulfonated Polyether Ether Ketone Nanocomposite Membranes Bearing Layered Double Hydroxides

by Ernestino Lufrano, Isabella Nicotera, Apostolos Enotiadis, Muhammad Habib Ur Rehman and Cataldo Simari

Membranes 2022, 12(4), 419; https://doi.org/10.3390/membranes12040419 - 13 Apr 2022

Cited by 3 | Viewed by 1591

Abstract

Conventional Nafion membranes demonstrate a strong affinity for methanol, resulting in a high fuel crossover, poor mechanical stability, and thus poor performance in direct methanol fuel cells (DMFCs). This study involves the synthesis and physiochemical characterization of an alternative polymer electrolyte membrane for DMFCs based on sulfonated poly(ether ether ketone) and a layered double hydroxide (LDH) material. Nanocomposite membranes (sPL), with filler loading ranging between 1 wt% and 5 wt%, were prepared by simple solution intercalation and characterized by XRD, DMA, swelling tests, and EIS. For the first time, water and methanol mobility inside the hydrophilic channels of sPEEK-LDH membranes were characterized by NMR techniques. The introduction of LDH nanoplatelets improved the dimensional stability while having a detrimental effect on methanol mobility, with its self-diffusion coefficient almost two orders of magnitude lower than that of water. It is worth noting that anionic lamellae are directly involved in the proton transport mechanism, thus enabling the formation of highly interconnected paths for proton conduction. In this regard, sPL₃ yielded a proton conductivity of 110 mS cm⁻¹ at 120 °C and 90% RH, almost attaining the performance of the Nafion benchmark. The nanocomposite membrane also showed an excellent oxidative stability (over more than 24 h) during Fenton’s test at 80 °C. These preliminary results demonstrate that an sPL₃ nanocomposite can be potentially and successfully applied in DMFCs. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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9 pages, 2716 KiB

Open AccessArticle

Investigation of the Resistivity and Emissivity of a Pellicle Membrane for EUV Lithography

by Seong Ju Wi, Yong Ju Jang, Haneul Kim, Kyeongjae Cho and Jinho Ahn

Membranes 2022, 12(4), 367; https://doi.org/10.3390/membranes12040367 - 26 Mar 2022

Cited by 4 | Viewed by 3822

Abstract

A pellicle is a thin membrane structure that protects an extreme ultraviolet (EUV) mask from contamination during the exposure process. However, its limited transmittance induces unwanted heating owing to the absorption of EUV photons. The rupture of the EUV pellicle can be avoided by improving its thermal stability, which is achieved by improving the emissivity of the film. However, the emissivity data for thin films are not easily available in the literature, and its value is very sensitive to thickness. Therefore, we investigated the dependence of emissivity on structural parameters, such as thickness, surface roughness, and grain size. We found a correlation between resistivity and emissivity using theoretical and experimental approaches. By changing the grain size of the Ru thin film, the relationship between resistivity and emissivity was experimentally verified and confirmed using the Lorentz–Drude model. Finally, we present a method to develop an EUV pellicle with better thermal stability that can withstand high-power EUV light sources. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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20 pages, 8650 KiB

Open AccessArticle

Dual Optimized Sulfonated Polyethersulfone and Functionalized Multiwall Carbon Tube Based Composites High Fouling Resistance Membrane for Protein Separation

by Muhammad Irfan, Masooma Irfan, Ani Idris, Abdullah Saad Alsubaie, Khaled H. Mahmoud, Noordin Mohd Yusof and Naeem Akhtar

Membranes 2022, 12(3), 329; https://doi.org/10.3390/membranes12030329 - 16 Mar 2022

Cited by 4 | Viewed by 2581

Abstract

Commercial grade sulfonated-Polyethersulfone (S-PES) and functionalized multiwall carbon nanotube (f-MWCNT)/polyvinylpyrrolidone (PVP) nanocomposites (NCs) were used to enhance and optimize the antifouling, protein resistance and protein separation properties of the S-PES ultrafiltration membranes. The polarities of sulfonic groups of S-PES, carbonyl carbon of pyrrolidone, hydroxyl and carboxyl groups of f-MWCNT in the membrane composition helped to strongly bind each other through hydrogen bonding, as shown by Fourier-transform infrared spectroscopy (FTIR). These binding forces greatly reduced the leaching of NCs and developed long finger-like projection, as confirmed by elution ratio and cross-sectional studies of the membranes via field emission scanning electron microscope (FESEM). The contact angle was reduced up to 48% more than pristine PES. Atomic force microscopy (AFM) was employed to study the various parameters of surface roughness with 3d diagrams, while grain analysis of membrane surface provided a quantitative estimation about volume, area, perimeter, length, radius and diameter. The NCs/S-PES enhanced the flux rate with an impressive (80–84%) flux recovery ratio and (58–62%) reversible resistance (R_r) value in situ, with 60% and 54.4% lesser dynamic and static protein adsorption. The best performing membrane were reported to remove 31.8%, 66.3%, 83.6% and 99.9% for lysozyme-(14.6 kDa), trypsin-(20 kDa), pepsin-(34.6 kDa) and bovine serum albumin (BSA-66 kDa), respectively. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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14 pages, 3162 KiB

