Zeolitic Imidazolate Framework-8/Polypropylene-Polycarbonate Barklike Meltblown Fibrous Membranes by a Facile in Situ Growth Method for Efficient PM2.5 Capture

Bio-inspired gradient poly(lactic acid) nanofibers for active capturing of PM0.3 and real-time respiratory monitoring

The concept of bio-inspired gradient hierarchies, in which the well-defined MOF nanocrystals serve as active nanodielectrics to create electroactive shell at poly(lactic acid) (PLA) nanofibers, is introduced to promote the surface activity and electroactivity of PLA nanofibrous membranes (NFMs). The strategy enabled significant refinement of PLA nanofibers during coaxial electrospinning (∼40 % decline of fiber diameter), accompanied by remarkable increase of specific surface area (nearly 1.5 m2/g), porosity (approximately 85 %) and dielectric constants for the bio-inspired gradient PLA (BG-PLA) NFMs. It largely boosted initial electret properties and electrostatic adsorption capability of BG-PLA NFMs, as well as charge regeneration by TENG mechanisms even under high-humidity environment. The BG-PLA NFMs thus featured exceptionally high PM0.3 filtration efficiencies with well-controlled air resistance (94.3 %, 163.4 Pa, 85 L/min), in contrast to the relatively low efficiency of only 80.0 % for normal PLA. During the application evaluation of outdoor air purification, excellent long-term filtering performance was demonstrated for the BG-PLA for up to 4 h (nearly 98.0 %, 53 Pa), whereas normal PLA exhibited a gradually declined filtration efficiency and an increased pressure drop. Moreover, the BG-PLA NFMs of increased electroactivity were ready to generate tribo-output currents as driven by respiratory vibrations, which enabled real-time monitoring of electrophysiological signals. This bio-inspired gradient strategy opens up promising pathways to engender biodegradable nanofibers of high surface activity and electroactivity, which has significant implications for intelligent protective membranes.

Research and application of polypropylene: a review

Polypropylene (PP) is a versatile polymer with numerous applications that has undergone substantial changes in recent years, focusing on the demand for next-generation polymers. This article provides a comprehensive review of recent research in PP and its advanced functional applications. The chronological development and fundamentals of PP are mentioned. Notably, the incorporation of nanomaterial like graphene, MXene, nano-clay, borophane, silver nanoparticles, etc., with PP for advanced applications has been tabulated with their key features and challenges. The article also conducts a detailed analysis of advancements and research gaps within three key forms of PP: fiber, membrane, and matrix. The versatile applications of PP across sectors like biomedical, automotive, aerospace, and air/water filtration are highlighted. However, challenges such as limited UV resistance, bonding issues, and flammability are noted. The study emphasizes the promising potential of PP while addressing unresolved concerns, with the goal of guiding future research and promoting innovation in polymer applications.

A Fiber Sliding-Orientation Based Micromechanics Failure Model for Melt-Blown Nonwovens

The mechanical model of melt-blown nonwovens (MNs) serves as the foundation for performance optimization, which can offer helpful guidance for product material selection, structural design, and cost control. However, it is challenging to describe the micromechanics failure mechanism of MNs using the traditional mechanical model, which aims to match the model curve with the experimental result at the macrolevel. Herein, a micromechanics failure model for MNs based on sliding-orientation competition is developed. Through in situ observations of fiber position changes and the fluctuation of stress-strain curves, fiber sliding and orientation are introduced into the failure process of MNs. Due to fiber bonding and static friction, only orientation happens during the first stage of stretching. In dramatic contrast, the fibers will slide and orient in the second stage of stretching to change their positions in response to the external force. Sliding friction, fiber bonding, and static friction make up the stress of MNs, and the conflict of fiber sliding and orientation causes variations in the stress. The model has been successfully applied to polylactic acid (PLA) MNs, which proves the effectiveness of the model in MNs.

