查看更多>>摘要：Air contamination caused by the ammonia slip phenomenon has gradually captured the researcher's ex-tensive attention.An effective strategy for controlling fugitive NH3 is critical to improving the air quality and living environment.In the present work,CuOx/La2Ce2O7 composite as a potential candidate catalyst is synthesized through the electrostatic adsorption method for the selective catalytic oxidation(SCO)of NH3 to N2.The 5％CuOx/La2Ce2O7 exhibits the best catalytic activity(T90=243℃)and ammonia con-version efficiency.The improvement of performance is mainly attributed to the superficial connection of[Ce-O-Cu],which enhances the capturing ability of ammonia molecule and accelerates the dissociating efficiency of N-H bonding for N2 evolution,simultaneously.This work provides a facile method to syn-thesis pyrochlore-like composite catalyst of NH3-SCO for solving the problem of ammonia slip pollution in the future.
查看更多>>摘要：The random mobility of charge carriers is a main factor causing the low photocatalytic efficiency of g-C3N4.Thus,the controllable migration of charge carriers is a rational strategy to suppress the charge recombination and facilitate charge separation.Herein,an ethylenediamine modified g-C3N4 displays im-proved photocatalytic activity.The excellent charge separation efficiency is confirmed to be a key factor for the enhancement.The TEM observation after photo-depositing Pt nanoparticles and DFT calculations verify the accumulation of electrons on some areas of g-C3N4 surface.The increased-NH2 groups signifi-cantly tune the electronic structure of g-C3N4 after the modification.The generation of midgap states also affects the charge separation.Our reports provide a simple method to manage the migration of charge carriers and enable electrons directional transfer,which suppresses the recombination and improves the photocatalytic activity.
查看更多>>摘要：In this work,a Bi2O2.33-CdS direct Z-scheme heterojunction was fabricated based on energy band en-gineering.The Bi2O2.33 core nanoflakes were first synthesized by electrodeposition which was followed by an annealing process to fabricate this heterojunction.Then the CdS shell was deposited on Bi2O2.33 nanoflakes utilizing the solution method,during which a suitable concentration of CdCl2 solution was used for forming a homogeneous and continuous integrated CdS shell.A space charge region and an in-ternal electric field from CdS(+)to Bi2O2.33(-),which drove a direct Z-scheme charge transfer process,were formed at the interface.The Bi2O2.33-CdS exhibited excellent photocatalytic performance for CO2 reduction mainly attributed to the satisfactory photoinduced charge separation and transport efficiency in the direct Z-scheme heterojunction.The photocatalytic CO2 reduction ability of Bi2O2.33-CdS was sig-nificantly enhanced compared with single Bi2O2.33 or CdS,with a CO yield rate of ca.2.9 μmol/(cm2 h)under a 300 W Xe lamp.The reduction of CO2 to CO demonstrated 94.0％selectivity.
查看更多>>摘要：Based on the effective continuum model,we study alternating-twist multilayer graphene system and emergence of magic angles and flat band topology.All the alternating-twist multilayer graphene sys-tem(from triple layers to few layers)are found to have flat bands at magic angles where the area of AA stacking equals n-fold(n is an integer)electron cyclotron area.From the pseudo-Landau-level represen-tation,there is always an isolated Dirac band in the alternating-twist graphene system constructed by odd number of layers.Since each pair of flat bands can be perceived as the zeroth pseudo-Landau-levels in two dimensional Dirac fermions,electron in the flat band pair can feel a pseudo-magnetic field with the same magnitude but the opposite sign.Calculated Chern number for each flat band is+1(or-1)which can be tuned by twisting in the vicinity of magic angles or by gating.The concurrent appearance of strong correlation and band topology of flat bands in the alternating-twist multilayer graphene may pave an avenue for the new understanding of superconductivity observed in triple-layered graphene,and supply a new playground for realizing(quantum)anomalous Hall effect.
