Natural fiber welded (NFW) yarns embedded with porous carbon ­materials are described for applications as electrodes in textile electrochemical capacitors. With this fabrication technique, many kinds of carbons can be embedded into cellulose based yarns and subsequently knitted into full ­fabrics on industrial knitting machines. Yarns welded with carbon and ­stainless steel have device capacitances as high as 37 mF cm‐1, one of the highest reported values for carbon‐based yarns. The versatility of this ­technique to weld any commercially available cellulose yarn with any ­micro‐ or nanocarbon means properties can be tuned for specific applications. Most importantly, it is found that despite having full flexibility, increased strength, and good electrochemical performance, not all of the electrode yarns are ­suitable for knitting. Therefore, it is recommended that all works reporting on fiber/yarn capacitors for wearables attempt processing into full fabrics.

Graphitic carbon nitride (g-CN) has recently emerged as a promising visible-light-responsive polymeric photocatalyst; however, a molecular-level understanding of material properties and its application for water purification were underexplored. In this study, we rationally designed nonmetal doped, supramolecule-based g-CN with improved surface area and charge separation. Density functional theory (DFT) simulations indicated that carbon-doped g-CN showed a thermodynamically stable structure, promoted charge separation, and had suitable energy levels of conduction and valence bands for photocatalytic oxidation compared to phosphorus-doped g-CN. The optimized carbon-doped, supramolecule-based g-CN showed a reaction rate enhancement of 2.3-10.5-fold for the degradation of phenol and persistent organic micropollutants compared to that of conventional, melamine-based g-CN in a model buffer system under the irradiation of simulated visible sunlight. Carbon-doping but not phosphorus-doping improved reactivity for contaminant degradation in agreement with DFT simulation results. Selective contaminant degradation was observed on g-CN, likely due to differences in reactive oxygen species production and/or contaminant-photocatalyst interfacial interactions on different g-CN samples. Moreover, g-CN is a robust photocatalyst for contaminant degradation in raw natural water and (partially) treated water and wastewater. In summary, DFT simulations are a viable tool to predict photocatalyst properties and oxidation performance for contaminant removal, and they guide the rational design, fabrication, and implementation of visible-light-responsive g-CN for efficient, robust, and sustainable water treatment.

Carbon nanotubes (CNTs) have unique physical and chemical properties that drive their use in a variety of commercial and industrial applications. CNTs are commonly oxidized prior to their use to enhance dispersion in polar solvents by deliberately grafting oxygen-containing functional groups onto CNT surfaces. In addition, CNT surface oxides can be unintentionally formed or modified after CNTs are released into the environment through exposure to reactive oxygen species and/or ultraviolet irradiation. Consequently, it is important to understand the impact of CNT surface oxidation on the environmental fate, transport, and toxicity of CNTs. In this review, we describe the specific role of oxygen-containing functional groups on the important environmental behaviors of CNTs in aqueous media (e.g., colloidal stability, adsorption, and photochemistry) as well as their biological impact. We place special emphasis on the value of systematically varying and quantifying surface oxides as a route to identifying quantitative structure−property relationships. The role of oxygen-containing functional groups in regulating the efficacy of CNT-enabled water treatment technologies and the influence of surface oxides on other carbon-based nanomaterials are also evaluated and discussed.

Airborne transmission of SARS-CoV-2 plays a critical role in spreading COVID-19. To protect public health, we designed and fabricated electrospun nanofibrous air filters that hold promise for applications in personal protective equipment (PPE) and the indoor environment. Due to ultrafine nanofibers (∼300 nm), the electrospun air filters had a much smaller pore size in comparison to the surgical mask and cloth masks (a couple of micrometers versus tens to hundreds of micrometers). A coronavirus strain served as a SARS-CoV-2 surrogate and was used to generate aerosols for filtration efficiency tests, which can better represent SARS-CoV-2 in comparison to other agents used for aerosol generation in previous studies. The electrospun air filters showed excellent performance by capturing up to 99.9% of coronavirus aerosols, which outperformed many commercial face masks. In addition, we observed that the same electrospun air filter or face mask removed NaCl aerosols equivalently or less effectively in comparison to the coronavirus aerosols when both aerosols were generated from the same system. Our work paves a new avenue for advancing air filtration by developing electrospun nanofibrous air filters for controlling SARS-CoV-2 airborne transmission.

For nanocellulose to function effectively as a nanofiller in polymers, its interfacial properties are often modified to enhance the dispersion of nanocellulose in the polymer matrix. However, the effect of different surface modification strategies on the persistence of nanocellulose in the environment is unclear. In this study, we examined the effect of three different hydrophobic silanization reagents on the structure, dispersion properties, and biodegradability of cellulose nanofibrils (CNFs). Specifically, we modified CNFs with hydrophobic alkoxysilanes containing methyl, propyl, or aminopropyl functional groups to form silane-modified CNFs (Si-CNFs). Using a combination of analytical techniques that included ATR-IR, XPS, and solid-state NMR, we demonstrated that silanization coated the CNFs with a nanometer-scale siloxane layer, and the extent of the siloxane coating could be controlled by varying the amount of silane added to the CNFs. The stability of Si-CNFs in chloroform-based casting solutions improved compared to untreated CNFs, and scaled with extent and hydrophobicity of the siloxane coating as quantified via a mass recovery settling test. Improvements in stability in casting solutions translated into improved Si-CNF dispersion in solution-blended polyhydroxyalkanoates composites as determined with optical microscopy and SEM. Conversely, the biodegradability of Si-CNFs, assessed by sample mineralization in a mixed microbial culture from an anaerobic sludge digester, was inversely related to both the degree and hydrophobicity of CNF surface modification. As mineralization of nanocellulose is rapid and complete, tracking biogas production served as a proportional measure of overall biodegradability. In the most extensively silanized samples, no mineralization of Si-CNFs was observed, demonstrating that a <2-nm-thick siloxane coating was sufficiently dense and uniform to prevent microbial access to the easily mineralized nanocellulose substrate. This study highlights the important and contrasting effects that changes to surface chemistry can have on the material and environmentally relevant properties of nanocellulose.

In our study, lignocellulose yarns were fabricated via natural fiber welding (NFW) into a robust, free-standing, sustainable catalyst for water treatment. First, a series of powder catalysts were created by loading monometallic palladium (Pd) and bimetallic palladium−copper (Pd−Cu) nanoparticles onto ball-milled yarn powders via incipient wetness (IW) followed by a gentle reduction method in hydrogen gas that preserved the natural fiber while reducing the metal ions to their zerovalent state. Material characterization revealed Pd preferentially reduced near the surface whereas Cu distributed more uniformly throughout the supports. Although no chemical bonding interactions were observed between the metals and their supports, small (5−10 nm), near-spherical crystalline nanoparticles were produced, and a Pd−Cu alloy formed on the surface of the supports. Catalytic performance was evaluated for each Pd-only and Pd−Cu powder catalyst via nitrite and nitrate reduction tests, respectively. Next, the optimized Pd−Cu linen powder catalyst was fiber-welded onto a macroporous linen yarn scaffold via NFW and its catalyst performance and reusability were evaluated. This fiber-welded catalyst reduced nitrate as effectively as the corresponding powder, and remained stable during five consecutive cycles of nitrate reduction tests. Although catalytic activity declined after the fiber-welded catalyst was left in air for several months, its reactivity could easily be regenerated by thermal treatment. Our research highlights how lignocellulose supported metal-based catalysts can be used for water purification, demonstrating a novel application of NFW for water treatment while presenting a sustainable approach to fabricate functional materials from natural fibers.

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