Designing materials with both structural load-bearing capacity and broadband electromagnetic(EM)wave absorption properties remains a significant challenge.In this work,SiOC/SiC/SiO_(2)composite with gyroid structures ...Designing materials with both structural load-bearing capacity and broadband electromagnetic(EM)wave absorption properties remains a significant challenge.In this work,SiOC/SiC/SiO_(2)composite with gyroid structures were prepared through digital light processing(DLP)3D printing,polymer-derived ceramics(PDCs),chemical vapor infiltration(CVI),and oxidation technologies.The incorporation of the CVISiC phase effectively increases the dissipation capability,while the synergistic interaction between the gyroid structure and SiO_(2)phase significantly improves impedance matching performance.The SiOC/SiC/SiO_(2)composite achieved a minimum reflection loss(RL min)of-62.2 d B at 4.3 mm,and the effective absorption bandwidth(EAB)covered the X-band,with a thickness range of 4.1 mm-4.65 mm.The CST simulation results explain the broadband and low-frequency absorption characteristics,with an EAB of 8.4 GHz(9.6-18 GHz)and an RL min of-21.5 dB at 5 GHz.The excellent EM wave attenuation performance is associated primarily with polarization loss,conduction loss,the gyroid structure's enhancement of multiple reflections and scattering of EM waves,and the resonance effect between the structural units.The SiOC/SiC/SiO_(2)composite also demonstrated strong mechanical properties,with a maximum compressive failure strength of 31.6 MPa in the height direction.This work opens novel prospects for the development of multifunctional structural wave-absorbing materials suitable for broadband microwave absorption and load-bearing properties.展开更多
Third-order nonlinear optical (NLO) materials have broad application prospects in high-density data storage, optical computer, modern laser technology, and other high-tech industries. The structures and frequencies of...Third-order nonlinear optical (NLO) materials have broad application prospects in high-density data storage, optical computer, modern laser technology, and other high-tech industries. The structures and frequencies of Dinaphtho[2,3-b:2’,3’-d]thiophene-5,7,12,13-tetraone (DNTTRA) and its 36 derivatives containing azobenzene were calculated by using density functional theory B3LYP and M06-2X methods at 6-311++g(d, p) level, respectively. Besides, the atomic charges of natural bond orbitals (NBO) were analyzed. The frontier orbitals and electron absorption spectra of A-G5 molecule were calculated by TD-DFT (TD-B3LYP/6-311++g(d, p) and TD-M06-2X/6-311++g(d, p)). The NLO properties were calculated by effective finite field FF method and self-compiled program. The results show that 36 molecules of these six series are D-π-A-π-D structures. The third-order NLO coefficients γ (second-order hyperpolarizability) of the D series molecules are the largest among the six series, reaching 10<sup>7</sup> atomic units (10<sup><span style="color:#4F4F4F;font-family:-apple-system, " font-size:14px;white-space:normal;background-color:#ffffff;"="">-</span>33</sup> esu) of order of magnitude, showing good third-order NLO properties. Last, the third-order NLO properties of the azobenzene ring can be improved by introducing strong electron donor groups (e.g. -N(CH<sub>3</sub>)<sub>2</sub> or -NHCH<sub>3</sub>) in the azobenzene ring, so that the third-order NLO materials with good performance can be obtained.展开更多
As a novel 2D material,Ti_(3)C_(2)T_(x)-MXene has become a major area of interest in the field of microwave absorption(MA).However,the MA effect of common Ti_(3)C_(2)T_(x)-MXene is not prominent and often requires com...As a novel 2D material,Ti_(3)C_(2)T_(x)-MXene has become a major area of interest in the field of microwave absorption(MA).However,the MA effect of common Ti_(3)C_(2)T_(x)-MXene is not prominent and often requires complex processes or combinations of other ma-terials to achieve enhanced performance.In this context,a kind of gradient woodpile structure using common Ti_(3)C_(2)T_(x)-MXene as MA ma-terial was designed