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Flavin mononucleotide (FMN) produces photo-induced reactive oxygen species (ROS), making it a bio-based and sustainable photosensitizer for micropollutant degradation. However, the rapid self-degradation of FMN under light poses challenges in practical applications. We propose for the first time to use porous organic polymer (POP) structures as particles and in situ grown on nanofibrous membranes to capture the ribityl side chain ("tail") of FMN by electrostatic-driven guest-host interaction. By restraining the free bending mode of FMN in POP, its self-degradation is highly inhibited, showing a prolonged half-life (102.7 and 79.7 times to that in solution and in β-cyclodextrin, respectively) without any impact on the ROS production even after 16 h of UVA irradiation. As a proof-of-concept, the photocatalytic degradation efficiency of FMN-POP complexes can be achieved at 58-93% against micropollutants under UVA. The stabilization of FMN by the "tail" capture in the POP allows its photocatalytic degradation function to be continuously online.

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.

Highly porous nucleophilic organic polymers (Nu-POPs) were synthesized in situ on cotton fibers by a condensation reaction between cyanuric chloride and melamine, and the products were employed as robust, wearable, and flexible cotton-based super-adsorptive fibrous equipment (SAFE-cotton) against exposure to vaporous pesticides. The covalent growth of the Nu-POP on surfaces of cotton fibers retained the physical characteristics of the Nu-POP to the greatest extent, which include specific surface area and porosity, while the cotton fabrics still remained wearable. The SAFE-cotton can repeatedly adsorb fumigant vapors instantly (i.e., equilibrium is reached in one minute) and massively (i.e., methyl iodide adsorption capacity of 596.88 mg g−1). The nitrogen atoms in the triazine rings of the Nu-POP on the SAFE-cotton are nucleophilic to detoxify sequestered fumigants during long-term use and storage. A colorimetric signal could reveal the failure of the SAFE-cotton functions due to the detoxification of the fumigants and the formation of a conjugated structure of the Nu-POP. The success of achieving SAFE-cotton without significant loss of the Nu-POP performance in terms of rapid fumigant adsorption and detoxification is expected to guide the design of next-generation protective materials with the advantages of flexible, wearable and easily processible properties.

Hydroxyl radical is the main reactive species in hydrogen peroxide (H2O2) bleaching of cotton fabrics. Ultraviolet (UV) irradiation of the H2O2 bleaching system can efficiently produce hydroxyl radicals (HO·) under neutral or alkaline conditions, which were proven experimentally and theoretically by computational modeling. Various UV/H2O2 bleaching routes were screened to obtain desired whiteness index and acceptable bursting strength of the bleached fabrics. The optimal properties of the bleached cotton knitted fabric could be obtained at UV irradiation of 312 nm on the fabrics with a hydrogen peroxide solution under alkaline conditions.

The sodium l-glutamate is reported as an efficient catalyst for the cross-linking between 1,2,3,4-butanetetracarboxylic acid (BTCA) and cellulose. Results presented ester absorbance of the treated fabrics strongly increased in the presence of the homemade l-glutamate salt, a mixture of l-glutamic acid (LGA) and NaOH at a specific ratio. Importantly, anti-wrinkle properties of the treated fabrics were significantly improved. Based on the relative concentration calculation, l-glutamate promoted the reaction of BTCA with cellulose by accelerating the formation of BTCA anhydrides and the esterification of anhydrides with cellulose. Besides, the improved anti-wrinkle property was partially attributed to the fact that the generated LGA reacted with cellulose and formed ionic cross-linking networks through amino groups with carboxyl groups in BTCA, which was confirmed by the Fourier transform infrared spectra and the computational calculations. Through detailed comparisons, l-glutamate catalyzed fabrics showed as good durability as sodium hypophosphite, indicating a possible alternative for phosphorus-containing catalysts.

