Super-hydrophobic Cellulose Nanofiber Air Filter with Highly Efficient Filtration and Humidity Resistance

Highly Permeable and Regenerative Microhoneycomb Filters

Allergic reactions can profoundly influence the quality of life. To address the health risks posed by allergens and overcome the permeability limitations of the current filter materials, this work introduces a novel microhoneycomb (MH) material for practical filter applications such as masks. Through a synthesis process integrating ice-templating and a gas-phase post-treatment with silane, MH achieves unprecedented levels of moisture resistance and mechanical stability while preserving the highly permeable microchannels. Notably, MH is extremely elastic, with a 92% recovery rate after being compressed to 80% deformation. The filtration efficiency surpasses 98.1% against pollutant particles that simulate airborne pollens, outperforming commercial counterparts with fifth-fold greater air permeability while ensuring unparalleled user comfort. Moreover, MH offers a sustainable solution, being easily regenerated through back-flow blowing, distinguishing it from conventional nonwoven fabrics. Finally, a prototype mask incorporating MH is presented, demonstrating its immense potential as a high-performance filtration material, effectively addressing health risks posed by allergens and other harmful particles.

Diaminated Cellulose Beads as a Sustainable Support for Industrially Relevant Lipases

Environmentally persistent polystyrene or polyacrylic beads are used as supports in enzyme large-scale bioprocesses, including conversion glucose isomerization for high-fructose corn syrup production, hydrolysis of lactose, and synthesis of active pharmaceutical ingredients. In this paper, we report the development of a novel sustainable and scalable method to produce diaminated cellulose beads (DAB) as highly efficient alternative supports for industrially relevant lipases. Regenerated cellulose beads were grafted with diaminated aliphatic hydrocarbons via periodate oxidation and reductive amination. The oxidation step indicated that aldehyde content can be easily tuned through the reaction time and concentration of reactants. Reductive amination of dialdehyde cellulose was more efficient as the length of the diaminated hydrocarbon compound increased. Morphological analysis of DAB showed that cellulose chemical grafting enabled the preservation of the bead shape and internal structure upon freeze-drying. Enzymatic degradability studies demonstrated that chemical functionalization did not undermine enzyme cellulose hydrolysis. The addition of aminated moieties on cellulose dramatically increased absorption efficiency for all industrially relevant lipases used, reaching 100% for Thermomyces lanuginosus lipase (TLL). Storage and recyclability experiments demonstrated that enzymes were retained and recyclable for at least nine cycles, although the activity gradually declined after each cycle. Medium chain triacylglycerol hydrolysis in a SpinChem reactor using TLL immobilized on 1,6 DAB exhibited higher activity compared to acrylic beads (588 vs 459 U/g) suggesting that biodegradable cellulose-based materials could be a valid and attractive alternative to plastics carriers.

Magnetic superhydrophobic cellulose nanofibril based aerogel with rope-ladder like structure incorporating both superelasticity and excellent oil absorption

Achieving an equilibrium between exceptional oil absorption and remarkable elasticity has emerged as a formidable challenge for magnetic porous materials designed for oil absorption. Here, we propose an original, magnetic and superhydrophobic cellulose nanofibril (CNF) based aerogel system with a rope-ladder like skeleton by to greatly improve the issue. Within this system, CNF as the skeleton was combined with multiwalled carbon nanotubes (MWCNT)@Fe3O4 as the magnetic and enhanced component, both methyltrimethoxysilane (MTMS) and acetonitrile-extracted lignin (AEL) as the soft-hard associating constituents. The resultant CNF based aerogel shows a rope-ladder like pore structure to contribute to high elasticity and excellent oil absorption (28.34-61.09 g/g for various oils and organic solvents) under the synergistic effect of Fe3O4@MWCNT, AEL and MTMS, as well as good specific surface area (27.97 m2/g), low density (26.4 mg/cm3). Notably, despite the introduced considerable proportion (0.5 times of mass-CNF) of Fe3O4@MWCNT, the aerogel retained an impressive compression-decompression rate (88%) and the oil absorption efficiency of above 87% for various oils due to the soft-hard associating structure supported by both MTMS and AEL. This study provides a prospective strategy to balance between high elasticity and excellent oil absorption of CNF based aerogel doping inorganic particles.

