Alpine treeline ecotones are highly sensitive to climate warming.The low temperature-determined alpine treeline is expected to shift upwards in response to global warming.However,little is known about how temperature ...Alpine treeline ecotones are highly sensitive to climate warming.The low temperature-determined alpine treeline is expected to shift upwards in response to global warming.However,little is known about how temperature interacts with other important factors to influence the distribution range of tree species within and beyond the alpine treeline ecotone.Hence,we used a GF-2 satellite image,along with bioclimatic and topographic variables,to develop an ensemble suitable habitat model based on the species distribution modeling algorithms in Biomod2.We investigated the distribution of suitable habitats for B.ermanii under three climate change scenarios(i.e.,low(SSP126),moderate(SSP370)and extreme(SSP585)future emission trajectories)between two consecutive time periods(i.e.,current-2055,and 2055-2085).By 2055,the potential distribution range of B.ermanii will expand under all three climate scenarios.The medium and high suitable areas will decline under SSP370 and SSP585scenarios from 2055 to 2085.Moreover,under the three climate scenarios,the uppermost altitudes of low suitable habitat will rise to 2,329 m a.s.l.,while the altitudes of medium and high suitable habitats will fall to 2,201 and2,051 m a.s.l.by 2085,respectively.Warming promotes the expansion of B.ermanii distribution range in Changbai Mountain,and this expansion will be modified by precipitation as climate warming continues.This interaction between temperature and precipitation plays a significant role in shaping the potential distribution range of B.ermanii in the alpine treeline ecotone.This study reveals the link between environmental factors,habitat distribution,and species distribution in the alpine treeline ecotone,providing valuable insights into the impacts of climate change on high-elevation vegetation,and contributing to mountain biodiversity conservation and sustainable development.展开更多
In order to restore a degraded alkaline grassland, the local government implemented a large restoration project using fences in Changling county, Jilin province, China, in 2000. Grazing was excluded from the protected...In order to restore a degraded alkaline grassland, the local government implemented a large restoration project using fences in Changling county, Jilin province, China, in 2000. Grazing was excluded from the protected area, whereas the grazed area was continuously grazed at 8.5 dry sheep equivalent(DSE)/hm2. In the current research, soil and plant samples were taken from grazed and fenced areas to examine changes in vegetation and soil properties in 2005, 2006 and 2008. Results showed that vegetation characteristics and soil properties improved significantly in the fenced area compared with the grazed area. In the protected area the vegetation cover, height and above- and belowground biomass increased significantly. Soil pH, electrical conductivity and bulk density decreased significantly, but soil organic carbon and total nitrogen concentration increased greatly in the protected area. By comparing the vegetation and soil characteristics with pre-degraded grassland, we found that vegetation can recover 6 years after fencing, and soil pH can be restored 8 years after fencing. However, the restoration of soil organic carbon, total nitrogen and total phosphorus concentrations needed 16, 30 and 19 years, respectively. It is recommended that the stocking rate should be reduced to 1/3 of the current carrying capacity, or that a grazing regime of 1-year of grazing followed by a 2-year rest is adopted to sustain the current status of vegetation and soil resources. However, if N fertilizer is applied, the rest period could be shortened, depending on the rate of application.展开更多
To objectively reflect the relevant situation of researches on think tank service of Chinese university libraries, this paper uses CNKI Database as the retrieval source, the bibliometric analysis method, and CiteSpace...To objectively reflect the relevant situation of researches on think tank service of Chinese university libraries, this paper uses CNKI Database as the retrieval source, the bibliometric analysis method, and CiteSpace, a citation network analysis tool, to make quantitative analysis on the literature data of researches on the think tank service of university libraries;draw the knowledge map of literature authors, organization distribution, keyword co-occurrence, research hotspot distribution, etc.;objectively and comprehensively analyzes the hot topics and cutting-edge trends of researches on the think tank service of libraries, the research includes the following aspects: First, the status quo and orientation of the existing university library think tanks in China;second, it is recommended to carry out research on policy support and system guarantee for university library think tank services;third, integrate big data technology is merged into the construction of university libraries think tanks;fourth, the transformation of library and information institutions to new types of think tanks, including the transformation of knowledge services, disciplinary services, and characteristic think tanks, in order to provide reference for researches and practical work of think tank service of libraries in China.展开更多
