Design of double-component metal–organic framework air filters with PM2.5 capture, gas adsorption and antibacterial capacities

Fabrication of Poly(Lactic Acid)@TiO2 Electrospun Membrane Decorated with Metal-Organic Frameworks for Efficient Air Filtration and Bacteriostasis

The development of high-performance filtration materials is essential for the effective removal of airborne particles, and metal-organic frameworks (MOFs) anchored to organic polymer matrices are considered to be one of the most promising porous adsorbents for air pollutants. Nowadays, most air filters are generally based on synthetic fiber polymers derived from petroleum residues and have limited functionality, so the use of MOFs in combination with nanofiber air filters has received a lot of attention. Here, a conjugated electrostatic spinning method is demonstrated for the one-step preparation of poly(lactic acid) (PLA) nanofibrous membranes with a bimodal diameter distribution and the anchoring of Zeolitic Imidazolate Framework-8 (ZIF-8) by the introduction of TiO2 and in situ generation to construct favorable multiscale fibers and rough structures. The prepared PLA/TZ maintained a good PM2.5 capture efficiency of 99.97%, a filtration efficiency of 96.43% for PM0.3, and a pressure drop of 96.0 Pa, with the highest quality factor being 0.08449 Pa-1. Additionally, ZIF-8 was uniformly generated on the surface of PLA and TiO2 nanofibers, obtaining a roughened structure and a larger specific surface area. An enhanced filtration retention effect and electrostatic interactions, as well as active free radicals, can be generated for the deep inactivation of bacteria. Compared with the unmodified membrane, PLA/TZ prepared antibacterial characteristics induced by photocatalysis and Zn2+ release, with excellent bactericidal effects against S. aureus and E. coli. Overall, this work may provide a promising approach for the development of efficient biomass-based filtration materials with antimicrobial properties.

Trans-scale interface engineering: Constructing nature-inspired spider-web networks for regulating thermal transport and mechanical performance of carbon fiber/phenolic composites

The development of interfacial engineering was crucial for achieving the industrialization of high-performance carbon fiber/phenolic composites. In this study, establishing scalable interpenetrating networks (cellulose nanofiber-zeolitic imidazolate frameworks-8/aramid nanofiber-boron nitride) on the fiber/matrix interphase, was in favor of realizing precise repairation of interfacial defects, further regulating thermal conductivity, mechanical and tribological properties of the composites. Based on the physical and chemical bridging-effects arising from above spider-web networks, the flexural strength and modulus of modified sample were 74.69 MPa and 6.22 GPa, showing an increase of 135.99% and 56.68%, respectively. Meanwhile, this trans-scale spider-web structure acted as a micron skeleton-nano unit continuous thermal conductive network, significantly reduced phonon scattering and displayed a 258.33% enhancement in the thermal management capability of modified sample. This study reveals key design principles of trans-scale interfacial structure to dynamicly regulate performances and meet service requirements of next-generation carbon fiber/phenolic composites.

Polyacrylonitrile@TiO2 nanofibrous membrane decorated by MOF for efficient filtration and green degradation of PM2.5

A systematic study was performed on PM2.5 filtration and photodegradation performance of polyacrylonitrile @TiO₂/ zeolitic imidazolate framework-8（PTZ）hybrid membrane. The hybrid membrane was prepared by electrospinning technique and in situ Metal-organic frameworks (MOFs) synthesis. The optimized membrane maintained a good PM2.5 capture efficiency (greater than 99%) and a pressure drop of 34 Pa. The larger specific surface area and higher pore structure enhance the filter interception effect and electrostatic interaction, which can have high applications for the filtering of PM2.5. In addition, zeolitic imidazolate framework-8 (ZIF-8) is uniformly coated on the surface of polyacrylonitrile @ TiO₂ (PT) nanofiber to form N-Ti-O bonds, thus reducing the reorganization of electron-hole pairs and improving the efficiency of photodegradation. Compared with PT, the hybrid structure formed by PTZ has a higher degradation efficiency for PM2.5 (increased from 66% to 85%). The produced PTZ membrane exhibits a promising future in the collection and green degradation of PM2.5.