Preparation of highly elastic superhydrophobic CNF/Fe3O4 based materials modified in aqueous phase for oil-water separation

Magnetic superhydrophobic materials have broad application prospect in oil-water separation. In this study, a magnetic and superhydrophobic aerogel with lamellar structure was successfully prepared using cellulose nanofibrils (CNF) as the skeleton, Fe3O4 as the magnetic ion, 1H, 1H, 2H, 2H trialkylfluorooctane triethoxysilane (FS) and 3-(2-aminoethyl amino)-propyl trimethoxysilane (AS) as the combined modifier. The prepared aerogel shows lower density (38.63 mg/cm3), excellent magnetic (15.13 emu/g), high elasticity and good oil sorption properties (21 g/g). In addition, FS/AS also exhibits excellent mechanical properties and superhydrophobic ability (water contact angle (WCA) of 151.9 ± 1.4°), as it provides sufficient toughness and low surface energy for the layer-branch structure. It should be noted that the entire preparation process is carried out in the aqueous phase, without the use of any organic solvents, providing a green oil-water separation strategy.

Fiber-Based Noncontact Sensor with Stretchability for Underwater Wearable Sensing and VR Applications

The rapid development of artificial intelligent wearable devices has led to an increasing need for seamless information exchange between humans, machines, and virtual spaces, often relying on touch sensors as the primary interaction medium. Additionally, the demand for underwater detection technologies is on the rise owing to the prevalent wet and submerged environment. Here, a fiber-based capacitive sensor with superior stretchability and hydrophobicity is proposed, designed to cater to noncontact and underwater applications. The sensor is constructed using bacterial cellulose (BC)@BC/carbon nanotubes (CNTs) (BBT) helical fiber as the matrix and methyltrimethoxysilane (MTMS) as the hydrophobic modified agent, forming a hydrophobic silylated BC@BC/CNT (SBBT) helical fiber by the chemical vapor deposition (CVD) technique. These fibers exhibit an impressive contact angle of 132.8°. The SBBT helicalfiber-based capacitive sensor presents capabilities for both noncontact and underwater sensing, which exhibits a significant capacitance change of -0.27 (at a distance of 0.5 cm). We have achieved interactive control between real space and virtual space through intelligent data analysis technology with minimal interference from the presence of water. This work has laid a solid foundation of noncontact sensing with attributes such as degradability, stretchability, and hydrophobicity. Moreover, it offers promising solutions for barrier-free communication in virtual reality (VR) and underwater applications, providing avenues for smart human-machine interfaces for submerged use.

Biodegradable Nanofiber/Metal-Organic Framework/Cotton Air Filtration Membranes Enabling Simultaneous Removal of Toxic Gases and Particulate Matter

The typical filters that protect us from harmful components, such as toxic gases and particulate matter (PM), are made from petroleum-based materials, which need to be replaced with other environmentally friendly materials. Herein, we demonstrate a route to fabricate biodegradable and dual-functional filtration membranes that effectively remove PM and toxic gases. The membrane was integrated using two layers: (i) cellulose-based nanofibers for PM filtration and (ii) metal-organic framework (MOF)-coated cotton fabric for removal of toxic gases. Zeolitic imidazolate framework (ZIF-8) was grown from the surface of the cotton fabric by the treatment of cotton fabric with an organic precursor solution and subsequent immersion in an inorganic precursor solution. Cellulose acetate nanofibers (NFs) were deposited on the MOF-coated cotton fabric via electrospinning. At the optimal thickness of the NF layer, the quality factor of 18.8 × 10-2 Pa-1 was achieved with a filtration efficiency of 93.1%, air permeability of 19.0 cm3/cm2/s, and pressure drop of 14.2 Pa. The membrane exhibits outstanding gas adsorption efficiencies (>99%) for H2S, formaldehyde, and NH3. The resulting membrane was highly biodegradable, with a weight loss of 62.5% after 45 days under standard test conditions. The proposed strategy should provide highly sustainable material platforms for practical multifunctional membranes in personal protective equipment.