Carabid beetles,predatory insects,are abundant in forests and sensitive to environmental changes.The distribution patterns and diversity of carabid beetles in several natural forests were studied to provide a basis fo...Carabid beetles,predatory insects,are abundant in forests and sensitive to environmental changes.The distribution patterns and diversity of carabid beetles in several natural forests were studied to provide a basis for evaluating the importance of a forest in the protection of carabid beetle diversity.Carabids were captured by pitfall traps during their seasonal activity from 2012 to 2013 in a poplar-birch forest,ash-walnut forest and broad-leaved Korean pine forest.A total of 5252 individuals,representing 21 species,were collected.Carabid abundance was highest in the broad-leaved Korean pine forest and lowest in the ash-walnut forest.Carabus billbergi Mannerheim and Pterostichus pertinax(Tschitscherine)were the dominant beetle species in each stand.Carabus canaliculatus Adams was dominant in the poplar-birch and ash-walnut forests,and Leistus niger Gebler was dominant in the ash-walnut forest.The carabids were affected differently by stand factors.C.billbergi and P.pertinax was positively correlated with mean DBH.C.canaliculatus and L.niger were not positively correlated with any stand factors.The broad-leaved Korean pine forest with greater age,large DBH and thick leaf litter fostered a high diversity of carabid species.The main yearly activity period for most carabids was during July.Different carabid species responded differently to seasonality,and the activity period of several species was relatively late(August)in the year.展开更多
Covalent organic frameworks(COFs)have garnered increasing attention as promising electrode materials for sodium-ion batteries(SIBs)due to their ordered backbones,uniform pore sizes,and high surface areas.However,they ...Covalent organic frameworks(COFs)have garnered increasing attention as promising electrode materials for sodium-ion batteries(SIBs)due to their ordered backbones,uniform pore sizes,and high surface areas.However,they also face challenges,including low capacity,unsatisfactory rate performance,and limited cycling stability,which pose the primary obstacles to their practical use.Herein,a pyrenoimidazole-based COF,denoted as PyIm-COF,has been synthesized as a novel electrode material for highperformance SIBs using an efficient synthetic strategy.With extended fully conjugated backbones and readily accessible redox-active sites,PyIm-COF demonstrates remarkable high-rate performance,delivering around 250 m Ah g^(−1)and excellent cycling stability,retaining 97.2%of its capacity even after 2500 cycles at 5 A g^(−1),which is higher than that of most previously reported COF-based SIBs.This work provides valuable insights into the development of nitrogen-rich conjugated COF electrode materials for rechargeable SIBs.展开更多
Comprehensive Summary,Although polyimides(PIs)have shown great potential for a broad range of applications,it remains very challenging to achieve the malleability,rehealability and recyclability for PIs and their comp...Comprehensive Summary,Although polyimides(PIs)have shown great potential for a broad range of applications,it remains very challenging to achieve the malleability,rehealability and recyclability for PIs and their composites targeting various applications,particularly for the rapidly emerging flexible and stretchable electronics.Herein,malleable conductive poly(imide-imine)hybrid(PIIH)vitrimer-graphene aerogel(GA)composites have been prepared,for the first time,via simple sol-gel film formation followed by heat-press.The resulting PIIH-GA composites exhibit not only the highly desired properties of thermosetting(strong mechanical strength)and thermoplastic(reprocessability)polymers,but also good conductivity enabled by the GA filler.PIIH3-GA-10(with 10 wt%GA)showed one of the highest electrical conductivities(26.7 S/m)for PI-based composites,as well as good electromagnetic interference(EMI)shielding performance.Moreover,the PIIH-GA films could maintain good performance during stretching and even after chemical recycling,which opens new opportunities for flexible and sustainable electronics development.展开更多