and manufactured through direct ink writing(DIW)3D printing.The minimum reflection loss(RL_(min))of the Ti_(3)C_(2)T_(x)-MXene-based gradient woodpile structures with a thickness of less than 3 mm can reach-70 dB,showing considerable improve-ment compared with that of a completely filled structure.In addition,the effective absorption bandwidth(EAB)reaches 7.73 GHz.This study demonstrates that a Ti_(3)C_(2)T_(x)-MXene material with excellent MA performance and tunable frequency band can be successfully fab-ricated with a macroscopic structural design and through DIW 3D printing without complex material hybridization and modification,of-fering broad application prospects by reducing electromagnetic wave radiation and interference.展开更多
The single-layer Ti_(3)C_(2)T_(x)/MXene has become a special electromagnetic wave absorber near the terahertz band because of its abundant surface groups and excellent conductivity.However,the macro-preparation of sin...The single-layer Ti_(3)C_(2)T_(x)/MXene has become a special electromagnetic wave absorber near the terahertz band because of its abundant surface groups and excellent conductivity.However,the macro-preparation of single-layer Ti_(3)C_(2)T_(x)/MXene shows significantly difficult to influence its application.The two-dimensional Ti_(3)C_(2)T_(x)is easily prepared to have high production,but its weak absorption ability due to high surface conductivity also restricts its application.To realize the strong electromagnetic wave absorption of two-dimensional Ti_(3)C_(2)T_(x)/MXene,a new strategy with magnetic FeNi nanoparticles decorating Ti_(3)C_(2)T_(x)/MXene composites(FeNi-Ti_(3)C_(2)T_(x))were proposed and the effective electromagnetic wave absorption features covering 170-220 GHz that means the absorption band width reach 50 GHz.With an absorber composite film thickness being only 0.6 mm,the absorptivity of the composite is enhanced with the increase of decorating FeNi nanoparticles and promote up to 75%when the FeNi nanoparticles loading content reaches 30 wt%.The improvement of absorption is attributed to the introduction of soft magnetic FeNi to adjust the high surface conductivity of MXene and improve the electromagnetic balance of the absorber.展开更多
Atomic-scale doping strategies and structure design play pivotal roles in tailoring the electronic structure and physicochemical property of electromagnetic wave absorption(EMWA)materials.However,the relationship betw...Atomic-scale doping strategies and structure design play pivotal roles in tailoring the electronic structure and physicochemical property of electromagnetic wave absorption(EMWA)materials.However,the relationship between configuration and electromagnetic(EM)loss mechanism has remained elusive.Herein,drawing inspiration from the DNA transcription process,we report the successful synthesis of novel in situ Mn/N co-doped helical carbon nanotubes with ultrabroad EMWA capability.Theoretical calculation and EM simulation confirm that the orbital coupling and spin polarization of the Mn–N4–C configuration,along with cross polarization generated by the helical structure,endow the helical converters with enhanced EM loss.As a result,HMC-8 demonstrates outstanding EMWA performance,achieving a minimum reflection loss of−63.13 dB at an ultralow thickness of 1.29 mm.Through precise tuning of the graphite domain size,HMC-7 achieves an effective absorption bandwidth(EAB)of 6.08 GHz at 2.02 mm thickness.Furthermore,constructing macroscale gradient metamaterials enables an ultrabroadband EAB of 12.16 GHz at a thickness of only 5.00 mm,with the maximum radar cross section reduction value reaching 36.4 dB m2.This innovative approach not only advances the understanding of metal–nonmetal co-doping but also realizes broadband EMWA,thus contributing to the development of EMWA mechanisms and applications.展开更多