Nanopatterned Electroactive Polylactic Acid Nanofibrous MOFilters for Efficient PM0.3 Filtration and Bacterial Inhibition

Biodegradable polylactic acid (PLA) nanofibrous membranes (NFMs) hold great potential to address the increasing airborne particulate matter (PM) and dramatic accumulation of plastic/microplastic pollution. However, the field of PLA NFM-based filters is still in its infancy, frequently dwarfed by the bottlenecks regarding relatively low surface activity, poor electroactivity, and insufficient PM capturing mechanisms. This effort discloses a microwave-assisted approach to minute-level synthesis of dielectric ZIF-8 nanocrystals with high specific surface area (over 1012 m2/g) and ultrasmall size (∼240 nm), which were intimately anchored onto PLA nanofibers (PLA@ZIF-8) by a combined "electrospinning-electrospray" strategy. This endowed the PLA@ZIF-8 NFMs with largely increased electroactivity in terms of elevated dielectric coefficient (an increase of 202%), surface potential (up to 5.8 kV), and triboelectric properties (output voltage of 30.8 V at 10 N, 0.5 Hz). Given the profound control over morphology and electroactivity, the PLA@ZIF-8 NFMs exhibited efficient filtration of PM0.3 (97.1%, 85 L/min) with a decreased air resistance (592.5 Pa), surpassing that of the pure PLA counterpart (88.4%, 650.9 Pa). This was essentially ascribed to realization of multiple filtration mechanisms for PLA@ZIF-8 NFMs, including enhanced physical interception, polar interactions, and electrostatic adsorption, and the unique self-charging function triggered by airflow vibrations. Moreover, perfect antibacterial performance was achieved for PLA@ZIF-8, showing ultrahigh inhibition rates of 99.9 and 100% against E. coli and S. aureus, respectively. The proposed hierarchical structuring strategy, offering the multifunction integration unattainable with conventional methods, may facilitate the development of biodegradable long-term air filters.

Electrospun Metal-Organic Framework-Fabric Nanocomposites as Efficient Bactericides

In this work, we utilized electrospinning to develop advanced composite membranes of polyvinyl chloride (PVC) loaded with postmetalated metal-organic frameworks (MOFs), specifically UiO-66(COOH)₂-Ag and ZIF-8-Ag. This innovative technique led to the creation of highly stable PVC/MOFs-Ag membrane composites, which were thoroughly characterized using various analytical techniques, including scanning electron microscopy, powder X-ray diffraction, thermogravimetric analysis, X-ray photoelectron spectroscopy, porosity analysis, and water contact angle measurement. The results verified the successful integration of MOF crystals within the nanofibrous PVC membranes. The obtained composites exhibited larger fiber diameters for 5 and 10% MOF loadings and a smaller diameter for 20% loading. Additionally, they displayed greater average pore sizes than traditional PVC membranes across most MOF loading percentages. Furthermore, we examined the antibacterial properties of the fabricated membranes at different MOFs-Ag loadings. The findings revealed that the membranes demonstrated significant antibacterial activity up to 95% against both Gram-negative (Escherichia coli) and Gram-positive (Staphylococcus aureus) bacteria as the MOFs-Ag loading increased, even when maintaining a constant silver concentration. This indicates a contact-based inhibition mechanism. The outcomes of this study have crucial implications for the development of novel, stable, and highly effective antibacterial materials, which could serve as superior alternatives for face masks and be integrated into materials requiring regular decontamination, as well as potential water filtration systems.

A novel investigations on medical and non-medical mask performance with influence of marine waste microplastics (polypropylene)

The entire human race is struggling with the spread of COVID-19. Worldwide, the wearing of face masks is indispensable to prevent such spread. Despite numerous studies reporting on the fabrication of face masks and surgical masks to reduce spread and thus human deaths, this novel work is considered the marine waste of microplastics, namely Polypropylene (PP) polymer, used to fabricate non-woven fabric masks through the melt-blown process. This experimental work aims to maximize the mask's quality and minimize its fabrication cost by optimizing the melt-blown process parameters and using microplastics. The melt-blown process was used to make masks. Parameters such as extruder temperature, hot air temperature, melt flow rate, and die-to-collector distance (DCD) were investigated as independent variables. The quality of the mask was investigated in terms of bacterial filtration efficiency (BFE), particle filtration efficiency (PFE), and differential pressure. The Taguchi L16 orthogonal array and Taguchi analysis were employed for experimental design and statistical optimization, respectively. The results reveal that the higher BFE and PFE are recorded at 96.7 % and 98.6 %, respectively. The surface morphological investigation on different layers ensured the fine and uniform porosity of the layers and exhibited minimum breath resistance (a low differential pressure of 0.00152 kPa/cm²). Hence the chemically treated marine waste microplastics improved the masks' performance.

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.

