High flux thin-film nanocomposites with embedded boron nitride nanotubes for nanofiltration

The effect of increasing temperature on simulated nanocomposites reinforced with SWBNNs and its effect on characteristics related to mechanics and the physical attributes using the MDs approach

This study examines the effect of increasing temperature (300, 350, 400, 450 and 500 K) on simulated nanocomposites reinforced with exploration of the impact of single-walled boron nitride nanotubes (SWBNNTs) on both the mechanical properties (including Young's modulus, Poisson's ratio, shear modulus, and bulk modulus) and the physical property of density, achieved through molecular dynamics (MDs) simulations. MDs utilized to simulate nanocomposite models consisting of five case studies of SWBNNs with different chiralities (5, 0), (10, 0), (15, 0), (20, 0), and (25, 0) as the reinforcement and using thermoplastic polyurethane (TPU) as the common matrix. The results reveal that with increasing temperature and chiralities of SWBNNTs, the density and Poisson's ratio increase dramatically, and Young's, shear, and bulk moduli decrease continuously. At a consistent temperature, there is a noteworthy trend in the mechanical properties of SWBNNTs with various chiralities. This includes the increase in Young's modulus, Poisson's ratio, shear modulus, and bulk modulus in the simulated nanocomposite, ranging from SWBNNTs (5, 0) to (25, 0). Similarly, the physical property of density exhibits an increasing trend from SWBNNTs (5, 0) to (20, 0) and then decreases at SWBNNTs (25, 0). To validate the accuracy of these findings, a Radial Distribution Function (RDF) diagram is generated using Materials Studio software.

Molecular modeling of thin-film nanocomposite membranes for reverse osmosis water desalination

The scarcity of freshwater resources is a major global challenge causedby population and economic growth. Water desalination using a reverse osmosis (RO) membrane is a promising technology to supply potable water from seawater and brackish water. The advancement of RO desalination highly depends on new membrane materials. Currently, the RO technology mainly relies on polyamide thin-film composite (TFC) membranes, which suffer from several drawbacks (e.g., low water permeability, permeability-selectivity tradeoff, and low fouling resistance) that hamper their real-world applications. Nanoscale fillers with specific characteristics can be used to improve the properties of TFC membranes. Embedding nanofillers into TFC membranes using interfacial polymerization allows the creation of thin-film nanocomposite (TFNC) membranes, and has become an emerging strategy in the fabrication of high-performance membranes for advanced RO water desalination. To achieve optimal design, it is indispensable to search for reliable methods that can provide fast and accurate predictions of the structural and transport properties of the TFNC membranes. However, molecular understanding of permeability-selectivity characteristics of nanofillers remains limited, partially due to the challenges in experimentally exploring microscopic behaviors of water and salt ions in confinement. Molecular modeling and simulations can fill this gap by generating molecular-level insights into the effects of nanofillers' characteristics (e.g., shape, size, surface chemistry, and density) on water permeability and ion selectivity. In this review, we summarize molecular simulations of a diverse range of nanofillers including nanotubes (carbon nanotubes, boron nitride nanotubes, and aquaporin-mimicking nanochannels) and nanosheets (graphene, graphene oxide, boron nitride sheets, molybdenum disulfide, metal and covalent organic frameworks) for water desalination applications. These simulations reveal that water permeability and salt rejection, as the major factors determining the desalination performance of TFNC membranes, significantly depend on the size, topology, density, and chemical modifications of the nanofillers. Identifying their influences and the physicochemical processes behind, via molecular modeling, is expected to yield important insights for the fabrication and optimization of the next generation high-performance TFNC membranes for RO water desalination.

Environmental treatment and remediation using h-BN based smart and hybrid membrane

Corrosion is a major problem resulting from acid gases found in natural gas being transported in pipelines. To solve this problem, high aspect ratio h-BN nanosheets have been incorporated and are properly assimilated in the CA matrix, this led to an increase in tortuous path of flow for the gas resulting in smooth, dense membrane samples causing exceptional permeability reduction. Hexagonal Boron Nitride (h-BN) nanosheets have been synthesized and incorporated into cellulose acetate (CA) matrix using solution casting method. Nanosheets of various sizes, separated by varying centrifugation speeds (i.e. 500 rpm, 700 rpm, 1500 rpm, 2000 rpm and 2500 rpm), have been prepared and used for our work. The resulting nanocomposites, having thickness ranging between 40 and 60 μm, were then tested for CO₂ gas permeability reduction using both short-term (8 h) tests as well as long-term (72-h tests). As a result of these tests, a maximum CO₂ permeability reduction of 99.84% is found with a minimum CO₂ permeability of 3.25 barrer. For dimensional analysis of both nanosheets and nanocomposites, scanning electron microscopy (SEM) analysis is used. For verifying the presence of the required functional groups in our synthesized samples, FT-IR spectroscopy is used. Moreover, to confirm the presence of crystalline phases, X-ray Diffraction (XRD) analysis is used. Also, tensile testing is used to analyze the mechanical robustness and it was found that nanocomposite samples exhibited higher tensile strength as compared to pristine samples. Furthermore, tribological property analysis was also carried out for adhesion testing of polymeric material with steel.

