Valence Structure Research Articles

Synthesis and Advanced Applications of Transition Metal Oxides

Transition metal oxide semiconductor materials have gained significant attention in recent years because of their unique electrical, magnetic, and optical features. Transition metal oxides (TMOs) with partially filled d-shells have a wide range of characteristics and play important roles in a variety of technological applications. They are influenced by stoichiometry changes, which alter their physical, chemical, and electrical properties. Controlled synthesis, doping, and post-synthesis treatments can all have an impact on the size, shape, crystal structure, and overall attributes of TMOs. These changes affect applications such as magnetic materials and smart windows. Effective techniques include valence state control, dopants, alloying, structure engineering, nano and defect structuring, and surface modification. This article discusses the synthesis methods, crystal structures, electrical properties, and applications of transition metal oxides, as well as their involvement in cutting-edge technologies such as electronics, optoelectronics, energy storage, and catalysis.

Research progress of Mn-based low-temperature SCR denitrification catalysts.

Selective catalytic reduction (SCR) is a efficiently nitrogen oxides removal technology from stationary source flue gases. Catalysts are key component in the technology, but currently face problems including poor low-temperature activity, narrow temperature windows, low selectivity, and susceptibility to water passivation and sulphur dioxide poisoning. To develop high-efficiency low-temperature denitrification activity catalyst, manganese-based catalysts have become a focal point of research globally for low-temperature SCR denitrification catalysts. This article investigates the denitrification efficiency of unsupported manganese-based catalysts, exploring the influence of oxidation valence, preparation method, crystallinity, crystal form, and morphology structure. It examines the catalytic performance of binary and multicomponent unsupported manganese-based catalysts, focusing on the use of transition metals and rare earth metals to modify manganese oxide. Furthermore, the synergistic effect of supported manganese-based catalysts is studied, considering metal oxides, molecular sieves, carbon materials, and other materials (composite carriers and inorganic non-metallic minerals) as supports. The reaction mechanism of low-temperature denitrification by manganese-based catalysts and the mechanism of sulphur dioxide/water poisoning are analysed in detail, and the development of practical and efficient manganese-based catalysts is considered.

Hämmern, verwandeln und entschärfen. Zur Valenz metaphorischer Verben des Erzielens und Verhinderns von Toren im Handball, Eishockey und Fußball

This article examines metaphorical verbs for describing the scoring and preventing of goals in the languages of handball, ice hockey and football, such as hämmern, donnern, verwandeln or entschärfen. The focus here is on the changes in the valency structure compared to the general language verbs as well as the relationship to the valency of prototypical base verbs such as werfen and schießen. Expansions and reductions of valency can be observed, as well as changes in argument types. The syntactic-semantic characteristics of metaphorical verbs are described as a result of terminologisation in the professional language of sport.

Resonant inelastic x-ray scattering in warm-dense Fe compounds beyond the SASE FEL resolution limit

Resonant inelastic x-ray scattering (RIXS) is a widely used spectroscopic technique, providing access to the electronic structure and dynamics of atoms, molecules, and solids. However, RIXS requires a narrow bandwidth x-ray probe to achieve high spectral resolution. The challenges in delivering an energetic monochromated beam from an x-ray free electron laser (XFEL) thus limit its use in few-shot experiments, including for the study of high energy density systems. Here we demonstrate that by correlating the measurements of the self-amplified spontaneous emission (SASE) spectrum of an XFEL with the RIXS signal, using a dynamic kernel deconvolution with a neural surrogate, we can achieve electronic structure resolutions substantially higher than those normally afforded by the bandwidth of the incoming x-ray beam. We further show how this technique allows us to discriminate between the valence structures of Fe and Fe2O3, and provides access to temperature measurements as well as M-shell binding energies estimates in warm-dense Fe compounds.

Air plasma activation of catalytic sites within MXene nanosheets for oxygen evolution and urea oxidation catalysis

Atmospheric pressure medium–blocked discharge plasma modified the hydroxyl and fluorine groups on the dispersed surface of MXene as well as the valence states of metal ions to promote electrocatalytic reactions efficiently. The plasma-treated samples maintain the nature and macroscopic morphology of the open active sites of the original framework structure, whereas the valence and electronic structures of the metal centers are altered. When dielectric barrier discharge plasma-modified MXene is used to assemble a monolithic hydrolysis device for hydrogen evolution reaction (HER)||oxygen evolution reaction (OER), the current density is up to 100 mA/cm2 at 2.1 V (actual data without IR compensation). Furthermore, in urea-assisted water electrolysis HER||urea oxidation reaction, the voltage is only 1.8 V, which is 300 mV lower than that of HER||OER. Meanwhile, the electrocatalytic system can operate continuously with high durability for more than 100 h. This work provides an effective electrocatalyst not only for efficient hydrogen production but also for urea wastewater purification.