Recent developments in nanocellulose-based aerogels as air filters: A review

Today, one of the world's critical environmental issues is air pollution, which is the most important parameter threatening human health and the environment. Synthetic polymers are widely used in industrial air filter production; however, they are incompatible with the environment due to their secondary pollution. Using renewable materials to manufacture air filters is not only environmentally friendly but also essential. Recently, a new generation of biopolymers called cellulose nanofiber (CNF)-based hydrogels have been proposed, with three dimensional (3D) nanofiber networks and unique physical and mechanical properties. CNFs have become a hot research topic for application as air filter materials because they can compete with synthetic nanofibers due to their advantages, such as abundant, renewable, nontoxic, high specific surface area, high reactivity, flexibility, low cost, low density, and network structure formation. The main focus of the current review is the recent progress in the preparation and employment of nanocellulose materials, especially CNF-based hydrogels, to absorb PM and CO2. This study summarizes the preparation methods, modification strategies, fabrications, and further applications of CNF-based aerogels as air filters. Lastly, challenges in the fabrication of CNFs, and trends for future developments are presented.

Application of cellulose nanofiber as a promising air filter for adsorbing particulate matter and carbon dioxide

Pollution from particulate matter (PM) and toxic chemicals in the air cause some of the most critical health and environmental hazards in developed and developing countries. It can have a very destructive effect on human health and other living creatures. In particular, PM air pollution caused by rapid industrialization and population growth is a grave concern in developing countries. Oil and chemical-based synthetic polymers are non-environmentally friendly materials that lead to secondary environmental pollution. Thus, developing new and environmentally compatible renewable materials to construct air filters is essential. The goal of this review is to study the use of cellulose nanofibers (CNF) to adsorb PM in the air. Some of CNF's advantages include being the most abundant polymer in nature, biodegradable, and having a high specific surface area, low density, surface properties (broad possibility of chemical surface modification), high modulus and flexural stiffness, low energy consumption, which provide this new class of bio-based adsorbent with promising potential applications in environmental remediation. Such advantages have made CNF a competitive and highly in-demand material compared to other synthetic nanoparticles. Today, refining membranes and nanofiltration manufacturing are two important industries that could use CNF to provide a practical step in protecting the environment and saving energy. CNF nanofilters are capable of nearly eliminating most sources of air pollution, including carbon monoxide, sulfur oxides, nitrogen oxides, and PM_2.5-10 μm. They also have a high porosity and low resistance air (pressure drop) ratio compared to ordinary filters made from cellulose fiber. If utilized correctly, humans do not need to inhale harmful chemicals.

MXene/bacterial cellulose/Fe3O4/methyltrimethoxylsilane flexible film with hydrophobic for effective electromagnetic shielding

Electromagnetic (EM) pollution has become a serious problem in modern society as it affects human lives. The fabrication of strong and highly flexible materials for electromagnetic interference (EMI) shielding applications is extremely urgent. Herein, a MXene Ti₃C₂T_x/Fe₃O₄ & bacterial cellulose (BC)/Fe₃O₄&Methyltrimethoxysilane (MTMS) flexible hydrophobic electromagnetic shielding film (SBTF_X-Y, X and Y were the number of layers of BC/Fe₃O₄ and the layers of Ti₃C₂T_x/Fe₃O₄), was fabricated. In the prepared film, MXene Ti₃C₂T_x absorbs a large amount of radio waves through polarization relaxation and conduction loss. Because of its extremely low reflectance of electromagnetic waves, BC@Fe₃O₄, as the outermost layer of the material, allows more electromagnetic waves to incident inside the material. The maximum electromagnetic interference (EMI) shielding efficiency (SE) of 68 dB was achieved for the composite film at 45 μm thickness. What's more, the SBTF_X-Y films show excellent mechanical properties, hydrophobicity and flexibility. The unique stratified structure of the film provides a new strategy for designing high-performance EMI shielding films with excellent surface and mechanical properties.

Swellable Array Strategy Based on Designed Flexible Double Hypercross-linked Polymers for Synergistic Adsorption of Toluene and Formaldehyde

