Porous carbon-based materials are promised to be lightweight dielectric microwave absorbents.Deeply understanding the influence of graphitization grade and porous structure on the dielectric parameters is urgently req...Porous carbon-based materials are promised to be lightweight dielectric microwave absorbents.Deeply understanding the influence of graphitization grade and porous structure on the dielectric parameters is urgently required.Herein,utilizing the low boiling point of Zn,porous N-doped carbon was fabricated by carbonization of ZIF-8(Zn)at different temperature,and the microwave absorption performance was investigated.The porous N-doped carbon inherits the high porosity of ZIF-8 precursor.By increasing the carbonization temperature,the contents of Zn and N elements are decreased;the graphitization degree is improved;however,the specific surface area and porosity are increased first and then decreased.When the carbonization temperature is 1000°C,the porous N-doped carbon behaves enhanced microwave absorption.With an ultrathin thickness of 1.29 mm,the ideal RL reaches-50.57 dB at 16.95 GHz and the effective absorption bandwidth is 4.17 GHz.The mechanism of boosted microwave absorption is ascribed to the competition of graphitization and porosity as well as N dopants,resulting in high dielectric loss capacity and good impedance matching.The porous structure can prolong the pathways and raise the contact opportunity between microwaves and porous carbon,causing multiple scattering,interface polarization,and improved impedance matching.Besides,the N dopants can induce electron polarization and defect polarization.These results give a new insight to construct lightweight carbon-based microwave absorbents by regulating the graphitization and porosity.展开更多
Toxic heavy metal ions,valuable noble metal ions and organic dyes are significant concerns in wastewater treatment.In this work,MoO_(3) nanobelts(MoO_(3) NBs)prepared by solvothermal method and MoS_(2) nanoarrays(MoS_...Toxic heavy metal ions,valuable noble metal ions and organic dyes are significant concerns in wastewater treatment.In this work,MoO_(3) nanobelts(MoO_(3) NBs)prepared by solvothermal method and MoS_(2) nanoarrays(MoS_(2) NAs)constructed using MoO_(3) NBs precursor were proposed to effectively remove heavy/noble metal ions and organic dyes,such as Pb(II),Au(III)and Methylene Blue(MB).The two adsorbents exhibited the excellent adsorption capacity towards Pb(II),Au(III)and MB.The maximum removal capacity of Pb(II)and MB on MoO_(3) NBs was 684.93 mg/g and 1408 mg/g,respectively,whereas that of Au(III)and MB on MoS_(2) NAs was 1280.2 mg/g and 768 mg/g,respectively.Furthermore,the thermodynamic parameters were calculated from the temperature-dependent curves,suggesting that the removal of Pb(II)and Au(III)on both adsorbents was spontaneous and endothermic.The new adsorbents introduced here were high adsorption activity,ease of fabrication,high scalability,good chemical stability,great repeatability and abundant and cheap supply,which were highly attractive for wastewater treatment.展开更多
Metal-organic frameworks(MOFs)derived magnetic carbon-based nanocomposites have drawn widespread attentions due to the well distributed nanocrystals in carbon matrix.Dynamically observing the formation process is urge...Metal-organic frameworks(MOFs)derived magnetic carbon-based nanocomposites have drawn widespread attentions due to the well distributed nanocrystals in carbon matrix.Dynamically observing the formation process is urgently needed.Herein,taking zeolitic imidazolate framework(ZIF)-67 as an example,the pyrolysis process is investigated by in-situ transmission electron microscopy(TEM)assisted with ex-situ characterizations.Co nanocrystals are evenly distributed in carbon at the initial stage of carbonization.By increasing pyrolysis temperature,the nanocrystals grow bigger and migrate to carbon surface.The carbon texture transfers from amorphous to crystalline at 600°C,and thoroughly converts at 800°C.In-situ heating TEM shows that more tiny Co nanocrystals move out from the carbon texture by increasing temperature from 700 to 800°C.At 1,000°C,some escaped tiny Co nanocrystals are volatilized and disappeared.The residual escaped Co nanocrystals catalyze the formation of carbon nanotubes(CNTs).Due to the synergistic effect between Co and carbon as well as porous structure,the nanocomposites show high-efficient microwave absorption performance,which can be tuned by pyrolysis temperature,heating rate,and mass fraction.When the mass fraction is 30 wt.%,the nanocomposites obtained at 600 or 700°C display remarkable microwave absorption with optimal reflection loss(RL)smaller than−70 dB and effective absorption band larger than 4.9 GHz.Combining the in-situ and ex-situ techniques,some key findings were observed:(1)graphitization of carbon;(2)volatilization of Co nanocrystals;(3)formation process of CNTs by Co catalyst.These findings are helpful to understand the formation of MOFs derived carbon-based composites and expand their practical applications,especially for microwave absorption.展开更多