Photothermal and Concus Finn capillary assisted superhydrophobic fibrous network enabling instant viscous oil transport for crude oil cleanup

Rapid and effective removal of highly viscous oil spills from the sea remains a great challenge globally. Superhydrophobic materials are attractive candidates for handling oil spills, but they are restrained to recover oils with low viscosity exclusively. Herein, we report a novel polypyrrole wrapped superhydrophobic fibrous network using cross-shaped polyester fibers as starting blocks. The polypyrrole coating enables the absorbent to convert light to heat, ensuring that the viscosity of heavy oils in the proximity can be easily controlled. In the meanwhile, the special structure of the starting fibers initiates Concus Finn (CFin) capillary allowing instant oil transport in the network. When the absorbent is exposed to light oils (0-500 mPa.s), the oils can be transported instantly via CFin capillary. Interestingly, under synergistic effect of light-to-heat conversion and CFin capillary, a drawing-sticking crude oil strip (10⁵ mPa.s) is sucked instantly against gravity by the absorbent. The absorbent is successfully applied to efficiently separate both oil/water mixtures and oil/water emulsions (efficiency > 99%). Such absorbent can absorb 62.99-74.23 g/g light oils on average and up to 123.3 g/g crude oil under 0-2 sun illumination, holding a huge potential in managing oil spills.

Enhancing mechanical properties of flash-spun filaments by pressure-induced phase separation control in supercritical high-density polyethylene solution

Flash-spun nonwoven (FS-NW) is gaining attention in the PPE field due to its excellent barrier and mechanical properties resulting from its non-uniform diameter distribution and unique filament morphology. The unique network structure of flash-spun filaments (FSF) comprising the FS-NW can be controlled by phase separation behavior in the supercritical fluid (SCF) process. This study proposes a simple method to control the microstructure of FSFs by controlling the pressure-induced phase separation (PIPS) process in polymer/SCF solution. This phase separation behavior of an HDPE/SCF solution was confirmed by using a high-pressure view cell. A multistage nozzle allowing for phase-separated pressure to form different phases was also designed. HDPE-FSFs were synthesized by flash-spinning, and their morphology, crystallinity, and mechanical properties were investigated. The results demonstrated that the filaments obtained by PSP control at 220 °C and with an HDPE concentration of 8 wt% showed a network structure composed of strands, wherein the diameters ranged from 1.39 to 40.9 μm. Optimal FSF was obtained at 76 bar, with a crystallinity of 64.0% and a tenacity of 2.88 g/d. The PIPS method can thus effectively control the microstructure more feasibly than temperature- or solvent-induced techniques and can allow the effective synthesis of various products.

Metal-organic framework-based materials for the abatement of air pollution and decontamination of wastewater

Developing new and efficient technologies for environmental remediation is becoming significant due to the increase in global concerns such as climate change, severe epidemics, and energy crises. Air pollution, primarily due to increased levels of H₂S, SO_x, NH₃, NO_x, CO, volatile organic compounds (VOC), and particulate matter (PM) in the atmosphere, has a significant impact on public health, and exhaust gases harm the natural sulfur, nitrogen, and carbon cycles. Similarly, wastewater discharged to the environment with metal ions, herbicides, pharmaceuticals, personal care products, dyes, and aromatics/organic compounds is a risk for health since it may lead to an outbreak of waterborne pathogens and increase the exposure to endocrine-disrupting agents. Therefore, developing new and efficient air and water quality management systems is critical. Metal-organic frameworks (MOFs) are novel materials for which the main application areas include gas storage and separation, water harvesting from the atmosphere, chemical sensing, power storage, drug delivery, and food preservation. Due to their versatile structural motifs that can be modified during synthesis, MOFs also have a great promise for green applications including air and water pollution remediation. The motivation to use MOFs for environmental applications prompted the modification of their structures via the addition of metal and functional groups, as well as the creation of heterostructures by mixing MOFs with other nanomaterials, to effectively remove hazardous contaminants from wastewater and the atmosphere. In this review, we focus on the state-of-the-art environmental applications of MOFs, particularly for water treatment and air pollution, by highlighting the groundbreaking studies in which MOFs have been used as adsorbents, membranes, and photocatalysts for the abatement of air and water pollution. We finally address the opportunities and challenges for the environmental applications of MOFs.

