Background Population-based studies have estimated health risks of short-term exposure to fine particles using mass of PM2.5 (particulate matter ≤ 2.5 μm in aerodynamic diameter) as the indicator. Evidence regarding the toxicity of the chemical components of the PM2.5 mixture is limited. Objective In this study we investigated the association between hospital admission for cardiovascular disease (CVD) and respiratory disease and the chemical components of PM2.5 in the United States. Methods We used a national database comprising daily data for 2000–2006 on emergency hospital admissions for cardiovascular and respiratory outcomes, ambient levels of major PM2.5 chemical components [sulfate, nitrate, silicon, elemental carbon (EC), organic carbon matter (OCM), and sodium and ammonium ions], and weather. Using Bayesian hierarchical statistical models, we estimated the associations between daily levels of PM2.5 components and risk of hospital admissions in 119 U.S. urban communities for 12 million Medicare enrollees (≥ 65 years of age). Results In multiple-pollutant models that adjust for the levels of other pollutants, an interquartile range (IQR) increase in EC was associated with a 0.80% [95% posterior interval (PI), 0.34–1.27%] increase in risk of same-day cardiovascular admissions, and an IQR increase in OCM was associated with a 1.01% (95% PI, 0.04–1.98%) increase in risk of respiratory admissions on the same day. Other components were not associated with cardiovascular or respiratory hospital admissions in multiple-pollutant models. Conclusions Ambient levels of EC and OCM, which are generated primarily from vehicle emissions, diesel, and wood burning, were associated with the largest risks of emergency hospitalization across the major chemical constituents of PM2.5.

Emergency Admissions for Cardiovascular and Respiratory Diseases and the Chemical Composition of Fine Particle Air Pollution

Traditional cooling systems consume tremendous amounts of energy and thus aggravate the greenhouse effect1,2. Passive radiative cooling, dissipating an object’s heat through an atmospheric transparency window (8–13 μm) to outer space without any energy consumption, has attracted much attention3–9. The unique feature of radiative cooling lies in the high emissivity in the atmospheric transparency window through which heat can be dissipated to the universe. Therefore, for achieving high cooling performance, the design and fabrication of selective emitters, with emission strongly dominant in the transparency window, is of essential importance, as such spectral selection suppresses parasitic absorption from the surrounding thermal radiation. Recently, various materials and structures with tailored spectrum responses have been investigated to achieve the effect of daytime radiative cooling6–8,10–15. However, most of the radiative cooling materials reported possess broad-band absorption/emission covering the whole mid-infrared wavelength11–15. Here we demonstrate that a hierarchically designed polymer nanofibre-based film, produced by a scalable electrostatic spinning process, enables selective mid-infrared emission, effective sunlight reflection and therefore excellent all-day radiative cooling performance. Specifically, the C–O–C (1,260–1,110 cm−1) and C–OH (1,239–1,030 cm−1) bonding endows the selective emissivity of 78% in 8–13 μm wavelength range, and the design of nanofibres with a controlled diameter allows for a high reflectivity of 96.3% in 0.3–2.5 μm wavelength range. As a result, we observe ~3 °C cooling improvement of this selective thermal emitter as compared to that of a non-selective emitter at night, and 5 °C sub-ambient cooling under sunlight. The impact of this hierarchically designed selective thermal emitter on alleviating global warming and temperature regulating an Earth-like planet is also analysed, with a significant advantage demonstrated. With its excellent cooling performance and a scalable process, this hierarchically designed selective thermal emitter opens a new pathway towards large-scale applications of all-day radiative cooling materials. A hierarchically designed polymer nanofibre-based film produced by a scalable electrospinning process enables selective mid-infrared emission and effective sunlight reflection, and thus realizes an excellent all-day radiative cooling performance.

Scalable and hierarchically designed polymer film as a selective thermal emitter for high-performance all-day radiative cooling.

In mammals, physiological respiration involves respiratory cycles of inhaled and exhaled breaths, which has traditionally been an underutilized resource potentially encompassing a wealth of physiologically relevant information as well as clues to potential diseases. Recently, triboelectric nanogenerators (TENGs) have been widely adopted for self-powered respiration monitoring owing to their compelling features, such as decent biocompatibility, wearing comfort, low-cost, and high sensitivity to respiration activities in the aspect of low frequency and slight amplitude body motions. Physiological respiration behaviors and exhaled chemical regents can be precisely and continuously monitored by TENG-based respiration sensors for personalized health care. This article presents an overview of TENG enabled self-powered respiration monitoring, with a focus on the working principle, sensing materials, functional structures, and related applications in both physical respiration motion detection and chemical breath analysis. Concepts and approaches for acquisition of physical information associated with respiratory rate and depth are covered in the first part. Then the sensing mechanism, theoretical modeling, and applications related to detection of chemicals released from breathing gases are systemically summarized. Finally, the opportunities and challenges of triboelectric effect enabled self-powered respiration monitoring are comprehensively discussed and criticized.

