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Squalene can react with indoor ozone to generate a series of volatile and semi-volatile organic compounds, some of which may be skin or respiratory irritants, causing adverse health effects. Better understanding of the ozone/squalene reaction and product transport characteristics is thus important. In this study, we developed a physical–chemical coupling model to describe the behavior of ozone/squalene reaction products, that is, 6-methyl-5-hepten-2-one (6-MHO) and 4-oxopentanal (4-OPA) in the gas phase and skin, by considering the chemical reaction and physical transport processes (external convection, internal diffusion, and surface uptake). Experiments without intervention were performed in a single-family house in California utilizing time- and space-resolved measurements. The key parameters in the model were extracted from 5 day data and then used to predict the behaviors in some other days. Predictions from the present model can reproduce the concentration profiles of the three compounds (ozone, 6-MHO, and 4-OPA) well (R2= 0.82–0.89), indicating high accuracy of the model. Exposure analysis shows that the total amount of 6-MHO and 4-OPA entering the blood capillaries in 4 days can reach 14.6 and 30.1 μg, respectively. The contribution of different sinks to ozone removal in the tested realistic indoor environment was also analyzed.

Volatile organic chemicals are produced from reactions of ozone with squalene in human skin oil. Both primary and secondary reaction products, i.e., 6-methyl-5-hepten-2-one (6-MHO) and 4-oxopentanal (4-OPA), have been reported in indoor occupied spaces. However, the abundance of these products indoors is a function of many variables, including the amount of ozone and occupants present as well as indoor removal processes. In this study, we develop a time-dependent kinetic model describing the behavior of ozone/squalene reaction products indoors, including the reaction process and physical adsorption process of products on indoor surfaces. The key parameters in the model were obtained by fitting time-resolved concentrations of 6-MHO, 4-OPA, and ozone in a university classroom on 1 day with multiple class sessions. The model predictions were subsequently tested against observations from four additional measurement days in the same classroom. Model predictions and experimental data agreed well (R2= 0.87–0.92) for all test days, including ∼7 class sessions covering a range of occupants (10–70) and ozone concentrations (0.09–32 ppb), demonstrating the effectiveness of the model. Accounting for surface uptake of 6-MHO and 4-OPA significantly improved model predictions (R2= 0.52–0.76 without surface uptake), reflecting the importance of including surface interactions to quantitatively represent product behavior in indoor environments.

Characterization of indoor emissions of cyclic volatile methylsiloxanes (cVMS) due to the use of personal care products is important for elucidating indoor air composition and associated health risks. This manuscript describes a mass transfer model to characterize the emission behaviors of decamethylcyclopentasiloxane (D5, the most abundant indoor cVMS) from skin lipids. A C-history method is introduced to determine the key parameters in the model, i.e., the initial concentration and diffusion coefficient of D5 inside the skin lipids. Experiments were conducted in a university classroom to examine the D5 emission behaviors by using a proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF-MS). Data from the first class session of two typical days was applied to obtain the key parameters, which were subsequently used for predicting D5 concentrations in other class sessions. Good agreement between model predictions and experiments demonstrates the effectiveness of the model and parameter determination method. With the model, we found that the reuse of personal care products has a significant impact on the D5 emissions. In addition, the time-dependent emission rate and remaining amount of D5 inside the skin can also be calculated. These results indicate a fast decay pattern during the initial emission period, which is consistent with prior experimental studies.

Settled dust is an important medium for semivolatile organic compound (SVOC) transport indoors. Understanding the mechanism of interaction between SVOCs and settled dust can greatly improve the exposure assessment. This study develops an analytical model to elucidate the mechanism of direct contact between SVOC sources and settled dust. The model incorporates the adsorption of SVOCs onto indoor surfaces, which was ignored in previous numerical models. Based on this model, a hybrid optimization method is applied to determine the key parameters of SVOC transport, i.e., the diffusion coefficient in the dust, the dust–air partition coefficient, and the chamber surface–air partition coefficient. Experiments of direct contact between SVOC source materials containing organophosphorus flame retardants (OPFRs) and settled dust were conducted in chambers. The key parameters were determined by performing curve fitting using data collected from the OPFR chamber tests and from the literature on phthalates. The reliability and robustness of the model and measurement method are demonstrated by the high fitting accuracy and sensitivity analysis. The obtained key parameters are more accurate than those from correlations in prior studies. Further analysis indicates that dust–air partition coefficient plays an important role and the adsorption effect on surfaces cannot be neglected for SVOC transport.

Rechargeable zinc-air batteries are promising candidates for energy storage due to their high energy density, environmentally friendliness, and low cost. However, such batteries are limited by the high cost and sluggish kinetics of noble metal catalysts. Here, we present a highly active bifunctional catalyst of Mn–Co–Fe–N/S@CNT, where the catalyst is synthesized by Mn, Co, and Fe oxides doped with N and S on porous carbon nanotubes. Mn–Co–Fe–N/S@CNT has higher electrocatalytic activity than the commercial catalysts of Pt/C and RuO2, demonstrating that the half-wave potential of the oxygen reduction reaction (ORR) of Mn–Co–Fe–N/S@CNT is 0.807 V (0.9 V with Pt/C), the initial potential is 0.85 V (0.789 V with Pt/C), the limiting current is 5.66 mA cm−2at 0.2 V (5.69 mA cm−2with Pt/C), and oxygen evolution reaction overpotential of Mn–Co–Fe–N/S@CNT is 0.386 V at 10 mA cm−2(0.371 V with RuO2). Moreover, a rechargeable zinc-air battery using Mn–Co–Fe–N/S@CNT outputs a discharging voltage of 1.2 V and a stable cycle life of over 150 h at 10 mA cm−2.

Zinc-air batteries would be a promising candidate for energy conversion and storage because of their dense energy and effective cost. The metal nickel is extensively used for current collection and framework support of the air electrode in consideration of its outstanding anticorrosion property and conductivity. However, the reaction of zinc and nickel in zinc-air batteries has not been reported. Here, we show a novel zinc-air battery with a reverse structure of the air electrode based on Zn–Ni reaction, where nickel foam of the air electrode is oriented toward the zinc electrode, protecting the catalytic layer of the air electrode from impurity coverage and inhibiting dendrite growth. A zinc-air primary battery with the reverse air electrode exhibits a stable discharging ability of >1000 h around 1.4 V, achieving a capacity of 0.73 A h gZn−1and a specific energy of 874 W h kgZn−1. Moreover, a zinc-air secondary battery with the reverse air electrode obtains more than 700 h cycles at the current density of 10 mA/cm−1without battery failure.

Flexible zinc-air batteries attract more attention due to their high energy density, safety, environmental protection and low cost. However, the traditional aqueous electrolyte has the disadvantages of leakage and water evaporation, which cannot meet application demand of flexible zinc-air batteries. Hydrogels possessing good conductivity and mechanical properties become a candidate as the electrolytes of flexible zinc-air batteries. In this work, advances in aspects of conductivity, mechanical toughness, environmental adaptability and interfacial compatibility of hydrogel electrolytes for flexible zinc-air batteries are investigated. First, the additives to improve conductivity of hydrogel electrolytes are summarized. Second, the measures to enhance the mechanical properties of hydrogels are taken by way of structure optimization and composition modification. Third, the environmental adaptability of hydrogel electrolytes is listed in terms of temperature, humidity and air composition. Fourth, the compatibility of electrolyte-electrode interface is discussed from physical properties of hydrogels. Finally, the prospect for development and application of hydrogels is put forward.