Sc_(2)O_(3),as a host for solid-state laser gain materials,has advantage of high thermal conductivity and easy matching with activating ions,which is promising in high-power laser applications.Currently,Yb-doped Sc_(2...Sc_(2)O_(3),as a host for solid-state laser gain materials,has advantage of high thermal conductivity and easy matching with activating ions,which is promising in high-power laser applications.Currently,Yb-doped Sc_(2)O_(3) ceramics have been fabricated at very high sintering temperatures,but their optical quality and sintering process still need further improvement.In this work,5%Yb:Sc_(2)O_(3)(in mass)nano-powders were obtained by co-precipitation,and then transparent ceramics were fabricated by vacuum pre-sintering and hot isostatic pressing(HIP)post-treatment.The cubic Yb:Sc_(2)O_(3) nano-powders with good dispersity and an average crystallite of 29 nm were obtained.Influence of pre-sintering temperatures(1500-1700℃)on densification process,microstructure changes,and optical transmittance of Yb:Sc_(2)O_(3) ceramics was detected.Experimental data revealed that all samples have a uniform microstructure,while the average grain sizes increase with the increase of the sintering temperatures.Impressively,the optimum in-line transmittance of Yb:Sc_(2)O_(3) ceramics,pre-sintered at 1550℃after HIP post-treatment,reaches 78.1%(theoretical value of 80%)at 1100 nm.Spectroscopic properties of the Yb:Sc_(2)O_(3) ceramics reveal that the minimum population inversion parameterβ2 and the luminescence decay time of 5%Yb:Sc_(2)O_(3) ceramics are 0.041 and 0.49 ms,respectively,which demonstrate that the optical quality of the Yb:Sc_(2)O_(3) has been improved.Meanwhile,their best vacuum sintering temperature can be controlled down to a lower temperature(1550℃).In conclusion,Yb:Sc_(2)O_(3) nano-powders are successfully synthesized by co-precipitation method,and good optical quality transparent ceramics are fabricated by vacuum pre-sintering at 1550℃and HIP post-treatment.展开更多
Polarization-dependent loss is important to the highly electromagnetic wave absorption(EWA)performance.Recently,metal–Nx moieties have been discovered to trigger polarization loss,but the physical origin and other po...Polarization-dependent loss is important to the highly electromagnetic wave absorption(EWA)performance.Recently,metal–Nx moieties have been discovered to trigger polarization loss,but the physical origin and other possible related loss mechanisms still need to be deeply explored.In this article,we reveal that the FeN_(4)moiety from iron phthalocyanine(FePc)can coordinate with Ti_(3)C_(2)T_(x)through Ti–OH groups,inducing dipole polarization and synchronous magnetic modulation in Fe/TiO_(2)/Ti_(3)C_(2)T_(x)composites.Interestingly,using the enhanced electric dipole moment and increased number of unpaired electrons in Fe atoms,the dipole polarization loss and possible magnetic response can be rapidly confirmed and evaluated.As a result,the minimum reflection loss(RLmin)of Fe/TiO_(2)/Ti_(3)C_(2)T_(x)composites reaches−67.12 dB at 6.72 GHz with a thickness of 3.32 mm.This study elaborates the EWA mechanism based on the atomic scale,and provides a new idea to design efficient EWA materials.展开更多
Transition metal carbides(MXenes)used as electromagnetic wave absorption materials face two critical challenges:impedance mismatch caused by high conductivity and the easy restacking and agglomeration of ultrathin nan...Transition metal carbides(MXenes)used as electromagnetic wave absorption materials face two critical challenges:impedance mismatch caused by high conductivity and the easy restacking and agglomeration of ultrathin nanosheets.To address these issues,this study proposes the construction of an S/N co-doped MXene nanoribbon/nanosheet composite structure.An alkali-assisted chemical scissor strategy was used to successfully prepare a nanoribbon/nanosheet hybrid,which effectively suppressed nanosheet stacking and significantly increased the number of active interfaces and defect sites.By controlling the doping temperature,the doping configurations of S and N in MXenes can be precisely regulated,including lattice substitution(LS),functional group substitution(FS),and surface absorption(SA).With increasing doping temperature,the configuration of S/N dopants evolves from a combination of FS-type N and LS-type S to a coexistence of SA-and LS-type