Vortex-based soft magnetic composite with ultrastable permeability up to gigahertz frequencies.

Soft magnetic materials with stable permeability up to hundreds of megahertz (MHz) are urgently needed for integrated transformers and inductors, which are crucial in the more-than-Moore era. However, traditional frequency-stable soft magnetic ferrites suffer from low saturation magnetization and temperature instability, making them unsuitable for integrated circuits. Herein, we fabricate a frequency-stable soft magnetic composite featuring a magnetic vortex structure via cold-sintering, where ultrafine FeSiAl particles are magnetically isolated and covalently bonded by Al2SiO5/SiO2/Fe2(MoO4)3 multilayered heterostructure. This construction results in an ultrastable permeability of 13 up to 1 gigahertz (GHz), relatively large saturation magnetization of 105 Am2/kg and low coercivity of 48 A/m, which we ascribe to the elimination of domain walls associated with almost uniform single-vortex structures, as observed by Lorentz transmission electron microscopy and reconstructed by micromagnetic simulation. Moreover, the ultimate compressive strength has been simultaneously increased up to 337.1 MPa attributed to the epitaxially grown interfaces between particles. This study deepens our understanding on the characteristics of magnetic vortices and provides alternative concept for designing integrated magnetic devices.

Atomic-scale observation of calcium occupation in spinel cobalt ferrite towards the regulation of intrinsic magnetic properties.

Spinel ferrites have drawn intensive attention because of their adjustable magnetic properties by ion doping, among which calcium (Ca) is an essential dopant that is widely employed in massive production. However, its exact lattice occupation and relationship with intrinsic magnetic properties remain unclear. Here, we successfully prepared Ca-doped cobalt ferrite (CoFe2O4) nanoparticles by electrospinning. Ca2+ is observed to occupy both the tetrahedral Fe site and the octahedral Co site using spherical aberration correction transmission electron microscopy (TEM) and prefers to occupy the octahedral site at a high doping level. Such dual occupation behavior affects the tetrahedral and octahedral sublattices differently, resulting in nonmonotonic saturation magnetization variation, reduced magnetocrystalline anisotropy and negative magnetization in the zero field cooling (ZFC) process. By controlling the Ca doping amount, increased saturation magnetization and reduced coercivity can be obtained simultaneously. Our findings establish the relationship between the atomic-scale structural change and the macroscopic magnetic properties of spinel ferrites, promoting the development of new ferrite materials.

Photothermal Effect- and Interfacial Chemical Bond-Modulated NiOx/Ta3N5 Heterojunction for Efficient CO2 Photoreduction.

Photothermal catalysis, which combines light promotion and thermal activation, is a promising approach for converting CO2 into fuels. However, the development of photothermal catalysts with effective light-to-heat conversion, strong charge transfer ability, and suitable active sites remains a challenge. Herein, the photothermal effect- and interfacial N-Ni/Ta-O bond-modulated heterostructure composed of oxygen vacancy-rich NiOx and Ta3N5 was rationally fabricated for efficient photothermal catalytic CO2 reduction. Beyond the charge separation capability conferred by the NiOx/Ta3N5 heterojunction, we observed that the N-Ni and Ta-O bonds linking NiOx and Ta3N5 form a spatial charge transfer channel, which enhances the interfacial electron transfer. Additionally, the presence of surface oxygen vacancies in NiOx induced nonradiative relaxation, resulting in a pronounced photothermal effect that locally heated the catalyst and accelerated the reaction kinetically. Leveraging these favorable factors, the NiOx/Ta3N5 hybrids exhibit remarkably elevated activity (≈32.3 µmol·g-1·h-1) in the conversion of CO2 to CH4 with near-unity selectivity, surpassing the performance of bare Ta3N5 by over 14 times. This study unveils the synergistic effect of photothermal and interfacial chemical bonds in the photothermal-photocatalytic heterojunction system, offering a novel approach to enhance the reaction kinetics of various catalysts.

Tunable CO2-to-syngas conversion via strong electronic coupling in S-scheme ZnGa2O4/g-C3N4 photocatalysts.