To improve the atomic utilization of metals and reduce the cost of industrialization,the one-step total monoatomization of macroscopic bulk metals,as opposed to nanoscale metals,is effective.In this study,we used a th...To improve the atomic utilization of metals and reduce the cost of industrialization,the one-step total monoatomization of macroscopic bulk metals,as opposed to nanoscale metals,is effective.In this study,we used a thermal diffusion method to directly convert commercial centimeter-scale Ni foam to porous Ni single-atom-loaded carbon nanotubes(CNTs).As expected,owing to the coating of single-atom on porous,highly conductive CNT carriers,Ni single-atom electrocatalysts(Ni-SACs)exhibit extremely high activity and selectivity in CO_(2)electroreduction(CO_(2)RR),yielding a current density of>350 mA/cm^(2),a selectivity for CO of>91%under a flow cell configuration using a 1 M potassium chloride(KCl)electrolyte.Based on the superior activity of the Ni-SACs electrocatalyst,an integrated gas-phase electrochemical zero-gap reactor was introduced to generate a significant amount of CO current for potential practical applications.The overall current can be increased to 800 mA,while maintaining CO Faradaic efficiencies(FEs)at above 90%per unit cell.Our findings and insights on the active site transformation mechanism for macroscopic bulk Ni foam conversion into single atoms can inform the design of highly active single-atom catalysts used in industrial CO_(2)RR systems.展开更多
Understanding and controlling defect in two-dimensional materials is important for both linear and nonlinear optoelectronic devices,especially in terms of tuning nonlinear optical absorption.Taking advantage of an ato...Understanding and controlling defect in two-dimensional materials is important for both linear and nonlinear optoelectronic devices,especially in terms of tuning nonlinear optical absorption.Taking advantage of an atomic defect formed easily by smaller size,molybdenum disulfide nanosheet is prepared successfully with a different size by gradient centrifugation.Interestingly,size-dependent sulfur vacancies are observed by high-resolution X-ray photoelectron spectroscopy,atomic force microscopy,and transmission electron microscopy.The defect effect on nonlinear absorption is investigated by Z-scan measurement at the wavelength of 800 nm.The results suggest the transition from saturable absorption to reverse saturable absorption can be observed in both dispersions and films.First principle calculations suggest that sulfur vacancies act as the trap state to capture the excited electrons.Moreover,an energy-level model with the trap state is put forward to explain the role of the sulfur vacancy defect in nonlinear optical absorption.The results suggest that saturable absorption and reverse saturable absorption originate from the competition between the excited,defect state and ground state absorption.Our finding provides a way to tune the nonlinear optical performance of optoelectronic devices by defect engineering.展开更多
We study and characterise the breather-induced quantised superfluid vortex filaments which correspond to the Kuznetsov-Ma breather and super-regular breather excitations developing from localised perturbations.Such vo...We study and characterise the breather-induced quantised superfluid vortex filaments which correspond to the Kuznetsov-Ma breather and super-regular breather excitations developing from localised perturbations.Such vortex filaments,emerging from an otherwise perturbed helical vortex,exhibit intriguing loop structures corresponding to the large amplitude of breathers due to the dual action of bending and twisting of the vortex.The loop induced by the Kuznetsov-Ma breather emerges periodically as time increases,while the loop structure triggered by the superregular breather—the loop pair—exhibits striking symmetry breaking due to the broken reflection symmetry of the group velocities of the super-regular breather.In particular,we identify explicitly the generation conditions of these loop excitations by introducing a physical quantity—the integral of the relative quadratic curvature—which corresponds to the effective energy of breathers.Despite the nature of nonlinearity,it is demonstrated that this physical quantity shows a linear correlation with the loop size.These results will deepen our understanding of breather-induced vortex filaments and be helpful for controllable ring-like excitations on the vortices.展开更多