The aggregation-caused self-quenching of photosensitizers (PS), especially on a solid substrate, has highly limited their photo-induced biocidal efficiency in practical applications. Here, we designed a unique “posture” of rose Bengal (RB) on cotton-based super-adsorptive fibrous equipment, with RB being separately captured in the mesopores of porous organic polymers (POPs). The resultant daylight-induced biocidal cotton fabric with enhanced efficiency was named as DBwEE-Cotton. The enhanced biocidal activity of the DBwEE-Cotton was achieved based on two mechanisms: (1) the separation of RB in mesopores on the fabric avoids the aggregation-caused self-quenching; and (2) other than singlet oxygen generation, RB is forced to undergo type I photoreaction by surrounding the RB with massive amounts of good hydrogen donors (i.e., POP) under daylight irradiation. Given the enhanced production efficiency of reactive oxygen species by the DBwEE-Cotton, 99.9999% of E. coli and L. innocua bacteria were killed within 20 min of daylight exposure. The DBwEE-Cotton also presents excellent wash and light durability with no biocidal function loss. The development of DBwEE-Cotton provides a facile strategy of avoiding aggregation-caused self-quenching and modulating photoreactions of PS on a flexible substrate, which may guide the design of novel personal protective equipment (PPE) integrated with improved biocidal efficiency, wearability, and repeated and long-term applicability for protecting people from lethal infectious diseases., RB captured by super-adsorptive cotton achieves enhanced biocidal activity by alleviating aggregation-caused self-quenching and modulating the photoreaction of RB.

Daylight-activated detoxifying nanofibrous membranes (LDNMs) are fabricated by grafting benzophenone-3,3′,4,4′-tetracarboxylic dianhydride (BD) and biological thiols successively on poly(vinyl alcohol-co-ethylene) (EVOH) nanofibrous membrane. Taking the merits of photoactivity of BD, high-reactivity of biological thiols, and high specific surface area and porosity of the nanofibrous membrane, 1,3-dichloropropene (1,3-D) can be efficiently detoxified on the LDNMs under daylight irradiation via a thiol-ene click reaction. The detoxification function of the LDNMs is “switched on” by light irradiation and continues by following a cascade of chemical attacks of thiyl radicals formed during the photoexcitation process. The resultant LDNMs present rapid detoxification rate (i.e., t1/2 = ~30 min) and massive detoxification amount (i.e., ~12 mg/g) against 1,3-D vapor under ambient conditions. More importantly, the LDNMs perform a detoxification tailing effect after moving the light-irradiated membrane to a dark environment, thus ensuring the protective function in the absence of sufficient light sources. The detoxification property of the LDNMs in an outdoor environment with sunlight irradiation shows comparable results to the lab-scale outcomes, enabling them to serve as innovative materials for personal protective equipment in practical applications. The successful fabrication of LDNMs may inspire new insights into the design of protective materials providing aggressive 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.

Highly sensitive and portable sensors are tools to improve personal protection from exposures to unwanted toxic chemicals. A paper-based colorimetric sensor was designed and prepared to sensitively and selectively detect trace amounts of methyl isothiocyanate (MITC) in the air. Taking advantage of a detoxification reaction existing in the mammalian body, glutathione (GSH) becomes unique in indirectly sensing the concentration of methyl isothiocyanate. The reaction mechanism was analyzed, and the detection conditions were optimized. Nanofibrous membrane materials were utilized as a solid substrate with ultrahigh surface areas. An organic polar solvent with high adsorptive capacity to MITC was applied on the fiber surfaces. A combination of three factors drives the detection of traces toxic gas in air kinetically favorable.

Detoxification reaction of chloropicrin in the human body with biological thiols was selected for detection of chloropicrin in the air. The consumption of free sulfhydryl group in biological thiols by chloropicrin is colorimetrically detectable with the addition of the Ellman's reagent. In this study, glutathione, N-acetyl-l-cysteine, l-homocysteine, cysteamine, and thioglycolic acid were tested as sensing agents for chloropicrin vapor detection in ppb concentration range. The reactivity of the selected biological thiols was investigated based on both their redox properties and the nucleophilic strength of the sulfhydryl groups. Nylon-6 nanofibrous membrane and an organic solvent were used as a sensor matrix and a vapor sorbent, respectively, to provide solid supports with ultrahigh surface area and enhanced adsorption to chloropicrin vapor. The tunable sensitivity and detection range by using different biological thiols was achieved on the sensors due to the different reactivity of thiols toward chloropicrin.

