Antiferromagnetic Semiconductor BaMnO₃ Hexagonal Perovskite with a Direct Bandgap

The unique properties of direct bandgap semiconductors make it important to search for semiconductors exhibiting this phenomenon in perovskite materials. In this study, we employed first-principles calculations to investigate the crystal structures, magnetic configurations, and electronic properties of hexagonal perovskite BaMnO3 in its 4H and 6H phases. The results indicate that both structures exhibit antiferromagnetic characteristics, in which the Mn–O–Mn superexchange plays the dominant role in the 4H phase, although there is a competition between the Mn–Mn direct exchange interaction and the Mn–O–Mn superexchange interaction. In contrast, these two interactions exhibit harmonious coexistence in the 6H phase, and the two antiferromagnetic transitions occurring in the experimental phase should be related to the synergistic effect between them. Despite their different internal arrangements, they exhibit the same charge combination of Ba2+Mn4+O2–3. More importantly, both phases exhibit semiconductor properties with a direct bandgap, making it suitable to serve as an alternative material for photovoltaic and optoelectronic devices. In particular, the band gap of the 4H phase is just the right size to absorb visible light, and the 6H phase should be a potential candidate to absorb light in the ultraviolet region

Tuning the Chemical Hardness of Boron Nitride Nanosheets by Doping Carbon for Enhanced Adsorption Capacity

The chemical hardness of adsorbents is an important physicochemical property in the process of adsorption based on the hard and soft acids and bases (HSAB) theory. Tuning chemical hardness of adsorbents modulated by their concomitants is a promising approach to enhance the adsorptive capacity in principle. In the present work, we report an efficient strategy that the adsorption capacity for aromatic sulfocompounds can be enhanced by tuning the chemical hardness. This strategy is first theoretically explored by introducing C element into the network of hexagonal boron nitride (h-BN) based on a series of model materials (model_<i>x</i>C, <i>x</i> = 1–5). Computational results show that the chemical hardness is reduced after gradually C-doping, which may lead to an enhancement of adsorption capacity according to the HSAB theory. Then, a series of C-doped h-BN materials (BCN-<i>x</i>, <i>x</i> = 10–50) were controlled synthesized. All of the as-prepared materials show better adsorption capacities (e.g., 27.43 mg g^–1 for BCN-50) than pure h-BN. Experiment results show that the adsorption capacity correlates well with the C content in the BCN-<i>x</i>, which is consistent with the results predicted by theoretical calculation. This strategy may be helpful to rationally design highly efficient adsorbents in separation engineering and may be expanded to similar two-dimensional materials, where the π–π interaction is the dominant driven force

A DFT Study of the Extractive Desulfurization Mechanism by [BMIM]⁺[AlCl₄]⁻ Ionic Liquid

In this work, the interaction nature between [BMIM]⁺[AlCl₄]⁻ ionic liquid (IL) and aromatic sulfur compounds (thiophene, benzothiophene, and dibenzothiophene) has been studied by means of density functional theory (M06-2X functional) combined with an implicit solvation model. Although [BMIM]⁺[AlCl₄]⁻ is a metal-containing IL, its extractive desulfurization mechanism is different from other metal-containing ILs but similar to non-metal-containing ILs. Important reactions involved in extractive desulfurization (EDS) were systematically studied. Our results have demonstrated that both the cation and the anion play important roles in EDS. On the basis of the structure analysis, reduced density gradient analaysis (RDG), and energy decomposition analysis, [BMIM]⁺ cation affords a π–π interaction while [AlCl₄]⁻ anion provides a hydrogen bonding interaction. Electrostatic potential analysis implies the dominant π–π interaction and hydrogen bonding interaction are driven by electrostatic interaction between IL and aromatic sulfur compounds. Interaction energy between [BMIM]⁺[AlCl₄]⁻ and thiophene (TH), benzothiophene (BT), and dibenzothiophene (DBT) follows the order TH < BT < DBT. Moreover, Al-containing IL with a high molar ratio of AlCl₃ ([BMIMCl]/2­[AlCl₃]) has also been studied. Results show that [Al₂Cl₇]⁻ species will be formed with excess AlCl₃. However, the [Al₂Cl₇]⁻-based IL cannot improve the EDS performance. Improvement of EDS performance with a high molar ratio of AlCl₃ is credited to the Lewis acidity of AlCl₃. Charge analysis reveals that there is no obvious charge transfer during the reaction, which is different from Fe-containing ILs as well as solid sorbents. In addition, CH−π interaction is not important for the current system

Graphene-Analogue Hexagonal BN Supported with Tungsten-based Ionic Liquid for Oxidative Desulfurization of Fuels

Graphene-analogue hexagonal boron nitride (G-<i>h</i>-BN), as a novel few-layer material, was prepared and used as a support to coat with tungsten-based ionic liquid (IL) in oxidative desulfurization. Designed G-<i>h</i>-BN supported with tungsten-based IL (IL/G-<i>h</i>-BN) heterogeneous catalyst was characterized by atomic force microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, X-ray diffraction, Raman and X-ray photoelectron spectroscopy. This few-layer material supported with IL strategy makes the usage amount of IL reduce remarkably, which not only presents excellent catalytic activity but also is superior to homogeneous catalysts of ILs themselves. Additionally, compared with the multilayer hexagonal boron nitrides (M-<i>h</i>-BN) or commercial bulk BN supported with IL, the IL/G-<i>h</i>-BN catalyst exhibited better catalytic activity in oxidation of dibenzothiophene, reaching 99.3% sulfur removal. The adsorption and catalytic oxidative desulfurization mechanism was further studied by gas chromatography–mass spectrometry, Fourier transform infrared spectroscopy, X-ray diffraction and UV-diffuse reflectance spectroscopy. Moreover, the IL/G-<i>h</i>-BN catalyst could be recycled five times with little decrease in catalytic activity