Gravity-driven rattan-based catalytic filter for rapid and highly efficient organic pollutant removal

Metal organic frameworks hold great promise as heterogeneous catalysts in sulfate radical (SO₄^∙-) based advanced oxidation. However, the aggregation of powdered MOF crystals and the complicated recovery procedure largely hinder their large-scale practical applications. It is important to develop eco-friendly and adaptable substrate-immobilized metal organic frameworks. Based on the hierarchical pore structure of the rattan, gravity-driven metal organic frameworks loaded rattan-based catalytic filter was designed to degrade organic pollutants by activating PMS at high liquid fluxes. Inspired by the water transportation of rattan, ZIF-67 was in-situ grown uniformly on the rattan channels inner surface using the continuous flow method. The intrinsically aligned microchannels in the vascular bundles of rattan acted as reaction compartments for the immobilization and stabilization of ZIF-67. Furthermore, the rattan-based catalytic filter exhibited excellent gravity-driven catalytic activity (up to 100 % treatment efficiency for a water flux of 10173.6 L·m^-2·h^-1), recyclability, and stability of organic pollutant degradation. After ten cycles, the TOC removal of ZIF-67@rattan was 69.34 %, maintaining a stable mineralisation capacity for pollutants. The inhibitory effect of the micro-channel promoted the interaction between active groups and contaminants, increasing the degradation efficiency and improving the stability of the composite. The design of a gravity-driven rattan-based catalytic filter for wastewater treatment provides an effective strategy for developing renewable and continuous catalytic systems.

Collaboration of two-star nanomaterials: The applications of nanocellulose-based metal organic frameworks composites

Nanocellulose, as the star nanomaterial in carbohydrate polymers, has excellent mechanical properties, biodegradability, and easy chemical modification. However, further practical applications of nanocellulose are limited by their inadequate functionalization. Metal-organic frameworks (MOFs), as the star nanomaterial in functional polymers, have a large surface area, high porosity, and adjustable structure. The collaboration of nanocellulose and MOFs is a desirable strategy to make composites especially interesting for multifunctional and multi-field applications. What sparks will be produced by the collaboration of two-star nanomaterials? In this review article, we highlight an up-to-date overview of nanocellulose-based MOFs composites. The sewage treatment, gas separation, energy storage, and biomedical applications are mainly summarized. Finally, the challenges and research trends of nanocellulose-based MOFs composites are prospected. We hope this review may provide a valuable reference for the development and applications of carbohydrate polymer composites soon.

A comprehensive review of hydrophobic silica and composite aerogels: synthesis, properties and recent progress towards environmental remediation and biomedical applications

The hydrophobicity of silica and composite aerogels has enabled them to acquire applications in a variety of fields. With remarkable structural, morphological, and physiochemical properties such as high porosity, surface area, chemical stability, and selectivity, these materials have gained much attention of researchers worldwide. Moreover, the hydrophobic conduct has enabled these aerogels to adsorb substances, i.e., organic pollutants, without collapsing the pore and network structure. Hence, considering such phenomenal properties and great adsorption potential, exploiting these materials for environmental and biomedical applications is trending. The present study explores the most recent advances in synthetic approaches and resulting properties of hydrophobic silica and composite aerogels. It presents the various precursors and co-precursors used for hydrophobization and gives a comparative analysis of drying methods. Moreover, as a major focus, the work presents the recent progress where these materials have shown promising results for various environmental remediation and biomedical applications. Finally, the bottlenecks in synthesis and applicability along with future prospects are given in conclusions.

Valuable aramid/cellulose nanofibers derived from recycled resources for reinforcing carbon fiber/phenolic composites

The scale-up preparation of aramid nanofiber (ANF) and cellulose nanofiber (CNF), still faces serious challenges such as extreme production cost and lengthy preparation cycle. Herein, a feasible top-down strategy was proposed to achieve the efficient reclamation of waste resources, further realizing the large-scale production of high value-added nanofibers. The ANF/CNF as nanoscale building blocks and their reinforcement effects on the mechanical performances of carbon fiber/phenolic composites were investigated. Related strength and modulus of ANF/CNF-enhanced composites in the tensile, bending, shear and nano indentation tests, increased by 118.1% (tensile strength), 141.2% (tensile modulus), 142.2% (flexural strength), 354.4% (flexural modulus), 38.8% (shear strength) and 94.4% (elastic modulus), respectively. Our work offers a valuable reference in the fabrication of low-cost ANF/CNF derived from waste resources, which would facilitate the wide application of nanofibers in fabricating high-performance advanced functional materials.