species.The former synergistically enhances conductive loss and polarization loss,whereas the latter suppresses electron transport and consequently reduces the complex permittivity of the material.The optimized composite exhibited considerably improved comprehensive electromagnetic wave-absorption performance at a low filler loading(10 wt%)and thin thickness(1.26 mm),achieving a minimum reflection loss(RLmin)of-53.77 dB and an effective absorption bandwidth(EAB)of 4.51 GHz.This work not only clarifies the regulatory mechanism of doping configurations on high-frequency electromagnetic properties but also provides a theoretical foundation for the rational design of high-performance MXene-based electromagnetic wave absorbing materials.展开更多
Oxygen carriers play a fundamental role in chemical looping combustion(CLC).Iron-based carriers have been extensively investigated owing to their abundance and environmentally friendly.However,the reactivity and separ...Oxygen carriers play a fundamental role in chemical looping combustion(CLC).Iron-based carriers have been extensively investigated owing to their abundance and environmentally friendly.However,the reactivity and separability of iron-based carriers require further enhancement.This study investigates the effect of the concentration of Mn doping on reactivity,elastic properties and magnetic properties based on density functional theory(DFT)calculations.Theoretical results demonstrate that Mn doping effectively enhances reactivity by reducing the oxygen vacancy formation energy(E_(vac))from 2.33 to 0.87 eV.However,Mn doping introduces HV/EV Ms lattice distortions that deteriorate elastic properties,thereby reducing wear resistance,as evidenced by a 54.54%decrease in the hardness-to-Young's modulus ratio(H_(v)/E_(v))forα-Fe_(2)O_(3)and an 83.33%reduction for Fe_(3)O_(4).Furthermore,Mn doping also modifies magnetic properties.The maximum of saturation magnetization(M_(s))of Fe_(3)O_(4)reaches 121.02 emu/g at 33.33%Mn doping concentration.Finally,systematic evaluation identifies 33.33%as the optimal Mn doping concentration,achieving a balance in enhanced reactivity,superior magnetic performance,and retained elastic stability.展开更多
基金financially supported by National Natural Science Foundation of China(Grant Nos.12141203,52202083,W2421013)the Natural Science Foundation Project of Shaanxi Province(Grant No.2024JC-YBMS-450)+1 种基金the Sichuan Science and Technology Program(Grant No.2024YFHZ0265)the Open Project of High-end Equipment Advanced Materials and Manufacturing Technology Laboratory(Grant No.2023KFKT0005)。
文摘Designing materials with both structural load-bearing capacity and broadband electromagnetic(EM)wave absorption properties remains a significant challenge.In this work,SiOC/SiC/SiO_(2)composite with gyroid structures were prepared through digital light processing(DLP)3D printing,polymer-derived ceramics(PDCs),chemical vapor infiltration(CVI),and oxidation technologies.The incorporation of the CVISiC phase effectively increases the dissipation capability,while the synergistic interaction between the gyroid structure and SiO_(2)phase significantly improves impedance matching performance.The SiOC/SiC/SiO_(2)composite achieved a minimum reflection loss(RL min)of-62.2 d B at 4.3 mm,and the effective absorption bandwidth(EAB)covered the X-band,with a thickness range of 4.1 mm-4.65 mm.The CST simulation results explain the broadband and low-frequency absorption characteristics,with an EAB of 8.4 GHz(9.6-18 GHz)and an RL min of-21.5 dB at 5 GHz.The excellent EM wave attenuation performance is associated primarily with polarization loss,conduction loss,the gyroid structure's enhancement of multiple reflections and scattering of EM waves,and the resonance effect between the structural units.The SiOC/SiC/SiO_(2)composite also demonstrated strong mechanical properties,with a maximum compressive failure strength of 31.6 MPa in the height direction.This work opens novel prospects for the development of multifunctional structural wave-absorbing materials suitable for broadband microwave absorption and load-bearing properties.