The conversion of CO2 into syngas, a mixture of CO and H2, via photocatalytic reduction, is a promising approach towards achieving a sustainable carbon economy. However, the evolution of highly adjustable syngas, particularly without the use of sacrifice reagents or additional cocatalysts, remains a significant challenge. In this study, a step-scheme (S-scheme) 0D ZnGa2O4 nanodots (∼7 nm) rooted g-C3N4 nanosheets (denoted as ZnGa2O4/C3N4) heterojunction photocatalyst was synthesized vis a facial in-situ growth strategy for efficient CO2-to-syngas conversion. Both experimental and theoretical studies have demonstrated that the polymeric nature of g-C3N4 and highly distributed ZnGa2O4 nanodots synergistically contribute to a strong interaction between metal oxide and C3N4 support. Furthermore, the desirable S-scheme heterojunction in ZnGa2O4/C3N4 efficiently promotes charge separation, enabling strong photoredox ability. As a result, the S-scheme ZnGa2O4/C3N4 exhibited remarkable activity and selectivity in photochemical conversion of CO2 into syngas, with a syngas production rate of up to 103.3 µ mol g-1 h-1, even in the absence of sacrificial agents and cocatalyst. Impressively, the CO/H2 ratio of syngas can be tunable within a wide range from 1:4 to 2:1. This work exemplifies the effectiveness of a meticulously designed S-scheme heterojunction photocatalyst for CO2-to-syngas conversion with adjustable composition, thus paving the way for new possibilities in sustainable energy conversion and utilization.

Impact of gadolinium doping into the frustrated antiferromagnetic lithium manganese oxide spinel.

Cubic spinel LiMn2O4 (LMO) are promising electrode materials for advanced technological devices owing to their rich electrochemical properties. Here, a series of Gd3+-doped LiMn2O4 were synthesized using a simple one-step sol-gel synthesis, and a systematized study on the effect of increasing Gd3+ concentration on magnetic properties is conferred. The Raman and density functional theory (DFT) calculations of the synthesized materials were correlated with the magnetic properties; we observed a high coercivity value for the doped LMO compared to pristine LMO, which scales down from 0.57T to 0.14T with an increase in Gd concentration. The samples exhibited paramagnetic (at 300K) to antiferromagnetic (at 5K) transition and variation in the magnetic moment due to the replacement of Mn+2 or Mn+3 ion by Gd+3 ion from the octahedral 16d lattice site. The observed phase transitions in the hysteresis curve below the Neel temperature (TN) at 5K are found to be due to the superexchange mechanism.

Experimental and computational studies on the Cinchona anchored calixarene catalysed asymmetric Michael addition reaction.

Lower-rim Cinchona anchored calix[4]arene cationic catalysts were developed for asymmetric Michael addition of acetylacetone to ß-nitrostyrenes. The desired Michael adducts were formed with high yields and enantioselectivities. Density functional theory investigations throw light on the catalyst-substrate interaction and the reaction mechanism.

Facet-Dependent Bactericidal Activity of Ag3PO4 Nanostructures against Gram-Positive/Negative Bacteria.

Ag3PO4 nanostructures (APNs) containing silver (Ag metal; of the noble metal families) have the potential to exhibit enzyme-mimetic activity. A nanostructure shape, including its surface facets, can improve the bioactivity of enzyme mimicry, yet the molecular mechanisms remain unclear. Herein, we report facet-dependent peroxidase and oxidase-like activity of APNs with both antibacterial and biofilm degrading properties through the generation of reactive oxygen species. Cubic APNs had superior antibacterial effects than rhombic dodecahedral shapes when inhibiting Gram-positive and Gram-negative bacterial pathogen proliferation and biofilm degradation. A similar performance was observed for rhombic dodecahedral shapes, being greater than tetrahedral-shaped APNs. The extent of enzyme-mimetic activity is attributed to the facets {100} present in cubic APNs that led the peroxide radicals to inhibit the proliferation of bacteria and degrade biofilm. These facets were compared to rhombic dodecahedral APNs {110} and tetrahedral APNs {111}, respectively, to reveal a facet-dependent enhanced antibacterial activity, providing a plausible mechanism for shape-dependent APNs material enzyme-mimetic effects on bacteria. Thus, our research findings can provide a direction to optimize bactericidal materials using APNs in clinically relevant applications.

Sulfur-doped wood-derived porous carbon for optimizing electromagnetic response performance.

