Biocidal and Rechargeable N-Halamine Nanofibrous Membranes for Highly Efficient Water Disinfection

High-strength hydrophilic N-halamines chitosan and cellulose nanofibers membranes with repeated bactericidal properties

Direct addition of disinfectants and membrane separation techniques have been common methods to address microbial contamination in water. However, disinfectants may generate toxic by-products, and even minor damage or biofilm formation on filtration membranes can lead to a heightened risk of microbial contamination. Consequently, how to quickly and safely disinfect microbial contaminated water sources remains a huge challenge. In this study, the high-strength broad-spectrum antibacterial CNF/CS composite membrane was fabricated by utilizing cellulose nanofibers (CNF) to reinforce the structure of chitosan (CS). The resulting CNF/CS composite membrane exhibits an impressive tensile strength of 148 MPa and boasts an active chlorine content of 5.29 %. Notably, even after undergoing 50 washing cycles and 10 repeated chlorination procedures, the structural integrity and high active chlorine content of the composite membrane remain preserved, validating its exceptional strength, stability, and chlorine rechargeability. Additionally, the CNF/CS antibacterial materials demonstrate remarkable attributes in terms of rapid sterilization, sustained and consistent release of active chlorine, and efficient inhibition of biofilm formation, demonstrating great potential in efficient, green, and safe sterilization.

Construction of Binary RGO/TiO2 Fibrous Membranes with Enhanced Mechanical Properties for E. coli Inactivation

For environmental remediation, it is significant to design membranes with good mechanical properties and excellent photocatalytic activity. In this work, RGO/TiO2 membranes with heterogeneous structures and good photocatalytic efficiency were synthesized using the method of electrospinning combined with a thermal treatment process. In the binary nanocomposites, RGO was tightly adhered to TiO2 fibers and by simply adjusting the loading of RGO, the strength and modulus of the fibrous membranes were improved. Notably, the RGO-permeated TiO2 fibers exhibited 1.41 MPa in tensile strength and 140.02 MPa in Young's modulus, which were 705% and 343% of the original TiO2 fibers, respectively. Benefiting from the enhanced light response and the homogeneous and compact heterogeneous structure, the synthesized RGO/TiO2 membranes displayed good antibacterial performance with a photocatalytic inactivation rate of 6 log against E. coli within 60 min. This study offers a highly efficient alternative to inactivate E. coli for the synthesis of TiO2-based membranes.

Polyvinylidene fluoride multi-scale nanofibrous membrane modified using N-halamine with high filtration efficiency and durable antibacterial properties for air filtration

HYPOTHESIS

Particulate matter (PM) pollution and the coronavirus (COVID-19) pandemic have increased demand for protective masks. However, typical protective masks only intercept particles and produce peculiar odors if worn for extended periods owing to bacterial growth. Therefore, new protective materials with good filtration and antibacterial capabilities are required.

EXPERIMENTS

In this study, we prepared multi-scale polyvinylidene fluoride (PVDF) nanofibrous membranes for efficient filtration and durable antibacterial properties via N-halamine modification.

FINDINGS

The N-halamine-modified nanofibrous membrane (PVDF-PAA-TMP-Cl) had sufficient active chlorine content (800 ppm), and the tensile stress and strain were improved compared with the original membrane, from 6.282 to 9.435 MPa and from 51.3 % to 56.4 %, respectively. To further improve the interception efficiency, ultrafine nanofibers (20-35 nm) were spun on PVDF-PAA-TMP-Cl nanofibrous membranes, and multi-scale PVDF-PAA-TMP-Cl nanofibrous membranes were prepared. These membranes exhibited good PM_0.3 interception (99.93 %), low air resistance (79 Pa), promising long-term PM_2.5 purification ability, and high bactericidal efficiency (>98 %). After ten chlorination cycles, the antibacterial efficiency against Escherichia coli and Staphylococcus aureus exceeded 90 %; hence, the material demonstrated highly efficient filtration and repeatable antibacterial properties. The results of this study have implications for the development of air and water filtration systems and multi-functional protective materials.

Efficacy of Electrospun Nanofiber Membranes on Fouling Mitigation: A Review

Despite the advantages of high contaminant removal, operational flexibility, and technical advancements offered, the undesirable fouling property of membranes limits their durability, thus posing restrictions on their usage. An enormous struggle is underway to conquer this major challenge. Most of the earlier reviews include the basic concepts of fouling and antifouling, with respect to particular separation processes such as ultrafiltration, nanofiltration, reverse osmosis and membrane bioreactors, graphene-based membranes, zwitterionic membranes, and so on. As per our knowledge, the importance of nanofiber membranes in challenging the fouling process has not been included in any record to date. Nanofibers with the ability to be embedded in any medium with a high surface to volume ratio play a key role in mitigating the fouling of membranes, and it is important for these studies to be critically analyzed and reported. Our Review hence intends to focus on nanofiber membranes developed with enhanced antifouling and biofouling properties with a brief introduction on fabrication processes and surface and chemical modifications. A summary on surface modifications of preformed nanofibers is given along with different nanofiller combinations used and blend fabrication with efficacy in wastewater treatment and antifouling abilities. In addition, future prospects and advancements are discussed.