Nanofiltration Membranes with Crumpled Polyamide Films: A Critical Review on Mechanisms, Performances, and Environmental Applications

Nanofiltration (NF) membranes have been widely applied in many important environmental applications, including water softening, surface/groundwater purification, wastewater treatment, and water reuse. In recent years, a new class of piperazine (PIP)-based NF membranes featuring a crumpled polyamide layer has received considerable attention because of their great potential for achieving dramatic improvements in membrane separation performance. Since the report of novel crumpled Turing structures that exhibited an order of magnitude enhancement in water permeance ( Science 2018, 360 (6388), 518-521), the number of published research papers on this emerging topic has grown exponentially to approximately 200. In this critical review, we provide a systematic framework to classify the crumpled NF morphologies. The fundamental mechanisms and fabrication methods involved in the formation of these crumpled morphologies are summarized. We then discuss the transport of water and solutes in crumpled NF membranes and how these transport phenomena could simultaneously improve membrane water permeance, selectivity, and antifouling performance. The environmental applications of these emerging NF membranes are highlighted, and future research opportunities/needs are identified. The fundamental insights in this review provide critical guidance on the further development of high-performance NF membranes tailored for a wide range of environmental applications.

Ganzoury M, Zhang N, de Lannoy CF. Nanocomposite Polymeric Membranes for Organic Micropollutant Removal: A Critical Review

The prevalence of organic micropollutants (OMPs) and their persistence in water supplies have raised serious concerns for drinking water safety and public health. Conventional water treatment technologies, including adsorption and biological treatment, are known to be insufficient in treating OMPs and have demonstrated poor selectivity toward a wide range of OMPs. Pressure-driven membrane filtration has the potential to remove many OMPs detected in water with high selectivity as a membrane's molecular weight cutoff (MWCO), surface charge, and hydrophilicity can be easily tailored to a targeted OMP's size, charge and octanol-water partition coefficient (Kow). Over the past 10 years, polymeric (nano)composite microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) membranes have been extensively synthesized and studied for their ability to remove OMPs. This review discusses the fate and transport of emerging OMPs in water, an assessment of conventional membrane-based technologies (NF, reverse osmosis (RO), forward osmosis (FO), membrane distillation (MD) and UF membrane-based hybrid processes) for their removal, and a comparison to the state-of-the-art nanoenabled membranes with enhanced selectivity toward specific OMPs in water. Nanoenabled membranes for OMP treatment are further discussed with respect to their permeabilities, enhanced properties, limitations, and future improvements.

Properties and applications of boron nitride nanotubes

Nanomaterials have received increasing attention due to their controllable physical and chemical properties and their improved performance over their bulk structures during the last years. Carbon nanostructures are one of the most widely searched materials for use in different applications ranging from electronic to biomedical because of their exceptional physical and chemical properties. However, BN nanostructures surpassed the attention of the carbon-based nanostructure because of their enhanced thermal and chemical stabilities in addition to structural similarity with the carbon nanomaterials. Among these nanostructures, one dimensional-BN nanostructures are on the verge of development as new materials to fulfill some necessities for different application areas based on their excellent and unique properties including their tunable surface and bandgap, electronic, optical, mechanical, thermal, and chemical stability. Synthesis of high-quality boron nitride nanotubes (BNNTs) in large quantities with novel techniques provided greater access, and increased their potential use in nanocomposites, biomedical fields, and nanodevices as well as hydrogen uptake applications. In this review, properties and applications of one-dimensional BN (1D) nanotubes, nanofibers, and nanorods in hydrogen uptake, biomedical field, and nanodevices are discussed in depth. Additionally, research on native and modified forms of BNNTs and also their composites with different materials to further improve electronic, optical, structural, mechanical, chemical, and biological properties are also reviewed. BNNTs find many applications in different areas, however, they still need to be further studied for improving the synthesis methods and finding new possible future applications.