Biomimetic Fibrous Leaf-Vein Membrane Enabling Unidirectional Water Penetration and Effective Antibacterial PM Filtration

Air pollution induced by pathogenic particulate matter (PM) has posed a serious threat to public health worldwide. Advanced air filters are thus required, not only exhibiting high PM capture efficiency, low breathing resistance, and high internal moisture transferring performance but also isolating and inactivating external pathogenic aerosols. In this study, we demonstrated a facile approach to construct a biomimetic fibrous leaf-vein membrane with unidirectional water penetration and effective antibacterial PM filtration by one-step electrospinning of poly(vinylidene fluoride) (PVDF)-based multilayer nanofibers. With ultrathin fibers penetrating the skeletal framework of bimodal thick fibers, the membranes showed gradient interconnected porous structures and achieved a highly efficient and stable (in an acid and alkali environment) PM_0.3 interception (>99.98%) with low air drag (51-71 Pa). In addition, the gradient narrow pores of the membranes contributed to a gradient higher hydrophilicity. The subsequent unidirectional water motion effectively isolates pathogenic aerosols typically generated by external individuals or ultrafast water penetration from the inverse face. Moreover, the membranes demonstrated an antibacterial efficacy (>99.99%) in a 5 min contact, inactivating the intercepted airborne pathogens efficiently. The test results proved that the proposed membranes were promising advanced air filters for respirator applications.

Removal of Size-Dependent Submicron Particles Using Metal-Organic Framework-Based Nanofiber Air Filters

Particulate matter poses a serious threat to human health. In particular, exposure to submicron particles can result in more severe health effects as they can deposit more deeply into human tissues. Metal-organic framework (MOF)-based nanofiber filters are regarded as promising candidates for efficient particle control. In this study, ZIF-8@PAN nanofiber filters that were developed via an in situ growth strategy were selected for the filtration of submicron particles. The addition of ZIF-8 more effectively enhanced the filtration of particles with smaller sizes. For the most penetrating particle size of around 0.3 μm, the MOF-based nanofiber filter exhibited an 8.9% increase in filtration efficiency compared with that of the pure nanofiber filter. Meanwhile, for particles with large aerodynamic diameters (in the range of 0.7-1 μm, for example), the role of ZIF-8 was negligible. This work provides important insights into the filtration performance of MOF-based nanofiber filters in capturing submicron particles and may aid in designing nanofiber filters for efficient control of particles.

ZIF-8/PI Nanofibrous Membranes With High-Temperature Resistance for Highly Efficient PM0.3 Air Filtration and Oil-Water Separation

Air and water pollution poses a serious threat to public health and the ecological environment worldwide. Particulate matter (PM) is the major air pollutant, and its primary sources are processes that require high temperatures, such as fossil fuel combustion and vehicle exhaust. PM_0.3 can penetrate and seriously harm the bronchi of the lungs, but it is difficult to remove PM_0.3 due to its small size. Therefore, PM_0.3 air filters that are highly efficient and resistant to high temperatures must be developed. Polyimide (PI) is an excellent polymer with a high temperature resistance and a good mechanical property. Air filters made from PI nanofibers have a high PM removal efficiency and a low air flow resistance. Herein, zeolitic imidazolate framework-8 (ZIF-8) was used to modify PI nanofibers to fabricate air filters with a high specific surface area and filtration efficiency. Compared with traditional PI membranes, the ZIF-8/PI multifunction nanofiber membranes achieved super-high filtration efficiency for ultrafine particles (PM_0.3, 100%), and the pressure drop was only 63 Pa. The filtration mechanism of performance improvement caused by the introduction of ZIF-8/PI nanofiber membrane is explored. Moreover, the ZIF-8/PI nanofiber membranes exhibited excellent thermal stability (300 C) and efficient water–oil separation ability (99.85%).

Superwetting Electrospun PDMS/PMMA Membrane for PM2.5 Capture and Microdroplet Transfer

Efficient acquiring and removal of a hazardous particulate matter (PM) have significant effects on human health. Here, we illustrate the fabrication of a superwetting electrospun polydimethylsiloxane/polymethyl methacrylate (PDMS/PMMA) membrane (EPPM) with multifunctional performance for PM_2.5 capture and microdroplet transfer, where PMMA was added as a carrier polymer to the superhydrophobic PDMS, which has very low cohesive energy density. The obtained EPPM, which is composed of special bead-on-string fibers with a mean fiber diameter of 350 nm, shows a porous structure with an aperture of 7.87 μm (calculated by the bubble pressure method) and superb thermostability (up to 325 °C). The EPPM possesses an excellent PM_2.5 purification efficiency of nearly up to 100% at a very low pressure drop (70 Pa, <0.07% of the atmospheric pressure) under the condition of high humidity (96 ± 3%), which is greatly advantageous over those hydrophilic filters frequently suffering the drawbacks of low efficiency or total invalidation in humid environments. In addition, benefitting from the superhydrophobic and strong adhesive properties of the membrane surface, the EPPM could complete the trace aqueous sample analysis such as "robotic hand" from superhydrophobic to hydrophilic surfaces without any contamination or loss and hold a high contact angle of 161.6° for water. Altogether, the EPPM may have technological advantages as a kind of novel fibrous filter in diverse environmental applications, including PM_2.5 capture, separation, microdroplet transfer, and so on.