文摘Third-order nonlinear optical (NLO) materials have broad application prospects in high-density data storage, optical computer, modern laser technology, and other high-tech industries. The structures and frequencies of Dinaphtho[2,3-b:2’,3’-d]thiophene-5,7,12,13-tetraone (DNTTRA) and its 36 derivatives containing azobenzene were calculated by using density functional theory B3LYP and M06-2X methods at 6-311++g(d, p) level, respectively. Besides, the atomic charges of natural bond orbitals (NBO) were analyzed. The frontier orbitals and electron absorption spectra of A-G5 molecule were calculated by TD-DFT (TD-B3LYP/6-311++g(d, p) and TD-M06-2X/6-311++g(d, p)). The NLO properties were calculated by effective finite field FF method and self-compiled program. The results show that 36 molecules of these six series are D-π-A-π-D structures. The third-order NLO coefficients γ (second-order hyperpolarizability) of the D series molecules are the largest among the six series, reaching 10<sup>7</sup> atomic units (10<sup><span style="color:#4F4F4F;font-family:-apple-system, " font-size:14px;white-space:normal;background-color:#ffffff;"="">-</span>33</sup> esu) of order of magnitude, showing good third-order NLO properties. Last, the third-order NLO properties of the azobenzene ring can be improved by introducing strong electron donor groups (e.g. -N(CH<sub>3</sub>)<sub>2</sub> or -NHCH<sub>3</sub>) in the azobenzene ring, so that the third-order NLO materials with good performance can be obtained.
基金support from the National Key Research and Development Program of China(No.2021YFB3701503)the Key Research and Development Program of Ningbo,China(No.2023Z107).
文摘As a novel 2D material,Ti_(3)C_(2)T_(x)-MXene has become a major area of interest in the field of microwave absorption(MA).However,the MA effect of common Ti_(3)C_(2)T_(x)-MXene is not prominent and often requires complex processes or combinations of other ma-terials to achieve enhanced performance.In this context,a kind of gradient woodpile structure using common Ti_(3)C_(2)T_(x)-MXene as MA ma-terial was designed and manufactured through direct ink writing(DIW)3D printing.The minimum reflection loss(RL_(min))of the Ti_(3)C_(2)T_(x)-MXene-based gradient woodpile structures with a thickness of less than 3 mm can reach-70 dB,showing considerable improve-ment compared with that of a completely filled structure.In addition,the effective absorption bandwidth(EAB)reaches 7.73 GHz.This study demonstrates that a Ti_(3)C_(2)T_(x)-MXene material with excellent MA performance and tunable frequency band can be successfully fab-ricated with a macroscopic structural design and through DIW 3D printing without complex material hybridization and modification,of-fering broad application prospects by reducing electromagnetic wave radiation and interference.
基金supported by the National Key R&D Program of China(Nos.2023YFF0718303 and 2022YFB3504804)the National Natural Science Foundation of China(Nos.51871219,52031014 and 52401255)the Science and Technology Project of Shenyang City(No.22-101-0-27).
文摘The single-layer Ti_(3)C_(2)T_(x)/MXene has become a special electromagnetic wave absorber near the terahertz band because of its abundant surface groups and excellent conductivity.However,the macro-preparation of single-layer Ti_(3)C_(2)T_(x)/MXene shows significantly difficult to influence its application.The two-dimensional Ti_(3)C_(2)T_(x)is easily prepared to have high production,but its weak absorption ability due to high surface conductivity also restricts its application.To realize the strong electromagnetic wave absorption of two-dimensional Ti_(3)C_(2)T_(x)/MXene,a new strategy with magnetic FeNi nanoparticles decorating Ti_(3)C_(2)T_(x)/MXene composites(FeNi-Ti_(3)C_(2)T_(x))were proposed and the effective electromagnetic wave absorption features covering 170-220 GHz that means the absorption band width reach 50 GHz.With an absorber composite film thickness being only 0.6 mm,the absorptivity of the composite is enhanced with the increase of decorating FeNi nanoparticles and promote up to 75%when the FeNi nanoparticles loading content reaches 30 wt%.The improvement of absorption is attributed to the introduction of soft magnetic FeNi to adjust the high surface conductivity of MXene and improve the electromagnetic balance of the absorber.