Detection of Cr(III) and Cr(VI) in lake water by inhibiting and enhancing oxidase-like activity of iron-manganese bimetallic oxide nano-cubes

In recent years, most of the researches on nanozymes have focused on improving their catalytic activity and direct synthesis, but this task is still very complicated. Bimetallic oxides are particularly popular because of their mixed valence and special structure. In this study, iron-manganese bimetallic oxide nano-cubes (IMBO NCs) were prepared by a rapid and effective solvothermal synthesis technique, and showed excellent oxidase-like activity. The exposure of Cr(III) and Cr(VI) inhibited and enhanced the catalytic activity of IMBO NCs respectively. On this basis, a simple, economical and accurate colorimetric sensor was established by combining with 3,3′,5,5′-tetramethylbenzidine (TMB). Using oxidase activity instead of traditional peroxidase activity to detect Cr(III) and Cr(VI) greatly shortens the detection time. The method has also been successfully applied to the quantitative monitoring of Cr(III) and Cr(VI) in lake water. This study provides theoretical support for the effective design of bimetallic oxide nanozyme activity and can guide the development of accurate detection systems for the analysis of Cr(III) in food and Cr(VI) in environment.

Bias-voltage dependence of structure in Mn–Ni–O/mica flexible films for high precise temperature sensing up to 600 °C

Mechanically deformable flexible temperature sensors are being used to fabricate next-generation smart electronics, but improving their high-temperature application range is still a major challenge. In this work, in pursuit of excellent performance, a series of Mn–Ni–O ultrathin flexible thermal thin films with dual-phase structure were successfully prepared by magnetron sputtering using the bias voltage adjustment method. The interactions of grain density, ionic valence and phase structure on the performance of high-temperature NTC are emphasized. By overcoming the significant drawbacks of the flexible thermal films such as poor stability and narrow temperature range under high temperature conditions, excellent thermal performance with a wide temperature range from 200 °C to 600 °C and a resistance drift rate as low as 1.5 % has been achieved. This opens up innovative prospects for the design and application of flexible high-temperature thermal materials.

Flame-retardant in-situ formed gel polymer electrolyte with different valance states of phosphorus structures for high-performance and fire-safety lithium-ion batteries

Lithium-ion batteries (LIBs) have been widely used today owing to portability, high energy storage, and reusability. However, commercial liquid electrolytes in LIBs possess intensive mobility and terrible flammability. Accordingly, leakage, combusting, and even exploding can frequently occur when LIBs work under abuse conditions. Herein, a novel flame-retardant gel polymer electrolyte (GPE) containing + 3 and + 5 phosphorus valence states of phosphorus structures was designed by in-situ thermal polymerization of tri(acryloyloxyethyl) phosphate (TAEP), diethyl vinylphosphonate (DEVP), and pentaerythritol tetraacrylate in electrolytes. After being ignited by fire, this GPE extinguished quickly with a combusting time of only 0.9 s, showing much lower flammability. Besides, the GPE is compatible with graphite anode, LiFePO4 (LFP), and even LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes. The as-assembled LFP and NCM811-based pouch cells (1 Ah-type) with TD-GPE achieved stable cycling, maintaining 88.52 % and 95.2 % of the initial capacities, respectively after 200 and 190 cycles at 0.5C. Moreover, the as-prepared TD-GPE dramatically reduced the fire hazard of NCM811 batteries without sacrificing the electrochemical performance. The thermal abuse test demonstrates that the leakage and combustion of NCM811||TD-GPE||Graphite pouch cell could be significantly suppressed in the test process, indicating that battery safety improves significantly via the combined use of different phosphorus valence structures. This is because the + 5 phosphorus valence of TAEP promoted the formation of carbon layers, and the + 3 phosphorus structure in DEVP captured free radicals by quenching effect. This work paves a different path for designing safe and high-performance GPEs in LIBs based on gaseous-phase and condensed-phase mechanisms.