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.

Bifunctional ZIF-8 Grown Webs for Advanced Filtration of Particulate and Gaseous Matters: Effect of Charging Process on the Electrostatic Capture of Nanoparticles and Sulfur Dioxide

Metal-organic framework (MOF), an emerging class of porous hybrid inorganic-organic crystals, has been applied for various environmental remediation strategies including liquid and air filtration. In this study, the role of the zeolite imidazole framework-8 (ZIF-8) was explored on the charge trapping ability and its contribution to capturing the targeted pollutants of NaCl nanoparticles and SO₂ gas. Poly(lactic acid) fibers with controlled surface pores were electrospun using water vapor-induced phase separation, and the fiber surface was uniformly coated with ZIF-8 crystals via an in situ growth method. As a novel process approach, the corona charging process was applied to the ZIF-8 grown webs. The ZIF-8 promoted the charge trapping in the corona process, and the charged ZIF-8 web showed a significantly improved electrostatic filtration efficiency. Also, the charged ZIF-8 web showed an enhanced SO₂ capture ability, both in the static and dynamic air flow states, demonstrating the applicability as a bifunctional filter for both particulate and gaseous matters. The approach of this study is novel in that both particulate and gas capture capabilities were associated with the charge trapping ability of ZIF-8, implementing the corona charging process to the ZIF-8 webs.

High-Performance Washable PM2.5 Filter Fabricated with Laser-Induced Graphene

This study demonstrates a novel application of laser-induced graphene (LIG) as a reusable conductive particulate matter (PM) filter. Four types of LIG-based filters were fabricated based on the laser-induced pyrolysis of thin polyimide (PI) sheets, each pyrolyzed on either a single side or both sides, with or without densification. The LIG filters exhibited a high removal efficiency while maintaining minimal pressure drop compared to a commercial fiberglass filter. The densified LIG (dLIG) filters displayed a higher PM_2.5 removal efficiency (>99.86%) than regular LIG filters. The dLIG filters also exhibited excellent durability when tested for washability by ultrasonication in tap water. After being cleaned and left to dry, the structures of the dLIG filters were well-maintained; their filtration efficiencies were also well-maintained (less than a 7% change in PM_2.5 removal efficiency), and their resistances only marginally increased (less than a 7% increase after five uses). These results demonstrate the robustness and reusability of the dLIG filters and the accessibility of their cleaning (not requiring aggressive cleaning agents). These promising features will enable the application of LIG in economical, scalable, and high-performance air cleaning.

Two methods for constructing ZIF-8 nanomaterials with good bio compatibility and robust antibacterial applied to biomedical

Metal-organic framework materials not only possess porous structures, but also have excellent antibacterial properties. It is of great practical significance to prepare new antibacterial materials with excellent antibacterial effect by metal-organic framework materials. In our study, Zeolitic Imidazolate Framework-8 (ZIF-8) nanomaterials with antibacterial properties were prepared via the solvent method and diethanolamine template method. The materials were characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), cold field-emission scanning electron microscope (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption experiment, antibacterial experiment, and biocompatibility experiment. Results showed that ZIF-8 prepared by solvent method has a more typical hexagonal structure, larger specific surface area, and smaller pore size, and the values are 1812.07 m²g^-1 and 2.2412 nm, respectively. At the same time, the materials prepared by the two methods have excellent antibacterial properties, and exhibit good biocompatibility at low concentrations, the antibacterial activity against Escherichia coli and Staphylococcus aureus are higher than 95%, and the cell viabilities of the selected five material concentrations of 12.5 µg mL^-1, 25 µg mL^-1, 50 µg mL^-1, 100 µg mL^-1 and 200 µg mL^-1 are more than 70%. Therefore, this study provides a feasible method for preparing Nano-scale antibacterial functional particles, and it is of great significance to broaden the application field of ZIF-8 materials and prepare ZIF-8 drug-delivery functional materials.

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.

