Local Redistribution Research Articles

Built-in electric field drives n-n heterojunction toward enhanced electrochemical freshwater and seawater oxidation

Optimizing the electron cloud density on the catalyst surface is the key to achieving fast kinetics for oxygen evolution reaction (OER). Here, a n-n Fe2P/NiCoP core/shell with strong built-in electric field (BEF) is successfully constructed to enable efficient local charge redistribution at heterointerface and contribute to extraordinary OER performance. Remarkably, the optimized Fe2P/NiCoP catalyst only requires the overpotentials of 272 and 291 mV to achieve a current density of 10 mA·cm−2 in 1 M KOH and alkaline seawater solutions, along with superb electrochemical stability over 140 h and 120 h, respectively. Detailed experimental and theoretical studies demonstrate that the well-designed BEF at the heterointerface of Fe2P/NiCoP n-n heterojunction can accelerate the charge transfer and enhance the conductivity. In addition, the self-propelled electron transfer across the n-n interface can prompt localized charge redistribution at the interface region, leading to enhanced adsorption of OH– and thus significantly boosting the kinetics of OER. This research paves a new avenue for the fabrication of heterostructured catalysts with BEF and optimized interfacial electron cloud for the enhanced OER.

Surface Hydroxyl and Oxygen Vacancies Engineering in ZnSnAl LDH: Synergistic Promotion of Photocatalytic Oxidation of Aromatic VOCs.

Photocatalytic oxidation has gained great interest in environmental remediation, but it is still limited by its low efficiency and catalytic deactivation in the degradation of aromatic VOCs. In this study, we concurrently regulated the surface hydroxyl and oxygen vacancies by introducing Al into ZnSn layered double hydroxide (LDH). The presence of distorted Al species induced local charge redistribution, leading to the remarkable formation of oxygen vacancies. These oxygen vacancies subsequently increased the amount of surface hydroxyl and elongated its bond length. The synergistic effects of surface hydroxyl and oxygen vacancies greatly enhanced reactant adsorption-activation and facilitated charge transfer to generate •OH, •O2-, and 1O2, resulting in highly efficient oxidation and ring-opening of various aromatic VOCs. Compared with commercial TiO2, the optimized ZnSnAl-50 catalyst exhibited about 2-fold activity for the toluene and styrene degradation and 10-fold activity for the chlorobenzene degradation. Moreover, ZnSnAl-50 demonstrated exceptional stability in the photocatalytic oxidation of toluene under a wide humidity range of 0-75%. This work marvelously improves the photocatalytic efficiency, stability, and adaptability through a novel strategy of surface hydroxyl and oxygen vacancies engineering.

Topologically Engineered Strain Redistribution in Elastomeric Substrates for Dually Tunable Anisotropic Plasmomechanical Responses.

The prompt visual response is considered to be a highly intuitive tenet among sensors. Therefore, plasmomechanical strain sensors, which exhibit dynamic structural color changes, have recently been developed by using mechanical stimulus-based elastomeric substrates for wearable sensors. However, the reported plasmomechanical strain sensors either lack directional sensitivity or require complex signal processing and device design strategies to ensure anisotropic optical responses. To the best of our knowledge, there have been no reports on utilizing anisotropic mechanical substrates to obtain directional optical responses. Herein, we propose an anisotropic plasmomechanical sensor to distinguish between the applied force direction and the force magnitude. We employ a simple strain-engineered topological elastomer to mechanically transform closely packed metallic nanoparticles (NPs) into anisotropic directional rearrangements depending on the applied force direction. The proposed structure consists of a heterogeneous-modulus elastomer that exhibits a highly direction-dependent Poisson effect owing to the periodically line-patterned local strain redistribution occurring due to the same magnitude of applied external force. Consequently, the reorientation of the self-assembled gold (Au)-NP array manifests dual anisotropy, i.e., force- and polarization-direction-dependent plasmonic coupling. The cost-effectiveness and simple design of our proposed heterogeneous-modulus platform pave the way for numerous optical applications based on dynamic transformation and topological inhomogeneities.

