Optically transparent microwave absorbers and multi-band stealth have extensive potential applications in military defense and wireless communication fields, and thus have attracted considerable attention. So far,most...Optically transparent microwave absorbers and multi-band stealth have extensive potential applications in military defense and wireless communication fields, and thus have attracted considerable attention. So far,most related work is based on inorganic transparent conductive metasurfaces. In this paper, we proposed and experimentally demonstrated a flexible, broadband and optically transparent microwave absorber using an organic metasurface. The metasurface absorber is composed of a sandwich structure, in which electric resonances and magnetic resonances are induced resulting in broadband absorption. A spraying process was developed to prepare this metasurface absorber. Both simulations and experiment show that this metasurface has broadband microwave absorption and good optical transparency. We further found that by using a multi-layer structure, visible, radar,and infrared stealth(multi-band stealth) can be achieved simultaneously. With the advantages of excellent foldability and low cost, the proposed metasurfaces may have applications in military and wireless communication fields.展开更多
The reduction of nitrobenzene to aniline is very important for both pollution control and chemical synthesis.Nevertheless,difficulties still remain in developing a catalytic system having high efficiency and selectivi...The reduction of nitrobenzene to aniline is very important for both pollution control and chemical synthesis.Nevertheless,difficulties still remain in developing a catalytic system having high efficiency and selectivity for the production of aniline.Herein,it was found that PdO nanoparticles highly dispersed on TiO_(2)support(PdO/TiO_(2))functioned as a highly efficient catalyst for the reduction of nitrobenzene in the presence of NaBH4.Under favorable conditions,95%of the added nitrobenzene(1 mmol/L)was reduced within 1 min with an ultra-low apparent activation energy of 10.8 kJ/mol by using 0.5%PdO/TiO_(2)as catalysts and 2 mmol/L of NaBH4 as reductants,and the selectivity to aniline even reached up to 98%.The active hydrogen specieswere perceived as dominant species during the hydrogenation of nitrobenzene by the results of isotope labeling experiments and ESR spectroscopic.A mechanismwas proposed as follows:PdO activates the nitro groups and leads to in-situ generation of Pd,and the generated Pd acts as the reduction sites to produce active hydrogen species.In this catalytic system,nitrobenzene prefers to be adsorbed on the PdO nanoparticles of the PdO/TiO_(2)composite.Subsequently,the addition of NaBH_(4) results in in-situ generation of a Pd/PdO/TiO_(2)composite from the PdO/TiO_(2)composite,and the Pd nanoclusters would activate NaBH_(4) to generate active hydrogen species to attack the adsorbed nitro groups.This work will open up a new approach for the catalytic transfer hydrogenation of nitrobenzene to aniline in green chemistry.展开更多
Dynamic adsorption processes of reaction intermediates for alkaline hydrogen evolution(HER)catalysts are still confusing to understand.Here,we report a series of A-site ordered quadruple perovskite ruthenium-based ele...Dynamic adsorption processes of reaction intermediates for alkaline hydrogen evolution(HER)catalysts are still confusing to understand.Here,we report a series of A-site ordered quadruple perovskite ruthenium-based electrocatalysts ACu_(3)Ru_(4)O_(12)(A=Na,Ca,Nd,and La),with the target sample SrCu_(3)Ru_(4)O_(12)exhibiting a very low overpotential(46 mV@10 mA·cm^(-2))and excellent catalytic stability with little decays after 48-h durability test.Precise tuning A-site cations can change the average valence state of Cu and Ru,thus the plot of HER activity versus the average Ru valence number shows a volcano-type relationship.Density functional theory indicates that the Ru 4d orbitals of SrCu3Ru4O12possesses the most suitable d-band center position among the five samples,which might be the key parameter to determine the catalytic performance.Our work provides further insight into the discovering advanced,efficient hydrogen evolution catalysts through designing precise descriptor.展开更多
