The integration of nano-semiconductors into electromagnetic wave absorption materials is a highly desirable strategy for intensifying dielectric polarization loss;achieving high-attenuation microwave absorption and re...The integration of nano-semiconductors into electromagnetic wave absorption materials is a highly desirable strategy for intensifying dielectric polarization loss;achieving high-attenuation microwave absorption and realizing in-depth comprehension of dielectric loss mechanisms remain challenges.Herein,ultrafine oxygen vacancy-rich Nb_(2)O_(5)semiconductors are confined in carbon nanosheets(ov-Nb_(2)O_(5)/CNS)to boost dielectric polarization and achieve high attenuation.The polarization relaxation,electromagnetic response,and impedance matching of the ov-Nb_(2)O_(5)/CNS are significantly facilitated by the Nb_(2)O_(5)semiconductors with rich oxygen vacancies,which consequently realizes an extremely high attenuation performance of-80.8 dB(>99.999999%wave absorption)at 2.76 mm.As a dielectric polarization center,abundant Nb_(2)O_(5)–carbon heterointerfaces can intensify interfacial polarization loss to strengthen dielectric polarization,and the presence of oxygen vacancies endows Nb_(2)O_(5)semiconductors with abundant charge separation sites to reinforce electric dipole polarization.Moreover,the three-dimensional reconstruction of the absorber using microcomputer tomography technology provides insight into the intensification of the unique lamellar morphology regarding multiple reflection and scattering dissipation characteristics.Additionally,ov-Nb_(2)O_(5)/CNS demonstrates excellent application potential by curing into a microwave-absorbing,machinable,and heat-dissipating plate.This work provides insight into the dielectric polarization loss mechanisms of nano-semiconductor/carbon composites and inspires the design of high-performance microwave absorption materials.展开更多
The initial field electron emission degradation behaviour of original nano-structured sp^2-bonded amorphous carbon films has been observed, which can be attributed to the increase of the work function of the film in t...The initial field electron emission degradation behaviour of original nano-structured sp^2-bonded amorphous carbon films has been observed, which can be attributed to the increase of the work function of the film in the field emission process analysed using a Fowler-Nordheim plot. The possible reason for the change of work function is suggested to be the desorption of hydrogen from the original hydrogen termination film surface due to field emission current-induced local heating. For the explanation of the emission degradation behaviour of the nano-structured sp2-bonded amorphous carbon film, a cluster model with a series of graphite （0001） basal surfaces has been presented, and the theoretical calculations have been performed to investigate work functions of graphite （0001） surfaces with different hydrogen atom and ion chemisorption sites by using first principles method based on density functional theory-local density approximation.展开更多
A new coordination polymer [Cd（bimc）2]n was obtained by the reaction of Hbimc with Cd（NO3） 2·4H2O in NaOH solution, and characterized by elemental analysis, IR and singlecrystal X-ray diffraction. The crystal...A new coordination polymer [Cd（bimc）2]n was obtained by the reaction of Hbimc with Cd（NO3） 2·4H2O in NaOH solution, and characterized by elemental analysis, IR and singlecrystal X-ray diffraction. The crystal belongs to orthorhombic, space group Pbcn with a = 12.533（4）, b = 15.705（5）, c = 15.200（5） A, V= 2991.8（15） A^3, Mr = 434.68, Z = 8, Dc = 1.930 g/cm^3, F（000） = 1712,μ（MoKa） = 1.492 mm^-1, the final R = 0.0410 and wR = 0.0804 for 1661 observed reflections （I 〉 2σ（I））. The Cd atom exhibits a distorted six-coordinate CdNzOa octahedral coordination geometry. The complex molecules are linked by both μ2-（η2-O, O^-）, NI and μ2-（η2-O, O^-）, N3 coordination modes of ligands to form cross-like wave （4, 4） layer structures which are further stacked through interlayer hydrogen bonds and π-π stacking interactions in an offset fashion to form a 3D supramolecular structure.展开更多