Quantifying cracking and strain localisation in a cold spray chromium coating on a zirconium alloy substrate under tensile loading at room temperature

The mechanical and cracking behaviour of a Cr coating, deposited on an Optimized ZIRLOTM substrate using the Cold Spraying (CS) technique, was investigated by in-situ scanning electron microscopy (SEM) tensile testing at room temperature. To achieve this, curved micro-tensile samples were machined from cladding tubes, and a styrene-assisted gold remodelled pattern was applied on the coating surface. The macroscopic crack density of the coating with applied axial strain was quantified through automated SEM image processing, whilst the localisation of strain was monitored with High Resolution Digital Image Correlation (HRDIC). Like with most brittle thin films deposited on ductile substrates, under applied external stress, parallel crack channelling appeared on the coating surface, perpendicular to the loading direction. The first crack was captured at 0.5% axial strain, whilst saturation was observed at 1.5%. Single crack formation in the coating was found to cause relaxation of local strains and redistribution towards the uncracked segment's midpoint. The local fracture strain of the coating was found to increase with the decreasing crack spacing, whilst shear bands appeared on the coating's surface at 35° and 145° with respect to the loading direction, which is evidence of plastic deformation. The crack density of the curved sample geometry was correlated with the tubes using a modified shear-lag model, considering the residual stresses in the coating measured by X-ray Diffraction (XRD). The CS Cr coating showed high levels of bonding and mechanical interlocking with the substrate, even after 3% axial strain.

Anchoring CoTiO3/TiO2 heterostructure on fiber network actuates flow-through Fenton-like oxidation: Electronic modulation and rapid pollutants degradation

Versatile catalytic oxidation filtration system, especially under low operating pressure conditions, is a frontier technology for organic wastewater purification. Herein, CoTiO3/TiO2 heterostructure was anchored on fiber network (CTO/TOF) to actuate flow-through peroxymonosulfate (PMS) based oxidation toward organics removal. The well-developed built-in electric field in CoTiO3/TiO2 heterostructure induced local charge redistribution, and promoted the targeted adsorption and activation of PMS, thereby facilitating the activation process. Meanwhile, the 3D network of CTO/TOF fully exposes active sites, providing an ideal platform for mass transfer and surface reactions. Above 91% for nimesulide degradation was maintained after 24 h of catalytic permeation under high permeate flux (300.7 L/m2·h), corresponding to ultrafast retention time (4.9 s). Practical application experiments demonstrated that CTO/TOF+PMS system had strong anti-interference capability under diverse conditions. Synergy of radical-nonradical mixed pathways for pollutant removal was verified by electron paramagnetic resonance spectra, quenching tests, and electrochemical measurements. The degradation intermediates and possible degradation pathways of nimesulide were also proposed. The toxicity assessments confirmed decreased toxicity of degradation products. This study is dedicated to designing high-performance filters and broadening Fenton-like oxidation in environmental remediation.

Plugging the Tax Leak: An Analysis of North Carolina’s Local Sales Tax Redistribution Policy

Amid rising concerns over the urban-rural divide, taxation equity, revenue generation, and local tax leakage, several states are contemplating measures to support jurisdictions perceived as bearing the brunt of evolving economic landscapes. In 2015, North Carolina introduced a system for local sales tax revenue sharing, wherein each county contributed to a pool of local sales tax revenue, subsequently redistributed among 79 of the 100 counties. This policy aimed to address tax leakage by ensuring that half of the base local sales tax remained at the point of sale, with the other half distributed on a per capita basis. In this analysis, we evaluate the policy’s effectiveness in achieving this equilibrium and identify limitations and shortcomings.