Stable Mesoscale Nonwovens of Electrospun Polyacrylonitrile and Interpenetrating Supramolecular 1,3,5-Benzenetrisamide Fibers as Efficient Carriers for Gold Nanoparticles

The immobilization of metal nanoparticles without agglomeration and leaching within composite nonwovens is often challenging and of great importance, for example, for catalytic applications. In this study, we prepared composite nonwovens based on electrospun polyacrylonitrile (PAN) short fibers and supramolecular terpyridine-functionalized benzene-1,3,5-tricarboxamide (BTA1) nanofibers by a sheet-forming wet-laid process. The formation of an interpenetrating and entangled network of supramolecular BTA1 nanofibers and PAN short fibers results in mechanically stable mesoscale nonwovens. Because of the peripheral terpyridine substituents of the BTA1, nonaggregated gold nanoparticles (AuNPs) could be immobilized efficiently in the composite nonwovens. The functionality of the resulting AuNPs-loaded composite nonwovens was verified by catalytic reduction of 4-nitrophenol to 4-aminophenol as a standard model reaction. The AuNPs-loaded PAN/BTA1 composite nonwovens showed high catalytic activity, reusability, and excellent stability.

Low-cost hydrogel adsorbent enhanced by trihydroxy melamine and β-cyclodextrin for the removal of Pb(II) and Ni(II) in water

Hydrogels have extensively studied as adsorbents, raw materials for the preparation of adsorbent hydrogels have low strength, while high strength hydrogels have weak adsorption capacity. In this study, PVA hydrogel was crosslinked via trihydroxy melamine and epichlorohydrin, and β-cyclodextrin with strong adsorption capacity was added to remove the heavy metal ions. Results showed that the addition of trihydroxy melamine with 8%, the compressive strength of the hydrogel was increased by approximately 20%. The Langmuir isotherm model showed that the adsorption capacity of the hydrogel for Pb(II) and Ni(II) reached 505.9 mg/g and 286.7 mg/g, respectively, and the efficiency of removing the low-concentration heavy metal ions in water more than 99%. The hydrogel is low cost, and maintained highly removal efficiency under low pH. The removal efficiency of the hydrogel remained above 90% after five repeated adsorption-desorption experiments. The hydrogels have a potential to be used in wastewater treatment as adsorbents.

Ionic Salts@Metal-Organic Frameworks: Remarkable Component to Improve Performance of Fabric Filters to Remove Particulate Matters from Air

The elimination of particulate matters (PMs) from the air is very important for our sustainability. In this study, highly porous metal-organic frameworks (MOFs) like MIL-101 and UiO-67 were first modified, coated onto cotton, and applied in PM removal via filtration. Ionic salts (ISs) like CaCl₂ and LiCl, after loading onto the MOFs, remarkably increased the PM removal efficiency. For example, CaCl₂(20)@MIL-101/cotton shows 5.7 times the quality factor (QF, which is the most important parameter in filtration) of that of bare cotton and has the most competitive performances in PM removal (with the highest QF of 0.085 Pa^-1) compared to any filter modified with porous materials or commercial filters. The noticeable performances of ISs@MOFs can be explained by the contribution of charge separation (that is effective for electrostatic interactions with PMs) of ISs and the high porosity of MOFs. Moreover, how MOFs with small pores of a few nanometers or less can remove large PMs with sizes in the micron range could be explained. Finally, loading ISs onto highly porous materials can be a promising strategy to improve the performances of filters to remove PMs from the air.

High performance, environmentally friendly and sustainable nanofiber membrane filter for removal of particulate matter 1.0

Particulate matter (PM) air pollution is becoming more and more serious and dangerous to public health, especially in developing countries where industrialization is accelerating. The use of electrospun membrane-based materials for air filtration is a widespread and effective way to help individuals avoid air pollution. However, most electrospun membrane preparation processes require the use of organic solvents, resulting in secondary environmental pollution. In this study, an environmentally friendly polyvinyl alcohol (PVA) - tannic acid (TA) composite nanofiber membrane filter was prepared by the green electrospinning and the physical cross-linking method. The filtration efficiency of the membrane filter for PM_1.0 reached 99.5%, and the pressure drop was only 35 Pa. In addition, due to the existence of intermolecular hydrogen bond between PVA and TA, the mechanical properties of the nanofiber membrane were improved to meet the requirements of practical application of the filter. Therefore, the PVA-TA composite nanofiber membrane is expected to provide a solution for the development of efficient and environmentally friendly air filter.