Bio-mass materials have been selected as one of the advanced electromagnetic (EM) functional materials due to their natural porous framework for dynamically and flexibly optimizing the EM response property. Herein, we demonstrate sulfur-doped wood-derived porous carbon EM materials (SPC) for optimizing the EM response performance via the coupling between doped heterostructures and the original 3D microchannels. The experimental results reveal that both the dielectric loss capacity and interfacial impedance matching could be increased by the sulfur-doped heterostructures. By tailoring the sulfur content, the microwave absorption (normalized RLmin) of SPC could be optimized to -15.90 dB mm-1, while the effective absorption bandwidth (EABRL≤-10 dB) could cover the K band. Moreover, the shielding effectiveness of SPC can be enhanced from 10 dB to 30 dB with the assistance of water, ascribed to the super-wettability performance. This present study provides a novel strategy to further optimize the EM response performance of wood-derived materials, and meanwhile could be widely extended to other bio-mass absorbers.

Novel Superstructure-Phase Two-Dimensional Material 1T-VSe2 at High Pressure.

A superstructure can elicit versatile new properties in materials by breaking their original geometrical symmetries. It is an important topic in the layered graphene-like two-dimensional transition metal dichalcogenides, but its origin remains unclear. Using diamond-anvil cell techniques, synchrotron X-ray diffraction, X-ray absorption, and first-principles calculations, we show that the evolution from weak van der Waals bonding to Heisenberg covalent bonding between layers induces an isostructural transition in quasi-two-dimensional 1T-type VSe2 at high pressure. Furthermore, our results show that high pressure induces a novel superstructure at 15.5 GPa rather than suppresses it as it would normally, which is unexpected. It is driven by Fermi-surface nesting, enhanced by pressure-induced distortion. The results suggest that the superstructure not only appears in the two-dimensional structure but also can emerge in the pressure-tuned three-dimensional structure with new symmetry and develop superconductivity.

Role of Aromatic Moiety in the Probe Property toward Picric Acid: Synthesis, Crystal Structure, Spectroscopy, Microscopy, and Computational Modeling of a Knoevenagel Condensation Product of d-Glucose.

Molecular probes for picric acid (PA) in both solution and solid states are important owing to their wide usage in industry. This paper deals with the design and development of a glucosyl conjugate of pyrene (L 1 ) along with control molecular systems, possessing anthracenyl (L 2 ), naphtyl (L 3 ), and phenyl (L 4 ) moieties, via Knoevenagel condensation of 2,4-pentanedione with d-glucose. The selectivity of L 1 toward PA has been demonstrated on the basis of fluorescence and absorption spectroscopy, and the species of recognition by electrospray ionization mass spectrometry. The role of the aromatic group in the selective receptor property has been addressed among L 1 , L 2 , L 3 , and L 4 . The structural features of the {L 1 + PA} complex were established by density functional theory computations. L 1 was demonstrated to detect PA in solid state selectively over other nitroaromatic compounds (NACs). To study the utility of L 1 in film, cellulose paper strips coated with L 1 were used and demonstrated the selective detection of PA. The observed microstructural features of L 1 and its complex {L 1 + PA} differ distinctly in both atomic force microscopy and scanning electron microscopy, all in the support of the complex formation. Thus, L 1 was demonstrated as a sensitive, selective, and inexpensive probe for PA over several NACs by visual, spectral, and microscopy methods.

Theoretical insight into the mechanism of photoreduction of CO2 to CO by graphitic carbon nitride.

Graphitic carbon nitride (g-C3N4) is a promising photocatalyst for the reduction of CO2 into fuels. However, the reduction mechanism of CO2 using g-C3N4 is not clear in the literature. In the present study, the fixation of CO2 and the formation of carbamate on the nitrogen atom at the edge of g-C3N4 were investigated using first-principles density functional theory. The calculated results shows that two adjacent bare nitrogen atoms at the edge of g-C3N4 could be the activation sites for the proton and CO2 molecule respectively, which are crucial to the formation of carbamate. The calculated energy barrier of carbamate formation is 0.95 eV for a preferential pathway. From studies on these micro processes, we propose a mechanism with proton assistance for the g-C3N4-catalyzed photoreduction of CO2 to CO.

Self-Supported FeCo2S4 Nanotube Arrays as Binder-Free Cathodes for Lithium-Sulfur Batteries.