Diamond like carbon films, prepared by RF glow discharge on glass substrates, were irradiated by γ rays. The as deposited and irradiated films were characterized by Raman spectroscopy, electrical resistivity, a...Diamond like carbon films, prepared by RF glow discharge on glass substrates, were irradiated by γ rays. The as deposited and irradiated films were characterized by Raman spectroscopy, electrical resistivity, and infrared transmittance. It is shown that the irradiation of the γ rays can lead to the breaking of SP 3 C H and SP 2 C H bonds, slight increasing of SP 3 C C bonds, and induced hydrogen recombination with H 2 molecules, subsequently diffusing to the surface of the films. When the γ rays irradiation dose reached 10×10 4 Gy, the numbers of SP 3 C H bonds was decreased by about 50%, the resistivity of irradiated DLC films was increased, and the diamond like character of the films became more obvious. The structure of DLC films was modified when irradiated by γ rays. The irradiation mechanisms are briefly discussed.展开更多
Visible light photocatalysis of covalent organic frameworks(COFs) has made significant progress in recent years. Benzotrithiophene(BTT), a planar, electron-rich building block, turns out to be foundational in assembli...Visible light photocatalysis of covalent organic frameworks(COFs) has made significant progress in recent years. Benzotrithiophene(BTT), a planar, electron-rich building block, turns out to be foundational in assembling COFs in which the fullπ-conjugation of BTT is essential to facilitate electron transfer. Herein, a sp~2 carbon-conjugated COF, namely BTT-sp~2c-COF, is assembled from benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene-2,5,8-tricarbaldehyde and [1,1′:4′,1′′-terphenyl]-4,4′′-dicarbonitrile towards photocatalysis. More importantly, TEMPO(2,2,6,6-tetramethylpiperidin-1-yl)oxyl, 1 mol%) could considerably accelerate the selective oxidation of organic sulfides with O_(2) over BTT-sp~2c-COF. TEMPO mediates hole transfer between BTT-sp~2c-COF and organic sulfides, and O-atoms are incorporated into sulfoxides via an electron transfer pathway. Merging BTT-sp~2c-COF photocatalysis with TEMPO generally applies to transforming organic sulfides into sulfoxides. This work implies the full π-conjugation of electron-rich building blocks into COFs is a viable strategy for selective visible light photocatalysis.展开更多
基金supported by National Natural Science Foundation of China(No.22078100,No.52102098,and No.22008073)Fundamental Research Funds for the Central Universities(No.222201718002)。
文摘The integration of nano-semiconductors into electromagnetic wave absorption materials is a highly desirable strategy for intensifying dielectric polarization loss;achieving high-attenuation microwave absorption and realizing in-depth comprehension of dielectric loss mechanisms remain challenges.Herein,ultrafine oxygen vacancy-rich Nb_(2)O_(5)semiconductors are confined in carbon nanosheets(ov-Nb_(2)O_(5)/CNS)to boost dielectric polarization and achieve high attenuation.The polarization relaxation,electromagnetic response,and impedance matching of the ov-Nb_(2)O_(5)/CNS are significantly facilitated by the Nb_(2)O_(5)semiconductors with rich oxygen vacancies,which consequently realizes an extremely high attenuation performance of-80.8 dB(>99.999999%wave absorption)at 2.76 mm.As a dielectric polarization center,abundant Nb_(2)O_(5)–carbon heterointerfaces can intensify interfacial polarization loss to strengthen dielectric polarization,and the presence of oxygen vacancies endows Nb_(2)O_(5)semiconductors with abundant charge separation sites to reinforce electric dipole polarization.Moreover,the three-dimensional reconstruction of the absorber using microcomputer tomography technology provides insight into the intensification of the unique lamellar morphology regarding multiple reflection and scattering dissipation characteristics.Additionally,ov-Nb_(2)O_(5)/CNS demonstrates excellent application potential by curing into a microwave-absorbing,machinable,and heat-dissipating plate.This work provides insight into the dielectric polarization loss mechanisms of nano-semiconductor/carbon composites and inspires the design of high-performance microwave absorption materials.