Although dynamic covalent chemistry(DCvC)has been widely utilized to synthesize small molecules and polymers,it remains challenging to construct highly ordered polymeric architectures via DCvC.Further exploration of n...Although dynamic covalent chemistry(DCvC)has been widely utilized to synthesize small molecules and polymers,it remains challenging to construct highly ordered polymeric architectures via DCvC.Further exploration of novel dynamic linkages(in addition to commonly used imine and boronate ester)will expand the library of readily accessible dynamic linkages,diversify the polymeric structures,and unlock new functionality.In this mini-review,the DCvC-based synthetic strategies for enhancing the structural orders of polymeric architectures will be discussed from both thermodynamic control and kinetic control aspects.The relationship between the structure,stability,and dynamic behavior of a DCvC bond will be presented.Then recent examples of constructing polymers with DCvC and supramolecular bonding interactions,such as metal-ligand coordination,host-guest binding,and hydrogen bonding,will be reviewed to demonstrate their synergistic relationship.Furthermore,polymers featuring relatively unexplored DCvC will be highlighted to underscore how developing novel dynamic linkages and fundamental DCvC studies can broaden the scope of functional polymeric architectures.In the end,the challenges in the current field and possible future directions will also be discussed.Advancements in using these design principles will undoubtedly lead to the development of intriguing chemistries,polymeric architectures,and functionality.展开更多
Graphene-polymer composites have attracted great attention as sensing materials due to their tailorable electrical conductivity, physicochemical properties, and sensitivity to geometric and functional changes.Herein, ...Graphene-polymer composites have attracted great attention as sensing materials due to their tailorable electrical conductivity, physicochemical properties, and sensitivity to geometric and functional changes.Herein, we report the first example of cylindrical monolithic polyimine vitrimer/graphene composites with excellent mechanical, compressive, rehealable and recyclable, and piezoresistive properties via simple infiltration of polymer monomers into the pores of graphene aerogel followed by thermal curing. The composites exhibit excellent durable compressibility(negligible reduction in the compression properties even after 3000 consecutive compression cycles), rapid recovery to the original size upon stress released,high compressive strength(up to 1.2 MPa), and high conductivity(up to 79 S/m). Excellent piezoresistive properties were observed, displaying consistent and reliable change of the electrical resistance with the compression ratio. Furthermore, rehealing with ~100% recovery of the compressive strength and electric conductivity was achieved under mild rehealing conditions, which is highly desired but has rarely been reported for electronic materials. The facile strategy for fabrication of rehealable monolithic polymer/GAs can open new possibilities for the sustainable development of composites with high electrical conductivity for various applications such as sensing, health monitoring, and movement detection.展开更多
Porous organic polymers(POPs) have recently emerged as promising candidates for catalyzing oxygen reduction reaction(ORR).Compared to conventional Pt-based ORR catalysts, these newly developed porous materials, includ...Porous organic polymers(POPs) have recently emerged as promising candidates for catalyzing oxygen reduction reaction(ORR).Compared to conventional Pt-based ORR catalysts, these newly developed porous materials, including both non-precious metal based catalysts and metal-free catalysts, are more sustainable and cost-effective. Their porous structures and large surface areas facilitate mass and electron transport and boost the ORR kinetics. This mini-review will give a brief summary of recent development of POPs as electrocatalysts for the ORR. Some design principles, different POP structures, key factors for their ORR catalytic performance, and outlook of POP materials will be discussed.展开更多
Although the past decade has witnessed tremendous progress in the development of covalent organic frameworks(COFs),three-dimensional(3D)COFs fabrications and characterizations are still much less studied compared with...Although the past decade has witnessed tremendous progress in the development of covalent organic frameworks(COFs),three-dimensional(3D)COFs fabrications and characterizations are still much less studied compared with two-dimensional(2D)COFs,due to their complicated topology structures caused by interpenetration and limited choices of node-building blocks.In this work,we constructed a novel 3D COF(SP-3D-COF-BPY)successfully using orthogonal dual-planar spirobifluorene and bipyridine as building blocks.Also,we demonstrated the application of 3D COF-supported Pd(II)catalyst in heterogeneous catalysis.A sevenfold interpenetrated dia structure was revealed for SP-3DCOF-BPY by powder X-ray diffraction(PXRD)in conjunction with structural simulation and Pawley refinement.The bipyridine-linked frameworks bear one-dimensional(1D)unobstructed rigid channels and offer a high density of discrete coordination sites for chelating Pd(II)species.Very high loading of Pd(II)(∼15 wt%)was achieved in the asymmetric(as)-prepared Pd(II)@3D-COF-BYP.The generated highly ordered porous channels and easily accessible catalytic sites,such as COF-supported Pd(II)complex,serves as a highly active and stable microporous heterogeneous catalyst in Suzuki–Miyaura coupling reactions.The observed catalytic efficiency was high and the catalyst could be conveniently reused multiple times without any noticeable decay in catalytic performance.展开更多