High-capacity adsorption and removal of complex volatile organic compounds (VOCs) from real-world environments is a tough challenge for researchers. Herein, a swellable array adsorption strategy was proposed to realize the synergistic adsorption of toluene and formaldehyde on the flexible double hypercross-linked polymers (FD-HCPs). FD-HCPs exhibited multiple adsorption sites awarded by a hydrophobic benzene ring/pyrrole ring and a hydrophilic hydroxyl structural unit. The array benzene ring, hydroxyl, and pyrrole N sites in FD-HCPs effectively captured toluene and formaldehyde molecules through π-π conjugation and electrostatic interaction and weakened their mutual competitive adsorption. Interestingly, the strong binding force of toluene molecules to the skeleton deformed the pore structure of FD-HCPs and generated new adsorption microenvironments for the other adsorbate. This behavior significantly improved the adsorption capacity of FD-HCPs for toluene and formaldehyde by 20% under multiple VOCs. Moreover, the pyrrole group in FD-HCPs greatly hindered H₂O molecule diffusion in the pore, thus efficiently weakening the competitive adsorption of H₂O toward VOCs. These fascinating properties enabled FD-HCPs to achieve synergistic adsorption for multicomponent VOC vapor under a highly humid environment and overcame single-species VOC adsorption properties on state-of-the-art porous adsorbents. This work provides the practical feasibility of synergistic adsorption to remove complex VOCs in real-world environments.

In-situ polycondensate-coated cellulose nanofiber heterostructure for polylactic acid-based composites with superior mechanical and thermal properties

Renewable yet biodegradable natural fiber (e.g., cellulose nanofiber (CNF)) reinforced bio-based polymers (e.g., polylactic acid (PLA)) are being applied for the manufacture of clean packaging products. The interface incompatibility between hydrophilic CNF and hydrophobic PLA still restricts the promotion of high-performance bio-based products. Herein, a polycondensate-coated CNF hybrid, wherein silane, aluminate, and titanate coupling agent monomers were in-situ polymerized onto the CNF surface via dehydration self-condensation, was designed and further employed as strengthening/toughening nanofillers for fabricating the CNF-reinforced PLA composite. Results showed that the polycondensate coatings could efficiently promote the dispersion of CNFs and enhance interfacial compatibility between CNFs and PLA. Attributing to the synergistic effect of polycondensate coatings and CNFs, a considerable improvement in processing, mechanical and thermal properties was obtained in resultant CNF/PLA composites. With adding 2.5 wt% polycondensate-coated CNFs, the tensile strength, Young's modulus, and tensile toughness of CNF-reinforced PLA composites was raised by about 27 %, 51 % and 68 %, respectively; also, such composite possessed greater elasticity and higher melt strength than pure PLA. This study provides a novel interface control strategy to fabricate low-cost yet high-performance PLA-based composites for sustainable packaging application.

Modifying the Fiber Structure and Filtration Performance of Polyester Materials Based on Two Different Preparation Methods

How to build a satisfactory indoor environment has become increasingly important. In this paper, the synthesis and improvement of the most widely used polyester materials in China were carried out based on two different preparation methods, and the structures and filtration performances were tested and analyzed. The results showed that a carbon black coating was wrapped on the surfaces of the new synthetic polyester filter fibers. Compared with the original materials, the filtration efficiencies of PM₁₀, PM_2.5, and PM₁ were increased by 0.88-6.26, 1.68-8.78, and 0.42-4.84%, respectively. The best filtration velocity was 1.1 m/s, and the new synthetic polyester materials with direct impregnation demonstrated superior filtration performance. The filtration efficiency of the new synthetic polyester materials was improved on the particulates with sizes of 1.0-5.0 μm. The filtration performance of G4 was better than that of G3. The filtration efficiencies of PM₁₀, PM_2.5, and PM₁ were improved by 4.89, 4.20, and 11.69%, respectively. The quality factor value can be used to assess the comprehensive filtration performance of air filters in practical applications. It could provide reference values for the selection of synthetic methods of new filter materials.

Argon plasma-modified bacterial cellulose filters for protection against respiratory pathogens

In this work, we present novel, sustainable filters based on bacterial cellulose (BC) functionalized with low-pressure argon plasma (LPP-Ar). The "green" production process involved BC biosynthesis by Komagataeibacter xylinus, followed by simple purification, homogenization, lyophilization, and finally LPP-Ar treatment. The obtained LPP-Ar-functionalized BC-based material (LPP-Ar-BC-bM) showed excellent antimicrobial and antiviral properties against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacteria, and an enveloped bacteriophage phage Φ6, with no cytotoxicity versus murine fibroblasts in vitro. Further, filters consisting of three layers of LPP-Ar-BC-bM had >99 % bacterial and viral filtration efficiency, while maintaining sufficiently low airflow resistance (6 mbar at an airflow of 95 L/min). Finally, as a proof-of-concept, we were able to prepare 80 masks with LPP-Ar-BC-bM filter and ~85 % of volunteer medical staff assessed them as "good" or "very good" in terms of comfort. We conclude that our novel sustainable, biobased, biodegradable filters are suitable for respiratory personal protective equipment (PPE), such as surgical masks and respirators.

