Artificial photosynthesis of hydrogen peroxide(H_(2)O_(2))using covalent organic frameworks(COFs)as photocatalysts holds promise for future applications.However,the influence of linkage chemistry on the photoelectroch...Artificial photosynthesis of hydrogen peroxide(H_(2)O_(2))using covalent organic frameworks(COFs)as photocatalysts holds promise for future applications.However,the influence of linkage chemistry on the photoelectrochemical properties and photocatalytic performance of COFs remains a significant challenge.Herein,we designed and synthesized a model system with different linkages,including imine-,amine-,azo-linked COFs,then investigated their photocatalytic activity of overall H_(2)O_(2)production.The photocatalytic results revealed varying activities for H_(2)O_(2)synthesis among these COFs,with the azo-linked TTA-Azo-COF(COF synthesized by 4,4’,4’’-(1,3,5-triazine-2,4,6-triyl)-trianiline and terephthalaldehyde)demonstrating the highest overall H2O2 photosynthesis activity of 2516μmol g^(–1)h^(–1)in an O2 atmosphere without any sacrificial agents,which is 6.72 and 2.85 times higher than that of imine-linked TTA-COF and amine-linked TTA-COF-AR,respectively.Furthermore,TTA-Azo-COF maintained a high photosynthesis H2O2 activity of 2116μmol g^(–1)h^(–1)under an air atmosphere,outperforming most COF-based photocatalytic systems under similar reaction conditions.Further characterizations and density functional theory calculations reveal these various linkages in different COFs result in distinct visible-light absorption,charge transfer capacities and formation energy barriers of key intermediates.This work revealed the significant impact of linkages on COFs and provided comprehensive guidance for the rational design of COFs with tailored linkages to fulfill specific requirements for future applications.展开更多
During the operation of electronic devices,a considerable amount of heat and electromagnetic radiation is emitted.Therefore,the investigation of materials with electromagnetic shielding and thermal management abilitie...During the operation of electronic devices,a considerable amount of heat and electromagnetic radiation is emitted.Therefore,the investigation of materials with electromagnetic shielding and thermal management abilities has significant importance.Hybrid materials of three-dimensional graphene networks containing both carbon nanotubes(CNTs)and SiC whiskers(3D graphene-CNT-SiC)were synthesized.Using an aqueous-phase reduction method for the self-assembly of the graphene oxide,a three-dimen-sional porous graphene structure was fabricated.SiC whiskers,inserted between the graphene layers,formed a framework for longit-udinal thermal conduction,while CNTs attached to the SiC surface,created a dendritic structure that increased the bonding between the SiC whiskers and graphene,improving dielectric loss and thermal conductivity.It was found that the thermal conductivity of the hybrid material reached 123 W·m^(-1)·K^(-1),with a shielding effectiveness of 29.3 dB when the SiC addition was 2%.This result indic-ates that 3D graphene-CNT-SiC has excellent thermal conductivity and electromagnetic shielding performance.展开更多
The microstructural evolution and mechanical properties of AZ31 magnesium alloy processed by the interactive alternating forward extrusion at different loading displacements(h=3,6,9 mm)were investigated.Optical micros...The microstructural evolution and mechanical properties of AZ31 magnesium alloy processed by the interactive alternating forward extrusion at different loading displacements(h=3,6,9 mm)were investigated.Optical microscopy(OM)and electron backscatter diffraction(EBSD)were used to analyze the evolution of microstructure,and the mechanical behavior was clarified by tensile tests and scanning electron microscopy(SEM).The results show that continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX)can achieve grain refinement jointly in interactive alternating forward extrusion.With the decrease of the loading displacement h,the proportion of recrystallization increases from 23.4%to 66.7%.The fiber texture gradually tilts to the extrusion direction(ED),and the grain orientation randomization of DDRX further weakens the fiber texture intensity.When h=3 mm,the ultimate tensile strength(UTS)is 249.1 MPa and the elongation can reach 29.4%.展开更多
The Ni(Ⅱ)-chiral(4S,4'S)-2,2'-(4,6-dibenzofurandiyl)bis[4,5-dihydro-4-phenyloxazole](DBFOX/Ph)-catalyzed asymmetric 1,3-dipolar cycloadditions of nitrile imines to N-α,β-unsaturated acylpyrazoles was presen...The Ni(Ⅱ)-chiral(4S,4'S)-2,2'-(4,6-dibenzofurandiyl)bis[4,5-dihydro-4-phenyloxazole](DBFOX/Ph)-catalyzed asymmetric 1,3-dipolar cycloadditions of nitrile imines to N-α,β-unsaturated acylpyrazoles was presented.This tactic rendered a facile and feasible route to prepare the optically active tetrasubstituted 5-3,5-dimethylpyrazole acyl dihydropyrazole cy-cloadducts bearing one or two contiguous stereocenters in good yields(up to 97%yield)with high regioselectivities(100%)and enantioselectivities(up to 97.5%ee).Following that,chiral cycloadducts could be obtained consistently in good chemical yields with excellent enantioselectivities within the gram scale process,additionally,toward five kinds of derivatization reac-tions like nucleophilic and reduction for further conversion of chiral cycloadducts to related chiral dihydropyrazole derivatives encompassing different substituents.展开更多
