Differential sensitization toward lanthanide metal-organic framework for detection of an anthrax biomarker.

A novel Tb-doped Eu-based metal-organic framework (Eu-MOF@Tb) has been developed by incorporating hexanuclear europium cluster and 2,2'-bipyridine-5,5'-dicarboxylic acid as well as coordination with Tb(III). Owing to the diverse coordination status of Tb(III) and Eu(III) in MOF, antenna effect emission from Tb(III) can be invoked by dipicolinic acid (DPA), but the luminescence originating from Eu(III) remains unchanged. Taking advantage of this phenomenon, a ratiometric luminescent method for detection of DPA, a biomarker for Bacillus subtilis spores, was developed through differential sensitization toward lanthanide ions. This analysis method allowed for the detection of DPA in the 0.2-10 µM concentration range, with a detection limit of 60 nM. It was further validated by spiked recoveries (89.3-110%) of real-world samples with RSD values in the range 3.9-11%. Alongside this, a paper indicator test was prepared for naked-eye detection of DPA via a dose-sensitive color evolution from red to green under UV light. The effectiveness of the proposed approach was explored in the detection of bacterial spores in real biological and environmental samples and indicated great potential for applications as a real-time monitoring system against the anthrax threat.

Oxidative Coupling of Methane: Examining the Inactivity of the MnOx -Na2 WO4 /SiO2 Catalyst at Low Temperature.

Oxidative coupling of methane (OCM) catalyzed by MnOx -Na2 WO4 /SiO2 has great industrial promise to convert methane directly to C2-3 products, but its high light-off temperature is the most challenging obstacle to commercialization and its working mechanism is still a mystery. We report the discovery of a low-temperature active and selective MnOx -Na2 WO4 /SiO2 catalyst enriched with Q2 units in the SiO2 carrier, being capable of converting 23 % CH4 with 72 % C2-3 selectivity at 660 °C. From experiments and theoretical calculations, a large number of Q2 units in the MnOx -Na2 WO4 /SiO2 catalyst is a trigger for markedly lowering the light-off temperature of the Mn3+ ↔Mn2+ redox cycle involved in the OCM reaction because of the easy formation of MnSiO3 . Notably, the MnSiO3 formation proceeds merely through the SiO2 -involved reaction in the presence of Na2 WO4 : Mn7 SiO12 +6 SiO2 ↔7 MnSiO3 +1.5 O2 . The Na2 WO4 not only drives the light-off of this cycle but also gets it working with substantial selectivity toward C2-3 products. Our findings shine a light on the rational design of more advanced MnOx -Na2 WO4 based OCM catalysts through establishing new Mn3+ ↔Mn2+ redox cycles with lowered light-off temperature.

Carbon coating on metal oxide materials for electrochemical energy storage.

During the past decades, nano-structured metal oxide electrode materials have received growing attention due to their low development cost and high theoretical specific capacity, accordingly, quite a lot of metal oxide electrode materials are being used in electrochemical energy storage devices. However, the further development was limited by the relatively low electrical conductivity and the volume expansion during electrochemical reactions. Thus, many approaches have been proposed to obtain high-efficiency metal oxide electrode materials, such as designing nanomaterials with ideal morphology and high specific surface area, optimizing with carbon-based materials (such as graphene and glucose) to prepare nanocomposites, combining with conductive substrates to enhance the conductivity of electrodes, etc. Owning to the advantages of low cost and high chemical stability of carbon materials, core-shell structure formed by carbon-coated metal oxides is considered to be a promising solution to solve these problems. Therefore, this review mainly focuses on recent research advances in the field of carbon-coated metal oxides for energy storage, summarizing the advantages and disadvantages of common metal oxides and different types of carbon sources, and proposing methods to optimize the material properties in terms of structure and morphology, carbon layer thickness, coating method, specific surface area and pore size distribution, as well as improving electrical conductivity. In addition, the double or multi-layer coating strategy is also a reflection of the continuous development of carbon coating method. Hopefully, this rereview may provide a new direction for the renewal and development of future energy storage electrode materials.

Multiple Firing Patterns in Coupled Hindmarsh-Rose Neurons with a Nonsmooth Memristor.