The role of SO42− in manipulating partial charge distribution to boost alkaline water oxidation in Co9S8/C–Ni(OH)2

Transition metal sulfides (TM sulfides) has long been regarded as highly promising materials for catalyzing oxygen evolution reaction (OER). The function of TM sulfides in OER occurs on TM oxyhydroxide and SO42−, which are formed through surface reconstruction under certain potentials. It is worth noting that the impact of SO42− on the local charge distribution among atoms, a crucial determinant of OER performance, has been insufficiently studied. This study aims to investigate the role of SO42− in mediating the partial redistribution of charges among Co, Ni and O atoms on a precatalyst Co9S8/C–Ni(OH)2 electrode. The electrode undergoes self-reconstruction to form a CoOOH/SO42−/NiOOH structure on its surface that is active for the OER. The results demonstrate that SO42− facilitates the local charge redistribution of active atoms, leading to optimized adsorption energy of OER intermediates and increased redox center of the material. Furthermore, SO42− serves as an electron mediator in the OER process under varying applied voltages. Consequently, CoOOH/SO42−/NiOOH achieves a Tafel slope of 56 mV dec−1, an overpotential of 250 mV, and maintains a high stability for over 100 h at a current density of 20 mA cm−2. Overall, this research provides valuable insights into catalytic reaction mechanisms and the design of efficient composite catalysts.

Robustness of complex networks under cost-constrained cascaded attack strategies

The robustness of complex networks to various kinds of attacks that could trigger cascading failures has attracted increasing attention. Most existing studies fail to consider that the cost to attack each network component (node or edge) may be unequal. Therefore, in this paper, we explore the network robustness to cascaded attacks based on heterogeneous costs. We introduce an attack cost model with both cost-sensitive and budget-constraint parameters. On this basis, three attack strategies are considered, including hub strategy, average degree strategy, and leaf strategy. Their cascaded attack effects are compared by considering the load local preferential redistribution rule. Both the fraction of failed nodes and the value of a new robustness metric, i.e. the budget-constraint threshold, are monitored in different complex networks. Numerical experiments indicate that as the attack cost changes from homogeneity to heterogeneity, the performance of the classic hub strategy decreases gradually. For the situation of weak heterogeneity of attack cost of each node, leaf strategy achieves the maximum attack performance gradually. Moreover, the budget, network structure, and robustness metrics may all affect the selection of the optimal attack strategy.

Molecular sensitised probe for amino acid recognition within peptide sequences

The combination of low-temperature scanning tunnelling microscopy with a mass-selective electro-spray ion-beam deposition established the investigation of large biomolecules at nanometer and sub-nanometer scale. Due to complex architecture and conformational freedom, however, the chemical identification of building blocks of these biopolymers often relies on the presence of markers, extensive simulations, or is not possible at all. Here, we present a molecular probe-sensitisation approach addressing the identification of a specific amino acid within different peptides. A selective intermolecular interaction between the sensitiser attached at the tip-apex and the target amino acid on the surface induces an enhanced tunnelling conductance of one specific spectral feature, which can be mapped in spectroscopic imaging. Density functional theory calculations suggest a mechanism that relies on conformational changes of the sensitiser that are accompanied by local charge redistributions in the tunnelling junction, which, in turn, lower the tunnelling barrier at that specific part of the peptide.

Nonuniversal impact of cholesterol on membranes mobility, curvature sensing and elasticity

Biological membranes, composed mainly of phospholipids and cholesterol, play a vital role as cellular barriers. They undergo localized reshaping in response to environmental cues and protein interactions, with the energetics of deformations crucial for exerting biological functions. This study investigates the non-universal role of cholesterol on the structure and elasticity of saturated and unsaturated lipid membranes. Our study uncovers a highly cooperative relationship between thermal membrane bending and local cholesterol redistribution, with cholesterol showing a strong preference for the compressed membrane leaflet. Remarkably, in unsaturated membranes, increased cholesterol mobility enhances cooperativity, resulting in membrane softening despite membrane thickening and lipid compression caused by cholesterol. These findings elucidate the intricate interplay between thermodynamic forces and local molecular interactions that govern collective properties of membranes.

Engineering Phase to Reinforce Dielectric Polarization in Nickel Sulfide Heterostructure for Electromagnetic Wave Absorption.