Self‐Powered Respiration Monitoring Enabled By a Triboelectric Nanogenerator

The sliding mode triboelectric nanogenerator (S-TENG) is an effective technology for in-plane low-frequency mechanical energy harvesting. However, as surface modification of tribo-materials and charge excitation strategies are not well applicable for this mode, output performance promotion of S-TENG has no breakthrough recently. Herein, we propose a new strategy by designing shielding layer and alternative blank-tribo-area enabled charge space-accumulation (CSA) for enormously improving the charge density of S-TENG. It is found that the shielding layer prevents the air breakdown on the interface of tribo-layers effectively and the blank-tribo-area with charge dissipation on its surface of tribo-material promotes charge accumulation. The charge space-accumulation mechanism is analyzed theoretically and verified by experiments. The charge density of CSA-S-TENG achieves a 2.3 fold enhancement (1.63 mC m-2) of normal S-TENG in ambient conditions. This work provides a deep understanding of the working mechanism of S-TENG and an effective strategy for promoting its output performance.

Boosting output performance of sliding mode triboelectric nanogenerator by charge space-accumulation effect.

Understanding of the triboelectric charge accumulation from the view of microcapacitor formation plays a critical role in boosting the output performance of the triboelectric nanogenerator (TENG). Here, an electrospun nanofiber-based TENG (EN-TENG) using a poly(vinylidene fluoride-trifluoroethylene) (PVDF-TrFE)/MXene nanocomposite material with superior dielectric constant and high surface charge density is reported. The influence of dielectric properties on the output performance of the EN-TENG is investigated theoretically and experimentally. The fabricated EN-TENG exhibited a maximum power density of 4.02 W/m2 at a matching external load resistance of 4 MΩ. The PVDF-TrFE/MXene nanocomposite improved the output performance of the EN-TENG fourfold. The EN-TENG successfully powered an electronic stopwatch and thermo-hygrometer by harvesting energy from human finger tapping. Moreover, it was utilized in smart home applications as a self-powered switch for controlling electrical home appliances, including fire alarms, fans, and smart doors. This work presents an effective and innovative approach toward self-powered systems, human-machine interfaces, and smart home applications.

Electrospun PVDF-TrFE/MXene Nanofiber Mat-Based Triboelectric Nanogenerator for Smart Home Appliances.

Electrically Activated Ultrathin PVDF‐TrFE Air Filter for High‐Efficiency PM1.0 Filtration

Performance enhancement of triboelectric nanogenerators (TENGs) has been largely limited by the relatively low output current density. Thus, extensive research efforts have been made to increase the output current density. In this respect, this work presents a method to effectively increase output current density of TENGs by adopting polarized ferroelectric polymers and MoS2 composite. Specifically, by compositing bulk MoS2 flakes with both Nylon-11 and PVDF-TrFE, respectively, charge density of each triboelectric charging surface was significantly increased. In addition, proper polarization of both ferroelectric composite layers has also led to an additional increase in the charge density. A combination of them synergistically increases the surface charge density, generating huge output current and the power output density. By optimizing the fabrication process, the output voltage and current density up to ∼145 V and ∼350 μA/cm2 are achieved, respectively. Consequently, the TENG exhibits a recordable output power density of ∼50 mW/cm2, which is one of the highest output power densities reported to date. The method introduced in this work can greatly increase the output current density of TENGs, facilitating the development of high-performance triboelectric energy harvesting devices.

Remarkable Output Power Density Enhancement of Triboelectric Nanogenerators via Polarized Ferroelectric Polymers and Bulk MoS 2 Composites

Ultra-flexible nanofiber-based multifunctional motion sensor

Output power density enhancement of triboelectric nanogenerators via ferroelectric polymer composite interfacial layers

Recently, the inherent piezoelectric properties of the 2D transition-metal dichalcogenides (TMDs) tin monosulfide (SnS) and tin disulfide (SnS2) have attracted much attention. Thus the piezoelectricity of these materials has been theoretically and experimentally investigated for energy-harvesting devices. However, the piezoelectric output performance of the SnS2- or SnS-based 2D thin film piezoelectric nanogenerator (PENG) is still relatively low, and the fabrication process is not suitable for practical applications. Here we report the formation of the SnS2/SnS heterostructure thin film for the enhanced output performance of a PENG using atomic layer deposition (ALD). The piezoelectric response of the heterostructure thin film was increased by ∼40% compared with that of the SnS2 thin film, attributed to large band offset induced by the heterojunction formation. Consequently, the output voltage and current density of the heterostructure PENG were 60 mV and 11.4 nA/cm2 at 0.6% tensile strain, respectively. In addition, thickness-controllable large-area uniform thin-film deposition via ALD ensures that the reproducible output performance is achieved and that the output density can be lithographically adjusted depending on the applications. Therefore, the SnS2/SnS heterostructure PENG fabricated in this work can be employed to develop a flexible energy-harvesting device or an attachable self-powered sensor for monitoring pulse and human body movement.

Minje Kim

Papers

Electrically Activated Ultrathin PVDF‐TrFE Air Filter for High‐Efficiency PM1.0 Filtration

Remarkable Output Power Density Enhancement of Triboelectric Nanogenerators via Polarized Ferroelectric Polymers and Bulk MoS 2 Composites

Ultra-flexible nanofiber-based multifunctional motion sensor

Output power density enhancement of triboelectric nanogenerators via ferroelectric polymer composite interfacial layers

Enhanced Piezoelectric Output Performance of the SnS2/SnS Heterostructure Thin-Film Piezoelectric Nanogenerator Realized by Atomic Layer Deposition.