Open AccessArticle

Effect of Dope Flow Rate and Post-Treatment on the Morphology, Permeation and Metal Ion Rejection from PES/LiBr-Based UF Hollow Fiber Membranes

by Muhammad Irfan, Masooma Irfan, Ani Idris, Abdullah Saad Alsubaie, Khaled H. Mahmoud, Noordin Mohd Yusof and Nawshad Muhammad

Membranes 2022, 12(3), 305; https://doi.org/10.3390/membranes12030305 - 09 Mar 2022

Viewed by 1878

Abstract

This study investigated the influence of dope extrusion rate (DER) and post-treatment effect on the morphology, permeation, and metal ion rejection by polyethersulfone/lithium bromide (PES/LiBr)-based hollow fiber (HF) membranes. HF fibers were spun with 2.25, 2.5, and 3.1 ratios of DER to bore fluid rate (BFR), wherein DER varied from 11.35, 12.5, to 15.6 mL/min with a fixed BFR (5 mL/min). Molecular weight cutoff (MWCO), pore size, water flux, and flux recovery ratio were determined, whereas lake water was used to observe the rejection rate of dissolved metallic ions. Results showed that with the increase of the DER wall thickness (WT), HFs increased from 401.5 to 419.5 um, and furthermore by the post-treatments up to 548.2 um, as confirmed by field emission scanning electron microscope (FESEM) analysis. Moreover, MWCO, pore size, and the pure water permeation (PWP) of the HF membranes decreased, while the separation performance for polyethylene glycol (PEG) solute increased with increasing DER. Post-treated HFs from 11.35 mL/min of DER showed 93.8% of MWCO value with up to 90% and 70% rejection of the arsenic and chromium metallic ions, respectively, in comparison with all other formulated HFs. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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11 pages, 4614 KiB

Open AccessArticle

Crosslinking Multilayer Graphene by Gas Cluster Ion Bombardment

by Nurlan Almassov, Sean Kirkpatrick, Zhanna Alsar, Nurzhan Serik, Christos Spitas, Konstantinos Kostas and Zinetula Insepov

Membranes 2022, 12(1), 27; https://doi.org/10.3390/membranes12010027 - 25 Dec 2021

Viewed by 2204

Abstract

In this paper, we demonstrate a new, highly efficient method of crosslinking multilayer graphene, and create nanopores in it by its irradiation with low-energy argon cluster ions. Irradiation was performed by argon cluster ions with an acceleration energy E ≈ 30 keV, and total fluence of argon cluster ions ranging from 1 × 10⁹ to 1 × 10¹⁴ ions/cm². The results of the bombardment were observed by the direct examination of traces of argon-cluster penetration in multilayer graphene, using high-resolution transmission electron microscopy. Further image processing revealed an average pore diameter of approximately 3 nm, with the predominant size corresponding to 2 nm. We anticipate that a controlled cross-linking process in multilayer graphene can be achieved by appropriately varying irradiation energy, dose, and type of clusters. We believe that this method is very promising for modulating the properties of multilayer graphene, and opens new possibilities for creating three-dimensional nanomaterials. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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19 pages, 4609 KiB

Open AccessArticle

Poly(ethylene glycol) Diacrylate Iongel Membranes Reinforced with Nanoclays for CO₂ Separation

by Ana R. Nabais, Rute O. Francisco, Vítor D. Alves, Luísa A. Neves and Liliana C. Tomé

Membranes 2021, 11(12), 998; https://doi.org/10.3390/membranes11120998 - 20 Dec 2021

Cited by 3 | Viewed by 2671

Abstract

Despite the fact that iongels are very attractive materials for gas separation membranes, they often show mechanical stability issues mainly due to the high ionic liquid (IL) content (≥60 wt%) needed to achieve high gas separation performances. This work investigates a strategy to improve the mechanical properties of iongel membranes, which consists in the incorporation of montmorillonite (MMT) nanoclay, from 0.2 to 7.5 wt%, into a cross-linked poly(ethylene glycol) diacrylate (PEGDA) network containing 60 wt% of the IL 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([C₂mim][TFSI]). The iongels were prepared by a simple one-pot method using ultraviolet (UV) initiated polymerization of poly(ethylene glycol) diacrylate (PEGDA) and characterized by several techniques to assess their physico-chemical properties. The thermal stability of the iongels was influenced by the addition of higher MMT contents (>5 wt%). It was possible to improve both puncture strength and elongation at break with MMT contents up to 1 wt%. Furthermore, the highest ideal gas selectivities were achieved for iongels containing 0.5 wt% MMT, while the highest CO₂ permeability was observed at 7.5 wt% MMT content, due to an increase in diffusivity. Remarkably, this strategy allowed for the preparation and gas permeation of self-standing iongel containing 80 wt% IL, which had not been possible up until now. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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Review