Engineering phase transition in micro-nanomaterials to optimize the dielectric properties and further enhance the electromagnetic microwave absorption (EMA) performance is highly desirable. However, the severe synthesis conditions restrict the design of EMA materials featuring controllable phases, which hinders the tunability of effective absorption bandwidth (EAB) and leads to an unclear loss mechanism. Herein, a seed phase decomposition-controlled strategy is proposed to induct nickel sulfide (NiSx) absorbers with controllable phases and hollow sphere nature. Transmission electron microscopy holography and theoretical calculations evidence that the reconstruction of atoms in phase transition induces numerous heterogeneous interfaces and lattice defects/sulfur vacancies to cause varied work functions and local electronic redistribution, which contributes to reinforced dielectric polarization. As a result, the optimized NiS2/NiS heterostructure enables enhanced EM attenuation capability with a wide EAB of 5.04GHz at only 1.6mm, compared to that of NiS2 and NiS. Moreover, the correlation between EAB and NiS phase content is demonstrated as the "volcano" feature. This study on the concept of phase transition of micro-nanomaterials can offer a novel approach to constructing highly efficient absorbers for EMA and other functionalities.

Turbulent boundary layer flow over a three-dimensional sinusoidal surface

The sinusoidal roughness effect is investigated using a direct numerical simulation (DNS) of a spatially developing turbulent boundary layer (TBL) over three-dimensional sinusoidal roughness. The validity of Townsend's outer-layer similarity hypothesis is assessed based on comparisons of mean and second-order flow statistics, with a DNS of smooth-wall TBL data set at a similar Reynolds number. The total, Reynolds and dispersive stress tensors are calculated using the double-averaging procedure. The mean and second-order statistical similarities in the outer layer between rough-wall and smooth-wall TBLs are generally observed. The transport between total, turbulent and dispersive kinetic energy is investigated utilising triple-decomposed kinetic energy transports equations. The transport behaviour of turbulent kinetic energy (TKE) is significantly affected by the local mean shear induced by the surface roughness. However, the TKE transport shows good collapse with the smooth-wall case in the outer region of the flow. On the other hand, the transport of dispersive kinetic energy, including local production, redistribution and dissipation, are confined within the roughness sublayer. The intercomponent transfer between TKE and dispersive kinetic energy is quantified from the triple-decomposed kinetic energy transport equations. The intercomponent energy transfer is associated with the local spatial gradients of the turbulent momentum fluxes generated near the roughness canopy.

3D Hydrophilic Nickel Foam Supported NiF3-NiF2 Catalyst for Alkaline Hydrogen Evolution Reaction

Alkaline water electrolysis is a low-cost method for large-scale and sustainable hydrogen production. However, slow kinetics of water dissociation in alkaline electrolyte limits the long-term stability and high-activity of the catalyst for hydrogen evolution reaction (HER). In this work, non-noble metal based HER catalyst NiF3-NiF2/HNF (hydrophilic nickel foam), synthesized by electrodeposition and fluorination on nickel foam (NF), shows an excellent control over both the factors. The catalyst exhibits the 3D porous structure, in which super-hydrophilicity caused by HNF and local charge redistribution by the interaction between NiF2 and NiF3, makes the catalyst to present relatively a good performance for HER. An overpotential of only 50 mV and 177 mV is required to achieve a current density of 10 mA cm−2 and 100 mA cm−2, respectively. Under chronoamperometric test, current density of 10 mA cm−2 remains constant for 48 h, revealing the long-term stability of catalyst. Overall, this work gives a new paradigm in the design of high-performance non-noble metal based catalyst for HER in alkaline electrolyte.

