Effects of Ti and Mn Co-substitution on P4mm BiFeO3: An Ab Initio Calculation

Tetragonal BiFeO₃ (BFO), which has a giant spontaneous polarization, has attracted a great deal of attention recently. In this paper, we systematically study the structural, magnetic, electronic and optic properties of BFO, BiFe_0.75Mn_0.25 O ₃ (BFMM), and BiFe_0.75Ti_0.125Mn_0.125 O ₃ (BFMT). Results show that doping Ti and Mn into the Fe sites increases the c/a ratio and enhances the magnetization of BiFeO₃ from 0 to 5 μ_B. The crystal symmetry changes from orthogonality to tetragonality with half of the Mn atoms being replaced by Ti in BiFe_0.75Mn_0.25 O ₃, which suppresses the energy splitting of the Mn 3d orbitals and thus enlarge the band gap to 1.21 eV for BiFe_0.75Ti_0.125Mn_0.125 O ₃. Our calculated Bader charge and charge density difference show that the smallest volume of BiFe_0.75Mn_0.25 O ₃ arises from the strong Mn–O bonds in BiFe_0.75Mn_0.25 O ₃. Further investigations indicate similar optical behaviors for BiFeO₃ and BiFe_0.75Ti_0.125Mn_0.125 O ₃. However, BiFe_0.75Mn_0.25 O ₃ exhibits strong absorption in the infrared region for the transition from O 2p to Mn \({e_{g}^{2}}\) and \(t_{2g}^{3}\).     

A Novel and Facile Route to Synthesize Atomic‐Layered MoS2 Film for Large‐Area Electronics

High‐quality and large‐area molybdenum disulfide (MoS₂) thin film is highly desirable for applications in large‐area electronics. However, there remains a challenge in attaining MoS₂ film of reasonable crystallinity due to the absence of appropriate choice and control of precursors, as well as choice of suitable growth substrates. Herein, a novel and facile route is reported for synthesizing few‐layered MoS₂ film with new precursors via chemical vapor deposition. Prior to growth, an aqueous solution of sodium molybdate as the molybdenum precursor is spun onto the growth substrate and dimethyl disulfide as the liquid sulfur precursor is supplied with a bubbling system during growth. To supplement the limiting effect of Mo (sodium molybdate), a supplementary Mo is supplied by dissolving molybdenum hexacarbonyl (Mo(CO)₆) in the liquid sulfur precursor delivered by the bubbler. By precisely controlling the amounts of precursors and hydrogen flow, full coverage of MoS₂ film is readily achievable in 20 min. Large‐area MoS₂ field effect transistors (FETs) fabricated with a conventional photolithography have a carrier mobility as high as 18.9 cm² V^?1 s^?1, which is the highest reported for bottom‐gated MoS₂‐FETs fabricated via photolithography with an on/off ratio of ≈10⁵ at room temperature.     

Design of Ultrathin Pt‐Based Multimetallic Nanostructures for Efficient Oxygen Reduction Electrocatalysis

Nanocatalysts with high platinum (Pt) utilization efficiency are attracting extensive attention for oxygen reduction reactions (ORR) conducted at the cathode of fuel cells. Ultrathin Pt‐based multimetallic nanostructures show obvious advantages in accelerating the sluggish cathodic ORR due to their ultrahigh Pt utilization efficiency. A focus on recent important developments is provided in using wet chemistry techniques for making/tuning the multimetallic nanostructures with high Pt utilization efficiency for boosting ORR activity and durability. First, new synthetic methods for multimetallic core/shell nanoparticles with ultrathin shell sizes for achieving highly efficient ORR catalysts are reviewed. To obtain better ORR activity and stability, multimetallic nanowires or nanosheets with well‐defined structure and surface are further highlighted. Furthermore, ultrathin Pt‐based multimetallic nanoframes that feature 3D molecularly accessible surfaces for achieving more efficient ORR catalysis are discussed. Finally, the remaining challenges and outlooks for the future will be provided for this promising research field.     

Transformation of monolayer MoS<Subscript>2</Subscript> into multiphasic MoTe<Subscript>2</Subscript>: Chalcogen atom-exchange synthesis route

Molybdenum ditelluride (MoTe2),which is an important transition-metal dichalcogenide,has attracted considerable interest owing to its unique properties,such as its small bandgap and large Seebeck coefficient.However,the batch production of monolayer MoTe2 has been rarely reported.In this study,we demonstrate the synthesis of large-domain (edge length exceeding 30 μm),monolayer MoTe2 from chemical vapor deposition-grown monolayer MoS2 using a chalcogen atom-exchange synthesis route.An in-depth investigation of the tellurization process reveals that the substitution of S atoms by Te is prevalently initiated at the edges and grain boundaries of the monolayer MoS2,which differs from the homogeneous selenization of MoS2 flakes with the formation of alloyed Mo-S-Se hybrids.Moreover,we detect a large compressive strain (approximately-10％) in the transformed MoTe2 lattice,which possibly drives the phase transition from 2H to 1T'at the reaction temperature of 500 ℃.This phase change is substantiated by experimental facts and first-principles calculations.This work introduces a novel route for the templated synthesis of two-dimensional layered materials through atom substitutional chemistry and provides a new pathway for engineering the strain and thus the intriguing physics and chemistry.     