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34 pages, 6243 KiB

Open AccessReview

A Review on Removal and Destruction of Per- and Polyfluoroalkyl Substances (PFAS) by Novel Membranes

by Suman Das and Avner Ronen

Membranes 2022, 12(7), 662; https://doi.org/10.3390/membranes12070662 - 27 Jun 2022

Cited by 25 | Viewed by 7912

Abstract

Per- and Polyfluoroalkyl Substances (PFAS) are anthropogenic chemicals consisting of thousands of individual species. PFAS consists of a fully or partly fluorinated carbon–fluorine bond, which is hard to break and requires a high amount of energy (536 kJ/mole). Resulting from their unique hydrophobic/oleophobic nature and their chemical and mechanical stability, they are highly resistant to thermal, chemical, and biological degradation. PFAS have been used extensively worldwide since the 1940s in various products such as non-stick household items, food-packaging, cosmetics, electronics, and firefighting foams. Exposure to PFAS may lead to health issues such as hormonal imbalances, a compromised immune system, cancer, fertility disorders, and adverse effects on fetal growth and learning ability in children. To date, very few novel membrane approaches have been reported effective in removing and destroying PFAS. Therefore, this article provides a critical review of PFAS treatment and removal approaches by membrane separation systems. We discuss recently reported novel and effective membrane techniques for PFAS separation and include a detailed discussion of parameters affecting PFAS membrane separation and destruction. Moreover, an estimation of cost analysis is also included for each treatment technology. Additionally, since the PFAS treatment technology is still growing, we have incorporated several future directions for efficient PFAS treatment. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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17 pages, 5100 KiB

Open AccessReview

Applications of Polymeric Membranes with Carbon Nanotubes: A Review

by Steve F. Nitodas, Mrinaleni Das and Raj Shah

Membranes 2022, 12(5), 454; https://doi.org/10.3390/membranes12050454 - 23 Apr 2022

Cited by 9 | Viewed by 3077

Abstract

Nanomaterials have been commonly employed to enhance the performance of polymeric membrane materials that are used in several industrial applications. Carbon nanotubes (CNTs) have gained notable attention over the years for use in membrane technology due to their anti-biofouling properties, salt rejection capability, exceptional electrical conductivity, and mechanical properties. This paper aims to discuss some of the recent applications of CNTs in membrane technology and their effect on a larger scale. The paper reviews successful case studies of incorporation of CNTs in membranes and their impact on water purification, desalination, gas separations, and energy storage, in an effort to provide a better understanding of their capabilities. Regarding the future trends of this technology, this review emphasizes improving the large-scale production processes and addressing environmental and health-related hazards of CNTs during production and usage. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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27 pages, 3082 KiB

Open AccessReview

Lignocellulosic Biomass-Derived Nanocellulose Crystals as Fillers in Membranes for Water and Wastewater Treatment: A Review

by Olawumi O. Sadare, Kelvin O. Yoro, Kapil Moothi and Michael O. Daramola

Membranes 2022, 12(3), 320; https://doi.org/10.3390/membranes12030320 - 11 Mar 2022

Cited by 14 | Viewed by 3823

Abstract

The improvement of membrane applications for wastewater treatment has been a focal point of research in recent times, with a wide variety of efforts being made to enhance the performance, integrity and environmental friendliness of the existing membrane materials. Cellulose nanocrystals (CNCs) are sustainable nanomaterials derived from microorganisms and plants with promising potential in wastewater treatment. Cellulose nanomaterials offer a satisfactory alternative to other environmentally harmful nanomaterials. However, only a few review articles on this important field are available in the open literature, especially in membrane applications for wastewater treatment. This review briefly highlights the circular economy of waste lignocellulosic biomass and the isolation of CNCs from waste lignocellulosic biomass for membrane applications. The surface chemical functionalization technique for the preparation of CNC-based materials with the desired functional groups and properties is outlined. Recent uses of CNC-based materials in membrane applications for wastewater treatment are presented. In addition, the assessment of the environmental impacts of CNCs, cellulose extraction, the production techniques of cellulose products, cellulose product utilization, and their end-of-life disposal are briefly discussed. Furthermore, the challenges and prospects for the development of CNC from waste biomass for application in wastewater treatment are discussed extensively. Finally, this review unraveled some important perceptions on the prospects of CNC-based materials, especially in membrane applications for the treatment of wastewater. Full article

(This article belongs to the Special Issue Nanotechnology and Hybrid Membranes)

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