Nanocellulose implantation enriched the pore structure of aerogel for effective particulate matter removal

Particulate matter (PM) pollution poses a serious threat to public health, disposable and degradable filter materials are expected to handle the problem in the future. Here, polyvinyl alcohol (PVA)/borax/cellulose nanofibrils (CNF) aerogels were implanted on a biodegradable corrugated paper to form composite air filters for the first time via freeze-drying the coated composite hydrogels. The low content of CNF and PVA could be cross-linked by borax to form hydrogels, which enhanced its maneuverability for surface implanting on the substrate. More importantly, the addition of CNF greatly enriched the pore structure of aerogels, which provided a structural basis for PM capture. The as-prepared composite air filters exhibited excellent filtration efficiencies of 92 % and 96 % toward PM1.0 and PM3.0, respectively. Moreover, the addition of dimethylol-5,5-dimethylhydantoin endowed the filters with an antibacterial property. This work shows a new possibility for the design of degradable and functional filter materials.

Integration of renewable energy in wastewater treatment during COVID-19 pandemic: Challenges, opportunities, and progressive research trends

SARS-CoV-2 has aroused drastic effects on the global economy and public health. In response to this, personal protective equipment, hand hygiene, and social distancing have been considered the most important ways to prevent the direct spread of the virus. SARS-CoV-2 would be possible survive in wastewater for a few days, leading to secondary transmission via contact with water and wastewater. Thus, the most economical and practical approaches for decentralized wastewater treatment are renewable energies such as the solar energy disinfestation process. However, as freshwater requirements increase and fossil fuels become unsustainable, renewable energy becomes more attractive for desalination applications. Solar photovoltaic, membrane-based, and electricity desalination technologies are becoming increasingly popular due to their lower energy requirements. Several aquatic environments could be benefitted from solar energy wastewater disinfection. Besides, utilizing solar energy during the day can inactivate SARS-CoV-2 to nearly 90%. However, conventional membrane-based desalination practices have also been integrated, including reverse osmosis (RO) and electrodialysis (ED). Several exciting membrane processes have been developed recently, including membrane distillation (MD), pressure-reduced osmosis (PRO), and reverse electrodialysis (RED). Such operations can produce clean and sustainable electricity from brine and impaired water, generally considered hazardous to the environment. As a result, neither PRO nor RED can produce electricity without mixing a high salinity solution (such as seawater or brine and wastewater, respectively) with a low salinity solution. Herein, we critically review the progress in applying renewable energy such as solar energy and geothermal energy for generating electricity from wastewater treatment and uniquely discuss the effects of these two types of renewable energy on SARS-CoV-2 in air and wastewater treatment. We also highlight the significant process made on the membrane processes utilizing renewable energy and research gaps from the standpoint of producing clean and sustainable energy. The significant points of this review are: (1) among various types of renewable energy, solar energy and geothermal energy have been predominantly studied for wastewater treatment, (2) effects of these two types of renewable energy on SARS-CoV-2 in air and wastewater treatment are critically analyzed, and (3) the knowledge gaps and anticipated future research outlook have been consequently proposed thereof.

Assembly of AIEgen-Based Fluorescent Metal-Organic Framework Nanosheets and Seaweed Cellulose Nanofibrils for Humidity Sensing and UV-Shielding

Integrating synthetic low-dimensional nanomaterials such as metal-organic framework (MOF) nanosheets with a sustainable biopolymer is a promising strategy to endow composites with attractive structural and functional properties for expanded applications. Herein, aggregation-induced-emission luminogen (AIEgen)-based MOF bulk crystals are successfully exfoliated into ultrathin 2D nanosheets. Seaweed cellulose nanofibrils (CNFs) are assembled with low amounts (0.3 to 4.0 wt%) of the 2D nanosheets to generate luminescent composites. The 2D nanosheets are adsorbed onto the CNFs in dilute water suspensions owing to the flexibility of the MOF nanosheets and the high aspect ratio of the CNFs. Transparent films are prepared by solution casting from a water suspension of the CNF-MOF assembly. The fluorescence emission of the composite films is enhanced because of the favored affinity between MOF nanosheets and CNFs. Remarkably, these films demonstrate excellent UV-shielding capacity and high optical transmittance at the visible wavelength range. The composite films also show reversible changes in fluorescence emission intensity in response to ambient humidity. The tensile strength and modulus of the composite films are also enhanced owing to the increased adhesion between CNFs through the adsorbed MOF nanosheets. This work provides a novel pathway to fabricate luminescent CNFs-based composites with tunable optical properties for functional materials.