Inhibiting the shuttle effect, buffering the volume expansion, and improving the utilization of sulfur have been the three strategic points for developing a high-performance lithium-sulfur (Li-S) battery. Driven by this background, a flexible sulfur host material composed of FeCo2S4 nanotube arrays grown on the surface of carbon cloth is designed for a binder-free cathode of the Li-S battery through two-step hydrothermal method. Among the rest, the interconnected carbon fiber skeleton of the composite electrode ensures the basic electrical conductivity, whereas the FeCo2S4 nanotube arrays not only boost the electron and electrolyte transfer but also inhibit the dissolution of polysulfides because of their strong chemical adsorption. Meanwhile, the hollow structures of these arrays can provide a large inner space to accommodate the volume expansion of sulfur. More significantly, the developed composite electrode also reveals a catalytic action for accelerating the reaction kinetic of the Li-S battery. As a result, the FeCo2S4/CC@S electrode delivers a high discharge capacity of 1384 mA h g-1 at the current density of 0.1 C and simultaneously exhibits a stable Coulombic efficiency of about 98%.

Tweaking the Electronic and Optical Properties of α-MoO3 by Sulphur and Selenium Doping - a Density Functional Theory Study.

First-principles calculations were carried out to understand how anionic isovalent-atom doping affects the electronic structures and optical properties of α-MoO3. The effects of the sulphur and selenium doping at the three unique oxygen sites (Ot, Oa, and Ot) of α-MoO3 were examined. We found that the valence p orbitals of Sulphur/Selenium dopant atoms give rise to impurity bands above the valence band maximum in the band structure of α-MoO3. The number of impurity bands in the doped material depends on the specific doping sites and the local chemical environment of the dopants in MoO3. The impurity bands give rise to the enhanced optical absorptions of the S- and Se-doped MoO3 in the visible and infrared regions. At low local doping concentration, the effects of the dopant sites on the electronic structure of the material are additive, so increasing the doping concentration will enhance the optical absorption properties of the material in the visible and infrared regions. Further increasing the doping concentration will result in a larger gap between the maximum edge of impurity bands and the conduction band minimum, and will undermine the optical absorption in the visible and infrared region. Such effects are caused by the local geometry change at the high local doping concentration with the dopants displaced from the original O sites, so the resulting impurity bands are no long the superpositions of the impurity bands of each individual on-site dopant atom. Switching from S-doping to Se-doping decreases the gap between the maximum edge of the impurity bands and conduction band minimum, and leads to the optical absorption edge red-shifting further into the visible and infrared regions.

Exploring the formation and electronic structure properties of the g-C3N4 nanoribbon with density functional theory.

The optical properties and condensation degree (structure) of polymeric g-C3N4 depend strongly on the process temperature. For polymeric g-C3N4, its structure and condensation degree depend on the structure of molecular strand(s). Here, the formation and electronic structure properties of the g-C3N4 nanoribbon are investigated by studying the polymerization and crystallinity of molecular strand(s) employing first-principle density functional theory. The calculations show that the width of the molecular strand has a significant effect on the electronic structure of polymerized and crystallized g-C3N4 nanoribbons, a conclusion which would be indirect evidence that the electronic structure depends on the structure of g-C3N4. The edge shape also has a distinct effect on the electronic structure of the crystallized g-C3N4 nanoribbon. Furthermore, the conductive band minimum and valence band maximum of the polymeric g-C3N4 nanoribbon show a strong localization, which is in good agreement with the quasi-monomer characters. In addition, molecular strands prefer to grow along the planar direction on graphene. These results provide new insight on the properties of the g-C3N4 nanoribbon and the relationship between the structure and properties of g-C3N4.

Differential Recognition of Anions with Selectivity towards F(-) by a Calix[6]arene-Thiourea Conjugate Investigated by Spectroscopy, Microscopy, and Computational Modeling by DFT.