A misfit layer sulfide(BiS)_(1.2)(TiS_(2))_(2) with a natural superlattice structure has been shown to be a promising thermoelectric material,but its high carrier concentration should be reduced so as to further optim...A misfit layer sulfide(BiS)_(1.2)(TiS_(2))_(2) with a natural superlattice structure has been shown to be a promising thermoelectric material,but its high carrier concentration should be reduced so as to further optimize the thermoelectric performance.However,ordinary acceptor doping has not succeeded because of the non-parabolic band structure.In this paper,we have successfully doped chromium ions into the Ti sites,which can maintain or even enhance the high effective mass of electrons so as to effectively improve ZT value.X-ray diffraction analysis,coupled with X-ray photoelectron spectroscopy,shows that chromium has been substituted into titanium sites in TiS2 layers and confirms its ionic state.The chromium doping has successfully reduced the carrier concentration with the subsequent reduction of electrical conductivity.Unlike other acceptor dopants(alkaline earth metals),chromium also enhances Seebeck coefficient and the effective mass,which can possibly be attributed to the formation of additional resonant states near Fermi level.Though the power factor does not improve,the significant reduction in the electronic part of the thermal conductivity leads to a measurable improvement in ZT.展开更多
We reported a wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on the intracavity loss tuning brought by the bent optical fiber. The bidirectional cavity structure achieved the self-swe...We reported a wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on the intracavity loss tuning brought by the bent optical fiber. The bidirectional cavity structure achieved the self-sweeping effect due to the appearance of the dynamic grating in the active fiber with the spatial hole burning effect. Under this, a section of fiber was bent into a circle for adjusting the loss of the cavity. With a descending diameter of bent fiber circle, the sweeping range moves to the shorter wavelength and covers a wide range from 1055.6 to 1034.6 nm eventually. Both the initial wavelength of self-sweeping regime and the threshold of the fiber laser show exponential correlation with the diameter of the circular fiber. Our work provides a compact and low-cost way to achieve the broad wavelength-flexible self-sweeping operation.展开更多
A biosensor for bovine serum albumin(BSA)detection by graphene oxide(GO)functionalized micro-taped long-period fiber grating(GMLPG)was demonstrated.The amide bond connected between the GO and BSA enabled the BSA to at...A biosensor for bovine serum albumin(BSA)detection by graphene oxide(GO)functionalized micro-taped long-period fiber grating(GMLPG)was demonstrated.The amide bond connected between the GO and BSA enabled the BSA to attach onto the fiber surface,which changed the effective refractive index of the cladding mode and characterized the concentration of the BSA.This real-time monitoring system demonstrated a sensing sensitivity of 1.263 nm/(mg/mL)and a detection limit of 0.043 mg/mL.Moreover,it illustrated superior measurement performance of higher sensitivity in the presence of glucose and urea as the interference,which showed static sensitivities of~1.476 nm/(mg/mL)and 1.504 nm/(mg/mL),respectively.The proposed GMLPG demonstrated a great potential for being employed as a sensor for biomedical and biochemical applications.展开更多
基金financially supported by National Natural Science Foundation of China(Nos.51572218 and 11504293)Natural Science Foundation of Shaanxi Province(No.2019JM-138)+1 种基金Natural Science Foundation from Department of Science and Technology of Shaanxi Province(Nos.2021JQ-431,2021JM-304,and 2021JQ-427)Scientific Research Program Funded by Shaanxi Provincial Education Department(No.20JK0946)。