A model is introduced by coupling two three-dimensional Hindmarsh-Rose models with the help of a nonsmooth memristor. The firing patterns dependent on the external forcing current are explored, which undergo a process from adding-period to chaos. The stability of equilibrium points of the considered model is investigated via qualitative analysis, from which it can be gained that the model has diversity in the number and stability of equilibrium points for different coupling coefficients. The coexistence of multiple firing patterns relative to initial values is revealed, which means that the referred model can appear various firing patterns with the change of the initial value. Multiple firing patterns of the addressed neuron model induced by different scales are uncovered, which suggests that the discussed model has a multiscale effect for the nonzero initial value.

Mechanistic Insights into Ethylene Transformations on Ir(111) by Density Functional Calculations and Microkinetic Modeling.

Ethylidyne, ethane, and carbon monomer formations from ethylene over Ir(111) at different coverages are investigated using density functional theory methods. Two possible reaction mechanisms for ethylidyne formation are investigated. The calculations show that vinyl prefers the dehydrogenation to yield vinylidene (M2) over the hydrogenation to produce ethylidene (M1) kinetically and thermodynamically at 1/9 (1/3) ML. Ethylidyne formation could be a competitive side reaction of ethylene hydrogenation, however, the ethylidyne species does not directly participate in the ethylene hydrogenation mechanism. The mechanism for C monomer formation is also studied. Microkinetic modeling shows that the ethylene hydrogenation reactivity decreases in the sequence Ir(111)>Rh(111)>Pd(111)>Pt(111) under typical hydrogenation conditions. The catalytic activity of ethylene hydrogenation decreases with increased stability of ethylene adsorption and reaction barrier of the rate-limiting step.

Chemical vapor deposition-prepared sub-nanometer Zr clusters on Pd surfaces: promotion of methane dry reforming.

An inverse Pd-Zr model catalyst was prepared by chemical vapor deposition (CVD) using zirconium-t-butoxide (ZTB) as an organometallic precursor. Pd-Zr interaction was then investigated with focus on the correlation of reforming performance with the oxidation state of Zr. As test reactions, dry reforming of methane (DRM) and methanol steam reforming (MSR) were chosen. Depending on treatments, either ZrOxHy or ZrO2 overlayers or Zr as sub-nanometer clusters could be obtained. Following the adsorption of ZTB on Pd(111), a partially hydroxylated Zr4+-containing layer was formed, which can be reduced to metallic Zr by thermal annealing in ultrahigh vacuum, leading to redox-active Zr0 sub-nanometer clusters. Complementary density functional theoretical (DFT) calculations showed that a single layer of ZrO2 on Pd(111) can be more easily reduced toward the metallic state than a double- and triple layer. Also, the initial and resulting layer compositions greatly depend on gas environment. The lower the water background partial pressure, the faster and more complete the reduction of Zr4+ species to Zr0 on Pd takes place. Under methanol steam reforming conditions, water activation by hydroxylation of Zr occurs. In excess of methanol, strong coking is induced by the Pd/ZrOxHy interface. In contrast, dry reforming of methane is effectively promoted if these initially metallic Zr species are present in the pre-catalyst, leading to a Pd/ZrOxHy phase boundary by oxidative activation under reaction conditions. These reaction-induced active sites for DRM are stable with respect to carbon blocking or coking. In essence, Zr doping of Pd opens specific CO2 activation channels, which are absent on pure metallic Pd.

Impact of branching on the supramolecular assembly of thioethers on Au(111).