Phosphotungstic Acid Immobilized on Ionic Liquid-Modified SBA-15: Efficient Hydrophobic Heterogeneous Catalyst for Oxidative Desulfurization in Fuel

A heterogeneous catalyst system was synthesized by immobilizing phosphotungstic acid on ionic liquid-modified mesoporous silica SBA-15 and applied in oxidative desulfurization. Structure and properties of catalyst were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), N₂ adsorption–desorption, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and the contact angle. The results demonstrated that the synthesized catalyst possessed ordered mesopore structure and high special surface area. Due to the introduction of imidazole-based ionic liquid, the catalyst exhibited good wettability for model oil, which had significant contribution to desulfurization activity. Both DBT and 4,6-DMDBT could be removed completely at mild conditions (60 °C, 40 min). The removal of BT also can reach 81.3% within 60 min. Furthermore, the catalyst was recovered and reused in four reaction runs with a slight decrease in activity

Taming Interfacial Oxygen Vacancies of Amphiphilic Tungsten Oxide for Enhanced Catalysis in Oxidative Desulfurization

Heterogeneous catalysis has become an important branch in the catalytic field, whereas catalytic activities of heterogeneous catalysts are controlled by surface features and structural textures. Herein, we reported a synthesis of an amphiphilic tungsten oxide catalyst with oxygen vacancies. Characterizations showed that oxygen vacancies had been successfully introduced in tungsten oxide by a solution etching process in an acidic condition. The process not only gave rise to oxygen vacancies but also maintained the excellent amphiphilic feature of the catalyst. Both advantages of the catalysts led to a 100% sulfur removal from fuel oil and a 15 times recycling performance without a significant decrease in activity. Additionally, the adsorption and catalytic oxidative desulfurization process was proposed and further studied by gas chromatography–mass spectrometry (GC–MS)

Direct Determination of Atomic Structure and Magnetic Coupling of Magnetite Twin Boundaries

Clarifying how the atomic structure of interfaces/boundaries in materials affects the magnetic coupling nature across them is of significant academic value and will facilitate the development of state-of-the-art magnetic devices. Here, by combining atomic-resolution transmission electron microscopy, atomistic spin-polarized first-principles calculations, and differential phase contrast imaging, we conduct a systematic investigation of the atomic and electronic structures of individual Fe₃O₄ twin boundaries (TBs) and determine their concomitant magnetic couplings. We demonstrate that the magnetic coupling across the Fe₃O₄ TBs can be either antiferromagnetic or ferromagnetic, which directly depends on the TB atomic core structures and resultant electronic structures within a few atomic layers. Revealing the one-to-one correspondence between local atomic structures and magnetic properties of individual grain boundaries will shed light on in-depth understanding of many interesting magnetic behaviors of widely used polycrystalline magnetic materials, which will surely promote the development of advanced magnetic materials and devices

Silver Nanoparticle-Decorated Boron Nitride with Tunable Electronic Properties for Enhancement of Adsorption Performance

In this paper, a series of silver nanoparticle (AgNP)-decorated boron nitride (Ag-BN) with different Ag amounts were successfully synthesized by a one-pot pyrolysis method and used as novel high-efficiency adsorbents for the removal of organic pollutant tetracycline (TC) and rhodamine B (RhB). According to the adsorption capacity of the samples, the obtained optimal Ag/B molar ratio was 1%. The adsorption data fitted well with the pseudo-second-order kinetics and Langmuir isotherm models with the maximum adsorption capacity of 358 and 880 mg/g for TC and RhB, respectively. The thermodynamic studies suggested that the adsorption process was spontaneous and endothermic in nature. The introduction of AgNP onto BN enhanced the adsorption capacity on account of tunable electronic properties. The adsorption mechanism is discussed in detail with the effect of pH, density function theory (DFT), and thermodynamics

<i>A</i>‑Site-Doping Enhanced <i>B</i>‑Site Ordering and Correlated Magnetic Property in La_2–<i>x</i>Bi_<i>x</i>CoMnO₆

A series of Bi-doped La_2–<i>x</i>Bi_<i>x</i>CoMnO₆ double perovskite oxides are synthesized, and the impact of doping on crystal structures and magnetic properties is investigated comprehensively. X-ray photoelectron spectroscopy and Raman spectrum analyses reveal that ordering of Co and Mn ions at <i>B</i>-site is gradually improved with the rise of Bi concentration. Meanwhile, magnetic disordering is suppressed greatly by showing larger magnetic moments. Structurally, the Rietveld refinement shows that the bonds are elongated, while the bond angles are shrunken after doping, giving rise to lowered Curie temperature. We also observe a large negative zero-field-cooling magnetization, which is attributed to the formation of spin antiparallel or canted ferromagnetic domains and clusters that are separated by the antiphase boundaries. First-principles calculations confirm the enhanced Co–Mn ordering upon Bi doping by taking into account both the ordering and disordering configurations of La₂CoMnO₆, LaBiCoMnO₆, and Bi₂CoMnO₆. Moreover, we find a spin-state transition in the antisite Co ions from high-spin (Co²⁺-t_2g⁵e_g²) to low-spin state (Co³⁺-t_2g⁶e_g⁰), which is consistent with the increased total magnetic moments by the Bi doping

Additional file 2: of Multi-disciplinary team for early gastric cancer diagnosis improves the detection rate of early gastric cancer

Data of patients with early gastric cancer during MDT. The data contain representative endoscopic and histopathologic images of additional 39 patients diagnosed as early gastric cancer during MDT. (PDF 2710 kb