Multifunctional porous β-cyclodextrin polymer for water purification

Keeping water clean is of vital significance for human health and environmental protection. In order to remove organic micro-pollutants and natural organic substances in water bodies and kill pathogenic microorganisms simultaneously, this study synthesized a multifunctional porous β-cyclodextrin polymer with a high specific surface area by introducing quaternary ammonium groups and rigid benzene rings, respectively, which was then polymerized with crosslinking agent-4,4'-bis (chloromethyl)-1,1'-biphenyl (BCMBP) in an ionic liquid system. The grafting of quaternary ammonium groups was beneficial for the removal of negative-charged humic acid (HA) and sterilization. The introduction of numerous rigid structures during benzylation and Friedel-Crafts alkylation reaction could significantly improve the porosity and specific surface area of the polymer, conducive to the exposure of cyclodextrin binding sites and contaminant adsorption. By changing the proportions of quaternization and benzylation, the structure and surface properties of the polymer could be adjusted, thus further regulating the adsorption performance. Compared with activated carbon, the polymer named BQCD-BP with a huge surface area of 1133 m² g^-1 prepared under optimized conditions showed outstanding adsorption performance and sterilization ability. The pseudo-second-order kinetic constant of BQCD-BP reached 1.2058 g·mg^-1·min^-1, which was approximately 50 times greater than that of activated carbon (0.0256 g·mg^-1·min^-1) under the same experimental condition. The adsorption capacity of BQCD-BP to HA was twice as high as that to AC, and the antibacterial ability of BQCD-BP was significant, achieving 90% at the dosage of 1g L^-1. Moreover, the adsorption process was hardly affected by the hydrochemical conditions, and the polymer was easy to regenerate. In addition, the excellent adsorption and antibacterial performance of the polymer were also identified by natural water treatment. COD was almost completely removed, and the removal efficiency of TP reached 92% after contact with BQCD-BP. The sterilization rate of BQCD-BP to viable bacteria in complex water bodies reached 82%. Undoubtedly, BQCD-BP is a potential multifunctional water treatment material with reasonable design in the actual water purification.

A Sustainable and Antimicrobial Food Packaging Film for Potential Application in Fresh Produce Packaging

N-halamines are a group of compounds containing one or more nitrogen-halogen covalent bond(s). This high-energy halide bond provides a strong oxidative state so that it is able to inactivate microorganisms effectively. In this study, a sustainable film was developed based on polylactic acid (PLA) with incorporated N-halamine compound 1-chloro-2,2,5,5-tetramethyl-4-imidazolidinone (MC), as a promising antimicrobial food packaging material. Results showed that the incorporation of MC prevented the crystallization of PLA and improved the physical properties of the films. In addition, both the moisture barrier and the oxygen permeability were improved with the presence of MC. Importantly, the antimicrobial film was able to inactivate inoculated microorganisms by a factor of seven log cycles in as little as 5 min of contact. Films that contained higher levels of MC further enhanced the antimicrobial efficacy. Fresh strawberries packed with the fabricated films maintained the quality for up to 5 days. Due to the ease of fabrication and the effective biocidal property, these films have a wide range of potential applications in the field of food packaging to extend the shelf life of fresh produce.

SuFEx modification of silk fibroin silicon aerogel and its adsorption behavior and antibacterial performance

A silk fibroin silicon-based composite aerogel (SSA) has been modified via a SuFEx reaction for application in the adsorption of anionic pollutants and antimicrobials in water. The tyrosine fragment in the silk fibroin was modified by a high yielding SuFEx click reaction. A quaternary ammonium salt functionality was introduced into the silk fibroin protein and the modified silk fibroin protein was crosslinked with tetraethyl orthosilicate. The aerogel was then prepared by freeze-drying. The aerogel obtained has biocompatibility and biodegradability properties. Four types of dyes (Methyl orange, Rhodamine B, Methylene blue and Acid red) were applied as targets and the saturated adsorption amounts were calculated. The adsorption behavior of the dyes towards SSA was studied by fitting Langmuir and Freundlich adsorption models. A pseudo-first order kinetic model and a pseudo-second order kinetic model were used to study the kinetics of the adsorption process. After 6 cycles, the removal rate of methyl orange by SSA remained at 81.25%. The adsorption capacity and anti-interference ability of SSA on some other polluting anions such as PO₄^3- and CrO₄^2- were also measured and the efficiency adsorption reached up to 70.94% and 77.91%, respectively. The antibacterial effect of SSA was evaluated with Escherichia coli and Staphylococcus aureus as representative examples.