The State-Of-The-Art Functionalized Nanomaterials for Carbon Dioxide Separation Membrane

Nanocomposite membrane (NCM) is deemed as a practical and green separation solution which has found application in various fields, due to its potential to delivery excellent separation performance economically. NCM is enabled by nanofiller, which comes in a wide range of geometries and chemical features. Despite numerous advantages offered by nanofiller incorporation, fabrication of NCM often met processing issues arising from incompatibility between inorganic nanofiller and polymeric membrane. Contemporary, functionalization of nanofiller which modify the surface properties of inorganic material using chemical agents is a viable approach and vigorously pursued to refine NCM processing and improve the odds of obtaining a defect-free high-performance membrane. This review highlights the recent progress on nanofiller functionalization employed in the fabrication of gas-separative NCMs. Apart from the different approaches used to obtain functionalized nanofiller (FN) with good dispersion in solvent and polymer matrix, this review discusses the implication of functionalization in altering the structure and chemical properties of nanofiller which favor interaction with specific gas species. These changes eventually led to the enhancement in the gas separation efficiency of NCMs. The most frequently used chemical agents are identified for each type of gas. Finally, the future perspective of gas-separative NCMs are highlighted.

Improved permeability and antifouling performance of polyethersulfone ultrafiltration membranes tailored by hydroxyapatite/boron nitride nanocomposites

To extend the use of polyethersulfone (PES) ultrafiltration membranes in water process engineering, the membrane's wettability and anti-fouling properties should be further improved. In this context, hydroxyapatite/boron nitride (HAp/BN) nanocomposites have been prepared and intercalated into PES membranes using a non-solvent-induced phase separation process. High-quality 2D transparent boron nitride nanosheets (BN NSs) were prepared using an environmentally friendly and green-template assisted synthesis method in which 1D hexagonal hydroxyapatite nanosheets (HAp NRs) were uniformly distributed and hydrothermally immobilized at 180 °C. SEM, XRD, and Raman spectroscopy techniques were used to characterize the HAp/BN nanocomposites. PES membranes intercalated with various nanocomposite amounts (0-4 wt %) were also characterized by permeability, porosity, and contact angle measurements. Additional pathways for water molecule transport were promoted by the high surface area of the BN NSs, resulting in high permeability. Membrane wettability and antifouling properties were also improved by the inclusion of negative charge groups (OH^- and PO₄^3-) on HAp. Hybrid membranes containing 4 wt% HAp/BN showed the best overall performance with ∼97% increase in water flux, 90% rejection of bovine serum albumin (BSA), high water flux recovery ratio, low irreversible fouling, and high reversible fouling pattern. The intercalation of HAp/BN with the PES matrix therefore opens up a new direction to enhance the PES UF membranes' hydrophilicity, water flux, and antifouling capacity.

Boron Nitride Nanotube (BNNT) Membranes for Energy and Environmental Applications

Owing to their extraordinary thermal, mechanical, optical, and electrical properties, boron nitride nanotubes (BNNTs) have been attracting considerable attention in various scientific fields, making it more promising as a nanomaterial compared to other nanotubes. Recent studies reported that BNNTs exhibit better properties than carbon nanotubes, which have been extensively investigated for most environment-energy applications. Irrespective of its chirality, BNNT is a constant wide-bandgap insulator, exhibiting thermal oxidation resistance, piezoelectric properties, high hydrogen adsorption, ultraviolet luminescence, cytocompatibility, and stability. These unique properties of BNNT render it an exceptional material for separation applications, e.g., membranes. Recent studies reported that water filtration, gas separation, sensing, and battery separator membranes can considerably benefit from these properties. That is, flux, rejection, anti-fouling, sensing, structural, thermal, electrical, and optical properties of membranes can be enhanced by the contribution of BNNTs. Thus far, a majority of studies have focused on molecular simulation. Hence, the requirement of an extensive review has emerged. In this perspective article, advanced properties of BNNTs are analyzed, followed by a discussion on the advantages of these properties for membrane science with an overview of the current literature. We hope to provide insights into BNNT materials and accelerate research for environment-energy applications.

Enhanced nanoparticle rejection in aligned boron nitride nanotube membranes

The rejection of particles with different charges and sizes, ranging from a few Ångstroms to tens of nanometers, is key to a wide range of industrial applications, from wastewater treatment to product purification in biotech processes. Carbon nanotubes (CNTs) have long held the promise to revolutionize filtration, with orders of magnitude higher fluxes compared to commercial membranes. CNTs, however, can only reject particles and ions wider than their internal diameter. In this work, the fabrication of aligned boron nitride nanotube (BNNT) membranes capable of rejecting nanoparticles smaller than their internal diameter is reported for the first time. This is due to a mechanism of charge-based rejection in addition to the size-based one, enabled by the BNNTs surface structure and chemistry and elucidated here using high fidelity molecular dynamics and Brownian dynamics simulations. This results in ∼40% higher rejection of the same particles by BNNT membranes than CNT ones with comparable nanotube diameter. Furthermore, since permeance is proportional to the square of the nanotubes' diameter, using BNNT membranes with ∼30% larger nanotube diameter than a CNT membrane with comparable rejection would result in up to 70% higher permeance. These results open the way to the design of more effective nanotube membranes, capable of high particle rejection and, at the same time, high water permeance.