Microfluidic spinning-induced heterotypic bead-on-string fibers for dual-cargo release and wound healing

The preparation of dual-release pharmaceutical microfibers provides an ideal material for new biomedical applications. We describe a microfluidic spinning method for engineering heterotypic bead-on-string fibers with the ability to carry dual cargos and to deliver on demand. The core of our technology is to combine microfluidic spinning with biomaterial preparation, in which hydrophobic and hydrophilic cargos can be integrated into a bead-on-string microfiber structure. We demonstrate the loading of bovine serum albumin (BSA) in the sodium alginate phase and ibuprofen in the polylactic acid (PLA) phase, respectively. The heterotypic bead-on-string fibers are biocompatible and show hemostatic ability in vivo. These heterotypic bead-on-string fibers are then woven as a skin scaffold and shown to promote wound healing by loading antibacterial and anti-inflammatory cargos.

Recyclable and degradable nonwoven-based double-network composite hydrogel adsorbent for efficient removal of Pb(II) and Ni(II) from aqueous solution

This study reports a novel adsorbent structure and shows the satisfactory removal performance of Pb(II) and Ni(II). The fabric structure increases the strength of the hydrogel. The hydrogel plays a major role in the composite structure as a matrix, while the fabric bears the applied load and protects the structure from mechanical damage. The double-network composite hydrogel is reinforced by plasma grafted polylactic acid melt-blown non-woven fabric and polyethylene glycol dimaleate, and its compressive strength reaches 40.6 kPa at 60% strain. The interface substantially improves the compression strength by 42.9%. Through the adsorption isotherm model, the adsorption capacity of the hydrogel for Pb(II) and Ni(II) reaches 233.12 and 165.06 mg/g, respectively, and the removal rate of heavy metal ions in water at low concentrations exceeds 95%, showing the excellent removal rate of heavy metals. Even after the fifth cycle, the removal efficiency barely declines, indicating the feasibility of repeatedly use. Cost analysis reveals that the adsorbent is relatively low cost, solving the problems of difficult recovery, low strength, and easy damage of hydrogel adsorbents, and promoting the industrial application of hydrogels as adsorbents.

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.

A hydrolytically stable cage-based metal–organic framework containing two types of building blocks for the adsorption of iodine and dyes

A metal–organic framework (SCNU-Z4) with high chemical stability in water and common organic solvents showed ability for iodine and dye adsorption.

Electrospun Wrinkled Porous Polyimide Nanofiber-Based Filter via Thermally Induced Phase Separation for Efficient High-Temperature PMs Capture

Benefiting from its superior thermal stability, polyimide (PI) fiber-based composites have attracted wide attention in the field of high-temperature filtration and separation. However, the trade-off between filtration efficiency and pressure drop of traditional PI filters with single morphology and structure still remains challenging. Herein, the electrospun PI high-temperature-resistant air filter was fabricated via thermal-induced phase separation (TIPS), employing polyacrylonitrile (PAN) as a template. The PI nanofibers exhibited special wrinkled porous structure, and the filter possessed a high specific surface area of 304.77 m²/g. The removal of PAN changed the chemical composition of the fiber and induced PI molecules to form complex folds on the surface of the fiber, thus forming the wrinkled porous structure. Additionally, the wrinkled porous PI nanofiber filter displayed a high PM0.3 removal efficiency of 99.99% with a low pressure drop of 43.35 Pa at room temperature, and the filtration efficiency was still over 97% after being used for long time. Moreover, the efficiency of the filter could even reach 95.55% at a high temperature of 280 °C. The excellent filtration performance was attributed to the special wrinkled porous surface, which could limit the Brownian motion of PMs and reinforce the mechanical interception effect to capture the particulate matters (PMs) on the surface of the filter. Therefore, this work provided a novel strategy for the fabrication of filters with special morphology to cope with increasingly serious air pollution in the industrial field.

Hybrid membrane with controllable surface microroughness by micro-nano structure processing for diluted PM2.5 capture