Copper hydroxide nanosheets-assembled nanofibrous membranes for anti-biofouling water disinfection

Copper hydroxide (Cu(OH)₂) has been elected as a newly-emerging green disinfectant to deal with membrane biofouling in the treatment of bacteria-contaminated water; however, the decoration strategy of it with the granular form on membrane substrates limits the practical application. Here a novel surface-confined methodology was proposed for preparing freestanding Cu(OH)₂ nanosheet-assembled nanofibrous membranes (CNNMs) with the anti-biofouling property via the in-suit coprecipitation and heat-induced growth method. The vertically aligned Cu(OH)₂ nanosheets were in-suit rooted on the surface of the nanofiber scaffold with high binding fastness. The acquired CNNMs possess comprehensive performances of high porosity, prominent mechanical strength, fatigue resistance, and superior bactericidal efficiency of 99.999%, which endowed the CNNMs ultrahigh filtration fluxes (24000 L m^-2 h^-1) and durability to disinfect bacteria-containing water effectively. This facile strategy may throw light on manufacturing novel inorganic nanosheet-rooted nanofibrous membranes for water disinfection and public health.

What We Are Learning from COVID-19 for Respiratory Protection: Contemporary and Emerging Issues

Infectious respiratory diseases such as the current COVID-19 have caused public health crises and interfered with social activity. Given the complexity of these novel infectious diseases, their dynamic nature, along with rapid changes in social and occupational environments, technology, and means of interpersonal interaction, respiratory protective devices (RPDs) play a crucial role in controlling infection, particularly for viruses like SARS-CoV-2 that have a high transmission rate, strong viability, multiple infection routes and mechanisms, and emerging new variants that could reduce the efficacy of existing vaccines. Evidence of asymptomatic and pre-symptomatic transmissions further highlights the importance of a universal adoption of RPDs. RPDs have substantially improved over the past 100 years due to advances in technology, materials, and medical knowledge. However, several issues still need to be addressed such as engineering performance, comfort, testing standards, compliance monitoring, and regulations, especially considering the recent emergence of pathogens with novel transmission characteristics. In this review, we summarize existing knowledge and understanding on respiratory infectious diseases and their protection, discuss the emerging issues that influence the resulting protective and comfort performance of the RPDs, and provide insights in the identified knowledge gaps and future directions with diverse perspectives.

Chlorine Rechargeable Halamine Biocidal Alginate/Polyacrylamide Hydrogel Beads for Improved Sanitization of Fresh Produce

Traditional fresh produce washing systems mainly rely on mechanical forces and usage of chlorine bleach solutions to aid in removal and sanitization of microorganisms attached on surfaces of fresh produce during washing processes. Frequent outbreaks of foodborne diseases from ready-to-eat produce indicate insufficient sanitization of the washing processes. Herein, we present a scalable methodology for creating antimicrobial and chlorine rechargeable hydrogel beads using an in situ formed network of polyacrylamide and natural polysaccharide alginate through an emulsion polymerization. The resulting hydrogel beads exhibited robust mechanical strength, rechargeable chlorination capability, rapid up to 99.99% bacterial killing efficiency, and high produce sanitizaiton efficiency, enabling the hydrogel beads as a promising additive in chlorine sanitization to effectively sanitize the produce and automatically being recharged and reused.

Immobilized Regenerable Active Chlorine within a Zirconium-Based MOF Textile Composite to Eliminate Biological and Chemical Threats

The most recent global health crisis caused by the SARS-CoV-2 outbreak and the alarming use of chemical warfare agents highlight the necessity to produce efficient protective clothing and masks against biohazard and chemical threats. However, the development of a multifunctional protective textile is still behind to supply adequate protection for the public. To tackle this challenge, we designed multifunctional and regenerable N-chlorine based biocidal and detoxifying textiles using a robust zirconium metal-organic framework (MOF), UiO-66-NH₂, as a chlorine carrier which can be easily coated on textile fibers. A chlorine bleaching converted the amine groups located on the MOF linker to active N-chlorine structures. The fibrous composite exhibited rapid biocidal activity against both Gram-negative bacteria (E. coli) and Gram-positive bacteria (S. aureus) with up to a 7 log reduction within 5 min for each strain as well as a 5 log reduction of SARS-CoV-2 within 15 min. Moreover, the active chlorine loaded MOF/fiber composite selectively and rapidly degraded sulfur mustard and its chemical simulant 2-chloroethyl ethyl sulfide (CEES) with half-lives less than 3 minutes. The versatile MOF-based fibrous composite designed here has the potential to serve as protective cloth against both biological and chemical threats.