查看更多>>摘要：The properties of modified conventional wrought aluminum alloys cannot be significantly enhanced by normal post-heat treatment in that the fine-grained strengthening,arising from high cooling rate in SLM,is underutilized.In this work,compared with the normal T6 heat treatment,a novel simple direct ag-ing regime was proposed to maintain the grain-boundary strengthening and to utilize the precipitation strengthening of secondary Al3Zr.It was found that a heterogeneous grain structure,which consisted of ultrafine equiaxed(～0.82 μm)and columnar(～1.80 μm)grains at the bottom and top of molten pool,respectively,was formed in the SLM processed sample.After direct aging(DA),the ultrafine grains were maintained and a mass of spherical coherent L12-Al3Zr particles with a mean radius of approximately 1.15 nm was precipitated.In contrast,after solution treatment and aging(STA),a significant grain coars-ening occurred in the equiaxed grain region.Meanwhile,the coarsening L12-Al3Zr particles,nano-sized S'phases and GPB zones were detected in the STA sample.This subsequently induced that the yield strength of the DA sample(～435 MPa)was higher than that of the STA sample(～402 MPa)owing to the grain boundary strengthening and precipitation strengthening.Both the STA and DA samples exhibited a higher strength than that of the other SLMed Al-Cu-Mg series alloys;this was comparable to that of the wrought AA2024-T6 alloy(～393 MPa).Both the STA and DA samples exhibited a higher strength than that of the other SLMed Al-Cu-Mg series alloys;this was comparable to that of the wrought AA2024-T6 alloy(～393 MPa).
查看更多>>摘要：The study of Frequency Selective Surface(FSS)by Direct ink writing(DIW)has attracted much atten-tion due to the convenience and effectiveness of 3D printing technology.However,the limited printing precision of DIW has heavily restricted its applications as the electromagnetic performance is highly sen-sitive to it,especially the precision at the microscale.Herein,the ultra-high printing precision of FSS was achieved through DIW by the uniformly dispersed graphene sheets to deeply modify the rheological be-havior and the steric hindrance effect.Thus,the highly precision of the printed filament width as thin as 67 μm with a space of only 42 μm were achieved,which is difficult for conventional DIW,and no struc-tural distortion is found after 3D printing,no matter it was 2D printed on a flat surface or the sharply skewed hook face,or even 3D printed to architectural structures.According to the highly improved pre-cision,the electromagnetic performance matching between the designed model and the printed physi-cal FSS device was perfectly achieved,reducing the center frequency error less than 0.3 GHz,and the transmission coefficient error less than 0.046.Our work promises an effective and easy preparation of high-quality FSS from the aid of graphene.
查看更多>>摘要：In recent years,graphene-based composite films have been greatly developed in the field of electromag-netic shielding interference(EMI).However,it is still a huge challenge to prepare graphene-based com-posite films with excellent mechanical properties,conductivity and electromagnetic shielding properties.In this work,we adopted a facile and effective method by annealing the alkali-treated polyacrylonitrile(aPAN)nanofibers reinforced graphene oxide(GO)composite films at 2000℃to obtain graphene-carbon nanofibers composite films(GCFs).Microscopically,carbon nanofibers(CNFs)were intercalated into the graphene sheets,and microgasbags structure was formed during the heat treatment process.The special structure makes GCFs have superior tensile strength(10.4 MPa)at 5％strain.After repeated folding over 1000 times,the films still demonstrate excellent structural integrity and flexibility performance.Interest-ingly,the graphene-based composite films with 10 wt％aPAN nanofibers exhibit an extremely low density of about 0.678 g/cm3 and excellent electrical conductivity of 1.72×105 S/m.Further,an outstanding elec-tromagnetic shielding effectiveness(SE)of 55-57 dB was achieved,and the corresponding value of the specific SE/thickness can reach 67,601-70,059 dB.cm2/g,which is the highest among reported graphene-based shielding materials.The significant electromagnetic shielding performance is due to the synergistic enhancement effect brought by the excellent conductivity of carbon nanofibers and graphene,the formed effective conductive network and the microgasbags structure.Electromagnetism simulation further clar-ified that the underlying mechanism should be mainly attributed to the conduction loss and multiple reflections caused by the special structure of GCFs.This work will provide new solutions for low den-sity,high flexibility and excellent electromagnetic shielding properties materials in the next generation of foldable and wearable electronics.