All-cellulose air filter composed with regenerated nanocellulose prepared through a facile method with shear-induced

High-speed shear system is usually used for the dispersion improvement of slurry, nanomaterials preparation, and even two-dimensional materials production. However, there is barely study that focused on the regenerated cellulose (RC) which was coagulated with shear induced. In this work, a new type of all-cellulose air filter was fabricated through high-speed shear in aqueous regeneration system using parenchyma cellulose from corn stalk. The obtained RC were aggregated by ribbon-like fine cellulose and nanocellulose sheets. The study exhibited the micro-structure of RC displayed excellent unidirectional alignment and a relatively high crystallinity. All-cellulose air filter which was produced via RC presented excellent filtration efficiency (PM_2.5 97.3 %, PM_10.0 97.7 %) with slightly pressure drop (19 Pa). Therefore, this work provides a facile method to obtain a novel RC with nanocellulose particles used for air filtration, which gives an effective strategy application in the conversion of all-cellulose materials from agricultural waste.

Smart Mask as Wearable for Post-Pandemic Personal Healthcare

A mask serves as a simple external barrier that protects humans from infectious particles from poor air conditions in the surrounding environment. As an important personal protective equipment (PPE) to protect our respiratory system, masks are able not only to filter pathogens and dust particles but also to sense, reflect or even respond to environmental conditions. This smartness is of particular interest among academia and industries due to its potential in disease detection, health monitoring and caring aspects. In this review, we provide an overlook of the current air filtration strategies used in masks, from structural designs to integrated functional modules that empower the mask's ability to sense and transfer physiological or environmental information to become smart. Specifically, we discussed recent developments in masks designed to detect macroscopic physiological signals from the wearer and mask-based disease diagnoses, such as COVID-19. Further, we propose the concept of next-generation smart masks and the requirements from material selection and function design perspectives that enable masks to interact and play crucial roles in health-caring wearables.

Superhydrophobic and highly moisture-resistant PVA@EC composite membrane for air purification

Electrospun fiber membranes have great potential in the field of air filtration because of their high porosity and small pore size. Conventional air filtration membranes are hydrophilic, leading to weak moisture-barrier properties, which hinders their application in high-humidity environments. In this study, eugenol was added to polyvinyl alcohol and ethyl cellulose (EC) for electrospinning and electrospraying, respectively, of superhydrophobic bilayer composite fiber membranes to efficiently filter particulate matter (PM) in air. Owing to its surface microstructure, electrosprayed EC increased the water contact angle of the PVA membrane from 142.8 to 151.1°. More importantly, the composite air-filter membrane showed a low filtration pressure drop (168.1 Pa) and exhibited high filtration efficiencies of 99.74 and 99.77% for PM1.0 and PM2.5, respectively, and their respective quality factors were 0.0351 and 0.0358 Pa-1. At the same time, the filtration performance of the air filtration membrane remained above 99% at high air humidity. This work reports composite membranes that can effectively capture PM of various sizes and thus may provide a reference for the manufacturing of green air filters for high-humidity environments.

Constructing Janus Microsphere Membranes for Particulate Matter Filtration, Directional Water Vapor Transfer, and High-Efficiency Broad-Spectrum Sterilization

Commercial masks have significant drawbacks, including low water vapor transmission efficiency and limited ability to inhibit harmful microorganisms, whereas in this contribution, a series of Janus microsphere membranes are developed with hierarchical structures by quenching and crystallizing 12-hydroxystearic acid and halicin layer-by-layer on a polypropylene non-woven fabric, laminating them with hydrophilic cotton fibers in a one-pot process, and further demonstrate the potential of this composite system as masks. Through further optimization, excellent superhydrophobic/superhydrophilic properties (contact angle 157.1°/0°), superior filtering effects (93.54% for PM_2.5 and 98.35% for PM₁₀ ), with a low-filtration resistance (57 Pa) and a quality factor of up to 0.072 Pa^-1 are achieved, all better than that of commercial N95 masks. In addition, the membrane allows for the directional transport of water vapor from the inside out, increasing the water vapor transmission rate by more than 20% compared with the monolayer hydrophobic microsphere membrane. It also has a bactericidal capacity of over 99.9999% against Escherichia coli and is tested for robustness and stability in various extreme environments. This work may shed light on designing novel filter media with versatile functions, meanwhile, the materials can also be used in protective equipment against the new coronavirus.