Advanced MOFs@aerogel composites: Construction and application towards environmental remediation

Environmental pollution has drawn forth advanced materials and progressive techniques concentrating on sustainable development. Metal-organic frameworks (MOFs) have aroused vast interest resulting from their excellent property in structure and function. Conversely, powdery MOFs in highly crystalline follow with fragility, poor processability and recoverability. Aerogels distinguished by the unique three-dimensional (3D) interconnected pore structures with high porosity and accessible surface area are promising carriers for MOFs. Given these, combining MOFs with aerogels at molecule level to obtain advanced composites is excepted to further enhance their performance with higher practicability. Herein, we focus on the latest studies on the MOFs@aerogel composites. The construction of MOFs@aerogel with different synthetic routes and drying methods are discussed. To explore the connection between structure and performance, pore structure engineering and quantitation of MOFs content are outlined. Furthermore, various types of MOFs@aerogel composites and their carbonized derivatives are reviewed, as well as the applications of MOFs@aerogel for environmental remediation referring to water purification and air clearing. More importantly, outlooks towards these emerging advanced composites have been presented from the perspective of practical application and future development.

Investigating the Influence of Metal-Organic Framework Loading on the Filtration Performance of Electrospun Nanofiber Air Filters

Integrating metal-organic frameworks (MOFs) into electrospun nanofiber filters has become an effective method for improving particle filtration efficiency. This study hypothesized that there is an optimal amount of MOFs that can be integrated into electrospun nanofiber filters to achieve the maximum particle removal efficiency while minimizing the corresponding MOF synthesis time. To test the hypothesis, this study systematically explored the influence of the time-dependent in situ growing process of zeolitic imidazolate framework-67 (ZIF-67), a typical type of MOFs, on the filtration performance of polyacrylonitrile (PAN) electrospun nanofibers. The results show that the surface morphology and chemical composition of the PAN/ZIF-67 hybrid nanofiber filters gradually changed with the reaction time. For PAN/ZIF-67 hybrid nanofiber filters with relatively low initial PM0.3-0.4 filtration efficiency, a reaction time of only 5 min was sufficient for the synthesis of the amount of ZIF-67 that maximized the PM0.3-0.4 filtration efficiency. However, for thick filters with high original PM0.3-0.4 filtration efficiency (>90%), the integration of ZIF-67 was not necessary, because the efficiency enhancement would not be significant. In addition, the enhancement of filtration efficiency for ultrafine particles was positively correlated with the amount of incorporated ZIF-67. In summary, this study shortened the synthesis time of the in situ incorporation of MOFs into electrospun nanofiber filters from more than 10 h (reported in the literature) to only 5 min.

Recent Advancements in MOF/Biomass and Bio-MOF Multifunctional Materials: A Review

Metal–organic frameworks (MOFs) and their derivatives have delivered perfect answers in detection, separation, solving water and electromagnetic pollution and improving catalysis and energy storage efficiency due to their advantages including their highly tunable porosity, structure and versatility. Recently, MOF/biomass, bio-MOFs and their derivatives have gradually become a shining star in the MOF family due to the improvement in the application performance of MOFs using biomass and biomolecules. However, current studies lack a systematic summary of the synthesis and advancements of MOF/biomass, bio-MOFs and their derivatives. In this review, we describe their research progress in detail from the following two aspects: (1) synthesis of MOF/biomass using biomass as a template to achieve good dispersion and connectivity at the same time; (2) preparing bio-MOFs by replacing traditional organic linkers with biomolecules to enhance the connection stability between metal ions/clusters and ligands and avoid the formation of toxic by-products. This enables MOFs to possess additional unique advantages, such as improved biocompatibility and mechanical strength, ideal reusability and stability and lower production costs. Most importantly, this is a further step towards green and sustainable development. Additionally, we showcase some typical application examples to show their great potential, including in the fields of environmental remediation, energy storage and electromagnetic wave absorption.