Alkanethiolate monolayers are one of the most comprehensively studied self-assembled systems due to their ease of preparation, their ability to be functionalized, and the opportunity to control their thickness perpendicular to the surface. However, these systems suffer from degradation due to oxidation and defects caused by surface etching and adsorbate rotational boundaries. Thioethers offer a potential alternative to thiols that overcome some of these issues and allow dimensional control of self-assembly parallel to the surface. Thioethers have found uses in surface modification of nanoparticles, and chiral thioethers tethered to catalytically active surfaces have been shown to enable enantioselective hydrogenation. However, the effect of structural, chemical, and chiral modifications of the alkyl chains of thioethers on their self-assembly has remained largely unstudied. To elucidate how molecular structure, particularly alkyl branching and chirality, affects molecular self-assembly, we compare four related thioethers, including two pairs of structural isomers. The self-assembly of structural isomers N-butyl methyl sulfide and tert-butyl methyl sulfide was studied with high resolution scanning tunneling microscopy (STM); our results indicate that both molecules form highly ordered arrays despite the bulky tert-butyl group. We also investigated the effect of intrinsic chirality in the alkyl tails on the adsorption and self-assembly of butyl sec-butyl sulfide (BSBS) with STM and density functional theory and contrast our results to its structural isomer, dibutyl sulfide. Calculations provide the relative stability of the four stereoisomers of BSBS and STM imaging reveals two prominent monomer forms. Interestingly, the racemic mixture of BSBS is the only thioether we have examined to date that does not form highly ordered arrays; we postulate that this is due to weak enantiospecific intermolecular interactions that lead to the formation of energetically similar but structurally different assemblies. Furthermore, we studied all of the molecules in their monomeric molecular rotor form, and the surface-adsorbed chirality of the three asymmetric thioethers is distinguishable in STM images.

Recent progress in hierarchical nanostructures for Ni-based industrial-level OER catalysts.

Exploring efficient and low-cost oxygen evolution reaction (OER) electrocatalysts reaching the industrial level current density is crucial for hydrogen production via water electrolysis. In this feature article, we summarize the recent progress in hierarchical nanostructures for the industrial-level OER. The contents mainly concern (i) the design of a hierarchical structure; (ii) a Ni-based hierarchical structure for the industrial current density OER; and (iii) the surface reconstruction of the hierarchical structure during the OER process. The work provides valuable guidance and insights for the manufacture of hierarchical nanomaterials and devices for industrial applications.

Crack Formation and Control in an AlCoCrFeNi High Entropy Alloy Fabricated by Selective Laser Melting.

The equiatomic AlCoCrFeNi high entropy alloy (HEA) is prone to cracking during the additive manufacturing process due to the high cooling rates observed, which limits its application to a large extent. In this study, the selective laser melting (SLM) technique was adopted to fabricate the alloy and the mechanism of crack formation was revealed. Most importantly, a new design strategy was proposed to suppress the generation of cracks, and the optimization of the preparation process was also studied in detail. It is found that the interlaminar crack is related to the heat input at the edge of the specimen, and the internal cracks are formed by solidification cracks. Alloys without interlaminar crack can be prepared by means of combination of the side inclination angle and the process parameters. Side inclination angle optimization provides a possibility for the preparation of crack-free AlCoCrFeNi HEA by SLM.

Carbon-Based Composites for Oxygen Evolution Reaction Electrocatalysts: Design, Fabrication, and Application.

The four-electron oxidation process of the oxygen evolution reaction (OER) highly influences the performance of many green energy storage and conversion devices due to its sluggish kinetics. The fabrication of cost-effective OER electrocatalysts via a facile and green method is, hence, highly desirable. This review summarizes and discusses the recent progress in creating carbon-based materials for alkaline OER. The contents mainly focus on the design, fabrication, and application of carbon-based materials for alkaline OER, including metal-free carbon materials, carbon-based supported composites, and carbon-based material core-shell hybrids. The work presents references and suggestions for the rational design of highly efficient carbon-based OER materials.

Structural engineering evoked multifunctionality in molybdate nanosheets for industrial oxygen evolution and dual energy storage devices inspired by multi-method calculations.

Structural engineering, including electronic and geometric modulations, is a good approach to improve the activity of electrocatalysts. Herein, we employed FeOOH and the second metal center Ni to modulate the electronic structure of CoMoO4 and used a low temperature solvothermal route and a chemical etching method to prepare the special hollow hierarchical structure. Based on the prediction of multi-method calculations by density functional theory (DFT) and ab initial molecular dynamics (AIMD), a series of materials were fabricated. Among them, the optimal hollow FeOOH/(Ni1Co1)MoO4 by coating (NiCo)MoO4 nanosheets on FeOOH nanotubes showed excellent performances toward high current density oxygen evolution reaction (OER) in alkaline and simulated seawater solutions, hybrid supercapacitor (HSC), and aqueous battery due to the well-controlled electronic and geometric structures. The optimal FeOOH/(Ni1Co1)MoO4 required overpotentials of 225 and 546 mV to deliver 10 and 1000 mA cm-2 current densities toward alkaline OER, and maintained a good stability for 100 h at 200 mA cm-2 with negligible attenuation. The FeOOH/(Ni1Co1)MoO4//Pt/C electrolyzer exhibited a low cell voltage of 1.52 and 1.79 V to drive 10 and 200 mA cm-2 and retained a long-term durability nearly 100 h at 1.79 V. As the electrode of energy storage devices, it possessed a specific capacity of 342 mA h g-1 at 1 A g-1. HSC and SC-type battery devices were fabricated. The assembled HSC kept a capacitance retention of 94 % after 10,000 cycles. This work provided a way to fabricate effective and stable multifunctional materials for energy storage and conversion with the aid of multi-method calculations.

