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Background There is a steadily increasing quantity of silver nanoparticles (AgNP) produced for numerous industrial, medicinal and private purposes, leading to an increased risk of inhalation exposure for both professionals and consumers. Particle inhalation can result in inflammatory and allergic responses, and there are concerns about other negative health effects from either acute or chronic low-dose exposure. Results To study the fate of inhaled AgNP, healthy adult rats were exposed to 1½-hour intra-tracheal inhalations of pristine 105 Ag-radiolabeled, 20 nm AgNP aerosols (with mean doses across all rats of each exposure group of deposited NP-mass and NP-number being 13.5 ± 3.6 μg, 7.9 ± 3.2•10 11 , respectively). At five time-points (0.75 h, 4 h, 24 h, 7d, 28d) post-exposure (p.e.), a complete balance of the [ 105 Ag]AgNP fate and its degradation products were quantified in organs, tissues, carcass, lavage and body fluids, including excretions. Rapid dissolution of [ 105 Ag]Ag-ions from the [ 105 Ag]AgNP surface was apparent together with both fast particulate airway clearance and long-term particulate clearance from the alveolar region to the larynx. The results are compatible with evidence from the literature that the released [ 105 Ag]Ag-ions precipitate rapidly to low-solubility [ 105 Ag]Ag-salts in the ion-rich epithelial lining lung fluid (ELF) and blood. Based on the existing literature, the degradation products rapidly translocate across the air-blood-barrier (ABB) into the blood and are eliminated via the liver and gall-bladder into the small intestine for fecal excretion. The pathway of [ 105 Ag]Ag-salt precipitates was compatible with auxiliary biokinetics studies at 24 h and 7 days after either intravenous injection or intratracheal or oral instillation of [ 110m Ag]AgNO 3 solutions in sentinel groups of rats. However, dissolution of [ 105 Ag]Ag-ions appeared not to be complete after a few hours or days but continued over two weeks p.e. This was due to the additional formation of salt layers on the [ 105 Ag]AgNP surface that mediate and prolonge the dissolution process. The concurrent clearance of persistent cores of [ 105 Ag]AgNP and [ 105 Ag]Ag-salt precipitates results in the elimination of a fraction > 0.8 (per ILD) after one week, each particulate Ag-species accounting for about half of this. After 28 days p.e. the cleared fraction rises marginally to 0.94 while 2/3 of the remaining [ 105 Ag]AgNP are retained in the lungs and 1/3 in secondary organs and tissues with an unknown partition of the Ag species involved. However, making use of our previous biokinetics studies of poorly soluble [ 195 Au]AuNP of the same size and under identical experimental and exposure conditions (Kreyling et al., ACS Nano 2018), the kinetics of the ABB-translocation of [ 105 Ag]Ag-salt precipitates was estimated to reach a fractional maximum of 0.12 at day 3 p.e. and became undetectable 16 days p.e. Hence, persistent cores of [ 105 Ag]AgNP were cleared throughout the study period. Urinary [ 105 Ag]Ag excretion is minimal, finally accumulating to 0.016. Conclusion The biokinetics of inhaled [ 105 Ag]AgNP is relatively complex since the dissolving [ 105 Ag]Ag-ions (a) form salt layers on the [ 105 Ag]AgNP surface which retard dissolution and (b) the [ 105 Ag]Ag-ions released from the [ 105 Ag]AgNP surface form poorly-soluble precipitates of [ 105 Ag]Ag-salts in ELF. Therefore, hardly any [ 105 Ag]Ag-ion clearance occurs from the lungs but instead [ 105 Ag]AgNP and nano-sized precipitated [ 105 Ag]Ag-salt are cleared via the larynx into GIT and, in addition, via blood, liver, gall bladder into GIT with one common excretional pathway via feces out of the body.

Traditionally, precipitates in a material are thought to serve as obstacles to dislocation glide and cause hardening of the material. This conventional wisdom, however, fails to explain recent discoveries of ultrahigh-strength and large-ductility materials with a high density of nanoscale precipitates, as obstacles to dislocation glide often lead to high stress concentration and even microcracks, a cause of progressive strain localization and the origin of the strength–ductility conflict. Here we reveal that nanoprecipitates provide a unique type of sustainable dislocation sources at sufficiently high stress, and that a dense dispersion of nanoprecipitates simultaneously serve as dislocation sources and obstacles, leading to a sustainable and self-hardening deformation mechanism for enhanced ductility and high strength. The condition to achieve sustainable dislocation nucleation from a nanoprecipitate is governed by the lattice mismatch between the precipitate and matrix, with stress comparable to the recently reported high strength in metals with large amount of nanoscale precipitates. It is also shown that the combination of Orowan’s precipitate hardening model and our critical condition for dislocation nucleation at a nanoprecipitate immediately provides a criterion to select precipitate size and spacing in material design. The findings reported here thus may help establish a foundation for strength–ductility optimization through densely dispersed nanoprecipitates in multiple-element alloy systems.

