Developing lightweight and broadband microwave absorbers for dealing with serious electromagnetic radiation pollution is a great challenge.Here,a novel Fe-Co/N-doped carbon/reduced graphene oxide(Fe-Co/NC/rGO)composit...Developing lightweight and broadband microwave absorbers for dealing with serious electromagnetic radiation pollution is a great challenge.Here,a novel Fe-Co/N-doped carbon/reduced graphene oxide(Fe-Co/NC/rGO)composite with hierarchically porous structure was designed and synthetized by in situ growth of Fe-doped Cobased metal organic frameworks(Co-MOF)on the sheets of porous cocoon-like rGO followed by calcination.The Fe-Co/NC composites are homogeneously distributed on the sheets of porous rGO.The Fe-Co/NC/rGO composite with multiple components(Fe/Co/NC/rGO)causes magnetic loss,dielectric loss,resistance loss,interfacial polarization,and good impedance matching.The hierarchically porous structure of the Fe-Co/NC/rGO enhances the multiple reflections and scattering of microwaves.Compared with the Co/NC and Fe-Co/NC,the hierarchically porous Fe-Co/NC/rGO composite exhibits much better microwave absorption performances due to the rational composition and porous structural design.Its minimum reflection loss(RLmin)reaches?43.26 dB at 11.28 GHz with a thickness of 2.5 mm,and the effective absorption frequency(RL≤?10 dB)is up to 9.12 GHz(8.88-18 GHz)with the same thickness of 2.5 mm.Moreover,the widest effective bandwidth of 9.29 GHz occurs at a thickness of 2.63 mm.This work provides a lightweight and broadband microwave absorbing material while offering a new idea to design excellent microwave absorbers with multicomponent and hierarchically porous structures.展开更多
Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5zeolite as the source and characterized by scanning electron microscopy,transmission el...Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5zeolite as the source and characterized by scanning electron microscopy,transmission electron microscopy,energy dispersive spectroscopy,X-ray diffraction,N2 adsorption-desorption measurement and NH3 temperature-programmed desorption.The catalytic performances for the methanol dehydration to dimethyl ether over H-ZSM-5/MCM-41 were evaluated.Among these catalysts,H-ZSM-5/MCM-41 prepared with NaOH dosage (nNa/nSi) varying from 0.4 to 0.47 presented excellent catalytic activity with more than 80%methanol conversion and 100%dimethyl ether selectivity in a wide temperature range of 170—300℃,and H-ZSM-5/MCM-41 prepared with nNa/nSi=0.47 showed constant methanol conversion of about 88.7%,100% dimethyl ether selectivity and excellent lifetime at 220℃.The excellent catalytic performances were due to the highly active and uniform acidic sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves.The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether process was also discussed.展开更多
Acidic ionic liquid([BsAIm][OTf]) was immobilized on sulfhydryl-group-modified SiO2(MPS-SiO2) via free radical addition reaction. The[BsAIm][OTf] loading on acidic ionic liquid-functionalized silica([BsAIm][OTf]/SiO2)...Acidic ionic liquid([BsAIm][OTf]) was immobilized on sulfhydryl-group-modified SiO2(MPS-SiO2) via free radical addition reaction. The[BsAIm][OTf] loading on acidic ionic liquid-functionalized silica([BsAIm][OTf]/SiO2) was controlled through tuning the sulfydryl(SH)content of MPS-SiO2. All the samples were characterized by FT-IR, elemental analysis, N2adsorption-desorption measurements and TGDTA. The catalytic performance of [BsAIm][OTf]/SiO2in the esterification of oleic acid and the transesterification of glycerol trioleate for biodiesel production was investigated. The results showed that with the increase of [BsAIm][OTf] loading on SiO2the specific surface area and pore volume of [BsAIm][OTf]/SiO2decreased, and the pore diameter of [BsAIm][OTf]/SiO2narrowed. In the esterificaiton of oleic acid, the oleic acid conversion increased with the increasing [BsAIm][OTf] loading. In the transesterification of glycerol trioleate, with the increasing[BsAIm][OTf] loading the glycerol trioleate conversion decreased and the selectivities to glycerol monooleate and methyl oleate increased.展开更多
With the development of a small interfering RNA(siRNA)delivery strategy,increasing siRNA therapeutics for tumor treatment appeared in clinical trials and pre-clinical development.However,the test results of such thera...With the development of a small interfering RNA(siRNA)delivery strategy,increasing siRNA therapeutics for tumor treatment appeared in clinical trials and pre-clinical development.However,the test results of such therapeutics unveiled that efficient siRNA delivery to tumor tissues is still challenging.Albumin is considered an ideal carrier for delivering hydrophobic agents into tumor tissue because it is highly concentrated and long-circulating in blood and has propensity of tumor enrichment.Herein,we synthesized lipid conjugated siRNAs(LsiRNAs),which showed high affinity to albumin.Mechanistically,LsiRNAs non-covalently bind to the hydrophobic core of albumin through its octadecyl tails.The small size of albumin/LsiRNAs allows the complex to penetrate tumor tissue efficiently.Biodistribution test proved that albumin extremely prolonged circulation time and increased tumor retention of associated LsiRNAs.Notably,LsiRNA against programmed death ligand-1(Pdl1)efficiently suppressed tumor growth as well as prolonged survival time of tumor bearing mice by increasing infiltration of CD8^(+)T cells as well as promoted the maturation of dendritic cells both in tumor and lymph.Together,LsiRNAs provide a simple but effective way for siRNA tumor delivery that“hitchhikes”on albumin.展开更多