Tremendous efforts have been devoted by researchers on air particulate matter pollution for the increasing harm, however, the Air Pollution Index (API) from "good" to "excellent" is something hard to achieve. Here, halloysite nanotubes/polyvinyl alcohol (HNTs/PVA) hybrid membrane with surface micro-nano structure processing using a one-step method for efficient PM_2.5 capture was prepared. The filtration efficiency is 45.35% and the pressure drop is 41.57 Pa of composite membrane with a 60 wt% halloysite dosage. Specially, it resulted in a relatively safer PM index value of about 16.54, which tends to be more stringent than the restriction by Government of China (PM_2.5 < 35 μg/m³). The filtration performance was mainly attributed to the controllable microroughness surface as well as the hierarchical structure constructed by one-step method, which has a functional role in obstruction and adsorption for diluted PM_2.5. The methodology can employ halloysite onto various polymers, like polyvinyl alcohol (PVA), polyvinylpyrrolidone (PVP), polyacrylonitrile (PAN) and also polycaprolactone (PCL) to yield hybrid membranes with the similar modification of surface and structure. Such versatile membrane filters can be purposely designed and scaled up, which endows the existing hybrid membrane with great potentials in both residential and public areas pollution control to achieve a healthier living environment.

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.

Flexible and transparent composite nanofibre membrane that was fabricated via a "green" electrospinning method for efficient particulate matter 2.5 capture

Air particulate pollution from ever-increasing industrialization poses an enormous threat to public health. Thus, the development of a green air filter with high efficiency and performance is of urgent necessity. In this study, we introduce a new effective air filtration membrane that can be used for outdoor protection. The air filter's composite nanofibre materials were prepared from polyvinyl alcohol (PVA)-sodium lignosulfonate (LS) via a "green" electrospinning method and thermal crosslinking. The addition of LS helped increase the PM_2.5 removal efficiency compared to that of a pure PVA nanofibre membrane. The pressure drops of the electrospun PVA-LS membranes exceeded those of the pristine PVA air filter. The remarkable air filtration performance was maintained even after 10 cycles of circulation filtration. In addition, the PVA-LS composite nanofibre membrane exhibited excellent mechanical properties and transparency due to the introduction of LS. This study provides new insight into the design and development of high-performance and high-visibility green filter media, which include personal protection and building screens.

Removal of Particulate Matters with Isostructural Zr-Based Metal-Organic Frameworks Coated on Cotton: Effect of Porosity of Coated MOFs on Removal

Effective removal of particulate matters (PMs) from air is very important for our safe environment, health, and sustainability. In this study, isostructural (with the same topology of fcu) Zr-metal-organic frameworks (Zr-MOFs) such as UiO-66, UiO-67, and DUT-52 (with different porosity) were coated onto cotton and utilized in PM removal from air to understand the contribution of MOFs in improving the performances of air filters. Moreover, UiO-66s with different porosities were also prepared under different conditions from the same reaction mixture. Experiments to remove PMs such as PM2.5 and PM10 showed a critical role of porosity of coated MOFs in the PM removal. Or, the removal efficiency or quality factor increased linearly with the increasing surface area of all the studied MOFs, irrespective of the applied linkers (for synthesizing different MOFs) and synthesis conditions (for different porosities of UiO-66s). Therefore, this work confirms, for the first time, that the porosity of MOF is one of the most important parameters to improve the performance of air filter (to remove PMs) that is modified with coated MOFs. Moreover, we could suggest why porous materials with small pores were effective in capturing PMs (larger in size than pores of porous materials) from air.

Bioinspired design of underwater superoleophobic Poly(N-isopropylacrylamide)/ polyacrylonitrile/TiO2 nanofibrous membranes for highly efficient oil/water separation and photocatalysis

Inspired by fish scales, this study prepares a thermo-responsive underwater oleophobic PNIPAM/PAN/TiO₂ nanofibrous membranes by traditional electrospinning technique using poly-N-isopropylacrylamide (PNIPAM) and polyacrylonitrile (PAN). Thermal properties, mechanical properties, surface chemical composition, wettability, photocatalysis, and oil/water separation of PNIPAM/PAN/TiO₂ membrane are explored compared to pure PNIPAM membrane. Result reveals that PAN/TiO₂ compounds make PNIPAM membrane with a smaller fiber diameter of 141 nm and high tensile stress of 7.4 MPa, and also decompose 98% of rhodamine B after UV light radiation. This bioinspired design structure endows the membrane with superhydrophilicity with a low water contact angle, and underwater superoleophobicity with a high oil contact angle of 157° (petroleum ether) and 151° (dichloromethane). This membrane can efficiency separate oil/water mixture with a high separation efficiency. Moreover, the resultant PNIPAM/PAN/TiO₂ membrane has the bionic fish scale structure, and has wettability respond at lower critical solution temperature making the water flux decreased from 10013 ± 367 L m^-2·h^-1 to 7713 ± 324 L m^-2·h^-1, and thus has a potential to be used in purification of reclaimed water and separation of oil from water.