Efficient capture of airborne PM by nanotubular conjugated microporous polymers based filters under harsh conditions

The exploitation of high-performance filters which can capture and remove airborne particulate matter (PM) in harsh conditions is greatly important to limit the serious effect of PM on human health. Herein, we demonstrate a simple approach for the creation of robust and hierarchically porous filters based on conjugated microporous polymers (CMPs) nanotubes for efficient PM capture. Taking advantage of their inherently superhydrophobic wettability, the CMPs-based filters possess high filtration efficiency of higher than 99.4% for PM_0.3 and 99.9% for PM_2.5 and PM₁₀, respectively, even in high humidity environment (RH ≥ 94%). The CMPs-based filters show highly physicochemical and thermal stability, e.g., by calcination at 500 °C for 2 h, the filtration efficiency of the samples still reaches as great as 99.4% for both PM_2.5 and PM₁₀ with a low-pressure drop of only 10 Pa. In addition, these CMPs-based filters can be easily regenerated and their high PM filtration efficiency remains nearly unchanged by a simple methanol washing. More interestingly, the CMPs-based filters also exhibit superior antibacterial performance, which enables them to sterilize or eliminate the bacteria possibly loaded on PM pollutions, thus showing great potential for various applications such as PM removal, air purification and so on.

Electrospun nanofiber-based respiratory face masks-a review

The severe acute respiratory syndrome coronavirus (SARS-CoV-2) pandemic of 2019 forced widespread use of face coverings as a mandatory step towards reducing infection by the virus. The face mask acts as a barrier for transmission of infected aerosols among its user and surrounding people. This has propelled pace of research and development of face masks around the world. This short review is an effort to present advances in materials and designs used for face masks. Details available in scientific literature and company brochures have been accessed and the use of nanomaterials and designs for the new generation of face masks have been discussed. Special attention was given to the face masks based on electrospun nanofiber-based membrane materials due to their nano-sized pores, light weight, and high filtration efficiency; therefore, they are commercially viable and popular among various products available in the market. Incorporation of metal organic framework (MOFs) and graphene have opened avenues to more advanced/multi-functional, reusable, and high capacity adsorption filtration membranes. Rapid prototyping/3-dimensional (3-D) printing techniques have been applied to shorten the time of manufacture of face masks. This review is expected to be very helpful for engineers, scientists, and entrepreneurs working on development of novel face masks required in plenty during this pandemic period.

Bifunctional conjugated microporous polymer based filters for highly efficient PM and gaseous iodine capture

Cross-linked conjugated microporous polymers (CMPs) based air filters obtained by a one-step cross-coupling reaction for effective capture of particulate matter and gaseous iodine from dusty air.

Organic transformations in the confined space of porous organic cage CC2; catalysis or inhibition

Porous organic cages have shape persistent cavities which provide a suitable platform for encapsulation of guest molecules with size suitably fitting to the cavity. The interactions of the guest molecule with the porous organic cage significantly alter the properties of the guest molecule. Herein, we report the effect of encapsulation on the kinetics of various organic transformations including 2 + 4 cycloaddition, 1,5-sigmatropic, 6π-electrocyclization, ring expansion, cheletropic, dyotropic, trimerization and tautomerization reactions. Non-bonding interactions are generated between the CC2 cage and encapsulated species. However, the number and nature/strength of interactions are different for reactant and TS with the CC2 cage and this difference detects the reaction to be accelerated or slowed down. A significant drop in the barrier of reactions is observed for reactions involving strong interactions of the transition state within the cage. However, for some reactions such as the Claisen rearrangement, reactants are stabilized more than the transition state and therefore an increase in activation barrier is observed. Furthermore, non-covalent analyses of all transition states (inside the cage) confirm the interaction between the CC2 cage and substrate. The current study will promote further exploration of the potential of other porous structures for similar applications.

Porous organic cages have shape persistent cavities which provide a suitable platform for encapsulation of guest molecules with size suitably fitting to the cavity.