Optimization of valence and crystal structure of nickel-cobalt composites for efficient catalytic hydrolysis of borohydrides

Borohydrides are promising for hydrogen storage applications owing to borohydride hydrolysis reactions (BHR) characterized by controlled hydrogen evolution. However, the understanding of electronic structure-activity relationships and macroscopic synthesis of transition metal-based catalysts remains challenging. Herein, we employed a high-gravity technique coupled with impregnation-phosphorization to prepare NiCo-P/O with homogeneous and small particle sizes. Experiments and characterizations reveal that the phosphorization procedure confers the material's ability to catalyze BHR by introducing low valence Ni and Co. The catalytic activity for BHR shows a strong dependence on the valence state. Besides, the particle size and crystal structure of the catalysts were optimized by modulating the high-gravity field, thus boosting the catalytic activity towards BHR. As a result, NiCo-P/O catalyzed BHR at 298 K could produce pure hydrogen at 2060 mL min−1 g−1. This work provides a valence-activity relationship insight and feasible macro-synthetic catalysis strategies for BHR.

Preparation of direct Z-scheme heterojunction la-doped Bi2WO6/CdS with enhanced visible light absorption and its photocatalytic degradation of antibiotics

In this paper, a novel direct Z-scheme heterojunction La-Bi2WO6/CdS composed of 3-dimensional flower-like Bi2WO6 and hexagonally stacked succulent CdS was successfully designed and synthesized. The morphology, optical properties, element valence and crystal structure of the catalysts were systematically characterized. When the dosage of LBC-40 was 1.0 g/L, the degradation rate of oxytetracycline (OTC, 20 mg/L, pH = 6) was 85.28 %, under low visible light illumination (65 W energy saving lamp) for 120 min and the reaction kinetic constant (0.01336 min−1) was 2.50 and 1.56 times that of pure Bi2WO6 and La-Bi2WO6, respectively. Moreover, La-Bi2WO6/CdS showed good photocatalytic activity for other single antibiotics, mixed antibiotics and antibiotics from different water sources. The photocatalytic activity only decreased by 7.69 % after 3 cycles. Furthermore, the possible photocatalytic degradation pathway and photocatalytic mechanism of OTC were proposed. The excellent photocatalytic performance of La-Bi2WO6/CdS is for that the doping of La3+ and the construction of direct Z-scheme heterojunction enhances the visible light absorption capacity and separation efficiency of photogenerated electron-hole pairs. This paper reports a new method, which can provide a reference for the design and development of visible light responsive photocatalysts with excellent photocatalytic properties.

A Corpus-Driven Perspective on the Verb Valency Structure of Chinese EFL Learners: A Case Study of "Suggest" and "Advise"

A Corpus-Driven Perspective on the Verb Valency Structure of Chinese EFL Learners: A Case Study of "Suggest" and "Advise"

Pulsed laser interference patterning of transition‐metal carbides for stable alkaline water electrolysis kinetics

AbstractWe investigated the role of metal atomization and solvent decomposition into reductive species and carbon clusters in the phase formation of transition‐metal carbides (TMCs; namely, Co3C, Fe3C, TiC, and MoC) by pulsed laser ablation of Co, Fe, Ti, and Mo metals in acetone. The interaction between carbon s–p‐orbitals and metal d‐orbitals causes a redistribution of valence structure through charge transfer, leading to the formation of surface defects as observed by X‐ray photoelectron spectroscopy. These defects influence the evolved TMCs, making them effective for hydrogen and oxygen evolution reactions (HER and OER) in an alkaline medium. Co3C with more oxygen affinity promoted CoO(OH) intermediates, and the electrochemical surface oxidation to Co3O4 was captured via in situ/operando electrochemical Raman probes, increasing the number of active sites for OER activity. MoC with more d‐vacancies exhibits strong hydrogen binding, promoting HER kinetics, whereas Fe3C and TiC with more defect states to trap charge carriers may hinder both OER and HER activities. The results show that the assembled membrane‐less electrolyzer with Co3C∥Co3C and MoC∥MoC electrodes requires ~2.01 and 1.99 V, respectively, to deliver a 10 mA cm−2 with excellent electrochemical and structural stability. In addition, the ascertained pulsed laser synthesis mechanism and unit‐cell packing relations will open up sustainable pathways for obtaining highly stable electrocatalysts for electrolyzers.

Prediction of pure carbon crystals with intrinsic antiferromagnetism: polymerized from C20 fullerenes.