Improved Recovery of Captured Airborne Bacteria and Viruses with Liquid-Coated Air Filters

The COVID-19 pandemic has revealed the importance of the detection of airborne pathogens. Here, we present composite air filters featuring a bioinspired liquid coating that facilitates the removal of captured aerosolized bacteria and viruses for further analysis. We tested three types of air filters: commercial polytetrafluoroethylene (PTFE), which is well known for creating stable liquid coatings, commercial high-efficiency particulate air (HEPA) filters, which are widely used, and in-house-manufactured cellulose nanofiber mats (CNFMs), which are made from sustainable materials. All filters were coated with omniphobic fluorinated liquid to maximize the release of pathogens. We found that coating both the PTFE and HEPA filters with liquid improved the rate at which Escherichia coli was recovered using a physical removal process compared to uncoated controls. Notably, the coated HEPA filters also increased the total number of recovered cells by 57%. Coating the CNFM filters did not improve either the rate of release or the total number of captured cells. The most promising materials, the liquid-coated HEPA, filters were then evaluated for their ability to facilitate the removal of pathogenic viruses via a chemical removal process. Recovery of infectious JC polyomavirus, a nonenveloped virus that attacks the central nervous system, was increased by 92% over uncoated controls; however, there was no significant difference in the total amount of genomic material recovered compared to that of controls. In contrast, significantly more genomic material was recovered for SARS-CoV-2, the airborne, enveloped virus, which causes COVID-19, from liquid-coated filters. Although the amount of infectious SARS-CoV-2 recovered was 58% higher, these results were not significantly different from uncoated filters due to high variability. These results suggest that the efficient recovery of airborne pathogens from liquid-coated filters could improve air sampling efforts, enhancing biosurveillance and global pathogen early warning.

A bioinspired, strong, all-natural, superhydrophobic cellulose-based straw

The promotion of cellulose-based paper straws is one of the important ways to improve white pollution nowadays. However, developing composite straws that are simultaneously highly biocompatible, safe, and non-toxic and that overcome the low water stability and physical strength problems caused by the inherent hydrophilicity of the raw material cellulose has become an important challenge in the development process. In this study, a new all-natural superhydrophobic straw (CFS) made of a composite of cellulose nanofibers and stearic acid was introduced. Stearic acid is a saturated fatty acid derived from plant and animal oils. Inspired by the specific hydrophobicity of sugarcane cane peel, a green straw with both superhydrophobicity (water contact angle up to 153°) and remarkable mechanical strength (tensile strength up to 67.15 MPa) was developed by controlling the hydrophobic modification conditions of stearic acid through solvent vaporization. Furthermore, the composite straws under wet conditions had lower water absorption and exhibited excellent wet tensile strength compared to commercial paper straws. In addition, the composite straw without the addition of chemical binders avoids the defects of non-renewable products, fits into the global green development concept, and brings new strategies for the development of cellulose-based materials.

Cellulose nanofiber assisted dispersion of hydrophobic SiO2 nanoparticles in water and its superhydrophobic coating

It is challenging to build a superhydrophobic coating with aqueous dispersions since hydrophobic substances are usually dispersed in pure organic or water/organic mixed solvents. In this study, hydrophobic SiO₂ nanoparticles were dispersed in water assisted with cellulose nanofiber (CNF) and the superhydrophobic surface was manufactured by coating a waterborne dispersion composed of CNF, hydrophobic SiO₂ nanoparticles and methyltrimethoxysilane (MTMS). It was found that the dispersion of SiO₂ in water can be improved by CNF. Meanwhile, the coated paper surface retained its hydrophobicity after 10 abrasion cycles due to the adhesion of the coating surface promoted by MTMS. When SiO₂ content over 0.25 wt%, the coated paper surface displayed a superhydrophobic property, and the moisture absorption decreased to 31-34%. The contact angle of the coating surface was 162°, the contact angle hysteresis was 1.96° and the rolling contact angle was 1.33° when SiO₂ content was 1 wt%.