查看更多>>摘要：Flame-retardant composites with high electromagnetic interference(EMI)shielding performance are de-sirable for electronic device packaging.Despite great potential of MXene for high EMI,it still remains a great challenge to develop high-performance flame-retardant polymer/MXene composites with excel-lent EMI shielding effectiveness because of the poor oxidative stability of MXene.Herein,phosphory-lated MXene/polypropylene(PP)composites are prepared by coating phosphorylated MXene on PP fabric followed by spraying polyethylenimine(PEI)and hot-pressing.The phosphorylated MXene proves to be more durable against oxidation than pure MXene due to the protection effect of polyphosphates.Upon hot-pressing,melted PP fibers are fused together at their contact points and thus as-prepared composites are bi-continuous with two interpenetrating phases.The composites show significantly improved thermal stability and flame retardancy relative to pure PP,with a low total heat release(THR)of 3.7 kj/g and a heat release rate(HRR)of 50.0 W/g,which are reduced by 78％and 87％,respectively.In addition,the composites exhibit a high electrical conductivity of～36,700 S/m and an EMI shielding performance of～90 dB over the whole frequency range of 8-12 GHz with a thickness of～400 μm.The as-developed PP/MXene composites hold great promise for reliable protection of next-generation electronic devices working in complex environments.
查看更多>>摘要：The complex micromechanical response among grains remains a persistent challenge to understand the deformation mechanism of titanium alloys during cold rolling.Therefore,in this work,a multiscale crystal plasticity finite element method of dual-phase alloy was proposed and secondarily developed based on LS-DYNA software.Afterward,the texture evolution and slip mode of a Ti-5.5Mo-7.2Al-4.5Zr-2.6Sn-2.1Cr alloy,based on the realistic 3D microstructure,during cold rolling(20％thickness reduction)were sys-tematically investigated.The relative activity of the<1120>{0001}slip system in the α phase gradually increased,and then served as the main slip mode at lower Schmid factor(<0.2).In contrast,the contri-bution of the<1123>{1011}slip system to the overall plastic deformation was relatively limited.For theβ phase,the relative activity of the<111>{110}slip system showed an upward tendency,indicating the important role of the critical resolved shear stress relationship in the relative activity evolutions.Further-more,the abnormally high strain of very few β grains was found,which was attributed to their severe rotations compelled by the neighboring pre-deformed α grains.The calculated pole figures,rotation axes,and compelled rotation behavior exhibited good agreement to the experimental results.
查看更多>>摘要：To improve the uniformity and the content of HfB2 in HfB2-Si-based ceramic coating and alleviate the damage of substrate,and then enhance the high-temperature(1700℃)oxidation and cyclic ablation resistances of carbon/carbon composites,a close-knit double layer HfB2-SiC/SiC coatings with a mosaic structure and high content of HfB2 were prepared by a novel dipping-carbonization assisted pack cemen-tation methods(DPC-HS/S).In contrast,a HfB2-SiC/SiC coatings were also fabricated by pack cementa-tion(PC-HS/S).Results revealed that the oxidation and ablation protective performances of the DPC-HS/S coatings were superior to those of PC-HS/S coatings.After 30 thermal cycles between 1500℃and room temperature,the mass gain of the coated sample was 0.78％,and the mass loss was 1.65％after oxidation at 1700℃for 156 h.Moreover,under an oxyacetylene torch ablation for 180 s(3 cycles),the linear abla-tion rate of the DPC-HS/S coated specimen was 1.62 um/s,which was much lower than that of PC-HS/S coated specimen(3.08μm/s).
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