Metal-organic frameworks/polydopamine synergistic interface enhancement of carbon fiber/phenolic composites for promoting mechanical and tribological performances

Carbon fiber/phenolic composites have wide application prospects in the transmission of vehicles, where the combination of prominent mechanical and tribological properties is required. Multiscale metal-organic frameworks (MOFs) and polydopamine (PDA) as binary reinforcements were employed to construct a rigid-flexible hierarchical structure for improving the interfacial performances of friction materials. This unique rigid-flexible (MOFs/PDA) reinforcement could act as an effective interfacial linker, significantly facilitating the integration of fibers into the matrix and establishing a strong mechanical interlocking and chemical bonding onto the fiber/matrix interphase, thus boosting the mechanical and tribological properties of the composites. Benefiting from the MOF/PDA synergistic enhancement effects, the interlaminar shear strength of ZIF-8-composites (P1), MOF-5-composites (P2) and UiO-66-(COOH)₂-composites (P3) was improved by 70.80%, 43.80% and 53.28%, respectively. In addition, the wear rate of P1 decreased from 3.55 × 10^-8 cm³ J^-1 to 2.45 × 10^-8 cm³ J^-1. This work provides a feasible approach for establishing rigid-flexible reinforced structures and opens up a double-component synergistic enhancement strategy to efficiently promote mechanical and tribological properties for fabricating high-performance carbon fiber/phenolic composites.

Preparation of Ag@ZIF-8@PP Melt-Blown Nonwoven Fabrics: Air Filter Efficacy and Antibacterial Effect

Serving as matrices, polypropylene (PP) melt-blown nonwoven fabrics with 4% electrostatic electret masterbatch were incorporated with a 6%, 10%, 14%, or 18% phosphorus-nitrogen flame retardant. The test results indicate that the incorporation of the 6% flame retardant prevented PP melt-blown nonwoven fabrics from generating a molten drop, which, in turn, hampers the secondary flame source while increasing the fiber diameter ratio. With a combination of 4% electrostatic electret masterbatch and the 6% flame retardant, PP melt-blown nonwoven fabrics were grafted with ZIF-8 and Ag@ZIF-8. The antibacterial effect of ZIF-8 and Ag@ZIF-8 was 40% and 85%, respectively. Moreover, four reinforcing measures were used to provide Ag@ZIF-8 PP melt-blown nonwoven fabrics with synergistic effects, involving lamination, electrostatic electret, and Ag@ZIF-8 grafting, as well as a larger diameter because of the addition of phosphorus-nitrogen flame retardants. As specified in the GB2626-2019 and JIS T8151-2018 respiratory resistance test standards, with a constant 60 Pa, Ag@ZIF-8 PP melt-blown nonwoven membranes were tested for a filter effect against PM 0.3. When the number of lamination layers was five, the filter effect was 88 ± 2.2%, and the respiratory resistance was 51 ± 3.6 Pa.

Removal of Particulate Matters by Using Zeolitic Imidazolate Framework-8s (ZIF-8s) Coated onto Cotton: Effect of the Pore Size of ZIF-8s on Removal

Removal of particulate matter (PM) like PM2.5 and PM10 from air was carried out with cotton coated with metal-organic frameworks (MOFs) having various pore sizes to understand the effect of the pore size of MOFs (here, ZIF-8s) on the performances in PM elimination. Both removal efficiency and quality factor, based on the unit surface area of ZIF-8s, in the filtration of PMs with ZIF-8/cotton did not rely considerably on the pore size of ZIF-8s. More importantly, small pores (even less than 0.5 nm) of conventional MOFs like ZIF-8 are more than enough in the elimination of large PMs like PM10 with a size of microns probably because small active sites (such as polar functional groups) on PMs can interact with porous materials having polarity. Additionally, electrostatic interactions between PMs and porous materials could be confirmed as a plausible mechanism for PM removal with ZIF-8/cotton.

Recent developments on MOF-based platforms for antibacterial therapy

With increasing pathogenic bacterial infection that is occurring worldwide, antibacterial therapy has become an important research field. There is great antimicrobial potential in the nanomaterial-based metal-organic framework (MOF) platform because it is highly biocompatible, biodegradable, and nontoxic, and it is now widely used in the anticancer agent industry and in the production of medical products. This review summarizes the possible mechanisms of representative MOF-based nanomaterials, and recounts recent progress in the design and development of MOF-based antibacterial materials for the remedy of postoperative infection. The existing shortcomings and future perspectives of the rapidly growing field of antimicrobial therapy addressing patient quality of life issues are also briefly discussed. Because of their wide applicability, further studies on the use of different MOF antimicrobial therapies will be of great interest.

