Coronavirus Disease 2019 (COVID-19) may spread through respiratory droplets released by infected individuals during coughing, sneezing, or speaking. Given the limited supply of professional respirators and face masks, the U.S. Centers for Disease Control and Prevention (CDC) has recommended home-made cloth face coverings for use by the general public. While there have been several studies on aerosol filtration performance of household fabrics, their effectiveness at blocking larger droplets has not been investigated. Here, we ascertained the performance of 11 common household fabrics at blocking large, high-velocity droplets, using a commercial medical mask as a benchmark. We also assessed the breathability (air permeability), texture, fiber composition, and water absorption properties of the fabrics. We found that most fabrics have substantial blocking efficiency (median values >70%). In particular, two layers of highly permeable fabric, such as T-shirt cloth, blocks droplets with an efficiency (>94%) similar to that of medical masks, while being approximately twice as breathable. The first layer allows about 17% of the droplet volume to transmit, but it significantly reduces their velocity. This allows the second layer to trap the transmitted droplets resulting in high blocking efficacy. Overall, our study suggests that cloth face coverings, especially with multiple layers, may help reduce droplet transmission of respiratory infections. Furthermore, face coverings made from materials such as cotton fabrics allow washing and reusing, and can help reduce the adverse environmental effects of widespread use of commercial disposable and non-biodegradable facemasks.

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Soil contamination by heavy metals threatens the quality of agricultural products and human health, so it is necessary to choose certain economic and effective remediation techniques to control the continuous deterioration of land quality. This paper is intended to present an overview on the application of biochar as an addition to the remediation of heavy-metal-contaminated soil, in terms of its preparation technologies and performance characteristics, remediation mechanisms and effects, and impacts on heavy metal bioavailability. Biochar is a carbon-neutral or carbon-negative product produced by the thermochemical transformation of plant- and animal-based biomass. Biochar shows numerous advantages in increasing soil pH value and organic carbon content, improving soil water-holding capacity, reducing the available fraction of heavy metals, increasing agricultural crop yield and inhibiting the uptake and accumulation of heavy metals. Different conditions, such as biomass type, pyrolysis temperature, heating rate and residence time are the pivotal factors governing the performance characteristics of biochar. Affected by the pH value and dissolved organic carbon and ash content of biochar, the interaction mechanisms between biochar and heavy metals mainly includes complexation, reduction, cation exchange, electrostatic attraction and precipitation. Finally, the potential risks of in-situ remediation strategy of biochar are expounded upon, which provides the directions for future research to ensure the safe production and sustainable utilization of biochar.

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Rechargeable aqueous Zn‐ion batteries (ZIBs) show attractive potential in energy storage devices on account of high safety and eco‐friendliness. Yet the lack of suitable cathode materials prevented the practical application of ZIBs. In our work, a Na0.56V2O5 (NVO) nanobelt cathode material has been fabricated via a hydrothermal reaction. The prepared NVO samples reveal an expanded layer spacing, assisted by the chemical intercalation of Na+ into the V2O5. Particularly, a mild hybrid cationic electrolyte (0.5HCE, containing 3 M ZnSO4 and 0.5 M Na2SO4) was employed to replace the traditional ZnSO4 electrolyte (ZE) in the Zn//NVO system. Owing to the enlarged interlayer spacing and the protective effect of 0.5HCE, the NVO cathode delivers a preferable capacity and good cyclic stability. More specifically, the NVO cathode in 0.5HCE displays a high initial discharge capacity of 317 mAh g−1 at 0.1 A g−1, and exhibits a good stability after 1000 cycles at the current density of 1 A g−1. Besides, the Zn//NVO battery also presents a favorable rate capability and a high reversibility. This study could provide new directions for the development of low‐cost zinc ion batteries.

An anion flow battery has recently emerged as an option to store electricity with high volumetric energy densities. In particular, fluoride ions are attractive for these batteries because they have the smallest size among anions, which is beneficial for charge transport. To date, reported fluoride ion batteries either operate with an ionic liquid, organic electrolyte or solid-state electrolyte at high temperatures. Herein, an aqueous fluoride ion flow battery is proposed that consists of bismuth fluoride as the anode, 4-hydroxy-TEMPO (TEMPO) as the cathode, and NaF salt solution as the aqueous electrolyte. During the charging process, bismuth fluoride electrochemically releases fluoride ions with the formation of bismuth metal, while TEMPO captures the fluoride ions. A reversible and stable discharge capacity of 89.5 mAh g −1 was achieved at 1000 mA g −1 after 85 cycles. The fluoride ion battery possesses excellent rate performance. To the best of our knowledge, this is the earliest demonstration that fluoride ion batteries can work in aqueous solutions, which can be used for future clean energy applications.

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Biological hydrogen production from anaerobic waste fermentation possesses potential benefits in simultaneously reducing organic wastes and generating sustainable energy sources. Three kinetic-based steady-state models for anaerobic fermentation of multiple substrates, including glucose and peptone, were evaluated. Experimental results obtained from a continuous stirred tank reactor (CSTR) were primarily used for model evaluation. The dual-substrate steady-state model developed and the associated kinetic parameters estimated in this study successfully described the anaerobic growth of hydrogen-producing bacteria. The model was able to capture the general trends of consumption of substrates and accumulation of products, including formate, acetate, butyrate, and hydrogen, at dilution rates (D) between 0.06 and 0.69/h. According to the model, the adverse effects of endogeneous and peptone metabolism on net hydrogen production can be minimized by increasing D. For the operational conditions of D > 0.69/h, however, substantial washout of hydrogen-producing bacteria from the CSTR was observed, and it resulted in a rapid drop in hydrogen production rate as well.