A Novel N-Halamine Biocidal Nanofibrous Membrane for Chlorine Rechargeable Rapid Water Disinfection Applications

Disinfecting pathogenic contaminated water rapidly and effectively on sites is one of the critical challenges at point-of-use (POU) situations. Currently available technologies are still suffering from irreversible depletion of disinfectants, generation of toxic by-products, and potential biofouling problems. Herein, we developed a chlorine rechargeable biocidal nanofibrous membrane, poly(acrylonitrile-co-5-methyl-5-(4'-vinylphenyl)imidazolidine-2,4-dione) (P(AN-VAPH)), via a combination of a free radical copolymerization reaction and electrospun technology. The copolymer exhibits good electrospinnability and desirable mechanical properties. Also, the 5-methyl-5-(4'-vinylphenyl)imidazolidine-2,4-dione (VAPH) moieties containing unique hydantoin structures are able to be chlorinated and converted to halamine structures, enabling the P(AN-VAPH) nanofibrous membrane with rapid and durable biocidal activity. The chlorinated P(AN-VAPH) nanofibrous membranes showed intriguing features of unique 3D morphological structures with large specific surface area, good mechanical performance, rechargeable chlorination capacity (>5000 ppm), long-term durability, and desirable biocidal activity against both bacteria and viruses (>99.9999% within 2 min of contact). With these attributes, the chlorinated P(AN-VAPH) membranes demonstrated promising disinfecting efficiency against concentrated bacteria-contaminated water during direct filtration applications with superior killing capacity and high flowing flux (5000 L m^-2 h^-1).

Bifunctional Regenerated Cellulose/Polyaniline/Nanosilver Fibers as a Catalyst/Bactericide for Water Decontamination

For antagonizing urgent water pollution and increasing environmental consciousness, the integration of renewable resources and nanotechnologies has become a trend to improve water quality in the ecosystem. Here, we designed a green route to fabricate regenerated cellulose fibers (CFs) with 3D micro- and nanoporous structures in NaOH/urea aqueous solvent systems via a scalable wet-spinning procedure as support materials for nanoparticles (NPs). Modification of CFs with polyaniline@Ag nanocomposites through in situ reduction of the silver ion with aqueous aniline led to enhanced pollutant removal efficiency of functional cellulose-based fibers (FCFs), demonstrating both rapid hydrogenation catalytic performance for the reduction of p-nitrophenol and high antibacterial properties for in-flow water purification. Most importantly, the hierarchically porous structures of FCFs not only provided carrier space but also formed a limiting domain guaranteeing the homogeneity of FCFs even with a Ag NP content as high as 36.47 wt %. The prepared functional fibers show good behavior in in-flow water purification, representing significant advancement in the use of biomass fibers for catalytic and bactericidal applications in liquid media.

Robust immobilization of anionic silver nanoparticles on cellulose filter paper toward a low-cost point-of-use water disinfection system with improved anti-biofouling properties

Silver nanoparticle (AgNP)-decorated cellulose filter paper (FP), a low-cost point-of-use (POU) water disinfection system, can supply affordable and safe drinking water for people in desperate need, especially in rural areas in developing countries. However, owing to the unstable immobilization of AgNPs, silver can leach into the treated drinking water from the FP and exceed the World Health Organization (WHO) drinking water limit (<100 μg L-1), which is a potential threat to both human health and the environment. In this work, in order to robustly immobilize anionic silver nanoparticles (GA@AgNPs), we facilely prepared lipoic acid-modified cellulose filter paper (LA-FP), in which GA@AgNPs were robustly immobilized onto filter paper (GA@AgNPs-LA-FP) by strong chelation via the disulfide bond of LA with the surface of the silver nanoparticles. GA@AgNPs-LA-FP exhibited both excellent bacterial anti-adhesion activity and strong bactericidal activity, which can synergistically mitigate biofouling by inhibiting biofilm formation on the paper surface. Moreover, employed as a gravity-driven bactericidal filter, the GA@AgNPs-LA-FP membrane treated 100 mL of river water within 10 min, and the resulting water quality met the WHO drinking water standards, indicating this material's practical application for POU water disinfection.

Fabrication of N-halamine polyurethane films with excellent antibacterial properties

An N-halamine precursor, namely, 2-amino-5-(2-hydroxyethyl)-6-methylpyrimidin-4-one (AHM), was used as a chain extender in the preparation of a series of N-halamine polyurethane (PU) films, in order to also instill antibacterial properties. The mechanical properties, thermodynamic performance, and antimicrobial performance of the functionalized PU films were systematically studied. The results showed that the addition of AHM could improve the thermodynamic and mechanical properties of the developed PU films. Conducting tests in the presence of Escherichia coli and Staphylococcus aureus as the model microorganisms revealed that prior to chlorination the antibacterial properties of the chlorinated PU-AHM-Cl films improved significantly relative to the analogous films. The excellent antibacterial properties and the overall superior performance of the PU-AHM-Cl films allow their potential application in microbiological protection materials and related fields.

Antibacterial N-halamine fibrous materials

Pathogenic microbial contamination poses serious threats to human healthcare and economies worldwide, which instigates the booming development of challenging antibacterial materials. N-halamine fibrous materials (NFMs), as an important part of antibacterial materials, featuring structural continuity, good pore connectivity, rapid sterilization, rechargeable bactericidal activity, and safety to humans and environment, have received significant research attention. This review aims to present a systematic discussion of the recent advances in N-halamine antibacterial fibrous materials. We firstly introduce the chemical structures and properties of N-halamine materials. Subsequently, the developed NFMs can be categorized based on their fabrication strategies, including surface modification and one-step spinning. Then some representative applications of these fibrous materials are highlighted. Finally, challenges and future research directions of the materials are discussed in the hope of giving suggestions for the following studies.