Chemically crosslinked cotton fabrics may show yellowish appearance, especially citric acid (CA) crosslinked ones. Hydrogen peroxide (H2O2) bleaching under alkaline condition could improve the whiteness of the CA-crosslinked cotton fabrics but sacrificing certain crosslinking performance of the products due to alkaline hydrolysis of ester connections. Regular H2O2 and UV irradiation (H2O2/UV) system can destroy color but also damage fibers due to the use of very short wavelength of UVC such as 254nm or shorter. Now, it was found that longer wavelength UV such as 312nm performed better in H2O2/UV systems on CA-crosslinked cotton fabrics. The reaction mechanism and potential product of the oxidation reaction on CA-crosslinked cotton were proposed and demonstrated. UV-vis spectrophotometer and Fourier transform infrared spectroscopy provided key evidence. Whiteness, wrinkle recovery angle and tensile strength of the fabrics were evaluated, and the results support the mechanism. The process is environmentally friendly and highly efficient.

Due to the fast development of human culture, environmental issues including water pollution, air pollution, and natural resources abuse present severe impacts on human life. The development of versatile and personal use sensors has become one of the most popular ways to improve personal protection from exposures to different types of environmental threats. The ultra-high-specific surface area and porosity of micromaterials or nanomaterials, and the easy operation of color signals make nanofibrous membrane-based colorimetric sensors highly attractive in sensitively monitoring environmental toxicants. In this chapter, we highlight recent progresses in developments of colorimetric sensors, which are mainly based on the use of nanofibrous membranes for toxic vapors by taking its merits of ultra-high specific surface areas, light weight, and flexibility. Different sensors targeting on volatile organic compounds, vaporous pesticides, volatile nerve agents, and corrosive gases are included. It is expected to provide guidance for the development of colorimetric sensors not only present remarkable sensitivity and selectivity but also are suitable to be embedded into the next generation of smart textiles.

In recent years, fluorescent carbon dots have attracted great attention due to their good luminescence and low toxicity. Here, blue fluorescent core-shell structured carbon polymer dots (CPDs) with high stability under a wide range of pH values, long storage time and excellent fluorescence in various solvents and even in solid state were prepared by hydrothermal synthesis of dendritic tris(2-aminoethyl)amine (TAEA) and citric acid. The CPDs core structure provides strong fluorescent luminescence, a shell structure of the core possesses high amount of dendritic primary amino groups connected by ethylene groups to the core. This unique structure prevents aggregation of the cores and self-quenching effect of CPDs. As a result, the CPDs have high fluorescence in both aqueous and hydrophobic solutions and even as pure solid-state powder. In addition, the CPDs are also insensitive to pH of solutions, and the fluorescence intensity of the solution was stable in the pH range of 4-14. The CPDs embedded polymer films and fibers revealed excellent fluorescent properties.

A nylon 6 nanofibrous membrane (N6NFM) was covalently modified with 2-diethylaminoethylchloride (DEAE-Cl) to provide self-catalytic functions to facilitate the formation of color compounds in reactions of 4-( p-nitrobenzyl)pyridine with alkylating fumigants. The 2-diethylaminoethyl group on the DEAE-Cl-modified N6NFM (DEAE@N6NFM) enables effective elimination of hydrohalogenic acids from intermediates that were formed from reactions between the alkylating fumigants and NBP and consequently improve their detection sensitivities, especially for 1,3-dichloropropene at room temperature. Moreover, DEAE@N6NFM can be recycled and reused multiple times without obvious loss in the sensing functions or any noticeable material damage. The naked-eye detection limits of the sensor to 1,3-dichloropropene, methyl iodide, and methyl bromide on DEAE@N6NFM are improved to 0.2, 0.1, and 0.1 ppm, respectively, which are much lower than their occupational exposure limits. The reaction mechanism is demonstrated through a computational method by analyzing the thermodynamics of the reaction. The modification of DEAE@N6NFM also provides an insight into the development of functionalized materials with improved reactivities for versatile sensing applications.

