Heterogeneous reactivity of N2O5 on aerosols is a critical parameter in assessing NOx fate, nitrate production, and particulate chloride activation. Accurate measurement of its uptake coefficient (gamma N2O5) and representation in air quality models are challenging, especially in the polluted environment. With an in situ aerosol flow-tube system, the gamma N2O5 was directly measured on ambient aerosols at two rural sites in northern and southern China. The results were analyzed together with the gamma N2O5 derived from previous field studies in China to obtain a holistic picture of gamma N2O5 uptake and the influencing factors under various climatic and chemical conditions. The field-derived or measured gamma N2O5 was generally promoted by the aerosol water content and suppressed by particle nitrate. Significant discrepancies were found between the measured gamma N2O5 and that estimated from laboratory-determined parameterizations. An observation-based empirical parameterization was derived in the present work, which better reproduced the mean value and variability of the observed gamma N2O5. Incorporating this new parameterization into a regional air quality model (WRF-CMAQ) has improved the simulation of N2O5, nitrogen oxides, and secondary nitrate in the polluted regions of China.
Reducing the voltage loss (Vloss) is a critical factor in optimizing the open-circuit voltage (Voc) and overall power-conversion efficiency (PCE) of polymer solar cells. In the current work, by designing a novel electron-accepting unit of coronenediimide (CDI) and using it as the main functional building block, a new polymer acceptor CDI-V is developed and applied to fabricate all-polymer solar cells. Compared with the perylenediimide-based polymer acceptors we previously reported, the current CDI-V polymer possesses a noticeably elevated lowest unoccupied molecular orbital (LUMO). Thereby, by virtue of the enlarged energy gap between the donor HOMO and acceptor LUMO, a high Voc value of 1.05 V is achieved by the all-polymer photovolatic device, along with an impressively low Vloss of 0.55 V. As remarkably, in spite of an extremely small LUMO level offset of 0.01 eV exhibited by the donor and acceptor polymers, effective charge separation still takes place in the all-polymer device, as evidenced by a proper short-circuit current (Jsc) of 9.5 mA·cm2 and a decent PCE of 4.63%.
Two-dimensional (2D) semiconductors hold great promise in flexible electronics because of their intrinsic flexibility and high electrical performance. However, the lack of facile synthetic and subsequent device fabrication approaches of high-mobility 2D semiconducting thin films still hinders their practical applications. Here, we developed a facile, rapid, and scalable solution-assisted method for the synthesis of a high-mobility semiconducting oxyselenide (Bi2O2Se) thin film by the selenization and decomposition of a precursor solution of Bi(NO3)3·5H2O. Simply by changing the rotation speed in spin-coating of the precursor solution, the thicknesses of Bi2O2Se thin films can be precisely controlled down to few atomic layers. The as-synthesized Bi2O2Se thin film exhibited a high Hall mobility of ∼74 cm2 V–1 s–1 at room temperature, which is much superior to other 2D thin-film semiconductors such as transition metal dichalcogenides. Remarkably, flexible top-gated Bi2O2Se transistors showed excellent electrical stability under repeated electrical measurements on flat and bent substrates. Furthermore, Bi2O2Se transistor devices on muscovite substrates can be readily transferred onto flexible polyvinyl chloride (PVC) substrates with the help of thermal release tape. The integration of a high-mobility thin-film semiconductor, excellent stability, and easy transfer onto flexible substrates make Bi2O2Se a competitive candidate for future flexible electronics.
Abstract On-chip electron sources with the advantages of high emission current and density, high emission efficiency, low working voltage, and easy fabrication are highly desired for scaling down free electron-based devices and systems, especially for realizing those on a chip, but remain challenging. Here, such an on-chip electron source is reported simply based on electroformed silicon oxide between concentric graphene films on silicon oxide substrate. It is demonstrated that electron emission from an electron emitter can be driven by a low voltage about 11 V, and a high emission efficiency of 33.6%. An on-chip electron source with 36 × 36 emitter array in an area of 594 × 594 µm2 exhibits an emission current up to 1 mA at 38 V working voltage, corresponding to a high emission density of 283 mA cm−2. Electron emission from the sources is thought to be generated from horizontal tunneling diodes formed in electroformed silicon oxide. Combined advantages of high emission current and density, high emission efficiency, low working voltage, and easy fabrication make this on-chip electron sources promising in realizing miniature and on-chip free electron-based devices and systems.
Abstract An important advancement towards the realization of miniaturized and fully integrated vacuum electronic devices will be the development of on-chip integrated electron sources with stable and reproducible performances. Here, the fabrication of high-performance on-chip thermionic electron micro-emitter arrays is demonstrated by exploiting suspended super-aligned carbon nanotube films as thermionic filaments. For single micro-emitter, an electron emission current up to ≈20 µA and density as high as ≈1.33 A cm−2 are obtained at a low-driven voltage of 3.9 V. The turn-on/off time of a single micro-emitter is measured to be less than 1 µs. Particularly, stable (±1.2% emission current fluctuation for 30 min) and reproducible (±0.2% driven voltage variation over 27 cycles) electron emission have been experimentally observed under a low vacuum of ≈5 × 10−4 Pa. Even under a rough vacuum of ≈10−1 Pa, an impressive reproducibility (±2% driven voltage variation over 20 cycles) is obtained. Moreover, emission performances of micro-emitter arrays are found to exhibit good uniformity. The outstanding stability, reproducibility, and uniformity of the thermionic electron micro-emitter arrays imply their promising applications as on-chip integrated electron sources.