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The chemical structures and properties of N-halamine materials are briefly introduced.

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Design and fabrication strategies of N-halamine fibrous materials are systematically reviewed.

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The functional applications of the N-halamine fibrous materials are discussed.

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Challenges and future research directions of the antibacterial N-halamine fibrous materials are provided.

Chlorine Rechargeable Biocidal N-Halamine Nanofibrous Membranes Incorporated with Bifunctional Zwitterionic Polymers for Efficient Water Disinfection Applications

An intrinsically hydrophilic nanofibrous membrane with chlorine rechargeable biocidal and antifouling functions was prepared by using a combination of chemically bonded N-halamine moieties and zwitterionic polymers (PEI-S). The designed nanofibrous membrane, named as PEI-S@BNF-2 h, can exhibit integrated features of reduced bacterial adhesion, rechargeable biocidal activity, and easy release of killed bacteria by using mild hydrodynamic forces. The representative functional performances of the PEI-S@BNF-2 h membrane include high active chlorine capacity (>4000 ppm), large specific surface area, ease of chlorine rechargeability, long-term stability, and exceptional biocidal activity (99.9999% via contact killing). More importantly, the zwitterionic polymer moieties (PEI-S) brought robust antifouling properties to this biocidal membrane, therefore reducing the biofouling-biofilm effect and prolonging the lifetime of the filtration membrane. These attributes enable the PEI-S@BNF-2 h nanofibrous membrane to effectively disinfect the microbe-contaminated water with high fluxes (10,000 L m^-2 h^-1) and maintain itself clean for a long-term application.

Daylight-Induced Antibacterial and Antiviral Nanofibrous Membranes Containing Vitamin K Derivatives for Personal Protective Equipment

During the development of antibacterial and antiviral materials for personal protective equipment (PPE), daylight active functional polymeric materials containing vitamin K compounds (VKs) and impacts of polymer structures to the functions were investigated. As examples, hydrophobic polyacrylonitrile (PAN) and hydrophilic poly(vinyl alcohol-co-ethylene) (PVA-co-PE) polymers were directly blended with three VK compounds and electrospun into VK-containing nanofibrous membranes (VNFMs). The prepared VNFMs exhibited robust photoactivity in generating reactive oxygen species (ROS) under both daylight (D65, 300-800 nm) and ultraviolet A (UVA, 365 nm) irradiation, resulting in high antimicrobial and antiviral efficiency (>99.9%) within a short exposure time (<90 min). Interestingly, the PVA-co-PE/VK₃ VNFM showed higher ROS production rates and better biocidal functions than those of the PAN/VK₃ VNFM under the same photoirradiation conditions, indicating that PVA-co-PE is a better matrix polymer material for these functions. Moreover, the prepared PVA-co-PE/VK₃ VNFM maintains its powerful microbicidal function even after five times of repeated exposures to bacteria and viruses, showing the stability and reusability of the antimicrobial materials. The fabrication of photoinduced antimicrobial VNFMs may provide new insights into the development of non-toxic and reusable photoinduced antimicrobial materials that could be applied in personal protective equipment with improved biological protections.

Daylight-Induced Antibacterial and Antiviral Cotton Cloth for Offensive Personal Protection

Cotton fabrics with durable and reusable daylight-induced antibacterial/antiviral functions were developed by using a novel fabrication process, which employs strong electrostatic interaction between cationic cotton fibers and anionic photosensitizers. The cationic cotton contains polycationic short chains produced by a self-propagation of 2-diehtylaminoehtyl chloride (DEAE-Cl) on the surface of cotton fibers. Then, the fabric (i.e., polyDEAE@cotton) can be readily functionalized with anionic photosensitizers like rose Bengal and sodium 2-anthraquinone sulfate to produce biocidal reactive oxygen species (ROS) under light exposure and consequently provide the photo-induced biocidal functions. The biocidal properties of the photo-induced fabrics (PIFs) were demonstrated by ROS production measurements, bactericidal performance against bacteria (e.g., E coli and L. innocua), and antiviral results against T7 bacteriophage. The PIFs achieved 99.9999% (6 log) reductions against bacteria and the bacteriophage within 60 min of daylight exposure. Moreover, the PIFs showcase excellent washability and photostability, making them ideal materials for reusable face masks and protective suits with improved biological protections compared with traditional PPE. This work demonstrated that the cationized cotton could serve as a platform for different functionalization applications, and the resulting fiber materials could inspire the development of reusable and sustainable PPE with significant bioprotective properties to fight the COVID-19 pandemic as well as the spread of other contagious diseases.