Anion recognition studies were performed with triazole-appended thiourea conjugates of calix[6]arene (i.e., compound (6) L) by absorption and (1) H NMR spectroscopy by using nineteen different anions. The composition of the species of recognition was derived from ESI mass spectrometry. The absorption spectra of compound (6) L showed a new band at λ=455 nm in the presence of F(-) due to a charge transfer from the anion to the thiourea moiety and the absorbance increases almost linearly in the concentration range 5 to 200 µm. This is associated with a strong visual color change of the solution. Other anions, such as H2 PO4 (-) and HSO4 (-) , exhibit a redshift of the λ=345 nm band and the spectral changes are associated with the formation of an isosbestic point at λ=343 nm. (1) H NMR studies further confirm the binding of F(-) efficiently to the thiourea group among the halides by shifting the thiourea proton signals downfield followed by their disappearance after the addition of more than one equivalent of F(-) . The other anions also showed interactions with compound (6) L, however, their binding strength follows the order F(-) >CO3 (2-) >H2 PO4 (-) ≈CH3 COO(-) >HSO4 (-) . The NMR spectral changes clearly revealed the anion-binding region of the arms in case of all these anions. The anion binding to compound (6) L indeed stabilizes a flattened-cone conformation as deduced based on the calix-aromatic proton signals and was further confirmed by VT (1) H NMR experiments. The stabilization of the flattened-cone conformation was further augmented by the interaction of the butyl moiety of the nBu4 N(+) counterion. The structural features of the anion-bound species were demonstrated by DFT computations and the resultant structures carried the features that were predicted based on the (1) H NMR spectroscopic measurements. In addition, SEM images showed a marigold flower-type morphology for compound (6) L and this has been transformed into a chain-like structure of connected spherical particles in the presence of F(-) . The anion-induced microstructural features are reflective of the binding strength, size, and shape of the anions. The binding strengths of the anions by compound (6) L were further compared with that of compound (4) L, a calix[4]arene analogue of compound (6) L, in order to address the role of the number of arms built on the calixarene platform based on absorption spectroscopy, (1) H NMR spectroscopy, and DFT computations and it was found that compound (6) L is a better receptor for F(-) , which extends its interactions from all the three arms.

The Effect of Excess Electron and hole on CO2 Adsorption and Activation on Rutile (110) surface.

CO2 capture and conversion into useful chemical fuel attracts great attention from many different fields. In the reduction process, excess electron is of key importance as it participates in the reaction, thus it is essential to know whether the excess electrons or holes affect the CO2 conversion. Here, the first-principles calculations were carried out to explore the role of excess electron on adsorption and activation of CO2 on rutile (110) surface. The calculated results demonstrate that CO2 can be activated as CO2 anions or CO2 cation when the system contains excess electrons and holes. The electronic structure of the activated CO2 is greatly changed, and the lowest unoccupied molecular orbital of CO2 can be even lower than the conduction band minimum of TiO2, which greatly facilities the CO2 reduction. Meanwhile, the dissociation process of CO2 undergoes an activated CO2(-) anion in bend configuration rather than the linear, while the long crossing distance of proton transfer greatly hinders the photocatalytic reduction of CO2 on the rutile (110) surface. These results show the importance of the excess electrons on the CO2 reduction process.

Al atom on MoO3(010) surface: adsorption and penetration using density functional theory.

Interfacial issues, such as the interfacial structure and the interdiffusion of atoms at the interface, are fundamental to the understanding of the ignition and reaction mechanisms of nanothermites. This study employs first-principle density functional theory to model Al/MoO3 by placing an Al adatom onto a unit cell of a MoO3(010) slab, and to probe the initiation of interfacial interactions of Al/MoO3 nanothermite by tracking the adsorption and subsurface-penetration of the Al adatom. The calculations show that the Al adatom can spontaneously go through the topmost atomic plane (TAP) of MoO3(010) and reach the 4-fold hollow adsorption-site located below the TAP, with this subsurface adsorption configuration being the most preferred one among all plausible adsorption configurations. Two other plausible configurations place the Al adatom at two bridge sites located above the TAP of MoO3(010) but the Al adatom can easily penetrate below this TAP to a relatively more stable adsorption configuration, with a small energy barrier of merely 0.2 eV. The evidence of subsurface penetration of Al implies that Al/MoO3 likely has an interface with intermixing of Al, Mo and O atoms. These results provide new insights on the interfacial interactions of Al/MoO3 and the ignition/combustion mechanisms of Al/MoO3 nanothermites.

Triazole-Linked Quinoline Conjugate of Glucopyranose: Selectivity Comparison among Zn2+, Cd2+, and Hg2+ Based on Spectroscopy, Thermodynamics, and Microscopy, and Reversible Sensing of Zn2+ and the Structure of the Complex Using DFT.