Beyond graphene, two-dimensional （2D） transition metal dichalcogenides （TMDs） have attracted significant attention owing to their potential in next-generation nanoelectronics and optoelectronics. Nevertheless, gra...Beyond graphene, two-dimensional （2D） transition metal dichalcogenides （TMDs） have attracted significant attention owing to their potential in next-generation nanoelectronics and optoelectronics. Nevertheless, grain boundaries are ubiquitous in large-area as-grown TMD materials and would significantly affect their band structure, electrical transport, and optical properties. Therefore, the characterization of grain boundaries is essential for engineering the properties and optimizing the growth in TMD materials. Although the existence of boundaries can be measured using scanning tunneling microscopy, transmission electron microscopy, or nonlinear optical microscop~ a universal, convenient, and accurate method to detect boundaries with a twist angle over a large scale is still lacking. Herein, we report a high-throughput method using mild hot H20 etching to visualize grain boundaries of TMDs under an optical microscope, while ensuring that the method is nearly noninvasive to grain domains. This technique utilizes the reactivity difference between stable grain domains and defective grain boundaries and the mild etching capacity of hot water vapor. As grain boundaries of two domains with twist angles have defective lines, this method enables to visualize all types of grain boundaries unambiguously. Moreover, the characterization is based on an optical microscope and therefore naturally of a large scale. We further demonstrate the successful application of this method to other TMD materials such as MoS2 and WSe2. Our technique facilitates the large-area characterization of grain boundaries and will accelerate the controllable growth of large single-crystal TMDs.展开更多
A series of Cu/Co/Cr nanocomposites with different Cu/Co/Cr molar ratios were obtained by calcination of Cu/ Co/Cr hydrotalcites precursors, which were prepared by a co-precipitation reaction. X-ray diffraction, induc...A series of Cu/Co/Cr nanocomposites with different Cu/Co/Cr molar ratios were obtained by calcination of Cu/ Co/Cr hydrotalcites precursors, which were prepared by a co-precipitation reaction. X-ray diffraction, inductively coupled plasma analysis, and transmission electron microscopy were used to characterize the structure, composition, and mor- phology of Cu/Co/Cr nanocomposites. The results show that Cu/Co/Cr nanocomposites have both CuCr204 and CoCr204 spinel phase. The particle size of Cu/Co/Cr nanocomposites is 15-20 nm and the specific surface area is 95-115 m2/g. Cu/ Co/Cr nanocomposites were used as new catalysts for improving thermal decomposition of ammonium perchlorate （AP）. Their catalytic activities were investigated using differential thermal analysis and thermal gravimetric analyzer coupled with an online mass spectrometer. The results show that the decomposition temperature of AP lowered 132-146℃ by adding 4 wt% Cu/Co/Cr nanocomposites. Catalytic activities of the prepared nanocomposites depend on the calcinations temperature and addition amount of corresponding nanocomposites. The possible catalytic mechanism of Cu/Co/Cr nanocomposites was also studied and discussed.展开更多
Ferrioxalate submicrorods/graphene composites were synthesized through a simple solvothermal process in a mixture of ethylene glycol and water. The in situ growth of ferrioxalate submicrorods and the reduction of grap...Ferrioxalate submicrorods/graphene composites were synthesized through a simple solvothermal process in a mixture of ethylene glycol and water. The in situ growth of ferrioxalate submicrorods and the reduction of graphene oxide （GO） were completed in a one-step reaction. Fourier transform infrared and Raman spectroscopy confirmed the reduction of GO. Uniform rod-like ferrioxalates with diameter of about 600 nm and length of several micrometers were well distributed on the graphene sheets. As-obtained composites exhibited better photocatalytic properties than pure ferrioxalate submicrorods. The influence of different contents of GO on photocatalytic performance was also investigated. A possible photocatalytic mechanism of ferrioxalate submicrorods/graphene composites was proposed.展开更多
基金the National Natural Science Foundation of China(No.21376029)and the Analysis&Testing Center,Beijing Institute of Technology for sponsoring this researchsupported by Beijing Key Laboratory for Chemical Power Source and Green Catalysis,Beijing Institute of Technology.