文摘Porous carbon-based materials are promised to be lightweight dielectric microwave absorbents.Deeply understanding the influence of graphitization grade and porous structure on the dielectric parameters is urgently required.Herein,utilizing the low boiling point of Zn,porous N-doped carbon was fabricated by carbonization of ZIF-8(Zn)at different temperature,and the microwave absorption performance was investigated.The porous N-doped carbon inherits the high porosity of ZIF-8 precursor.By increasing the carbonization temperature,the contents of Zn and N elements are decreased;the graphitization degree is improved;however,the specific surface area and porosity are increased first and then decreased.When the carbonization temperature is 1000°C,the porous N-doped carbon behaves enhanced microwave absorption.With an ultrathin thickness of 1.29 mm,the ideal RL reaches-50.57 dB at 16.95 GHz and the effective absorption bandwidth is 4.17 GHz.The mechanism of boosted microwave absorption is ascribed to the competition of graphitization and porosity as well as N dopants,resulting in high dielectric loss capacity and good impedance matching.The porous structure can prolong the pathways and raise the contact opportunity between microwaves and porous carbon,causing multiple scattering,interface polarization,and improved impedance matching.Besides,the N dopants can induce electron polarization and defect polarization.These results give a new insight to construct lightweight carbon-based microwave absorbents by regulating the graphitization and porosity.
基金supported by the National Natural Science Foundation of China(No.21505106)the Fundamental Research Funds for the Central Universities(No.2452017177)。
文摘Toxic heavy metal ions,valuable noble metal ions and organic dyes are significant concerns in wastewater treatment.In this work,MoO_(3) nanobelts(MoO_(3) NBs)prepared by solvothermal method and MoS_(2) nanoarrays(MoS_(2) NAs)constructed using MoO_(3) NBs precursor were proposed to effectively remove heavy/noble metal ions and organic dyes,such as Pb(II),Au(III)and Methylene Blue(MB).The two adsorbents exhibited the excellent adsorption capacity towards Pb(II),Au(III)and MB.The maximum removal capacity of Pb(II)and MB on MoO_(3) NBs was 684.93 mg/g and 1408 mg/g,respectively,whereas that of Au(III)and MB on MoS_(2) NAs was 1280.2 mg/g and 768 mg/g,respectively.Furthermore,the thermodynamic parameters were calculated from the temperature-dependent curves,suggesting that the removal of Pb(II)and Au(III)on both adsorbents was spontaneous and endothermic.The new adsorbents introduced here were high adsorption activity,ease of fabrication,high scalability,good chemical stability,great repeatability and abundant and cheap supply,which were highly attractive for wastewater treatment.
基金the National Natural Science Foundation of China(Nos.51572218,11504293,51771085,and 51801087)the Natural Science Foundation of Shaanxi Province(No.2019JM-138)+2 种基金the Natural Science Foundation from Department of Science and Technology of Shaanxi Province(Nos.2021JQ-431,2021JM-304,and 2021JQ-427)the Scientific Research Program Funded by Shaanxi Provincial Education Department(No.20JK0946)the Key Project of Research and Development of Shaanxi Province(No.2018ZDCXL-GY-08-05).
文摘Metal-organic frameworks(MOFs)derived magnetic carbon-based nanocomposites have drawn widespread attentions due to the well distributed nanocrystals in carbon matrix.Dynamically observing the formation process is urgently needed.Herein,taking zeolitic imidazolate framework(ZIF)-67 as an example,the pyrolysis process is investigated by in-situ transmission electron microscopy(TEM)assisted with ex-situ characterizations.Co nanocrystals are evenly distributed in carbon at the initial stage of carbonization.By increasing pyrolysis temperature,the nanocrystals grow bigger and migrate to carbon surface.The carbon texture transfers from amorphous to crystalline at 600°C,and thoroughly converts at 800°C.In-situ heating TEM shows that more tiny Co nanocrystals move out from the carbon texture by increasing temperature from 700 to 800°C.At 1,000°C,some escaped tiny Co nanocrystals are volatilized and disappeared.The residual escaped Co nanocrystals catalyze the formation of carbon nanotubes(CNTs).Due to the synergistic effect between Co and carbon as well as porous structure,the nanocomposites show high-efficient microwave absorption performance,which can be tuned by pyrolysis temperature,heating rate,and mass fraction.When the mass fraction is 30 wt.%,the nanocomposites obtained at 600 or 700°C display remarkable microwave absorption with optimal reflection loss(RL)smaller than−70 dB and effective absorption band larger than 4.9 GHz.Combining the in-situ and ex-situ techniques,some key findings were observed:(1)graphitization of carbon;(2)volatilization of Co nanocrystals;(3)formation process of CNTs by Co catalyst.These findings are helpful to understand the formation of MOFs derived carbon-based composites and expand their practical applications,especially for microwave absorption.