Polyaniline-graphene based composites electrode materials in supercapacitor: synthesis, performance and prospects.

Supercapacitors (SCs) have become one of the most popular energy-storage devices for high power density and fast charging/discharging capability. Polyaniline is a class of conductive polymer materials with ultra-high specific capacitance, and the excellent mechanical properties will play a key role in the research of flexible SCs. The synergistic effect between polyaniline and graphene is often used to overcome their respective inherent shortcomings, thus the high-performance polyaniline-graphene based nanocomposite electrode materials can be prepared. The development of graphene-polyaniline nanocomposites as electrode materials for SCs depends on their excellent microstructure design. However, it is still difficult to seek a balance between graphene performance and functionalization to improve the weak interfacial interaction between graphene and polyaniline. In this manuscript, the latest preparation methods, research progress and research results of graphene-polyaniline nanocomposites on SCs are reviewed, and the optimization of electrode structures and performances is discussed. Finally, the prospect of graphene-polyaniline composites is expected.

Decreased structural pathways mediating functional connectivity in obstructive sleep apnea.

BACKGROUND: Obstructive sleep apnea (OSA) is a common sleep breathing disorder that is often accompanied by changes in structural connectivity (SC) and functional connectivity (FC). However, the current understanding of the interaction between SC and FC in OSA is still limited. METHODS: The aim of this study is to integrate complementary neuroimaging modalities into a unified framework using multi-layer network analysis methods and to reveal their complex interrelationships. We introduce a new graph metric called SC-FC bandwidth, which measures the throughput of SC mediating FC in a multi-layer network. The bandwidth differences between two groups are evaluated using the network-based statistics (NBS) method. Additionally, we traced and analyzed the SC pathways corresponding to the abnormal bandwidth. RESULTS: In both the healthy control and patients with OSA, the majority offunctionally synchronized nodes were connected via SC paths of length 2. With the NBS method, we observed significantly lower bandwidth between the right Posterior cingulate gyrus and right Cuneus, bilateral Middle frontal gyrus, bilateral Gyrus rectus in OSA patients. By tracing the high-proportion SC pathways, it was found that OSA patients typically exhibit a decrease in direct SC-FC, SC-FC triangles, and SC-FC quads intra- and inter-networks. CONCLUSION: Complex interrelationship changes have been observed between the SC and FC in patients with OSA, which might leads to abnormal information transmission and communication in the brain network.

Surface interactions of C and C(3) polyols with γ-Al2O3 and the role of coadsorbed water.

The formation of surface species from two- and three-carbon polyols on γ-Al(2)O(3) in the presence and absence of coadsorbed water is investigated. Aqueous-phase adsorption isotherms indicate that competitive adsorption between water and polyol inhibits the uptake of the polyol molecules on γ-Al(2)O(3) and that the polyol with the most hydroxyl groups, glycerol, experienced the greatest uptake. Deuterium solid echo pulse NMR measurements support the fact that glycerol strongly interacts with γ-Al(2)O(3) in the presence of physisorbed water and that ethylene glycol interacts with γ-Al(2)O(3) only after the physisorbed water has been removed. In situ high-vacuum FT-IR analysis combined with DFT simulations demonstrate that glycerol readily forms a multidentate alkoxy species through its primary hydroxyl groups with coordinatively unsaturated Al atoms of γ-Al(2)O(3) in the presence of physisorbed water. This surface species exhibits a bridging alkoxy bond from one of its primary hydroxyl groups and a strong interaction with the remaining primary hydroxyl group. FT-IR analysis of 1,3-propanediol on γ-Al(2)O(3) also demonstrates the formation of a multidentate alkoxy species in the presence of coadsorbed water. In contrast, polyols with hydroxyl groups only on the one- and two-carbon atoms, ethylene glycol, and 1,2-propanediol do not form alkoxy bonds with the γ-Al(2)O(3) surface when coadsorbed water is present. These polyols will form alkoxy bonds to γ-Al(2)O(3) when coadsorbed water is removed, and these alkoxy species are removed when water is readsorbed on the sample. The formation of strongly bound, stable multidentate alkoxy species by ethylene glycol and 1,2-propanediol on γ-Al(2)O(3) is prevented by steric limitations of vicinal alcohol groups.