文摘Developing lightweight and broadband microwave absorbers for dealing with serious electromagnetic radiation pollution is a great challenge.Here,a novel Fe-Co/N-doped carbon/reduced graphene oxide(Fe-Co/NC/rGO)composite with hierarchically porous structure was designed and synthetized by in situ growth of Fe-doped Cobased metal organic frameworks(Co-MOF)on the sheets of porous cocoon-like rGO followed by calcination.The Fe-Co/NC composites are homogeneously distributed on the sheets of porous rGO.The Fe-Co/NC/rGO composite with multiple components(Fe/Co/NC/rGO)causes magnetic loss,dielectric loss,resistance loss,interfacial polarization,and good impedance matching.The hierarchically porous structure of the Fe-Co/NC/rGO enhances the multiple reflections and scattering of microwaves.Compared with the Co/NC and Fe-Co/NC,the hierarchically porous Fe-Co/NC/rGO composite exhibits much better microwave absorption performances due to the rational composition and porous structural design.Its minimum reflection loss(RLmin)reaches?43.26 dB at 11.28 GHz with a thickness of 2.5 mm,and the effective absorption frequency(RL≤?10 dB)is up to 9.12 GHz(8.88-18 GHz)with the same thickness of 2.5 mm.Moreover,the widest effective bandwidth of 9.29 GHz occurs at a thickness of 2.63 mm.This work provides a lightweight and broadband microwave absorbing material while offering a new idea to design excellent microwave absorbers with multicomponent and hierarchically porous structures.
基金supported by the National Nature Science Foundation of China (No: 20976013)International Science & Technology Cooperation Program of China (No: 2012DFR40240)
文摘Micro-mesoporous composite molecular sieves H-ZSM-5/MCM-41 were prepared by the hydrothermal technique with alkali-treated H-ZSM-5zeolite as the source and characterized by scanning electron microscopy,transmission electron microscopy,energy dispersive spectroscopy,X-ray diffraction,N2 adsorption-desorption measurement and NH3 temperature-programmed desorption.The catalytic performances for the methanol dehydration to dimethyl ether over H-ZSM-5/MCM-41 were evaluated.Among these catalysts,H-ZSM-5/MCM-41 prepared with NaOH dosage (nNa/nSi) varying from 0.4 to 0.47 presented excellent catalytic activity with more than 80%methanol conversion and 100%dimethyl ether selectivity in a wide temperature range of 170—300℃,and H-ZSM-5/MCM-41 prepared with nNa/nSi=0.47 showed constant methanol conversion of about 88.7%,100% dimethyl ether selectivity and excellent lifetime at 220℃.The excellent catalytic performances were due to the highly active and uniform acidic sites and the hierarchical porosity in the micro-mesoporous composite molecular sieves.The catalytic mechanism of H-ZSM-5/MCM-41 for the methanol dehydration to dimethyl ether process was also discussed.
基金supported by the National Natural Science Foundation of China(No.20706006 and 20976013)
文摘Acidic ionic liquid([BsAIm][OTf]) was immobilized on sulfhydryl-group-modified SiO2(MPS-SiO2) via free radical addition reaction. The[BsAIm][OTf] loading on acidic ionic liquid-functionalized silica([BsAIm][OTf]/SiO2) was controlled through tuning the sulfydryl(SH)content of MPS-SiO2. All the samples were characterized by FT-IR, elemental analysis, N2adsorption-desorption measurements and TGDTA. The catalytic performance of [BsAIm][OTf]/SiO2in the esterification of oleic acid and the transesterification of glycerol trioleate for biodiesel production was investigated. The results showed that with the increase of [BsAIm][OTf] loading on SiO2the specific surface area and pore volume of [BsAIm][OTf]/SiO2decreased, and the pore diameter of [BsAIm][OTf]/SiO2narrowed. In the esterificaiton of oleic acid, the oleic acid conversion increased with the increasing [BsAIm][OTf] loading. In the transesterification of glycerol trioleate, with the increasing[BsAIm][OTf] loading the glycerol trioleate conversion decreased and the selectivities to glycerol monooleate and methyl oleate increased.
基金supported by the Beijing Natural Science Foundation(No.7214302)the Natural Science Foundation of Guangdong Province(No.2019A1515010776)+3 种基金the National Natural Science Foundation of China(Nos.31901053,32001008,32171394)the Beijing-Tianjin-Hebei Basic Research Cooperation Project(No.19JCZDJC64100)the Beijing Nova Program from Beijing Municipal Science&Technology Commission(No.Z201100006820005)the National Key Research&Development Program of China(Nos.2021YFE0106900,2021YFA1201000,2021YFC2302400).