Pure carbon materials with magnetic properties have attracted considerable research interest due to their advantages over traditional magnetic materials. Nevertheless, such materials are exceedingly rare. Disrupting the Kekulé valence structures in carbon materials potentially leads to the emergence of magnetism. In this study, using first principles calculations, we developed a range of pure carbon allotropes derived from the smallest fullerene C20 which potentially disrupts the Kekulé valence structures after polymerization. The results indicate that some of the allotropes disrupting the Kekulé valence structures exhibit intrinsic antiferromagnetic ordering, and the magnetism originates from the presence of isolated three-fold coordinated C atoms. The other allotropes adhering to the Kekulé valence structures show non-magnetism with all three-fold coordinated C atoms forming dimers. In all magnetic polymers, magnetism arises from unpaired electrons on the isolated three-fold coordinated carbon atoms, with magnetic moments of about 0.40μB at these sites. The adsorption of dopant atoms can significantly alter the magnetic properties of polymers, for instance, the C20-71 polymer with Immm symmetry undergoes a transition from non-magnetic to anti-magnetic ordering upon adsorption of hydrogen atoms. Electronic calculations indicate that these polymers display a range of electronic properties, encompassing both metallic and semiconducting characteristics. Notably, certain magnetic phases exhibit superhard properties, with the hardness value exceeding 40 GPa. This study presents a potential method for designing magnetic carbon materials. Specifically, certain compounds address the gap in magnetic superhard materials composed of light elements, and can be utilized in the field of spintronics where traditional superhard materials are unsuitable.

Carbon quantum dot regulated electrochemical activation of Co0.03Ni0.97LDH for energy storage

The valence and coordination structure of transition metals in electrode materials play a crucial role in the electrochemical energy storage process.

Structure-activity relationship study of high entropy oxides catalysts for oxygen evolution reaction

High entropy oxides (HEOs) are promising catalysts of oxygen evolution reactions (OER) in water splitting. However, multi-components, complicated phases and numbers of defects make a lack of deep understanding to the structure–activity relationship of HEOs catalysts. In this paper, different transition metal elements of Fe, Cr, Mn, Mg and Al were doped into (CoNiCuZn)O to form five quinary HEOs. To explore the structure–activity relationship of OER catalysts of HEOs, the phase structure, element valence, oxygen vacancies and electronic structure were characterized and their OER performance was tested. The results show that among all the HEOs, (FeCoNiCuZn)O has the optimal OER catalytic performance: an overpotential of 323 mV at a current density of 10 mA cm−2 in 1 M KOH solution, a Tafel slope of 64.5 mV dec-1, maintaining a high stability for at least 50 h. Its superior OER performance can be attributed to a combination of three main factors: an appropriate band gap of transition metal (TM) 3d and oxygen (O) 2p, a high concentration of oxygen vacancies and a spinel phase precipitation. Among them, the band gap of TM 3d and O 2p showing a volcano relationship with the intrinsic OER activity can be the most decisive descriptor of the intrinsic OER activity of HEOs. A moderate band gap of TM 3d and O 2p being tuned by various cations will lead to more reasonable intermediate adsorption and desorption abilities of HEOs.

Single intravitreal administration of a tetravalent siRNA exhibits robust and efficient gene silencing in mouse and pig photoreceptors

Inherited retinal dystrophies caused by dominant mutations in photoreceptor cell expressed genes, are a major cause of irreversible vision loss. Oligonucleotide therapy has been of interest in diseases that conventional medicine cannot target. In the early days, small interfering RNAs (siRNAs) were explored in clinical trials for retinal disorders with limited success due to a lack of stability and efficient cellular delivery. Thus, an unmet need exists to identify siRNA chemistry that targets photoreceptor cell expressed genes. Here we evaluated 12 different fully chemically modified siRNA configurations, where the valency and conjugate structure were systematically altered. The impact on retinal distribution following intravitreal delivery was examined. We found that the increase in valency (tetravalent siRNA) supports the best photoreceptor accumulation. A single intravitreal administration induces multi-months efficacy in rodent and porcine retinas while showing a good safety profile. The data suggest that this configuration can treat retinal diseases caused by photoreceptor cell expressed genes with 1-2 intravitreal injections per year.