Electromagnetic wave-absorbing materials play a crucial role in modern electronics,particularly in stealth and communication technologies.Carbon-based materials demonstrate considerable potential for the development a...Electromagnetic wave-absorbing materials play a crucial role in modern electronics,particularly in stealth and communication technologies.Carbon-based materials demonstrate considerable potential for the development and use of effective wave-absorbing substances,attributed to their complex structure,lightweight nature,excellent corrosion resistance,and affordability.Notably,nitrogen-doped carbon-based two-dimensional(2D)materials exhibit a more pronounced depletion effect on electromagnetic waves owing to their increased specific surface area and numerous polarization states.This article presents the successful synthesis of nitrogen-doped carbon(NC)2D flakes using a hydrothermal method.In addition,single Fe atoms were successfully incorporated onto their surfaces,forming Fe@NC.The wave-absorbing capabilities of the Fe@NC samples were considerably improved,achieving a minimum reflection loss(RLmin)of−69.22 dB at 11.48 GHz and an effective absorption bandwidth of 5.79 GHz.The enhancement in electromagnetic wave absorption is attributed to the synergistic effects of magnetic loss,relaxation processes,dipole polarization,and electrical conduction loss.The successful synthesis of Fe@NC opens up new avenues for the development of atomically dispersed wave-absorbing materials.展开更多
文摘目的探讨术前酰胺质子转移(APT)成像联合血清糖类抗原125(cancer antigen 125,CA125)预测宫颈癌淋巴脉管间隙侵犯(LVSI)的价值。方法选取40例术前行MRI检查并术后病理资料完整的宫颈癌患者。术前1~2周进行盆腔MRI检查和静脉采血,分别获得相应的APT值和血清CA125水平,并根据术后病理结果确定是否发生LVSI。比较单独或联合应用APT值和血清CA125对宫颈癌LVSI的预测作用。结果40例中经病理证实29例发生LVSI,11例无LVSI。术前APT值、血清CA125水平预测宫颈癌LVSI的受试者工作特征(receiver operating characteristic,ROC)曲线下面积(area under the curve,AUC)分别为0.889、0.687,APT值为2.9%时,其对应的约登指数最大(0.702),敏感度为79.3%,特异度为90.9%。术前血清CA125水平临界值为25.3 U/mL时,其对应的约登指数最大(0.508),敏感度为69.0%,特异度为81.8%。术前APT成像联合血清CA125预测宫颈癌LVSI的敏感度为82.7%,特异度为100%,约登指数为0.828,AUC为0.923。结论术前APT成像联合血清CA125在预测宫颈癌LVSI中具有重要的价值,当APT值>2.9%、血清CA125>25.3 U/mL时诊断效能最佳。
基金supported by the National Key R&D Program of China (Grant Nos. 2023YFC3010703, 2020YFB1708800, and 2023YFC3010705)。
文摘Optically transparent microwave absorbers and multi-band stealth have extensive potential applications in military defense and wireless communication fields, and thus have attracted considerable attention. So far,most related work is based on inorganic transparent conductive metasurfaces. In this paper, we proposed and experimentally demonstrated a flexible, broadband and optically transparent microwave absorber using an organic metasurface. The metasurface absorber is composed of a sandwich structure, in which electric resonances and magnetic resonances are induced resulting in broadband absorption. A spraying process was developed to prepare this metasurface absorber. Both simulations and experiment show that this metasurface has broadband microwave absorption and good optical transparency. We further found that by using a multi-layer structure, visible, radar,and infrared stealth(multi-band stealth) can be achieved simultaneously. With the advantages of excellent foldability and low cost, the proposed metasurfaces may have applications in military and wireless communication fields.
基金supported by the National Natural Science Foundation of China (No.22076052)the Natural Science Foundation of Hubei Province (Nos.2021CFB535 and 2020CFB437)+2 种基金the Knowledge Innovation Program of Wuhan-Basic Research (No.SZY23005)the Fundamental Research Funds for the Central Universities,South-Central Minzu University (No.CZQ22002)Wuhan University (No.2042020kf0036).