基金supported by the National Natural Science Foundation of China(22265021)the Aeronautical Science Foundation of China(2020Z056056003)Jiangxi Provincial Natural Science Foundation(20232BAB212004).
文摘Atomic-scale doping strategies and structure design play pivotal roles in tailoring the electronic structure and physicochemical property of electromagnetic wave absorption(EMWA)materials.However,the relationship between configuration and electromagnetic(EM)loss mechanism has remained elusive.Herein,drawing inspiration from the DNA transcription process,we report the successful synthesis of novel in situ Mn/N co-doped helical carbon nanotubes with ultrabroad EMWA capability.Theoretical calculation and EM simulation confirm that the orbital coupling and spin polarization of the Mn–N4–C configuration,along with cross polarization generated by the helical structure,endow the helical converters with enhanced EM loss.As a result,HMC-8 demonstrates outstanding EMWA performance,achieving a minimum reflection loss of−63.13 dB at an ultralow thickness of 1.29 mm.Through precise tuning of the graphite domain size,HMC-7 achieves an effective absorption bandwidth(EAB)of 6.08 GHz at 2.02 mm thickness.Furthermore,constructing macroscale gradient metamaterials enables an ultrabroadband EAB of 12.16 GHz at a thickness of only 5.00 mm,with the maximum radar cross section reduction value reaching 36.4 dB m2.This innovative approach not only advances the understanding of metal–nonmetal co-doping but also realizes broadband EMWA,thus contributing to the development of EMWA mechanisms and applications.
基金National Key R&D Program of China(2023YFE3812005)International Partnership Program of Chinese Academy of Sciences(121631KYSB20200039)+1 种基金National Center for Research and Development(WPC2/1/SCAPOL/2021)Chinese Academy of Sciences President’s International Fellowship Initiative(2024VEA0005,2024VEA0014)。
文摘Sc_(2)O_(3),as a host for solid-state laser gain materials,has advantage of high thermal conductivity and easy matching with activating ions,which is promising in high-power laser applications.Currently,Yb-doped Sc_(2)O_(3) ceramics have been fabricated at very high sintering temperatures,but their optical quality and sintering process still need further improvement.In this work,5%Yb:Sc_(2)O_(3)(in mass)nano-powders were obtained by co-precipitation,and then transparent ceramics were fabricated by vacuum pre-sintering and hot isostatic pressing(HIP)post-treatment.The cubic Yb:Sc_(2)O_(3) nano-powders with good dispersity and an average crystallite of 29 nm were obtained.Influence of pre-sintering temperatures(1500-1700℃)on densification process,microstructure changes,and optical transmittance of Yb:Sc_(2)O_(3) ceramics was detected.Experimental data revealed that all samples have a uniform microstructure,while the average grain sizes increase with the increase of the sintering temperatures.Impressively,the optimum in-line transmittance of Yb:Sc_(2)O_(3) ceramics,pre-sintered at 1550℃after HIP post-treatment,reaches 78.1%(theoretical value of 80%)at 1100 nm.Spectroscopic properties of the Yb:Sc_(2)O_(3) ceramics reveal that the minimum population inversion parameterβ2 and the luminescence decay time of 5%Yb:Sc_(2)O_(3) ceramics are 0.041 and 0.49 ms,respectively,which demonstrate that the optical quality of the Yb:Sc_(2)O_(3) has been improved.Meanwhile,their best vacuum sintering temperature can be controlled down to a lower temperature(1550℃).In conclusion,Yb:Sc_(2)O_(3) nano-powders are successfully synthesized by co-precipitation method,and good optical quality transparent ceramics are fabricated by vacuum pre-sintering at 1550℃and HIP post-treatment.