Graphite-N modified single Fe atom sites embedded in hollow leaf-like nanosheets as air electrodes for liquid and flexible solid-state Zn-air batteries

The oxygen reduction procedure requires the development of an extremely effective, easily fabricated, and non-noble metal electrocatalyst. In this paper, we offer an unique method for manufacturing a defect-rich Fe single-atom catalyst loaded on the N-doped porous carbon nanosheets carrier (Fe-N4@NC-PCSs) by in-situ pyrolysis of a double-layered leaf-like compound (ZIF-L@PDA-FePhen) using dopamine hydrochloride aided precursor ZIF-L. The Fe-N4@NC-PCSs catalyst exhibits exceptional oxygen reduction reaction (ORR) activity across the pH-universal range, particularly in alkaline electrolytes, with a prominent half-wave potential of 0.938 V, outperforming practically previously described non-noble electrocatalysts as well as the commercial Pt/C catalyst (0.84 V). At pH-universal, the Fe-N4@NC-PCSs catalyst exhibits exceptional half-wave potential and an impressive electron/proton transfer ability resulting from its rich iron nitrogen active sites and a significant number of metal defects. Furthermore, the liquid zinc-air battery, as well as the flexible solid-state battery based on Fe-N4@NC-PCSs work excellently, with open circuit voltage of 1.465 V, maximum peak power density of 207 mV cm−2, and good charge–discharge endurance and mechanical flexibility. Calculations using density functional theory show that graphitic nitrogen can improve the local electronic redistribution for active sites and give them a lower free-energy barrier to ORR. This work serves as motivation for the creation of nitrogen moiety regulation extremely reactive atomic metal catalysts.

Strategies to remove hydrological effects in continuous gravity time series

Multi-annual gravity time series offer a unique, noninvasive way to monitor mass redistributions within the Earth. However, for non-hydrological purposes, gravity time series must be corrected from hydrological effects to properly quantify mass redistribution involved in other geodynamic processes, such as volcanic activities or sedimentation processes. Such a hydrological correction remains challenging. The objective of this work is to investigate various ways to remove hydrological effects from a 11-years long gravity time series acquired by a superconducting gravimeter (SG) located at the Onsala Space Observatory (Sweden). For that we use hydrological loading corrections distributed by the EOST loading service, and local in situ groundwater level measurements. The most efficient approaches correct up to 89% of the seasonal component of the hydrological signal in the gravity series. On the other hand, for that specific site, we observe local water redistributions at shorter time scales, hours to few days, have a negligible influence on the gravity time series.

Ni–Fe–P/Fe–Si electrocatalysts on iron sheets: Regulating surface structure to amorphous heterojunction for excellent oxygen evolution reaction

Nickel iron bimetallic phosphide alloys are a promising electrocatalyst for oxygen evolution reaction (OER). In this work, a highly active Ni–Fe–P/Fe–Si heterojunction electrocatalyst for OER has been synthesized by one-step electrodeposition on iron plate. The synergism effect of Ni–Fe–P alloy and Fe–Si alloy particles after dealloying treatment promotes the construction of nanoflower-like heterogeneous structure with rich lattice defects and exposes a highly open multi-stage nanostructure surface. Furthermore, Si induced the localized electron redistribution optimizes catalytic performance by accelerating electron transfer. The optimal Ni–Fe–P/Fe–Si OER catalyst requires a much low overpotential of 209 mV at a current density of 10 mA cm−2, and 270 mV at a current density of 200 mA cm−2. The prepared Ni–Fe–P/Fe–Si electrode can maintain a current density of 10 mA cm−2 within 24 h, which shows significant electrochemical stability. This study provides a new prospect for the preparation of cost-effective heterogeneous catalysts.

Target-prepared sludge biochar-derived synergistic Mn and N/O induces high-performance periodate activation for reactive iodine radicals generation towards ofloxacin degradation

Converting waste activated sludge into catalysts for the removal of antibiotics in water fulfils the dual purpose of waste-to-resource and hazardous pollution elimination. In this study, sludge-derived biochar (SDB) for efficient periodate (PI) activation was first prepared via one-step pyrolysis of potassium permanganate-polyhexamethylenebiguanide conditioned sludge without additional modification. The SDB (750 °C)-PI system degraded 100% ofloxacin (OFL, 41.5 μM) within 6 min and was almost undisturbed by inorganic ions or humic acids. The experimental results confirmed that the predominant role of reactive iodine species (RIS) and the auxiliary involvement of singlet oxygen (1O2) jointly contributed to the OFL degradation. Theoretical calculations further indicated that the synergy between Mn and N/O induced local charge redistribution and improved electron transfer capability of SDB, leading to the formation of electron-rich Mn sites and enhanced Mn(II)↔Mn(III)↔Mn(IV) redox to promote PI activation. More importantly, the enhanced adsorption and charge transfer of PI on the Mn site of the Mn-N/O-C structures induced the I-O bond stretching and the rapid generation of RIS. This study offered a cost-effective strategy for developing SDB-based catalysts, further advancing the comprehension of sludge management and the intricate mechanisms underlying RIS formation in PI-advanced oxidation processes.