Personal protective equipment (PPE) is crucial for ensuring occupational safety when handling toxic chemicals or in close contact with biological pathogens. The increased poisoning and infection cases outside the working scenario have attracted public attention, which drove the development and application of PPE for the professionals and the public. The use of PPE can effectively lower the risk of acute and chronic diseases caused by pesticide exposures and significantly reduce the spread of infectious diseases. However, conventional PPE mostly only functions as physical blocking or electrostatic repulsion materials, which still poses potential risks caused by cross- and post-contamination from the PPE. Although sensors are not usually considered as a necessary component of PPE, the detection of health threats in the environment could benefit preparations for unprepared risks promptly, especially in non-occupational situations, thus improving the protection of human safety. In this review, we discuss the needs of novel PPE by surveying some insufficient protection cases and threats that occurred during conventional PPE applications. Then, we summarize recent progress in developing single-functional decontamination and colorimetric sensing PPE, mostly fiber-based media against agricultural toxicants and microorganisms, with intension to inspire the future design of novel PPE with the integrated “decontamination-and-sensing” property. Some recently developed conventional dual-functional materials against either pesticide or microorganism exposures are highlighted. Finally, strategies and limitations of developing decontamination and sensing material using unique interactions and reactions of targets with functionalized fibrous substrates are discussed by comparing the successful approaches and practical challenges in PPE applications.

Colorimetric sensors were fabricated by incorporation of anionic colorimetric probes on a hierarchical nanofibrous membrane containing poly-cationic nanodots through intense electrostatic interaction. Unique poly-cationic nanodots were covalently grown on poly (4-vinylpyridine)/polyacrylonitrile nanofibrous membrane through a self-propagation reaction of 2-diethylaminoethyl chloride (DEAE-Cl). The nanodots on the nanofiber surfaces possess strong adsorption affinity and high adsorption capacity toward anionic probes, which contributed to excellent detection sensitivity and sensor stability compared with the co-electrospun sensor. As a proof-of-concept study, phenol red was selected to functionalize the as-fabricated substrate (polyDEAE@P4VP/PAN NFM) to a colorimetric sensor, which shows responses to alkaline vapors. The as-fabricated sensor showed rapid color changes to ammonia and triethylamine (response time 10 s), whose detection limits reached 1 ppm and 5 ppm, respectively. The sensor can be repeatedly used for at least 20 cycles by regenerating it in air for 1 min. Taking advantage of the intense attractive force between poly-cationic nanodots and anionic probes, polyDEAE@P4VP/PAN NFM is a promising media to be used for the development of robust, rapid, and ultrasensitive colorimetric sensors.

Given the strong yet easy-to-form electrostatic interaction, innovative hierarchical materials can be fabricated as a universal substrate for functional materials. Here, we introduce an approach to prepare novel functional poly-cationic nanodots on the surface of nucleophilic nanofibrous membranes. The poly-cationic nanodots were formed from a self-propagation of 2-diethylaminoethyl chloride, a reaction that has not been reported elsewhere for preparing hierarchical nanostructures on nucleophilic nanofibrous membranes. The nanodots showed cationic property independence of pH conditions (i.e., pH = 3–11) and presented robust attraction toward anionic chemicals. The powerful electrostatic interaction of the nanodots was illustrated through dye adsorption experimentally and theoretically. The fabrication of the poly-cationic nanodots was expanded to other nucleophilic materials such as chitosan and cellulose, and the resulted products exhibited intense attractions to various anionic compounds. The poly-cationic nanodots on different substrates can be readily functionalized to smart materials through the strong chemisorption.