Three-dimensional composite electrospun nanofibrous membrane by multi-jet electrospinning with sheath gas for high-efficiency antibiosis air filtration

Three-dimensional (3D) composite polyvinylidene fluoride (PVDF)/polyacrylonitrile (PAN) electrospun nanofibrous membranes combining both thick and thin nanofibers have been fabricated by the method of multi-jet electrospinning with sheath gas to realize high-efficiency air filtration under a low pressure drop. The thin PAN nanofibers form a dense membrane, with a strong capturing ability on the ultra-fine particles, while the thick PVDF nanofibers play a 3D supporting effect on the thin PAN nanofibers. In this case, the combination results in a fluffy membrane with higher porosity, which could achieve the airflow passing through the membrane without the air pressure drop. The effects of the composite manner of thick nanofibers and thin nanofibers are investigated, in order to optimize the air filtration performance of the 3D composite nanofibrous membrane. As a result, the maximum quality factor for air filtration could reach up to 0.398 Pa^-1. The particle-fiber interaction model was used to simulate the air filtration process as well, and the simulation results were fairly consistent with the experimental results, providing a guidance method for the optimization of composite nanofibrous membrane for high-efficiency air filtration. More interestingly, a cationic poly[2-(N,N-dimethyl amino) ethyl methacrylate] (PDMAEMA) was added in the PVDF solution to obtain a composite air filtration membrane with excellent antibiosis performance, which achieved the highest inhibition rate of approximately 90%. In short, this work provides an effective way to promote antibiosis air filtration performance by using an electrospun nanofibrous membrane, and might also effectively accelerate the biological protection application of current air filtration membranes.

The effects of DOPO modified Co-based metalorganic framework on flame retardancy, stiffness and thermal stability of epoxy resin

In this work, the effect of a modified metal organic framework material on the fire resistance and mechanical properties of epoxy resin (EP) has been explored. The cobalt based metal organic framework (ZIF-67) was synthesized from an organic ligand with a Schiff base structure. Then DOPO@ZIF-67 was synthesized by modifying ZIF-67 with 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO), and its effect on EP modification was explored. Compared with the pure EP, 4% DOPO@ZIF-67/EP passed the UL94 V-0 level and the ultimate oxygen index (LOI) reached 32.1%. The SEM pictures of carbon residue indicated that DOPO@ZIF-67 formed a more continuous and dense microstructure, which can enhance the thermal barrier and the physical barrier effect. The addition of DOPO@ZIF-67 also can effectively improve the stiffness and damping coefficient of EP composite material. The porous skeleton structure of DOPO@ZIF-67 can endow EP with rigidity and flame-retardant properties. Furthermore, the existence of DOPO made the combination of ZIF-67 with EP better. The results of this study suggest that DOPO@ZIF-67 may be a good additive for modification of the properties of epoxy thermosetting materials.

Recent advances in process engineering and upcoming applications of metal-organic frameworks

Progress in metal-organic frameworks (MOFs) has advanced from fundamental chemistry to engineering processes and applications, resulting in new industrial opportunities. The unique features of MOFs, such as their permanent porosity, high surface area, and structural flexibility, continue to draw industrial interest outside the traditional MOF field, both to solve existing challenges and to create new businesses. In this context, diverse research has been directed toward commercializing MOFs, but such studies have been performed according to a variety of individual goals. Therefore, there have been limited opportunities to share the challenges, goals, and findings with most of the MOF field. In this review, we examine the issues and demands for MOF commercialization and investigate recent advances in MOF process engineering and applications. Specifically, we discuss the criteria for MOF commercialization from the views of stability, producibility, regulations, and production cost. This review covers progress in the mass production and formation of MOFs along with future applications that are not currently well known but have high potential for new areas of MOF commercialization.

Antibacterial application and toxicity of metal-organic frameworks

Metal-organic frameworks (MOFs), which are also referred to as coordination polymers, have been widely used in adsorption separation and catalysis, especially in the field of physical chemistry in the past few years, because of their unique physical structure and potential chemical properties. In recent years, particularly with the continuous expansion of the research field, deepening of research levels, and sustained advancements in science and technology, powerful and diverse MOFs that have demonstrated great biomedical application potential have been successively developed. Consequently, this study summarizes the origin, development, and common synthesis methods of MOFs, with major emphasis on their antibacterial application and safety evaluation in biomedicine.