Gating is a fundamental process in ion channels configured to open and close in response to specific stimuli such as voltage across cell membranes thereby enabling the excitability of neurons. Here we report on voltage-gated solid-state nanopores by electrically tunable chemical reactions. We demonstrate repetitive precipitation and dissolution of metal phosphates in a pore through manipulations of cation flow by transmembrane voltage. Under negative voltages, precipitates grow to reduce ionic current by occluding the nanopore, while inverting the voltage polarity dissolves the phosphate compounds reopening the pore to ionic flux. Reversible actuation of these physicochemical processes creates a nanofluidic diode of rectification ratio exceeding 40000. The dynamic nature of the in-pore reactions also facilitates a memristor of sub-nanowatt power consumption. Leveraging chemical degrees of freedom, the present method may be useful for creating iontronic circuits of tunable characteristics toward neuromorphic systems. Ion channels in cell membranes open and close in response to electrical stimuli, playing a critical role in cellular signaling and homeostasis. Here, the authors show a similar gating functionality in solid-state nanopores, achieved through transmembrane voltage control of in-pore chemistry.

Seawater electroreduction is attractive for future H 2 production and intermittent energy storage, which has been hindered by aggressive Mg 2+ /Ca 2+ precipitation at cathodes and consequent poor stability. Here we present a vital microscopic bubble/precipitate traffic system (MBPTS) by constructing honeycomb-type 3D cathodes for robust anti-precipitation seawater reduction (SR), which massively/uniformly release small-sized H 2 bubbles to almost every corner of the cathode to repel Mg 2+ /Ca 2+ precipitates without a break. Noticeably, the optimal cathode with built-in MBPTS not only enables state-of-the-art alkaline SR performance (1000-h stable operation at –1 A cm −2 ) but also is highly specialized in catalytically splitting natural seawater into H 2 with the greatest anti-precipitation ability. Low precipitation amounts after prolonged tests under large current densities reflect genuine efficacy by our MBPTS. Additionally, a flow-type electrolyzer based on our optimal cathode stably functions at industrially-relevant 500 mA cm −2 for 150 h in natural seawater while unwaveringly sustaining near-100% H 2 Faradic efficiency. Note that the estimated price (~1.8 US$/kg H2 ) is even cheaper than the US Department of Energy’s goal price (2 US$/kg H2 ). Seawater electroreduction is a promising technique for producing hydrogen, but it is hindered by cathodic Mg2 + /Ca2+ precipitation. Here, the authors propose a microscopic bubble/precipitate traffic system that releases small-sized bubbles across the cathode to repel Mg2 + /Ca2+ precipitates from almost the entire surface area of the catalyst.

Electrolysis that reduces carbon dioxide (CO 2 ) to useful chemicals can, in principle, contribute to a more sustainable and carbon-neutral future 1 – 6 . However, it remains challenging to develop this into a robust process because efficient conversion typically requires alkaline conditions in which CO 2 precipitates as carbonate, and this limits carbon utilization and the stability of the system 7 – 12 . Strategies such as physical washing, pulsed operation and the use of dipolar membranes can partially alleviate these problems but do not fully resolve them 11 , 13 – 15 . CO 2 electrolysis in acid electrolyte, where carbonate does not form, has therefore been explored as an ultimately more workable solution 16 – 18 . Herein we develop a proton-exchange membrane system that reduces CO 2 to formic acid at a catalyst that is derived from waste lead–acid batteries and in which a lattice carbon activation mechanism contributes. When coupling CO 2 reduction with hydrogen oxidation, formic acid is produced with over 93% Faradaic efficiency. The system is compatible with start-up/shut-down processes, achieves nearly 91% single-pass conversion efficiency for CO 2 at a current density of 600 mA cm −2 and cell voltage of 2.2 V and is shown to operate continuously for more than 5,200 h. We expect that this exceptional performance, enabled by the use of a robust and efficient catalyst, stable three-phase interface and durable membrane, will help advance the development of carbon-neutral technologies. We develop a proton-exchange membrane system that reduces CO 2 to formic acid at a catalyst that is derived from waste lead–acid batteries and in which a lattice carbon activation mechanism contributes.

High-strength aluminum alloys are important for lightweighting vehicles and are extensively used in aircraft and, increasingly, in automobiles. The highest-strength aluminum alloys require a series of high-temperature “bakes” (120° to 200°C) to form a high number density of nanoparticles by solid-state precipitation. We found that a controlled, room-temperature cyclic deformation is sufficient to continuously inject vacancies into the material and to mediate the dynamic precipitation of a very fine (1- to 2-nanometer) distribution of solute clusters. This results in better material strength and elongation properties relative to traditional thermal treatments, despite a much shorter processing time. The microstructures formed are much more uniform than those characteristic of traditional thermal treatments and do not exhibit precipitate-free zones. These alloys are therefore likely to be more resistant to damage.