The adsorption of single Au atom and nucleation on γ-Al2O3 surfaces.

Single-atom catalysts (SACs) in heterogeneous catalysts have attracted increasing attention and the adsorption and nucleation of single atom on the surface are closely related to the performance of the catalyst. The present work employed density functional theory calculations to examine the adsorption of single Au atom and nucleation on γ-Al2O3 surfaces at the atomic level. The effect of surface hydroxyls group on the adsorption and nucleation of single Au atom on γ-Al2O3 surfaces is explored. It was found that the spillover reactions of surface hydroxyls H atoms with the deposited Au- are not available on the hydroxylated surface. The interaction of Au to the clean surface is the stronger than to the hydroxylated surface. The even-odd alternations of Aux and weak binding of single Au atoms to γ-Al2O3 leads to large even-numbered Au cluster on the surface. Density of states and electron density difference analysis show that the electronic structure of Au/γ-Al2O3 is quite different from the reported Cu and Pd on Al2O3.

Bio-inspired design of NiFeP nanoparticles embedded in (N,P) co-doped carbon for boosting overall water splitting.

The design and synthesis of cost-effective and stable bifunctional electrocatalysts for water splitting via a green and sustainable fabrication way remain a challenging problem. Herein, a bio-inspired method was used to synthesize NiFeP nanoparticles embedded in (N,P) co-doped carbon with the added carbon nanotubes. The obtained Ni0.8Fe0.2P-C catalyst displayed excellent hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances in both alkaline and alkaline simulated seawater solutions. The optimal Ni0.8Fe0.2P-C/NF only needs overpotentials of 45 and 242 mV to reach the current density of 10 mA cm-2 under HER and OER working conditions in 1.0 M KOH solution, respectively. First-principles calculations revealed the presence of a strong interaction between the carbon layer and metal phosphide nanoparticles. Benefiting from this and carbon nanotubes modification, the fabricated Ni0.8Fe0.2P-C presents impressive stability, working continuously for 100 h without collapse. A low alkaline cell voltage of 1.56 V for the assembled Ni0.8Fe0.2P-C/NF//Ni0.8Fe0.2P-C/NF electrocatalyzer could afford a current density of 10 mA cm-2. Moreover, when integrated with a photovoltaic device, the bifunctional Ni0.8Fe0.2P-C electrocatalyst demonstrates application potential for sustainable solar-driven water electrolysis.

S-Species-Evoked High-Valence Ni2+ δ of the Evolved ß-Ni(OH)2 Electrode for Selective Oxidation of 5-Hydroxymethylfurfural.

An efficient NiSx -modified ß-Ni(OH)2 electrode is reported for the selective oxidation reaction of 5-hydroxymethylfurfural (HMFOR) with excellent electrocatalytic 5-hydroxymethylfurfural (HMF) selectivity (99.4%), conversion (97.7%), and Faradaic efficiency (98.3%). The decoration of NiSx will evoke high-valence Ni2+ δ species in the reconstructed ß-Ni(OH)2 electrode, which are the real active species for HMFOR. The generated NiSx /Ni(OH)O modulates the proton-coupled electron-transfer (PCET) process of HMFOR, where the electrocatalytically generated Ni(OH)O can effectively trap the protons from the CHO end in HMF to realize electron transfer. The oxygen evolution reaction (OER) competes with the HMFOR when NiSx /Ni(OH)O continues to accumulate, to generate the NiSx /NiOx (OH)y intermediate. Density functional theory (DFT) calculations and experimental results verify that the adsorption energy of HMF can be optimized through the increased NiSx composition for more efficient capture of protons and electrons in the HMFOR.