Polypropylene/Polyvinyl Alcohol/Metal-Organic Framework-Based Melt-Blown Electrospun Composite Membranes for Highly Efficient Filtration of PM2.5

Particulate matter 2.5 (PM2.5) has become a public hazard to people's lives and health. Traditional melt-blown membranes cannot filter dangerous particles due to their limited diameter, and ultra-fine electrospinning fibers are vulnerable to external forces. Therefore, creating highly efficient air filters by using an innovative technique and structure has become necessary. In this study, a combination of polypropylene (PP) melt-blown and polyvinyl alcohol (PVA)/zeolite imidazole frameworks-8 (ZIF-8) electrospinning technique is employed to construct a PP/PVA/ZIF-8 membrane with a hierarchical fibrous structure. The synergistic effect of hierarchical fibrous structure and ZIF-8 effectively captures PM2.5. The PP/PVA composite membrane loaded with 2.5% loading ZIF-8 has an average filtration efficacy reaching as high as 96.5% for PM2.5 and quality factor (Qf) of 0.099 Pa-1. The resultant membrane resists 33.34 N tensile strength and has a low pressure drop, excellent filtration efficiency, and mechanical strength. This work presents a facile preparation method that is suitable for mass production and the application of membranes to be used as air filters for highly efficient filtration of PM2.5.

A Bimodal Protein Fabric Enabled via In Situ Diffusion for High-Performance Air Filtration

Design and fabrication of bimodal structures are essential for successful development of advanced air filters with ultralow airflow resistance. To realize this goal, simplified processing procedures are necessary for meeting the practical needs. Here, a bimodal protein fabric with high-performance air filtration, and effectively lowered airflow resistance is reported. The various functional groups of proteins provide versatile interactions with pollutants. By utilizing a novel and cost-effective "cross-axial" configuration with an optimized condition (75° of contacting angle between solution nozzle and cospinning solvent nozzle), the diffusion in Taylor cone is in situ controlled, which results in the successful production of bimodal protein fabric. The bimodal protein fabric (16.7 g/m² areal density) is demonstrated to show excellent filtration performance for removing particulate matter (PM) pollutants and only causes 17.1 Pa air pressure drop. The study of multilayered protein fabric air filters shows a further improvement in filtration performance of removing 97% of PM_0.3 and 99% of PM_2.5 with a low airflow resistance (34.9 Pa). More importantly, the four-layered bimodal protein fabric shows an exceptional long-term performance and maintains a high removal efficiency in the humid environment. This study presents an effective and viable strategy for fabricating bimodal fibrous materials for advanced air filtration.

Hazardous wastes treatment technologies

A review of the literature published in 2019 on topics related to hazardous waste management in water, soils, sediments, and air. The review covered treatment technologies applying physical, chemical, and biological principles for the remediation of contaminated water, soils, sediments, and air. PRACTICAL POINTS: This report provides a review of technologies for the management of waters, wastewaters, air, sediments, and soils contaminated by various hazardous chemicals including inorganic (e.g., oxyanions, salts, and heavy metals), organic (e.g., halogenated, pharmaceuticals and personal care products, pesticides, and persistent organic chemicals) in three scientific areas of physical, chemical, and biological methods. Physical methods for the management of hazardous wastes including general adsorption, sand filtration, coagulation/flocculation, electrodialysis, electrokinetics, electro-sorption ( capacitive deionization, CDI), membrane (RO, NF, MF), photocatalysis, photoelectrochemical oxidation, sonochemical, non-thermal plasma, supercritical fluid, electrochemical oxidation, and electrochemical reduction processes were reviewed. Chemical methods including ozone-based, hydrogen peroxide-based, potassium permanganate processes, and Fenton and Fenton-like process were reviewed. Biological methods such as aerobic, anoxic, anaerobic, bioreactors, constructed wetlands, soil bioremediation and biofilter processes for the management of hazardous wastes, in mode of consortium and pure culture were reviewed. Case histories were reviewed in four areas including contaminated sediments, contaminated soils, mixed industrial solid wastes and radioactive wastes.