A water-soluble triazole-linked quinoline conjugate of glucopyranose (L) has been synthesized and characterized, and its single-crystal X-ray diffraction (XRD) structure has been established. Binding of L toward different biologically relevant metal ions has been studied using fluorescence and absorption spectroscopy in HEPES buffer at pH 7.4. The conjugate L detects Zn2+ and Cd2+ with 30 ± 2 and 14 ± 1-fold fluorescence enhancement, respectively, but in the case of Hg2+, only a fluorescence quench was observed. The stoichiometry of the complex is 1:2 metal ion to the ligand in the case of Zn2+ and Cd2+ resulting in [Zn(L)2] and [Cd(L)2], and it is 1:1 in the case of Hg2+, as confirmed from their electrospray ionization mass spectrometry (ESIMS) spectra. Zn2+ shows greater exothermicity over Cd2+, whereas Hg2+ shows endothermicity , which supports the differences in their binding strength and the nature of the corresponding complex. L exhibits rod-shaped particles and upon complexation with Zn2+, it exhibits sphere-like morphological features in scanning electron microscopy (SEM) images. However, clustered aggregates are observed in Cd2+, whereas the [HgL] complex exhibits small fused spherical structures, and therefore the signature of these ions is seen in microscopy images. The computational studies revealed that the syn-[Zn(L)2] complex is stabilized by 9.7 kcal mol-1 more than that in the case of anti-[Zn(L)2] owing to the formation of hydrogen bonds between the two glucosyl moieties within the syn-complex. Among the anions studied, [Zn(L)2] is sensitive and selective toward the phosphate ion (H2PO4 -) with a minimum detection limit of 16 ± 2 ppb. Similarly, the [HgL] can act as a secondary sensor for CN- while also exhibiting reversibility. Based on the input-output characteristics, INHIBIT logic gate was built in the case of Zn2+ vs H2PO4 - and IMPLICATION logic gate was built in the case of Hg2+ vs CN-.

Ternary structure reveals mechanism of a membrane diacylglycerol kinase.

Diacylglycerol kinase catalyses the ATP-dependent conversion of diacylglycerol to phosphatidic acid in the plasma membrane of Escherichia coli. The small size of this integral membrane trimer, which has 121 residues per subunit, means that available protein must be used economically to craft three catalytic and substrate-binding sites centred about the membrane/cytosol interface. How nature has accomplished this extraordinary feat is revealed here in a crystal structure of the kinase captured as a ternary complex with bound lipid substrate and an ATP analogue. Residues, identified as essential for activity by mutagenesis, decorate the active site and are rationalized by the ternary structure. The γ-phosphate of the ATP analogue is positioned for direct transfer to the primary hydroxyl of the lipid whose acyl chain is in the membrane. A catalytic mechanism for this unique enzyme is proposed. The active site architecture shows clear evidence of having arisen by convergent evolution.

Water-Soluble 8-Hydroxyquinoline Conjugate of Amino-Glucose As Receptor for La(3+) in HEPES Buffer, on Whatman Cellulose Paper and in Living Cells.

A water-soluble glucopyranosyl conjugate, L, has been synthesized and characterized by different analytical and spectral techniques. The L has been demonstrated to have switch-on fluorescence enhancement of ∼75 fold in the presence of La(3+) among the nine lanthanide ions studied in the HEPES buffer at pH 7.4. A minimum detection limit of 140 nM (16 ± 2 ppb) was shown by L for La(3+) in the buffer at physiological pH. The utility of L has been demonstrated by showing its sensitivity toward La(3+) on Whatman filter paper strips. The reversible and reusable action of L has been demonstrated by monitoring the fluorescence changes as a function of the addition of La(3+) followed by F(-) and HPO4(2-) ions. The complexation of L by La(3+) was shown by absorption spectra wherein isosbestic behavior was observed. The Job's plot suggests a 2:1 complex between L and La(3+), and the same was supported by ESI-MS. The control molecular study revealed the necessity of hydroxy quinoline and the amine group for La(3+) ion binding and the glyco-moiety to bring water solubility and biocompatibility. The structural features of the [2L+La(3+)] complex were established by DFT computational calculations. The chemo-ensemble, [2L+La(3+)], is shown responsible for providing intracellular fluorescence imaging in HepG2 cells.