基金supported by the Young Scientists Fund of the National Natural Science Foundation of China(No.22101182)Guangdong Basic and Applied Basic Research Foundation(No.2020A1515110499)+2 种基金Shenzhen Science and Technology Program(No.JCYJ20210324095202006),Shenzhen University Young Teacher Research Project(No.000002110713)the Shccig-Qinling Program(No.2021JLM-27)the Jinchuan Group Co.Ltd.Chemical Environmental Protection Industry Joint Laboratory(No.20-0837).
文摘To improve the atomic utilization of metals and reduce the cost of industrialization,the one-step total monoatomization of macroscopic bulk metals,as opposed to nanoscale metals,is effective.In this study,we used a thermal diffusion method to directly convert commercial centimeter-scale Ni foam to porous Ni single-atom-loaded carbon nanotubes(CNTs).As expected,owing to the coating of single-atom on porous,highly conductive CNT carriers,Ni single-atom electrocatalysts(Ni-SACs)exhibit extremely high activity and selectivity in CO_(2)electroreduction(CO_(2)RR),yielding a current density of>350 mA/cm^(2),a selectivity for CO of>91%under a flow cell configuration using a 1 M potassium chloride(KCl)electrolyte.Based on the superior activity of the Ni-SACs electrocatalyst,an integrated gas-phase electrochemical zero-gap reactor was introduced to generate a significant amount of CO current for potential practical applications.The overall current can be increased to 800 mA,while maintaining CO Faradaic efficiencies(FEs)at above 90%per unit cell.Our findings and insights on the active site transformation mechanism for macroscopic bulk Ni foam conversion into single atoms can inform the design of highly active single-atom catalysts used in industrial CO_(2)RR systems.
基金National Natural Science Foundation of China(11774288,11974279)Natural Science Foundation of Shaanxi Province(2019JC-25,2019-JM131,2019JM-236)。
文摘Understanding and controlling defect in two-dimensional materials is important for both linear and nonlinear optoelectronic devices,especially in terms of tuning nonlinear optical absorption.Taking advantage of an atomic defect formed easily by smaller size,molybdenum disulfide nanosheet is prepared successfully with a different size by gradient centrifugation.Interestingly,size-dependent sulfur vacancies are observed by high-resolution X-ray photoelectron spectroscopy,atomic force microscopy,and transmission electron microscopy.The defect effect on nonlinear absorption is investigated by Z-scan measurement at the wavelength of 800 nm.The results suggest the transition from saturable absorption to reverse saturable absorption can be observed in both dispersions and films.First principle calculations suggest that sulfur vacancies act as the trap state to capture the excited electrons.Moreover,an energy-level model with the trap state is put forward to explain the role of the sulfur vacancy defect in nonlinear optical absorption.The results suggest that saturable absorption and reverse saturable absorption originate from the competition between the excited,defect state and ground state absorption.Our finding provides a way to tune the nonlinear optical performance of optoelectronic devices by defect engineering.