We have constructed a novel porous pyrene-based organic cage,PyTC1,through the condensation reaction of cyclohexanediamine with 5,5′-(pyrene-1,6-diyl)diisophthalaldehyde.Single-crystal X-ray diffraction analysis reve...We have constructed a novel porous pyrene-based organic cage,PyTC1,through the condensation reaction of cyclohexanediamine with 5,5′-(pyrene-1,6-diyl)diisophthalaldehyde.Single-crystal X-ray diffraction analysis reveals the effective intercage C–H...πinteraction between cyclohexanediimine and pyrene segments.Such a soft intercage C–H...πinteraction,rather than a classic J-aggregate with slippedπ–π-stacking configuration,induced an unusual bathochromic shift of pyrene-based chromophore absorption from an ultraviolet region of PyTC1 in solution to the visible light region of PyTC1 in solid-state.展开更多
Single-ion conducting polymer electrolytes have attracted great attention as safe alternatives to liquid electrolytes in high energy density lithium-ion batteries.Herein,we report the first example of a crystalline an...Single-ion conducting polymer electrolytes have attracted great attention as safe alternatives to liquid electrolytes in high energy density lithium-ion batteries.Herein,we report the first example of a crystalline anionic helical polymer as a single lithium-ion conducting solid polymer electrolyte(SPE).Single-crystal X-ray analysis shows that the polymer folds into densely packed double helices,with bundles of unidirectional negatively charged channels formed that can facilitate lithium-ion transportation.展开更多
We report a series of highly stable metallophthalocyanine-based covalent organic frameworks(MPc-dxCOFs) linked by robust 1,4-dioxin bonds constructed through nucleophilic aromatic substitution(SNAr)reaction. The chemi...We report a series of highly stable metallophthalocyanine-based covalent organic frameworks(MPc-dxCOFs) linked by robust 1,4-dioxin bonds constructed through nucleophilic aromatic substitution(SNAr)reaction. The chemical structures and crystallinity of the COFs largely remain unchanged even after treating with boiling water(90°C), concentrated acids(12 mol/L HCl) or bases(12 mol/L Na OH), oxidizing(30% H_(2)O_(2)) or reducing agents(1 mol/L NaBH;) for three days due to their stable M-Pc building blocks and resilient dioxin linkers. With metallated phthalocyanine active sites regularly arranged in the stable framework structures, MPc-dx-COFs can be directly used as efficient electrocatalysts for the oxygen reduction reaction(ORR) without pyrolysis treatment that has commonly been used in previous studies.展开更多
基金the National Key R&D Program of China(Grant NO.2022YFF1300904)the National Natural Science Foundation of China(Grant NO.42001106,42371075,42271119)+2 种基金the Joint Fund of National Natural Science Foundation of China(Grant NO.U19A2042,U19A2023,U20A2083)the Natural Science Foundation of Jilin Province,China(YDZJ202201ZYTS483)Youth Innovation Promotion Association,Chinese Academy of Sciences(2023238)。
文摘Alpine treeline ecotones are highly sensitive to climate warming.The low temperature-determined alpine treeline is expected to shift upwards in response to global warming.However,little is known about how temperature interacts with other important factors to influence the distribution range of tree species within and beyond the alpine treeline ecotone.Hence,we used a GF-2 satellite image,along with bioclimatic and topographic variables,to develop an ensemble suitable habitat model based on the species distribution modeling algorithms in Biomod2.We investigated the distribution of suitable habitats for B.ermanii under three climate change scenarios(i.e.,low(SSP126),moderate(SSP370)and extreme(SSP585)future emission trajectories)between two consecutive time periods(i.e.,current-2055,and 2055-2085).By 2055,the potential distribution range of B.ermanii will expand under all three climate scenarios.The medium and high suitable areas will decline under SSP370 and SSP585scenarios from 2055 to 2085.Moreover,under the three climate scenarios,the uppermost altitudes of low suitable habitat will rise to 2,329 m a.s.l.,while the altitudes of medium and high suitable habitats will fall to 2,201 and2,051 m a.s.l.by 2085,respectively.Warming promotes the expansion of B.ermanii distribution range in Changbai Mountain,and this expansion will be modified by precipitation as climate warming continues.This interaction between temperature and precipitation plays a significant role in shaping the potential distribution range of B.ermanii in the alpine treeline ecotone.This study reveals the link between environmental factors,habitat distribution,and species distribution in the alpine treeline ecotone,providing valuable insights into the impacts of climate change on high-elevation vegetation,and contributing to mountain biodiversity conservation and sustainable development.