Effect of stents coated with a combination of sirolimus and alpha-lipoic acid in a porcine coronary restenosis model

The aim of this study was to evaluate antiproliferative sirolimus- and antioxidative alpha-lipoic acid (ALA)-eluting stents using biodegradable polymer [poly-l-lactic acid (PLA)] in a porcine coronary overstretch restenosis model. Forty coronary arteries of 20 pigs were randomized into four groups in which the coronary arteries had a bare metal stent (BMS, n = 10), ALA-eluting stent with PLA (AES, n = 10), sirolimus-eluting stent with PLA (SES, n = 10), or sirolimus- and ALA-eluting stent with PLA (SAS, n = 10). A histopathological analysis was performed 28 days after the stenting. The ALA and sirolimus released slowly over 30 days. There were no significant differences between groups in the injury or inflammation score; however, there were significant differences in the percent area of stenosis (56.2 ± 11.78 % in BMS vs. 51.5 ± 12.20 % in AES vs. 34.7 ± 7.23 % in SES vs. 28.7 ± 7.30 % in SAS, P < 0.0001) and fibrin score [1.0 (range 1.0–1.0) in BMS vs. 1.0 (range 1.0–1.0) in AES vs. 2.0 (range 2.0–2.0) in SES vs. 2.0 (range 2.0–2.0) in SAS, P < 0.0001] between the four groups. The percent area of stenosis based on micro-computed tomography corresponded with the restenosis rates based on histopathological stenosis in different proportions in the four groups (54.8 ± 7.88 % in BMS vs. 50.4 ± 14.87 % in AES vs. 34.5 ± 7.22 % in SES vs. 28.9 ± 7.22 % in SAS, P < 0.05). SAS showed a better neointimal inhibitory effect than BMS, AES, and SES at 1 month after stenting in a porcine coronary restenosis model. Therefore, SAS with PLA can be a useful drug combination for coronary stent coating to suppress neointimal hyperplasia.     

不同材料双层球缺罩侵彻特性的研究

采用数值模拟及钢靶侵彻试验两种方法研究了单层钛合金球缺罩、钛合金/铜、铝合金/铜双层球缺罩形成的3种杆式射流对45#钢锭靶板侵彻深度和开孔的问题。研究结果表明:不同材料的双层球缺罩形成的杆式射流对45#钢锭靶板的开孔孔径和侵彻深度大小均有直接影响,且钛合金/铜双层罩杆式射流破甲深度相对于铝合金/铜双层罩有一定提高,其开孔孔径明显增大。而单层钛合金药型罩杆式射流整体速度最大,开孔孔径较钛合金/铜、铝合金/铜双层罩杆式射流有明显提高,但破甲能力较低。研究结果对于武器战斗部设计具有一定的指导作用。     

Highly Exposed ?NH2 Edge on Fragmented g-C3N4 Framework with Integrated Molybdenum Atoms for Catalytic CO2 Cycloaddition: DFT and Techno-Economic Assessment

This study focuses on the applicability of single-atom Mo-doped graphitic carbon nitride (GCN) nanosheets which are specifically engineered with high surface area (exfoliated GCN),  NH₂ rich edges, and maximum utilization of isolated atomic Mo for propylene carbonate (PC) production through CO₂ cycloaddition of propylene oxide (PO). Various operational parameters are optimized, for example, temperature (130 °C), pressure (20 bar), catalyst (Mo₂GCN), and catalyst mass (0.1 g). Under optimal conditions, 2% Mo-doped GCN (Mo₂GCN) has the highest catalytic performance, especially the turnover frequency (TOF) obtained, 36.4 h⁻¹ is higher than most reported studies. DFT simulations prove the catalytic performance of Mo₂GCN significantly decreases the activation energy barrier for PO ring-opening from 50–60 to 4.903 kcal mol⁻¹. Coexistence of Lewis acid/base group improves the CO₂ cycloaddition performance by the formation of coordination bond between electron-deficient Mo atom with O atom of PO, while  NH₂ surface group disrupts the stability of CO₂ bond by donating electrons into its low-level empty orbital. Steady-state process simulation of the industrial-scale consumes 4.4 ton h⁻¹ of CO₂ with PC production of 10.2 ton h⁻¹. Techno-economic assessment profit from Mo₂GCN is estimated to be 60.39 million USD year⁻¹ at a catalyst loss rate of 0.01 wt% h⁻¹.