Biomimetic and Superelastic Silica Nanofibrous Aerogels with Rechargeable Bactericidal Function for Antifouling Water Disinfection

Disinfecting drinking water in a reliable, sustainable, and affordable manner is a great challenge, especially for water contaminated with pathogenic microbes, and traditional water disinfection strategies still suffer from biofouling, irreversible depletion of disinfectants, and energy consumption. In this study, we developed biomimetic and superelastic skeletal-structured silica nanofibrous aerogels (SNAs) with rechargeable bactericidal and antifouling property via the combination of electrospun silica nanofibers and a functional Si-O-Si bonding network. The premise for our design is that the Si-O-Si network comprising rechargeable N-halamine moieties can provide the aerogels with structural stability yet durable bactericidal activity. The resulting aerogels exhibit intriguing properties of high porosity, superhydrophilicity, superelasticity, rechargeable chlorination capability (>4800 ppm), and exceptional bactericidal activity (99.9999%), enabling the aerogels to effectively disinfect the bacteria-contaminated water with ultrahigh flux (57 600 L m^-2 h^-1) and antifouling function. The synthesis of the SNAs opens pathways for exploring antibacterial and antifouling materials in a renewable and nanofibrous form.

Ultrathin Cellulose Voronoi-Nanonet Membranes Enable High-Flux and Energy-Saving Water Purification

Creating a desirable porous membrane with high-flux and energy-saving properties for the purification of water containing submicron-sized contaminants, especially pathogenic microbes, is of great significance, yet a great challenge. Herein, we demonstrate a facile methodology to construct an innovative membrane with continuous cellulose Voronoi-nanonet structures via nonsolvent-induced phase separation. This approach enables cellulose Voronoi nanonets to tightly weld with electrospun nanofibrous substrates by controlling the solvent-nonsolvent mutual diffusion process. The resultant membranes exhibit integrated properties of small pore size (0.23 μm), high porosity (90.7%), good interconnectivity, and ultrathin thickness (∼600 nm, 2 orders of magnitude thinner than the conventional microfiltration membrane). As a result, the prepared membranes can effectively intercept submicron particles (∼0.3 μm) with robust rejection efficiency (>99.80%) and ultrahigh permeation flux (maximum of 8834 L m^-2 h^-1) under an extremely low driving pressure (≤20 kPa). More importantly, prominent bacterial rejection efficiency with a log reduction value (LRV) of 8.0 (overcoming the previous limitation of LRV <7) and outstanding antifouling function are also achieved for the membranes. The successful fabrication of such a versatile membrane may provide new insights into the development of next-generation high-performance separation materials for various applications.

Bactericidal and antifouling electrospun PVA nanofibers modified with a quaternary ammonium salt and zwitterionic sulfopropylbetaine

Bacterial adhesion and colonization on material surfaces have attracted great attention due to their potential threat to human health. Combining bactericidal and antifouling functions has been confirmed as an optimal strategy to prevent microbial infection. In this work, biodegradable electrospun polyvinyl alcohol (PVA) nanofibers were chosen due to its high specific area and abundant reactive hydroxyl groups. A quaternary ammonium salt (IQAS) and zwitterionic sulfopropylbetaine (ISB), both containing isocyanate (NCO) groups, were chemically bonded to the PVA nanofiber surface via a coupling reaction between the OH groups of the PVA nanofibers and the NCO groups of IQAS or ISB. The results indicated that the antimicrobial rates of PVA nanofibers modified by IQAS (0.5%) reached 99.9% against both gram-positive Staphylococcus aureus (S. aureus, ATCC 6538) and gram-negative Escherichia coli (E. coli, ATCC 25922). Additionally, the live/dead staining and cytotoxicity test indicated that the dual functional IQAS/ISB/PVA nanofibers exhibited excellent bactericidal and antifouling activities with low cytotoxicity. This work may provide practical guidelines to fabricate bactericidal and antifouling materials for healthcare applications, including but not limited to wound dressings, textile, food packaging and air filtration.

Multifunctional β-Cyclodextrin Polymer for Simultaneous Removal of Natural Organic Matter and Organic Micropollutants and Detrimental Microorganisms from Water

Natural organic matter (NOM), organic micropollutants (OMPs), and detrimental microorganisms are three major pollutants that affect water quality. To remove these pollutants, a quaternary ammonium-functionalized β-cyclodextrin polymer (β-CDP) is successfully synthesized in the aqueous phase. The N₂ and CO₂ adsorption/desorption analysis showed that the polymer mainly contains ultra-micropores (<1 nm), with a Langmuir surface area of 89 m² g^-1. Two kinds of NOM, humic acid and fulvic acid, and five OMPs, 2-naphthol (2-NO), 3-phenylphenol (3-PH), 2,4,6-trichlorophenol (2,4,6-TCP), bisphenol A (BPA), and bisphenol S (BPS), were selected as model pollutants to study the performance of β-CDP and three kinds of commercial adsorbents, including granular activated carbon, DARCO-AC, and two resins, XAD-4 and D-201, were used for comparison. The polymer shows ultrarapid adsorption kinetics for the removal of these pollutants, with pseudo-second-order rate constants two to three orders of magnitude higher than that of the commercial activated carbon and resins. Due to the different adsorption sites of NOM and OMPs, β-CDP can simultaneously remove these pollutants without competitive adsorption. The maximum adsorption capacity of β-CDP for HA, FA, 2-NO, 3-PH, 2,4,6-TCP, BPA, and BPS based on the Langmuir model is 40, 166, 74, 101, 108, 103, and 117 mg g^-1, respectively. After use, the polymer can be easily regenerated at room temperature. In addition, β-CDP also showed excellent bactericidal properties due to the quaternary ammonium groups. At a concentration of 15 g L^-1, β-CDP can remove 98% of the tested Escherichia coli. Moreover, the synthesis of β-CDP is simple, green, and easy to industrialize. All of these findings indicate that β-CDP, as an ideal multifunctional material, presents potential for practical applications for water treatment and disinfection.