基金supported by the National Key Basic Research Program of China (2011CB403203)the Strategic Science and Technology Guide Project of Chinese Academy of Sciences (XDA05050401)
文摘In order to restore a degraded alkaline grassland, the local government implemented a large restoration project using fences in Changling county, Jilin province, China, in 2000. Grazing was excluded from the protected area, whereas the grazed area was continuously grazed at 8.5 dry sheep equivalent(DSE)/hm2. In the current research, soil and plant samples were taken from grazed and fenced areas to examine changes in vegetation and soil properties in 2005, 2006 and 2008. Results showed that vegetation characteristics and soil properties improved significantly in the fenced area compared with the grazed area. In the protected area the vegetation cover, height and above- and belowground biomass increased significantly. Soil pH, electrical conductivity and bulk density decreased significantly, but soil organic carbon and total nitrogen concentration increased greatly in the protected area. By comparing the vegetation and soil characteristics with pre-degraded grassland, we found that vegetation can recover 6 years after fencing, and soil pH can be restored 8 years after fencing. However, the restoration of soil organic carbon, total nitrogen and total phosphorus concentrations needed 16, 30 and 19 years, respectively. It is recommended that the stocking rate should be reduced to 1/3 of the current carrying capacity, or that a grazing regime of 1-year of grazing followed by a 2-year rest is adopted to sustain the current status of vegetation and soil resources. However, if N fertilizer is applied, the rest period could be shortened, depending on the rate of application.
文摘To objectively reflect the relevant situation of researches on think tank service of Chinese university libraries, this paper uses CNKI Database as the retrieval source, the bibliometric analysis method, and CiteSpace, a citation network analysis tool, to make quantitative analysis on the literature data of researches on the think tank service of university libraries;draw the knowledge map of literature authors, organization distribution, keyword co-occurrence, research hotspot distribution, etc.;objectively and comprehensively analyzes the hot topics and cutting-edge trends of researches on the think tank service of libraries, the research includes the following aspects: First, the status quo and orientation of the existing university library think tanks in China;second, it is recommended to carry out research on policy support and system guarantee for university library think tank services;third, integrate big data technology is merged into the construction of university libraries think tanks;fourth, the transformation of library and information institutions to new types of think tanks, including the transformation of knowledge services, disciplinary services, and characteristic think tanks, in order to provide reference for researches and practical work of think tank service of libraries in China.
基金supported by grants from the National Natural Science Foundation of China(31600517)the Science and Technology Development Project of Jilin Province(20180201059NY)+2 种基金Science and Technology Research Project of Jilin Provincial Education Department(JJKH20190651KJ)Open Project of Key Laboratory of Geographical Processes and Ecological Security of Changbai Mountains,Ministry of Education(GPES202003)National College Students’Innovation and Entrepreneurship Training Program(202110201030)。
文摘Carabid beetles,predatory insects,are abundant in forests and sensitive to environmental changes.The distribution patterns and diversity of carabid beetles in several natural forests were studied to provide a basis for evaluating the importance of a forest in the protection of carabid beetle diversity.Carabids were captured by pitfall traps during their seasonal activity from 2012 to 2013 in a poplar-birch forest,ash-walnut forest and broad-leaved Korean pine forest.A total of 5252 individuals,representing 21 species,were collected.Carabid abundance was highest in the broad-leaved Korean pine forest and lowest in the ash-walnut forest.Carabus billbergi Mannerheim and Pterostichus pertinax(Tschitscherine)were the dominant beetle species in each stand.Carabus canaliculatus Adams was dominant in the poplar-birch and ash-walnut forests,and Leistus niger Gebler was dominant in the ash-walnut forest.The carabids were affected differently by stand factors.C.billbergi and P.pertinax was positively correlated with mean DBH.C.canaliculatus and L.niger were not positively correlated with any stand factors.The broad-leaved Korean pine forest with greater age,large DBH and thick leaf litter fostered a high diversity of carabid species.The main yearly activity period for most carabids was during July.Different carabid species responded differently to seasonality,and the activity period of several species was relatively late(August)in the year.