The surface structure, stability, and catalytic performances toward O2 reduction of CoP and FeCoP2.

The systematic atomistic level investigation of low-index surface structures, stabilities, and catalytic performances of CoP and FeCoP2 towards the O2 reduction reaction (ORR) is vital for their applications. Employing first-principles calculations, it is revealed that CoP and FeCoP2 present the same surface stability in the order of (101) ≈ (011) > (111) > (001) > (110) > (010) > (100). They also possess a similar Wulff equilibrium crystal shape with (101) and (011) exposing the largest surface area. From the electronic view, FeCoP2 presents improved electronic conductivity compared with CoP. From the energy view, whether FeCoP2 delivers improved electrocatalytic activity toward the ORR with respect to CoP depends on the reactive surfaces and sites. Among the 4 surfaces considered, only CoP(101), FeCoP2(101) and FeCoP2(011) delivered ORR performances theoretically when the bridge metal-metal site acts as the reactive center, which makes CoP(011) the only exception. CoP(101)-bCo-Co and FeCoP2(011)-bFe-Co exhibit a larger thermodynamic limiting potential than FeCoP2(101)-bCo-Co, suggesting their higher performances toward the ORR. The last step of HO* desorption as the rate-limiting step accounts for 3/4. The third step of transformation from O* to HO* as the most sluggish step accounts for 1/4. The work function, d-band center, Bader charge, and electronic localization function calculations are performed to reveal the HO adsorption nature. The present work provides fundamental insight into the effect of Fe doping into CoP, the determination of the catalyst surface and the key species adsorption nature to guide the rational design of high-performance materials.

Rational design of 3D N-doped graphene with a holey structure as a bifunctional electrode for sensitive methyl parathion detection and supercapacitors.

N-doped graphene with nano-sized holes possesses abundant electrochemically active sites at the exposed edge and an open porous structure, leading to a better electrochemical performance and faster electron and ion transport than the basal planes in graphene. In this study, three-dimensional graphene with a porous structure and abundant doped N (3d-NHG) were synthesized as bifunctional electrodes for methyl parathion (MP) detection and supercapacitors. The roles of N-doping and the holey construction in the electrochemical performance of the 3d-NHG were systematically investigated through a combined theory-experiment strategy. The 3d-NHG-based electrochemical sensor successfully detected methyl parathion in the range of 38 nm-380 µM with a low detection limit (2.27 nM) and superior sensitivity. Furthermore, the 3d-NHG also demonstrated potential for use in supercapacitors with a specific capacitance of 207 F g-1 at 1 A g-1 and excellent rate capability (76% capacitance retention at 10 A g-1). Density functional theory calculations revealed that the exposed carbon sites at the edge are the reactive sites for species adsorption. Moreover, the holey structure in 3d-NHG plays a dominating role in electrochemical processes and in the enhanced electrocatalysis. This work provides guidance for the rational design of high-performance bifunctional electrodes for MP detection and supercapacitors by defect engineering.

Carbon-incorporated bimetallic phosphide nanospheres derived from MOFs as superior electrocatalysts for hydrogen evolution.

Preparing low-cost and highly efficient electrocatalysts for the hydrogen evolution reaction using a simple strategy still faces challenges. In this work, we proposed a facile phosphating process to successfully transform CoFe-BTC (BTC = 1,3,5-benzenetricarboxylate) precursors into carbon-incorporated bimetallic phosphide (CoFe-P/C) nanospheres. Due to the synergistic effect between bimetals and uniformly covered carbon shells outside, the as-synthesized porous bimetallic phosphide nanospheres exhibit superior HER activity, enhanced kinetics, and excellent cycle durability in both acidic and alkaline solutions. The optimized material could afford a current density of 10 mA cm-2 with overpotentials of 138 and 193 mV for the HER in acidic and alkaline solutions, respectively. Meanwhile, it delivered small Tafel slopes of 84 and 78 mV dec-1 for the HER in 0.5 M H2SO4 and 1.0 M KOH, respectively. Moreover, an assembled alkaline electrolyzer enabled a low voltage of 1.62 V to drive a current density of 10 mA cm-2 for overall water splitting. DFT calculations indicate that the CoP-Fe2P composite is supposed to exhibit better HER performance than each component, revealing the vital role of the interfacial site in catalyzing the HER.