Alkylating fumigants are widely used in agricultural production for the control of soil-borne pests, but the acute toxicity and carcinogenicity of these chemicals pose a health threat to farm workers, as well as residents. A nanofibrous membrane-based colorimetric sensor relying on the nucleophilic substitution reaction of 4-( p-nitrobenzyl)pyridine (NBP) is introduced for the convenient and portable detection of alkylating fumigants. Comparing with the traditional use of NBP in detecting alkylating agents, this sensor system achieves a parts per billion level detection sensitivity toward alkylating fumigant gases without a high-temperature incubation or the addition of extra bases. The mechanisms of the detection reaction and the detection sensitivities of different fumigants were studied with computational methods, and the results comprehensively prove the proposed optimized detection mechanisms. The detection limit of methyl iodide, methyl bromide, and 1,3-dichloropropene successfully reaches to the limiting exposure concentrations (PEL or REL) with a naked-eye detectable color difference within 5 min with a dynamic detection procedure. The designed sensing system is promising for a real-time monitoring of the air quality related to alkylating fumigants in the environment, especially in agricultural and industrial areas.

Living organisms, including human beings, rapidly show skin color changes after chemical poisonings, a result of toxicological or detoxification reactions caused by biological thiol compounds. On the other side, quick and portable detection of highly-volatile toxicants is an urgent need for improving human safety and personal protection, especially real-time monitoring of fumigants at low level for protection of farm workers and residents from overexposure of fumigants, vaporous pesticides. Here, we designed a rapid and portable detection method for methyl isothiocyanate (MITC) vapor by mimicking detoxification reactions of biological thiols in human bodies with MITC. The detection reaction was implemented on a nylon-6 nanofibrous membrane with ultrahigh surface areas to show color signals with the addition of Ellman’s reagent. The reactivities of glutathione, N-acetyl-L-cysteine, L-homocysteine, cysteamine, and thioglycolic acid toward MITC were experimentally explored and theoretically discussed. The detection sensitivity is tunable in different biological thiol systems, which broadens the sensor applications in detection of trace amount of MITC in ambient environment and improves the protection of human safety. The new sensor system reduced the sensor operation time to 15 min and achieved the detection limit of 99 ppb, much lower than its permissible exposure limit (220 ppb).

1,2,3,4-Butanetetracarboxylic acid (BTCA) reacts with cellulose in two steps with catalysis of alkaline salts such as sodium hypophosphite: anhydride formation and esterification of anhydride with cellulose. The alkali metal ions were found effective in catalyzing formation of BTCA anhydride in a previous report. In this work, catalytic functions of the alkaline salts in the esterification reaction between BTCA anhydride and cellulose were investigated. Results revealed that acid anions play an important role in the esterification reaction by assisting removal of protons on intermediates and completion of the esterification between cellulose and BTCA. Besides, alkaline salts with lower pKa1 values of the corresponding acids are more effective ones for the reaction since addition of these salts could lead to lower pH values and higher acid anion concentrations in finishing baths. The mechanism explains the results of FTIR and wrinkle recovery angles of the fabrics cured under different temperatures and times.

Polycarboxylic acids have been employed as formaldehyde-free crosslinking agents in anti-wrinkle treatment for cotton fabrics. Cotton fabrics treated by citric acid (CA) catalyzed with effective catalysts have shown satisfactory anti-wrinkle properties. Meanwhile, CA is a natural-based and environmental friendly compound. However, the yellowing of CA treated fabrics is a stumbling block for its practical application. Due to the fact that CA firstly forms aconitic acid (AA) before forming anhydrides, the cause of the yellowing, hydrogen peroxide (H2O2) bleaching was adopted to treat the CA treated fabrics in order to break the CC bond structure and reduce the yellow color but retaining the desired anti-wrinkle properties. Thermogravimetric analysis and Fourier transformed infrared spectroscopy were employed to investigate the reactions. The results revealed that the H2O2 bleaching can effectively improve the whiteness and also maintain a good anti-wrinkle performance of the CA treated fabrics under an appropriate bleaching temperature and time.