文摘The reduction of nitrobenzene to aniline is very important for both pollution control and chemical synthesis.Nevertheless,difficulties still remain in developing a catalytic system having high efficiency and selectivity for the production of aniline.Herein,it was found that PdO nanoparticles highly dispersed on TiO_(2)support(PdO/TiO_(2))functioned as a highly efficient catalyst for the reduction of nitrobenzene in the presence of NaBH4.Under favorable conditions,95%of the added nitrobenzene(1 mmol/L)was reduced within 1 min with an ultra-low apparent activation energy of 10.8 kJ/mol by using 0.5%PdO/TiO_(2)as catalysts and 2 mmol/L of NaBH4 as reductants,and the selectivity to aniline even reached up to 98%.The active hydrogen specieswere perceived as dominant species during the hydrogenation of nitrobenzene by the results of isotope labeling experiments and ESR spectroscopic.A mechanismwas proposed as follows:PdO activates the nitro groups and leads to in-situ generation of Pd,and the generated Pd acts as the reduction sites to produce active hydrogen species.In this catalytic system,nitrobenzene prefers to be adsorbed on the PdO nanoparticles of the PdO/TiO_(2)composite.Subsequently,the addition of NaBH_(4) results in in-situ generation of a Pd/PdO/TiO_(2)composite from the PdO/TiO_(2)composite,and the Pd nanoclusters would activate NaBH_(4) to generate active hydrogen species to attack the adsorbed nitro groups.This work will open up a new approach for the catalytic transfer hydrogenation of nitrobenzene to aniline in green chemistry.
基金Project supported financially by the National Key Research and Development Program of China(Grant No.2023YFA1406000)the National Natural Science Foundation of China(Grant Nos.22171283 and 12474002)+3 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.2023ZCJH03 and 2021XD-A041)the Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications,China)the Teaching Reform Projects at BUPT(Grant No.2022CXCYB03)the BUPT Excellent Ph.D.Students Foundation(Grant No.CX2023108)。
文摘Dynamic adsorption processes of reaction intermediates for alkaline hydrogen evolution(HER)catalysts are still confusing to understand.Here,we report a series of A-site ordered quadruple perovskite ruthenium-based electrocatalysts ACu_(3)Ru_(4)O_(12)(A=Na,Ca,Nd,and La),with the target sample SrCu_(3)Ru_(4)O_(12)exhibiting a very low overpotential(46 mV@10 mA·cm^(-2))and excellent catalytic stability with little decays after 48-h durability test.Precise tuning A-site cations can change the average valence state of Cu and Ru,thus the plot of HER activity versus the average Ru valence number shows a volcano-type relationship.Density functional theory indicates that the Ru 4d orbitals of SrCu3Ru4O12possesses the most suitable d-band center position among the five samples,which might be the key parameter to determine the catalytic performance.Our work provides further insight into the discovering advanced,efficient hydrogen evolution catalysts through designing precise descriptor.
基金supported by the Fundamental Research Funds for the Central Universities(Grant No.2021XD-A04-2)the National Natural Science Foundation of China(Grant Nos.61874014 and 61874013)+1 种基金the Fund of State Key Laboratory of Information Photonics and Optical Communications(Beijing University of Posts and Telecommunications,China)BUPT Excellent Ph.D.Students Foundation(Grant No.CX2022237).
文摘Electromagnetic wave-absorbing materials play a crucial role in modern electronics,particularly in stealth and communication technologies.Carbon-based materials demonstrate considerable potential for the development and use of effective wave-absorbing substances,attributed to their complex structure,lightweight nature,excellent corrosion resistance,and affordability.Notably,nitrogen-doped carbon-based two-dimensional(2D)materials exhibit a more pronounced depletion effect on electromagnetic waves owing to their increased specific surface area and numerous polarization states.This article presents the successful synthesis of nitrogen-doped carbon(NC)2D flakes using a hydrothermal method.In addition,single Fe atoms were successfully incorporated onto their surfaces,forming Fe@NC.The wave-absorbing capabilities of the Fe@NC samples were considerably improved,achieving a minimum reflection loss(RLmin)of−69.22 dB at 11.48 GHz and an effective absorption bandwidth of 5.79 GHz.The enhancement in electromagnetic wave absorption is attributed to the synergistic effects of magnetic loss,relaxation processes,dipole polarization,and electrical conduction loss.The successful synthesis of Fe@NC opens up new avenues for the development of atomically dispersed wave-absorbing materials.