文摘Artificial photosynthesis of hydrogen peroxide(H_(2)O_(2))using covalent organic frameworks(COFs)as photocatalysts holds promise for future applications.However,the influence of linkage chemistry on the photoelectrochemical properties and photocatalytic performance of COFs remains a significant challenge.Herein,we designed and synthesized a model system with different linkages,including imine-,amine-,azo-linked COFs,then investigated their photocatalytic activity of overall H_(2)O_(2)production.The photocatalytic results revealed varying activities for H_(2)O_(2)synthesis among these COFs,with the azo-linked TTA-Azo-COF(COF synthesized by 4,4’,4’’-(1,3,5-triazine-2,4,6-triyl)-trianiline and terephthalaldehyde)demonstrating the highest overall H2O2 photosynthesis activity of 2516μmol g^(–1)h^(–1)in an O2 atmosphere without any sacrificial agents,which is 6.72 and 2.85 times higher than that of imine-linked TTA-COF and amine-linked TTA-COF-AR,respectively.Furthermore,TTA-Azo-COF maintained a high photosynthesis H2O2 activity of 2116μmol g^(–1)h^(–1)under an air atmosphere,outperforming most COF-based photocatalytic systems under similar reaction conditions.Further characterizations and density functional theory calculations reveal these various linkages in different COFs result in distinct visible-light absorption,charge transfer capacities and formation energy barriers of key intermediates.This work revealed the significant impact of linkages on COFs and provided comprehensive guidance for the rational design of COFs with tailored linkages to fulfill specific requirements for future applications.
文摘During the operation of electronic devices,a considerable amount of heat and electromagnetic radiation is emitted.Therefore,the investigation of materials with electromagnetic shielding and thermal management abilities has significant importance.Hybrid materials of three-dimensional graphene networks containing both carbon nanotubes(CNTs)and SiC whiskers(3D graphene-CNT-SiC)were synthesized.Using an aqueous-phase reduction method for the self-assembly of the graphene oxide,a three-dimen-sional porous graphene structure was fabricated.SiC whiskers,inserted between the graphene layers,formed a framework for longit-udinal thermal conduction,while CNTs attached to the SiC surface,created a dendritic structure that increased the bonding between the SiC whiskers and graphene,improving dielectric loss and thermal conductivity.It was found that the thermal conductivity of the hybrid material reached 123 W·m^(-1)·K^(-1),with a shielding effectiveness of 29.3 dB when the SiC addition was 2%.This result indic-ates that 3D graphene-CNT-SiC has excellent thermal conductivity and electromagnetic shielding performance.
基金supported by the National Natural Science Foundation of China (No.51975166)。
文摘The microstructural evolution and mechanical properties of AZ31 magnesium alloy processed by the interactive alternating forward extrusion at different loading displacements(h=3,6,9 mm)were investigated.Optical microscopy(OM)and electron backscatter diffraction(EBSD)were used to analyze the evolution of microstructure,and the mechanical behavior was clarified by tensile tests and scanning electron microscopy(SEM).The results show that continuous dynamic recrystallization(CDRX)and discontinuous dynamic recrystallization(DDRX)can achieve grain refinement jointly in interactive alternating forward extrusion.With the decrease of the loading displacement h,the proportion of recrystallization increases from 23.4%to 66.7%.The fiber texture gradually tilts to the extrusion direction(ED),and the grain orientation randomization of DDRX further weakens the fiber texture intensity.When h=3 mm,the ultimate tensile strength(UTS)is 249.1 MPa and the elongation can reach 29.4%.
基金Project supported by the National Natural Science Foundation of China(Nos.22278098,21908034,22008045)the Natural Science Foundation of Heilongjiang Province(Nos.LH2021H001,LH2023B013)。
文摘The Ni(Ⅱ)-chiral(4S,4'S)-2,2'-(4,6-dibenzofurandiyl)bis[4,5-dihydro-4-phenyloxazole](DBFOX/Ph)-catalyzed asymmetric 1,3-dipolar cycloadditions of nitrile imines to N-α,β-unsaturated acylpyrazoles was presented.This tactic rendered a facile and feasible route to prepare the optically active tetrasubstituted 5-3,5-dimethylpyrazole acyl dihydropyrazole cy-cloadducts bearing one or two contiguous stereocenters in good yields(up to 97%yield)with high regioselectivities(100%)and enantioselectivities(up to 97.5%ee).Following that,chiral cycloadducts could be obtained consistently in good chemical yields with excellent enantioselectivities within the gram scale process,additionally,toward five kinds of derivatization reac-tions like nucleophilic and reduction for further conversion of chiral cycloadducts to related chiral dihydropyrazole derivatives encompassing different substituents.