文摘With the development of a small interfering RNA(siRNA)delivery strategy,increasing siRNA therapeutics for tumor treatment appeared in clinical trials and pre-clinical development.However,the test results of such therapeutics unveiled that efficient siRNA delivery to tumor tissues is still challenging.Albumin is considered an ideal carrier for delivering hydrophobic agents into tumor tissue because it is highly concentrated and long-circulating in blood and has propensity of tumor enrichment.Herein,we synthesized lipid conjugated siRNAs(LsiRNAs),which showed high affinity to albumin.Mechanistically,LsiRNAs non-covalently bind to the hydrophobic core of albumin through its octadecyl tails.The small size of albumin/LsiRNAs allows the complex to penetrate tumor tissue efficiently.Biodistribution test proved that albumin extremely prolonged circulation time and increased tumor retention of associated LsiRNAs.Notably,LsiRNA against programmed death ligand-1(Pdl1)efficiently suppressed tumor growth as well as prolonged survival time of tumor bearing mice by increasing infiltration of CD8^(+)T cells as well as promoted the maturation of dendritic cells both in tumor and lymph.Together,LsiRNAs provide a simple but effective way for siRNA tumor delivery that“hitchhikes”on albumin.
文摘Beyond graphene, two-dimensional （2D） transition metal dichalcogenides （TMDs） have attracted significant attention owing to their potential in next-generation nanoelectronics and optoelectronics. Nevertheless, grain boundaries are ubiquitous in large-area as-grown TMD materials and would significantly affect their band structure, electrical transport, and optical properties. Therefore, the characterization of grain boundaries is essential for engineering the properties and optimizing the growth in TMD materials. Although the existence of boundaries can be measured using scanning tunneling microscopy, transmission electron microscopy, or nonlinear optical microscop~ a universal, convenient, and accurate method to detect boundaries with a twist angle over a large scale is still lacking. Herein, we report a high-throughput method using mild hot H20 etching to visualize grain boundaries of TMDs under an optical microscope, while ensuring that the method is nearly noninvasive to grain domains. This technique utilizes the reactivity difference between stable grain domains and defective grain boundaries and the mild etching capacity of hot water vapor. As grain boundaries of two domains with twist angles have defective lines, this method enables to visualize all types of grain boundaries unambiguously. Moreover, the characterization is based on an optical microscope and therefore naturally of a large scale. We further demonstrate the successful application of this method to other TMD materials such as MoS2 and WSe2. Our technique facilitates the large-area characterization of grain boundaries and will accelerate the controllable growth of large single-crystal TMDs.
基金financially supported by the Engineering Research Center of Starch and Vegetable Protein Processing, Ministry of Education, South China University of Technology (No.2012ERC03)
文摘A series of Cu/Co/Cr nanocomposites with different Cu/Co/Cr molar ratios were obtained by calcination of Cu/ Co/Cr hydrotalcites precursors, which were prepared by a co-precipitation reaction. X-ray diffraction, inductively coupled plasma analysis, and transmission electron microscopy were used to characterize the structure, composition, and mor- phology of Cu/Co/Cr nanocomposites. The results show that Cu/Co/Cr nanocomposites have both CuCr204 and CoCr204 spinel phase. The particle size of Cu/Co/Cr nanocomposites is 15-20 nm and the specific surface area is 95-115 m2/g. Cu/ Co/Cr nanocomposites were used as new catalysts for improving thermal decomposition of ammonium perchlorate （AP）. Their catalytic activities were investigated using differential thermal analysis and thermal gravimetric analyzer coupled with an online mass spectrometer. The results show that the decomposition temperature of AP lowered 132-146℃ by adding 4 wt% Cu/Co/Cr nanocomposites. Catalytic activities of the prepared nanocomposites depend on the calcinations temperature and addition amount of corresponding nanocomposites. The possible catalytic mechanism of Cu/Co/Cr nanocomposites was also studied and discussed.
文摘Ferrioxalate submicrorods/graphene composites were synthesized through a simple solvothermal process in a mixture of ethylene glycol and water. The in situ growth of ferrioxalate submicrorods and the reduction of graphene oxide （GO） were completed in a one-step reaction. Fourier transform infrared and Raman spectroscopy confirmed the reduction of GO. Uniform rod-like ferrioxalates with diameter of about 600 nm and length of several micrometers were well distributed on the graphene sheets. As-obtained composites exhibited better photocatalytic properties than pure ferrioxalate submicrorods. The influence of different contents of GO on photocatalytic performance was also investigated. A possible photocatalytic mechanism of ferrioxalate submicrorods/graphene composites was proposed.