文摘The initial field electron emission degradation behaviour of original nano-structured sp^2-bonded amorphous carbon films has been observed, which can be attributed to the increase of the work function of the film in the field emission process analysed using a Fowler-Nordheim plot. The possible reason for the change of work function is suggested to be the desorption of hydrogen from the original hydrogen termination film surface due to field emission current-induced local heating. For the explanation of the emission degradation behaviour of the nano-structured sp2-bonded amorphous carbon film, a cluster model with a series of graphite （0001） basal surfaces has been presented, and the theoretical calculations have been performed to investigate work functions of graphite （0001） surfaces with different hydrogen atom and ion chemisorption sites by using first principles method based on density functional theory-local density approximation.
基金This work was supported by the NNSFC (No. 30460153 20561001), NSF of Guangxi Province (No. 0447019), and the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institutions of Chinese Ministry of Education
文摘A new coordination polymer [Cd（bimc）2]n was obtained by the reaction of Hbimc with Cd（NO3） 2·4H2O in NaOH solution, and characterized by elemental analysis, IR and singlecrystal X-ray diffraction. The crystal belongs to orthorhombic, space group Pbcn with a = 12.533（4）, b = 15.705（5）, c = 15.200（5） A, V= 2991.8（15） A^3, Mr = 434.68, Z = 8, Dc = 1.930 g/cm^3, F（000） = 1712,μ（MoKa） = 1.492 mm^-1, the final R = 0.0410 and wR = 0.0804 for 1661 observed reflections （I 〉 2σ（I））. The Cd atom exhibits a distorted six-coordinate CdNzOa octahedral coordination geometry. The complex molecules are linked by both μ2-（η2-O, O^-）, NI and μ2-（η2-O, O^-）, N3 coordination modes of ligands to form cross-like wave （4, 4） layer structures which are further stacked through interlayer hydrogen bonds and π-π stacking interactions in an offset fashion to form a 3D supramolecular structure.
文摘Diamond like carbon films, prepared by RF glow discharge on glass substrates, were irradiated by γ rays. The as deposited and irradiated films were characterized by Raman spectroscopy, electrical resistivity, and infrared transmittance. It is shown that the irradiation of the γ rays can lead to the breaking of SP 3 C H and SP 2 C H bonds, slight increasing of SP 3 C C bonds, and induced hydrogen recombination with H 2 molecules, subsequently diffusing to the surface of the films. When the γ rays irradiation dose reached 10×10 4 Gy, the numbers of SP 3 C H bonds was decreased by about 50%, the resistivity of irradiated DLC films was increased, and the diamond like character of the films became more obvious. The structure of DLC films was modified when irradiated by γ rays. The irradiation mechanisms are briefly discussed.
基金supported by the National Natural Science Foundation of China (22072108)。
文摘Visible light photocatalysis of covalent organic frameworks(COFs) has made significant progress in recent years. Benzotrithiophene(BTT), a planar, electron-rich building block, turns out to be foundational in assembling COFs in which the fullπ-conjugation of BTT is essential to facilitate electron transfer. Herein, a sp~2 carbon-conjugated COF, namely BTT-sp~2c-COF, is assembled from benzo[1,2-b:3,4-b′:5,6-b′′]trithiophene-2,5,8-tricarbaldehyde and [1,1′:4′,1′′-terphenyl]-4,4′′-dicarbonitrile towards photocatalysis. More importantly, TEMPO(2,2,6,6-tetramethylpiperidin-1-yl)oxyl, 1 mol%) could considerably accelerate the selective oxidation of organic sulfides with O_(2) over BTT-sp~2c-COF. TEMPO mediates hole transfer between BTT-sp~2c-COF and organic sulfides, and O-atoms are incorporated into sulfoxides via an electron transfer pathway. Merging BTT-sp~2c-COF photocatalysis with TEMPO generally applies to transforming organic sulfides into sulfoxides. This work implies the full π-conjugation of electron-rich building blocks into COFs is a viable strategy for selective visible light photocatalysis.