Online platforms provide a public sphere for discussion, debate, and deliberation among citizens. The engagement of online deliberation enables participants to exchange viewpoints and form communities. This paper aims to explore the influencing factors on engagement level of online deliberation by examining the relationship between an initial post’s content features and length and the engagement of the discussion thread it initiates. We sampled 254 discussion threads with 254 initial posts and 2934 following posts and conducted quantitative and qualitative analysis of the posts. Findings show that initial posts which are longer and allocentric (as opposed to egocentric) would evoke longer following posts in a discussion. Different content type (social interaction, claim, argument) of initial posts would lead to significant different engagement, arguments would trigger higher level engagement (average posts per participant and average length of posts in discussions). Whether an initial post holds a clear position has no significant impact on discussion engagement. These findings contribute to a deeper understanding of online deliberation and its engagement and can be useful in promoting engagements in online deliberation.
Hexavalent chromium Cr(VI) is a highly toxic groundwater contaminant. In this study, we demonstrate a selective electrochemical process tailored for removal of Cr(VI) using a hybrid MOF@rGO nanomaterial synthesized by in situ growth of a nanocrystalline, mixed ligand octahedral metal–organic framework with cobalt metal centers, [Co2(btec)(bipy)(DMF)2]n (Co-MOF), on the surface of reduced graphene oxide (rGO). The rGO provides the electric conductivity necessary for an electrode, while the Co-MOF endows highly selective adsorption sites for CrO42–. When used as an anode in the treatment cycles, the MOF@rGO electrode exhibits strong selectivity for adsorption of CrO42– over competing anions including Cl–, SO42–, and As(III) and achieves charge efficiency (CE) >100% due to the strong physisorption of CrO42– by Co-MOF; both electro- and physisorption capacities are regenerated with the reversal of the applied voltage, when highly toxic Cr(VI) is reduced to less toxic reduced Cr species and subsequently released into brine. This approach allows easy regeneration of the nonconducting Co-MOF without any chemical addition while simultaneously transforming Cr(VI), inspiring a novel electrochemical method for highly selective degradation of toxic contaminants using tailor-designed electrodes with high affinity adsorbents.
Interactions between graphene oxide (GO) and cell membranes play a crucial role in the nanotoxicity of GO toward organisms. However, little is known about interactions of GO with lipid membranes in the presence of heavy metals. This study investigated the attachment of GO and adsorption of heavy metals onto simulated cell membranes (spherical supported lipid bilayers, SSLBs) formed by cationic, neutral and anionic lipids, i.e., SSLB(+), SSLB(0) and SSLB(−), using batch experiments, density functional theory (DFT) calculations, and spectroscopic analyses. In the binary systems, the SSLBs bind with GO through hydrogen binding and with heavy metals via complexation. The attachment of GO or adsorption of heavy metals onto SSLBs decreased in the order SSLB(−) > SSLB(0) > SSLB(+), largely controlled by the type and number of functional groups in the SSLBs. Evidence from batch experiments, DFT calculations and spectroscopic analyses confirmed that in the ternary system GO first binds with metals, and then the GO–metal complexes attach to SSLBs via hydrogen bonding through GO rather than cation bridging through metals. Moreover, metal adsorption onto GO strengthens hydrogen bonding by withdrawing electrons from the GO surface. Therefore, in the ternary system, heavy metals promoted the GO attachment to SSLBs. However, GO suppressed the adsorption of heavy metals onto SSLBs by blocking the adsorption sites via steric hindrance. This study highlighted the importance of molecular interactions on assessing the nanotoxicity of GO to cells in the coexistence of heavy metals.
The management of river-lake systems is hindered by limitations in the applicability of existing models that describe the relationship between environmental factors and phytoplankton community characteristics but rarely include common and indirect effects on algae dynamics. In this study, we assumed that the interaction of light, water, temperature, pH, and nutrients, including direct and indirect effects, are the potential factors affecting phytoplankton dynamics. We determined which of these are the main drivers of phytoplankton community structure and production in a river-lake system by using three different models based on the partial least squares structural equation modeling method. Our results indicated that the models achieved more than 60% of the overall explanatory power of various environmental factors on phytoplankton characteristics, including indirect and direct effects. In particular, light, pH, and nutrient content and ratios commonly control phytoplankton dynamic characteristics rather than a single nutrient, but light is the main driving force of phytoplankton community characteristics. Controlling the underwater light conditions, and nitrogen and phosphorus pollution load could effectively regulate algal blooms, increase productivity, promote ecological balance, and reduce water pollution. Our findings provide a scientific and theoretical basis for water resource management and pollution control.