基金supported by the Taishan Young Scholar Program(tsqn202306267)the National Natural Science Foundation of China(51802168)the Natural Science Foundation of Shandong Province(ZR2024ME182,ZR2021ME122)。
文摘Polarization-dependent loss is important to the highly electromagnetic wave absorption(EWA)performance.Recently,metal–Nx moieties have been discovered to trigger polarization loss,but the physical origin and other possible related loss mechanisms still need to be deeply explored.In this article,we reveal that the FeN_(4)moiety from iron phthalocyanine(FePc)can coordinate with Ti_(3)C_(2)T_(x)through Ti–OH groups,inducing dipole polarization and synchronous magnetic modulation in Fe/TiO_(2)/Ti_(3)C_(2)T_(x)composites.Interestingly,using the enhanced electric dipole moment and increased number of unpaired electrons in Fe atoms,the dipole polarization loss and possible magnetic response can be rapidly confirmed and evaluated.As a result,the minimum reflection loss(RLmin)of Fe/TiO_(2)/Ti_(3)C_(2)T_(x)composites reaches−67.12 dB at 6.72 GHz with a thickness of 3.32 mm.This study elaborates the EWA mechanism based on the atomic scale,and provides a new idea to design efficient EWA materials.
基金financially supported by the National Natural Science Foundation of China(Nos.52222106,52371171,51971008,and 52121001)the National Key R&D Program of China(No.2021YBF3501304)the Fundamental Research Funds for the Central Universities.The authors acknowledge the facilities and the scientific and technical assistance of the Analysis&Testing Center,Beihang University.
文摘Transition metal carbides(MXenes)used as electromagnetic wave absorption materials face two critical challenges:impedance mismatch caused by high conductivity and the easy restacking and agglomeration of ultrathin nanosheets.To address these issues,this study proposes the construction of an S/N co-doped MXene nanoribbon/nanosheet composite structure.An alkali-assisted chemical scissor strategy was used to successfully prepare a nanoribbon/nanosheet hybrid,which effectively suppressed nanosheet stacking and significantly increased the number of active interfaces and defect sites.By controlling the doping temperature,the doping configurations of S and N in MXenes can be precisely regulated,including lattice substitution(LS),functional group substitution(FS),and surface absorption(SA).With increasing doping temperature,the configuration of S/N dopants evolves from a combination of FS-type N and LS-type S to a coexistence of SA-and LS-type species.The former synergistically enhances conductive loss and polarization loss,whereas the latter suppresses electron transport and consequently reduces the complex permittivity of the material.The optimized composite exhibited considerably improved comprehensive electromagnetic wave-absorption performance at a low filler loading(10 wt%)and thin thickness(1.26 mm),achieving a minimum reflection loss(RLmin)of-53.77 dB and an effective absorption bandwidth(EAB)of 4.51 GHz.This work not only clarifies the regulatory mechanism of doping configurations on high-frequency electromagnetic properties but also provides a theoretical foundation for the rational design of high-performance MXene-based electromagnetic wave absorbing materials.
基金Supported by National Natural Science Foundation of China(50976032,51776070)。
文摘Oxygen carriers play a fundamental role in chemical looping combustion(CLC).Iron-based carriers have been extensively investigated owing to their abundance and environmentally friendly.However,the reactivity and separability of iron-based carriers require further enhancement.This study investigates the effect of the concentration of Mn doping on reactivity,elastic properties and magnetic properties based on density functional theory(DFT)calculations.Theoretical results demonstrate that Mn doping effectively enhances reactivity by reducing the oxygen vacancy formation energy(E_(vac))from 2.33 to 0.87 eV.However,Mn doping introduces HV/EV Ms lattice distortions that deteriorate elastic properties,thereby reducing wear resistance,as evidenced by a 54.54%decrease in the hardness-to-Young's modulus ratio(H_(v)/E_(v))forα-Fe_(2)O_(3)and an 83.33%reduction for Fe_(3)O_(4).Furthermore,Mn doping also modifies magnetic properties.The maximum of saturation magnetization(M_(s))of Fe_(3)O_(4)reaches 121.02 emu/g at 33.33%Mn doping concentration.Finally,systematic evaluation identifies 33.33%as the optimal Mn doping concentration,achieving a balance in enhanced reactivity,superior magnetic performance,and retained elastic stability.