Resazurin assay for assessment of antimicrobial properties of electrospun nanofiber filtration membranes

We developed a simple and fast microplate assay for evaluation of the antimicrobial activity of electrospun nanofiber filtration membranes or similar porous materials for water treatment technologies. Resazurin (alamarBlue®) was used as an indicator of the amount of viable experimental microorganisms Gram-negative Escherichia coli, Gram-positive Enterococcus faecalis, and natural wastewater treatment plant effluent bacteria. A bacterial inoculum of concentration 1-3 × 105 CFU mL-1 was pipetted onto the surface of assessed both functionalized and respective control membranes and incubated in 12-well plates for 4 h at 37 °C. Kinetics of resazurin metabolization, i.e. its reduction to fluorescent resorufin, was evaluated fluorimetrically (λex520/λem590 nm). A number of viable bacteria on the membranes expressed as CFU mL-1 was calculated from the kinetic curves by using calibration curves that were constructed for both experimental bacterial species. Antimicrobial activities of the membranes were evaluated by either resazurin assay or modified ISO 20743 plate count assay. Results of both assays showed the significant antimicrobial activity of membranes functionalized with silver nanoparticles for both bacterial species and wastewater treatment plant effluent bacteria as well (log CFU reduction compared to control membrane > 4), while membranes containing specific quaternary ammonium salts were inefficient (log CFU reduction < 1). The suitability of resazurin microplate assay for testing nanofiber filtration membranes and analogous matrices has proven to be a faster and less demanding alternative to the traditionally used approach providing comparable results.

Novel ZnO/N-halamine-Mediated Multifunctional Dressings as Quick Antibacterial Agent for Biomedical Applications

Cutaneous hemorrhage often occurs in daily life which may cause infection and even amputation. This research aims to develop a novel chitosan dressing impregnated with ZnO/N-halamine hybrid nanoparticles for quick antibacterial performance, outstanding hemostatic potential, high porosity, and favorable swelling property through combining sonication and lyophilization processing. After 30 days of storage, about 90% bacterial cell viability loss could be observed toward both Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli O157:H7 within 30 min of contact by colony counting method. The hybrids assembled much more platelet and red blood cell as compared with pure chitosan control. Moreover, the lower blooding clotting index value gave evidence that these composites could control hemorrhaging and reduce the probability of wound infection. No potential skin irritation and toxicity were detected using in vitro cytocompatibility and a skin stimulation test. Therefore, this work demonstrated a facile and cost-effective approach for the preparation of N-halamine-based hybrid sponges which show promising application for wound dressings.

Rechargeable Antibacterial N-Halamine Films with Antifouling Function for Food Packaging Applications

Pathogenic microbial contamination from microbial adhesion and subsequent formation of the biofilm on surfaces of plastic food packaging materials, especially with robust resistance to antimicrobial agents, is a major reason for the outbreak of foodborne infections. Conventional strategies in controlling the contaminations are significantly limited either by biofouling or by the irreversible consumption of antimicrobial agents. Herein, we report a robust methodology to create rechargeable biocidal poly(vinyl alcohol- co-ethylene) films (SBMA@HAF films) with antifouling function via chemically incorporating both N-halamine (HAF) and zwitterionic moieties [[2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA)]. The promise of the design exhibits three features to defeat bacterial contaminations: (i) zwitterionic moieties can effectively reduce bacterial attachment onto the films, (ii) N-halamine with robust rechargeable biocidal activity can rapidly kill any attached bacteria, and (iii) any inactivated bacterial debris can be easily released to avoid biofilm formation due to the superhydrophilicity of the zwitterions. The resulting SBMA@HAF films exhibit integrated properties of high transparency, robust mechanical property, great hydrophilicity, ease of chlorine recharging (>250 ppm), long-term stability, high biocidal efficacy (>99.9999% via contact killing), and promising antifouling functions, which enable the SBMA@HAF films to serve as a biocidal material in food packaging applications.

