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.
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.
Carboxymethyl cellulose stabilized iron sulfide (CMC-FeS) nanoparticles have been shown promising for reductive immobilization of U(VI) in water and soil. This work aimed to fill some critical knowledge gaps on the effects of the stabilizer and water chemistry, reaction mechanisms, and long-term stability of stabilized uranium. The optimal CMC-to-FeS molar ratio was determined to be 0.0010. CMC-FeS performed effectively over pH 6.0–9.0, with the best removal being at pH 7.0 and 8.0. The retarded first-order model adequately interpreted the kinetic data, representing a mechanistically sounder model for heterogeneous reactants of decaying reactivity. The presence of Ca2+ (1 mM) or bicarbonate (1 mM) lowered the initial rate constant by a factor of 1.6 and 9.5, respectively, while 1 mM of Na+ showed negligible effect. Humic acid at 1.0 mg/L (as total organic carbon) doubled the removal rate, but inhibited the removal at elevated concentrations (≥5.0 mg/L). Fourier transform infrared spectroscopy, X-ray diffractometer, X-ray photoelectron spectroscopy, and extraction studies indicated that reductive conversion of UO22+ to UO2(s) was the primary reaction mechanism, accounting for 90% of U removal at pH 7.0. S2− and S22− were the primary electron sources, whereas sorbed and structural Fe(II) acted as supplementary electron donors. The immobilized U remained stable under anoxic conditions after 180 days of aging, while 26% immobilized U was remobilized when exposed to air for 180 days. The long-term stability is attributed to the protective reduction potential of CMC-FeS, the formation of uraninite and associated structural resistance to oxidation, and the high affinity of FeS oxidation products toward U(VI).