Dual improvement in sensitivity and selectivity of SnO2 nanospheres for formaldehyde sensing based on molecular imprinting and Ag doping

In order to develop a gas sensitive material with both high sensitivity and good selectivity, Ag–SnO2 MIPs were designed and synthesized by adopting molecular imprinting technique. Specifically, SnO2 nanospheres synthesized through hydrothermal method were used as substrate. Then, Ag–SnO2 was assembled by decorating nano-sized Ag on the surface of SnO2 nanospheres. Molecular imprinting modification with formaldehyde as template molecules was in next conducted to get Ag–SnO2 MIPs. The morphology, valence and crystal structure of the samples were characterized using SEM, XRD, TEM and XPS. The characterization results showed that uniform SnO2 nanospheres were successfully synthesized with metallic Ag distributed on the surface, and the molecular imprinting process did not change the morphology of the material. According to gas sensing measurement results, it was found that the sensor based on Ag–SnO2 MIPs exhibited superior formaldehyde sensing performance. The molecular imprinting modification effectively improved the sensor's selectivity towards formaldehyde gas. Owning to the catalytic property of Ag, the sensing response of sensor was greatly enhanced. Additionally, Ag–SnO2 MIPs also exhibits high reproducibility and long-term stability.

A blue-emitting porous MOF incorporated with red-emitting Eu(III) ions for nitro compounds fluorescence sensing: Improving ratiometric selectivity and sensitivity by synergistic effect of a dendritic auxiliary ligand

Due to the high nitrogen oxidation valence and electron-deficient structure, organic nitro compounds are generally known as potential explosive which are also considered as environmental threat. Optical sensing is an attractive quantification method with simple operation procedure and limited requirement for equipment, but traditional optical sensing platforms for nitro compounds suffered from limited sensitivity and poor selectivity. To solve this problem, this work designed applied a ratiometric sensing platform. Here red-emitting Eu(III) was incorporated into a blue-emitting host bio-MOF-1. A dendritic auxiliary ligand (denoted as BBB) was adopted to stabilize the adduct between Eu(III) and TPA (2,4,6-trinitrophenol). By so doing, the blue emission intensity from bio-MOF-1 was increased, while the Eu3+ emission intensity was minimized. The sensing behavior upon auxiliary ligand BBB was compared to that upon a reference ligand (1,10-phenanthroline). The sensing mechanism was proved as an irreversible Eu(III) leak and coordination with TPA/BBB guaranteed by BBB steric hindrance. Finally, a linear working equation with improved sensitivity (by sixfold) and unique selectivity was observed.

Resonating holes vs molecular spin-orbit coupled states in group-5 lacunar spinels

The valence electronic structure of magnetic centers is one of the factors that determines the characteristics of a magnet. This may refer to orbital degeneracy, as for jeff = 1/2 Kitaev magnets, or near-degeneracy, e.g., involving the third and fourth shells in cuprate superconductors. Here we explore the inner structure of magnetic moments in group-5 lacunar spinels, fascinating materials featuring multisite magnetic units in the form of tetrahedral tetramers. Our quantum chemical analysis reveals a very colorful landscape, much richer than the single-electron, single-configuration description applied so far to all group-5 GaM4X8 chalcogenides, and clarifies the basic multiorbital correlations on M4 tetrahedral clusters: while for V strong correlations yield a wave-function that can be well described in terms of four V4+V3+V3+V3+ resonant valence structures, for Nb and Ta a picture of dressed molecular-orbital jeff = 3/2 entities is more appropriate. These internal degrees of freedom likely shape vibronic couplings, phase transitions, and the magneto-electric properties in each of these systems.

Using electron energy-loss spectroscopy to measure nanoscale electronic and vibrational dynamics in a TEM.

Electron energy-loss spectroscopy (EELS) can measure similar information to x-ray, UV-Vis, and IR spectroscopies but with atomic resolution and increased scattering cross-sections. Recent advances in electron monochromators have expanded EELS capabilities from chemical identification to the realms of synchrotron-level core-loss measurements and to low-loss, 10-100meV excitations, such as phonons, excitons, and valence structures. EELS measurements are easily correlated with electron diffraction and atomic-scale real-space imaging in a transmission electron microscope (TEM) to provide detailed local pictures of quasiparticle and bonding states. This perspective provides an overview of existing high-resolution EELS (HR-EELS) capabilities while also motivating the powerful next step in the field-ultrafast EELS in a TEM. Ultrafast EELS aims to combine atomic-level, element-specific, and correlated temporal measurements to better understand spatially specific excited-state phenomena. Ultrafast EELS measurements also add to the abilities of steady-state HR-EELS by being able to image the electromagnetic field and use electrons to excite photon-forbidden and momentum-specific transitions. We discuss the technical challenges ultrafast HR-EELS currently faces, as well as how integration with in situ and cryo measurements could expand the technique to new systems of interest, especially molecular and biological samples.