基金the National Natural Science Foundation of China(NSFC)(Grant Nos.11705145,11875220,11947301,11434013,and 11425522)Natural Science Basic Research Plan in Shaanxi Province of China(Grant No.2018JQ1003)the Major Basic Research Program of Natural Science of Shaanxi Province(Grant Nos.2017KCT-12,2017ZDJC-32)。
文摘We study and characterise the breather-induced quantised superfluid vortex filaments which correspond to the Kuznetsov-Ma breather and super-regular breather excitations developing from localised perturbations.Such vortex filaments,emerging from an otherwise perturbed helical vortex,exhibit intriguing loop structures corresponding to the large amplitude of breathers due to the dual action of bending and twisting of the vortex.The loop induced by the Kuznetsov-Ma breather emerges periodically as time increases,while the loop structure triggered by the superregular breather—the loop pair—exhibits striking symmetry breaking due to the broken reflection symmetry of the group velocities of the super-regular breather.In particular,we identify explicitly the generation conditions of these loop excitations by introducing a physical quantity—the integral of the relative quadratic curvature—which corresponds to the effective energy of breathers.Despite the nature of nonlinearity,it is demonstrated that this physical quantity shows a linear correlation with the loop size.These results will deepen our understanding of breather-induced vortex filaments and be helpful for controllable ring-like excitations on the vortices.
文摘A misfit layer sulfide(BiS)_(1.2)(TiS_(2))_(2) with a natural superlattice structure has been shown to be a promising thermoelectric material,but its high carrier concentration should be reduced so as to further optimize the thermoelectric performance.However,ordinary acceptor doping has not succeeded because of the non-parabolic band structure.In this paper,we have successfully doped chromium ions into the Ti sites,which can maintain or even enhance the high effective mass of electrons so as to effectively improve ZT value.X-ray diffraction analysis,coupled with X-ray photoelectron spectroscopy,shows that chromium has been substituted into titanium sites in TiS2 layers and confirms its ionic state.The chromium doping has successfully reduced the carrier concentration with the subsequent reduction of electrical conductivity.Unlike other acceptor dopants(alkaline earth metals),chromium also enhances Seebeck coefficient and the effective mass,which can possibly be attributed to the formation of additional resonant states near Fermi level.Though the power factor does not improve,the significant reduction in the electronic part of the thermal conductivity leads to a measurable improvement in ZT.
基金supported by the National Natural Science Foundation of China (No. 61905193)the National Key R&D Program of China (No. 2017YFB0405102)the Key R&D Project of Shaanxi Province–International Science and Technology Cooperation Project (No. 2020KW-018)。
文摘We reported a wavelength-flexible all-polarization-maintaining self-sweeping fiber laser based on the intracavity loss tuning brought by the bent optical fiber. The bidirectional cavity structure achieved the self-sweeping effect due to the appearance of the dynamic grating in the active fiber with the spatial hole burning effect. Under this, a section of fiber was bent into a circle for adjusting the loss of the cavity. With a descending diameter of bent fiber circle, the sweeping range moves to the shorter wavelength and covers a wide range from 1055.6 to 1034.6 nm eventually. Both the initial wavelength of self-sweeping regime and the threshold of the fiber laser show exponential correlation with the diameter of the circular fiber. Our work provides a compact and low-cost way to achieve the broad wavelength-flexible self-sweeping operation.
基金supported by the International Cooperative Program(Grant No.2014DFR10780)the National Science Foundation of China(Grant No.11874299)the Science and Technology Innovation and Entrepreneurship Double Tutor Project of Shaanxi Province(Grant No.2018JM1059).
文摘A biosensor for bovine serum albumin(BSA)detection by graphene oxide(GO)functionalized micro-taped long-period fiber grating(GMLPG)was demonstrated.The amide bond connected between the GO and BSA enabled the BSA to attach onto the fiber surface,which changed the effective refractive index of the cladding mode and characterized the concentration of the BSA.This real-time monitoring system demonstrated a sensing sensitivity of 1.263 nm/(mg/mL)and a detection limit of 0.043 mg/mL.Moreover,it illustrated superior measurement performance of higher sensitivity in the presence of glucose and urea as the interference,which showed static sensitivities of~1.476 nm/(mg/mL)and 1.504 nm/(mg/mL),respectively.The proposed GMLPG demonstrated a great potential for being employed as a sensor for biomedical and biochemical applications.