Role of Horizontal Heat Advection in Arctic Surface Warming During Early Spring

AbstractReanalysis data and numerical model are employed to uncover the mechanisms of spring (March–April) Arctic surface warming. Different from other seasons, little additional solar radiation absorption or seasonal heat storage release contributes to Arctic surface warming in spring. Both observation and numerical results suggest that horizontal heat advection dominates Arctic surface air warming. However, horizontal advection originates from lower latitudes instead of local energy redistribution as in other seasons. Furthermore, Arctic warming weakens the meridional potential vorticity gradient, which strengthens the synoptic atmospheric blocking event. As a result, more warm (cold) air is transported to higher (lower) latitudes along the edge of high pressure, which is an accumulation of atmospheric blocking events. The results suggest that anomalous meridional heat transport plays more important roles in Arctic surface warming when the anomalous radiative forcing is weak. Without being absorbed by the ocean, additional available energy induces strong Arctic springtime surface warming.

Methyl-terminated graphite carbon nitride with regulatable local charge redistribution for ultra-high photocatalytic hydrogen production and antibiotic degradation

Intramolecular-tailored graphite carbon nitride (g-C3N4) has great potential to greatly optimize the photo-response performance and carrier separation ability, but exquisite molecular structure engineering is still challenging. Firstly, a series of oxygen and terminal methyl moiety co-modified g-C3N4 (CNNx) has been systematically prepared by using N-Hydroxysuccinimide (HOSu) as a novel copolymerized precursor and urea. The density functional theory (DFT) calculations demonstrated that the presence of oxygen can lower the binding energy for the C–C bond to make the terminal modification easier. The terminal methyl and Oxygen not only caused abundant alveolar defects to break the periodic symmetry but also acted as an electron-accepting platform to tune the local charge redistribution within g-C3N4 molecular. The synthesized CNNx (CNN25) achieved ultra-high photocatalytic activity and chemical stability under visible light toward antibiotic degradation (99% tetracycline, 92% doxycycline, 65% ofloxacin and 74% sulfathiazole degradation within 30 min) and hydrogen production (an apparent quantum efficiency of 2.10% at 400 nm). CNN25 also maintains good efficiency in surface water and groundwater. Moreover, the TC solution treated with CNN25 had hardly any harm to the growth of E. coli. We believe our findings will provide a facile and green strategy for the preparation of non-metallic modified g-C3N4.

The seasonal variation of shallow meridional overturning circulation in the South China Sea and the related dynamics

The shallow meridional overturning circulation (SMOC) in the South China Sea (SCS) contributes to the local heat redistribution. Most investigations focused on its annual mean structure but paid little attention to its seasonal variation. In this study, the products of Ocean General Circulation Model for the Earth Simulator (OFES) are used to study the seasonal variation of the SMOC in the SCS. Results indicate that the SMOC can be formed in both winter and summer, and its structure has a prominent seasonal variation. The SMOC is clockwise and appears between 9°N and 18°N in winter, while it is anticlockwise and confined to the southern SCS in summer. Related dynamics of the SMOC seasonal variation are further investigated. It is found that the winter monsoon is essential for the formation of the clockwise winter SMOC, and the buoyancy flux also contributes to the winter SMOC formation via influencing the mixed layer depth. Although the SCS conditions are dramatically changed in summer, the summer monsoon can still circulate the water around in the circuit of the anticlockwise summer SMOC. The monsoon is the primary driving factor that dominates the formation and seasonal variation of the SMOC in the SCS.