Rechargeable polyamide-based N-halamine nanofibrous membranes for renewable, high-efficiency, and antibacterial respirators

Emerging infectious diseases (EIDs) have been acknowledged as a major public health concern worldwide. Unfortunately, most protective respirators used to prevent EID transmission suffer from the disadvantage of lacking antimicrobial activity, leading to an increased risk of cross-contamination and post-infection. Herein, we report a novel and facile strategy to fabricate rechargeable and biocidal air filtration materials by creating advanced N-halamine structures based on electrospun polyamide (PA) nanofibers. Our approach can endow the resultant nanofibrous membranes with powerful biocidal activity (6 log CFU reduction against E. coli), an ultrahigh fine particle capture efficiency of 99.999% (N100 level for masks), and can allow the antibacterial efficacy and air filtration performance to be renewed in a one-step chlorination process, which has never been reported before. More importantly, for the first time, we revealed the synergistic effect involving the intrinsic structure of polymers and the assembling structure of nanofibers on the chlorination capacity. The successful fabrication of such a fascinating membrane can provide new insights into the development of nanofibrous materials in a multifunctional, durable, and renewable form.

Novel Inorganic-Based N-Halamine Nanofibrous Membranes As Highly Effective Antibacterial Agent for Water Disinfection

Novel superhydrophilic inorganic-based N-halamine nanofibrous membranes with high active chlorine contents, outstanding rechargeability, favorable water swelling resistance, and superior mechanical performance were prepared through the combination of electrospinning and sol-gel processing, which could be applied to the dynamic disinfection of bacteria-contaminated water with high disinfection efficiency, large processing flux, and long-term durability. The successful preparation of such silica nanofiber membranous N-halamine antimicrobial with intriguing properties would provide the reference for developing novel antimicrobial nanofibers for multifunctional applications.

Photocatalytic degradation of naphthalene using calcined FeZnO/ PVA nanofibers

Recently, the incorporation of metal oxide nanoparticles into polymers has gained great attention owing to their ample of applications. The green mediated synthesis Fe-doped ZnO nanoparticles have been incorporated into PVA nanofibers through electro spinning for the application of photocatalytic degradation. The PVA polymer concentration was optimized to obtain uniform fibers without beads. The Fe-doped ZnO nanofibers were characterized by various analyzing techniques. The results show that good physicochemical with high surface area, uniformity in fiber with an average diameter ranges from 150 to 300 and 50-200 nm for un-calcined and calcined Fe-doped ZnO nanofiber respectively. The photocatalytic activity of nanofibers was examined by the degradation of naphthalene. The efficiency was observed 96 and 81% for calcined and un-calcined nanofibers, respectively. The reusable efficacy of Fe-doped ZnO calcined nanofiber as a catalyst was studied. These studies corroborated that the calcined Fe-doped ZnO nanofiber as promising material for catalytic applications.

Highly Bactericidal Macroporous Antimicrobial Polymeric Gel for Point-of-Use Water Disinfection

Access to clean and safe water supply remains inadequate in many developing countries. One of the key challenges is to remove pathogenic bacteria from the water supply via effective water disinfection technologies to prevent the spread of diseases and to ensure the safety of consumers. Herein, a highly effective point-of-use (on-demand) water disinfection technology, in the form of a polymeric scaffold called macroporous antimicrobial polymeric gel (MAPG), is demonstrated. MAPG is easy to fabricate, completely organic and possess inherent antimicrobial property which makes it non-reliant on inorganic compounds such as silver where the long-term toxicity remains unknown. MAPG is highly bactericidal and can disinfect bacteria-contaminated water (ca. 10⁸ CFU mL^-1) at a capacity of about >50 times the mass of the organic material used, inactivating >99% of both Gram-negative and Gram-positive bacteria including Escherichia coli, Vibrio cholerae and Staphylococcus aureus within 20 minutes of treatment. When fabricated in a syringe, MAPG eliminates E. coli from contaminated water source by >8.0 log₁₀ reduction in bacteria counts (i.e., no viable bacteria were detected after treatment), and the syringe can be reused multiple times without losing potency. The MAPG technology is not only restricted to water disinfection but may also be applicable in other bacteria inactivation applications.

Antibacterial and rechargeable surface functional nanofiber membrane for healthcare textile application

The membrane could create a clean environment for doctors and patients to prevent nosocomial cross infection and the activity could be recharged.

Mussel-Inspired Fabrication of Konjac Glucomannan/Poly (Lactic Acid) Cryogels with Enhanced Thermal and Mechanical Properties

Three-dimensional nanofibers cryogels (NFCs) with both thermally-tolerant and mechanically-robust properties have potential for wide application in biomedical or food areas; however, creating such NFCs has proven to be extremely challenging. In this study, konjac glucomannan (KGM)/poly (lactic acid) (PLA)-based novel NFCs were prepared by the incorporation of the mussel-inspired protein polydopamine (PDA) via a facile and environmentally-friendly electrospinning and freeze-shaping technique. The obtained KGM/PLA/PDA (KPP) NFCs were characterized by field emission scanning electron microscopy (FE-SEM), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and compressive and tensile test. The results showed that the hierarchical cellular structure and physicochemical properties of KPP NFCs were dependent on the incorporation of PDA content. Moreover, the strong intermolecular hydrogen bond interactions among KGM, PLA and PDA also gave KPP NFCs high thermostability and mechanically-robust properties. Thus, this study developed a simple approach to fabricate multifunctional NFCs with significant potential for biomedical or food application.