Precipitation-hardening high-entropy alloys (PH-HEAs) with good strength−ductility balances are a promising candidate for advanced structural applications. However, current HEAs emphasize near-equiatomic initial compositions, which limit the increase of intermetallic precipitates that are closely related to the alloy strength. Here we present a strategy to design ultrastrong HEAs with high-content nanoprecipitates by phase separation, which can generate a near-equiatomic matrix in situ while forming strengthening phases, producing a PH-HEA regardless of the initial atomic ratio. Accordingly, we develop a non-equiatomic alloy that utilizes spinodal decomposition to create a low-misfit coherent nanostructure combining a near-equiatomic disordered face-centered-cubic (FCC) matrix with high-content ductile Ni 3 Al-type ordered nanoprecipitates. We find that this spinodal order–disorder nanostructure contributes to a strength increase of ~1.5 GPa (>560%) relative to the HEA without precipitation, achieving one of the highest tensile strength (1.9 GPa) among all bulk HEAs reported previously while retaining good ductility (>9%). High entropy alloys usually emphasize equiatomic compositions, which restrict the compositions available to induce strengthening via precipitation. Here the authors use spinodal decomposition in a five-element alloy to obtain high content nanophases and the highest tensile strength reported to date.

Additively manufactured metallic materials exhibit excellent mechanical strength. However, they often fail prematurely owing to external defects (pores and unmelted particles) that act as sites for crack initiation. Cracks then propagate through grain boundaries and/or cellular boundaries that contain continuous brittle second phases. In this work, the premature failure mechanisms in selective laser melted (SLM) materials were studied. A submicron structure was introduced in a SLM Ag–Cu–Ge alloy that showed semicoherent precipitates distributed in a discontinuous but periodic fashion along the cellular boundaries. This structure led to a remarkable strength of 410 ± 3 MPa with 16 ± 0.5% uniform elongation, well surpassing the strength-ductility combination of their cast and annealed counterparts. The hierarchical SLM microstructure with a periodic arrangement of precipitates and a high density of internal defects led to a high strain hardening rate and strong strengthening, as evidenced by the fact that the precipitates were twinned and encircled by a high density of internal defects, such as dislocations, stacking faults and twins. However, the samples fractured before necking owing to the crack acceleration along the external defects. This work provides an approach for additively manufacturing materials with an ultrahigh strength combined with a high ductility provided that premature failure is alleviated.Additive manufacturing: 3D-printed alloys find their hidden strengthAn analysis of metallic alloys fabricated through layer-by-layer deposition processes has revealed critical factors in preventing these materials from unexpectedly breaking. In selective laser melting (SLM) technology, thin layers of metal powders are assembled into three-dimensional objects using rapid heating and cooling steps. Zhi Wang from the South China University of Technology in Guangzhou and colleagues now show that the microstructure of a silver-copper-germanium alloy formed through SLM can affect the material’s strength. Using optical and X-ray microscopy, the team found that regularly spaced precipitates formed inside the 3D-printed alloy prevented abrupt atomic sliding movements, giving the material a higher natural strength and good ductility. Fractures that occurred at lower than expected stress levels were identified as arising from errors in the printing process, such as pores and unmelted powder particles.

Hydrogen embrittlement of high-strength steel is an obstacle for using these steels in sustainable energy production. Hydrogen embrittlement involves hydrogen-defect interactions at multiple-length scales. However, the challenge of measuring the precise location of hydrogen atoms limits our understanding. Thermal desorption spectroscopy can identify hydrogen retention or trapping, but data cannot be easily linked to the relative contributions of different microstructural features. We used cryo-transfer atom probe tomography to observe hydrogen at specific microstructural features in steels. Direct observation of hydrogen at carbon-rich dislocations and grain boundaries provides validation for embrittlement models. Hydrogen observed at an incoherent interface between niobium carbides and the surrounding steel provides direct evidence that these incoherent boundaries can act as trapping sites. This information is vital for designing embrittlement-resistant steels.

Cells harvest energy from ionic gradients by selective ion transport across membranes, and the same principle is recently being used for osmotic power generation from salinity gradients at ocean-river interfaces. Common to these ionic gradient conversions is that they require intricate nanoscale structures. Here, we show that natural submarine serpentinite-hosted hydrothermal vent (HV) precipitates are capable of converting ionic gradients into electrochemical energy by selective transport of Na + , K + , H + , and Cl - . Layered hydroxide nanocrystals are aligned radially outwards from the HV fluid channels, constituting confined nanopores that span millimeters in the HV wall. The nanopores change the surface charge depending on adsorbed ions, allowing the mineral to function as a cation- and anion-selective ion transport membrane. Our findings indicate that chemical disequilibria originating from flow and concentration gradients in geologic environments generate confined nanospaces which enable the spontaneous establishment of osmotic energy conversion. Nakamura and colleagues show selective ion transport through mineral nanochannels in submarine hydrothermal vent (HV) precipitates, enabling HVs to convert ionic gradients into electrochemical energy, similar to cellular systems