Polyphenylene sulfide fabric with enhanced oxidation resistance and hydrophobicity through polybenzoxazine surface coating for emission control in harsh environment

Emissions from power generation and municipal waste incineration sources are primarily at high temperatures and contain corrosive gases, particulate pollutants and are enormously challenging on the performance of the filtration systems in use. Here, polyphenylene sulfide (PPS) nonwoven fabric, a primary material used commercially in such settings, is modified with a polybenzoxazine precursor as a coating to deliver improved thermal and oxidation resistance to the fibrous substrate. The polybenzoxazine precursor undergoes chain propagation and crosslinking upon the treatment process to provide a protective layer over the PPS fibers such that enhanced structural stability in a harsh environment was demonstrated. We have shown the improved overall tensile strength (+15%), Young's modulus (+26%), and more hydrophobic nature of the modified PPS fabric, while the superior environmental stability and better filtration performance could be achieved. Such methodology may lead to higher service temperature and extended service time of the PPS filtration bags in harsh fire exhaustion airstreams encountered in power plants or municipal garbage incineration facilities. The crosslinkable benzoxazine could also be the most cost-effective high temperature coating layer on fibers, enabling future high-performance air filtration materials.

Multilevel structured PASS nanofiber filter with outstanding thermal stability and excellent mechanical property for high-efficiency particulate matter removal

Particulate matter (PM) pollution from industrialization poses a great threat to people's health. Although fiber-based filters are used effectively to capture PM, the traditional filters with large diameter suffer from low filtration efficiency, high pressure drop and low temperature resistance. In this study, multilayer poly arylene sulfide sulfone (M-PASS) composite filter was designed and fabricated via electrospinning technology. The M-PASS composite filter is sandwich-structure. Due to the unique structure and composition, the M-PASS filter exhibited outstanding removal efficiency of 99.97 ± 0.0050%, extremely low air resistance of 44.3 ± 0.7 Pa, excellent quality factor (QF) of 0.19 ± 0.0019 Pa^-1, and desirable mechanical strength of 7.0 ± 0.2 MPa. Furthermore, the as-prepared M-PASS filter can remain outstanding filtration performance at 200.0 ℃ due to the high thermal stability of PASS and the removal efficiency was still above 95.2 ± 0.4% after long-term filtration test. These results demonstrate that the structure of filter is the important one for air filtration and the M-PASS nanofiber filters have great potential in PM removal, especially under high temperature conditions.

Advances in particulate matter filtration: Materials, performance, and application

Air-borne pollutants in particulate matter (PM) form, produced either physically during industrial processes or certain biological routes, have posed a great threat to human health. Particularly during the current COVID-19 pandemic, effective filtration of the virus is an urgent matter worldwide. In this review, we first introduce some fundamentals about PM, including its source and classification, filtration mechanisms, and evaluation parameters. Advanced filtration materials and their functions are then summarized, among which polymers and MOFs are discussed in detail together with their antibacterial performance. The discussion on the application is divided into end-of-pipe treatment and source control. Finally, we conclude this review with our prospective view on future research in this area.

Nanocellulose-based membrane as a potential material for high performance biodegradable aerosol respirators for SARS-CoV-2 prevention: a review

The controversy surrounding the transmission of COVID-19 in 2020 has revealed the need to better understand the airborne transmission route of respiratory viruses to establish appropriate strategies to limit their transmission. The effectiveness in protecting against COVID-19 has led to a high demand for face masks. This includes the single-use of non-degradable masks and Filtering Facepiece Respirators by a large proportion of the public, leading to environmental concerns related to waste management. Thus, nanocellulose-based membranes are a promising environmental solution for aerosol filtration due to their biodegradability, renewability, biocompatibility, high specific surface area, non-toxicity, ease of functionalization and worldwide availability. Although the technology for producing high-performance aerosol filter membranes from cellulose-based materials is still in its initial stage, several promising results show the prospects of the use of this kind of materials. This review focuses on the overview of nanocellulose-based filter media, including its processing, desirable characteristics and recent developments regarding filtration, functionalization, biodegradability, and mechanical behavior. The porosity control, surface wettability and surface functional groups resulting from the silylation treatment to improve the filtration capacity of the nanocellulose-based membrane is discussed. Future research trends in this area are planned to develop the air filter media by reinforcing the filter membrane structure of CNF with CNCs. In addition, the integration of sol-gel technology into the production of an air filter can tailor the pore size of the membrane for a viable physical screening solution in future studies.