基金the Natural Science Foundation of Liaoning province(grant no.2019-MS-046)W.Zhang thanks the University of Colorado Boulder for financial support of this work+1 种基金W.Huang acknowledges the support from the National Natural Science Foundation of China(grant no.21875206)The authors acknowledge the assistance of the Dalian University of Technology Instrumental Analysis Center.
文摘Covalent organic frameworks(COFs)have garnered increasing attention as promising electrode materials for sodium-ion batteries(SIBs)due to their ordered backbones,uniform pore sizes,and high surface areas.However,they also face challenges,including low capacity,unsatisfactory rate performance,and limited cycling stability,which pose the primary obstacles to their practical use.Herein,a pyrenoimidazole-based COF,denoted as PyIm-COF,has been synthesized as a novel electrode material for highperformance SIBs using an efficient synthetic strategy.With extended fully conjugated backbones and readily accessible redox-active sites,PyIm-COF demonstrates remarkable high-rate performance,delivering around 250 m Ah g^(−1)and excellent cycling stability,retaining 97.2%of its capacity even after 2500 cycles at 5 A g^(−1),which is higher than that of most previously reported COF-based SIBs.This work provides valuable insights into the development of nitrogen-rich conjugated COF electrode materials for rechargeable SIBs.
基金supported by the National Natural Science Foundation of China(21875208,51962036)Key Project of the Natural Science Foundation of Yunnan(Grant 202201AS070011)High-Level Talents Introduction in Yunnan Province(C619300A025).
文摘Comprehensive Summary,Although polyimides(PIs)have shown great potential for a broad range of applications,it remains very challenging to achieve the malleability,rehealability and recyclability for PIs and their composites targeting various applications,particularly for the rapidly emerging flexible and stretchable electronics.Herein,malleable conductive poly(imide-imine)hybrid(PIIH)vitrimer-graphene aerogel(GA)composites have been prepared,for the first time,via simple sol-gel film formation followed by heat-press.The resulting PIIH-GA composites exhibit not only the highly desired properties of thermosetting(strong mechanical strength)and thermoplastic(reprocessability)polymers,but also good conductivity enabled by the GA filler.PIIH3-GA-10(with 10 wt%GA)showed one of the highest electrical conductivities(26.7 S/m)for PI-based composites,as well as good electromagnetic interference(EMI)shielding performance.Moreover,the PIIH-GA films could maintain good performance during stretching and even after chemical recycling,which opens new opportunities for flexible and sustainable electronics development.
文摘Although dynamic covalent chemistry(DCvC)has been widely utilized to synthesize small molecules and polymers,it remains challenging to construct highly ordered polymeric architectures via DCvC.Further exploration of novel dynamic linkages(in addition to commonly used imine and boronate ester)will expand the library of readily accessible dynamic linkages,diversify the polymeric structures,and unlock new functionality.In this mini-review,the DCvC-based synthetic strategies for enhancing the structural orders of polymeric architectures will be discussed from both thermodynamic control and kinetic control aspects.The relationship between the structure,stability,and dynamic behavior of a DCvC bond will be presented.Then recent examples of constructing polymers with DCvC and supramolecular bonding interactions,such as metal-ligand coordination,host-guest binding,and hydrogen bonding,will be reviewed to demonstrate their synergistic relationship.Furthermore,polymers featuring relatively unexplored DCvC will be highlighted to underscore how developing novel dynamic linkages and fundamental DCvC studies can broaden the scope of functional polymeric architectures.In the end,the challenges in the current field and possible future directions will also be discussed.Advancements in using these design principles will undoubtedly lead to the development of intriguing chemistries,polymeric architectures,and functionality.
基金financially supported by National Natural Science Foundation of China (No. 21875208)Yunnan University (Nos. WX160117, C176220100005)+3 种基金University of Colorado Boulder, HighLevel Talents Introduction in Yunnan Province (No. C619300A025)the Key Project of Natural Science Foundation of Yunnan (No. 202201AS070011)Major Science and Technology Project of Precious Metal Materials Genetic Engineering in Yunnan Province (Nos. 2019ZE001-1, 202002AB080001)International Joint Research Center for Advanced Energy Materials of Yunnan Province (No. 202003AE140001)。
文摘Graphene-polymer composites have attracted great attention as sensing materials due to their tailorable electrical conductivity, physicochemical properties, and sensitivity to geometric and functional changes.Herein, we report the first example of cylindrical monolithic polyimine vitrimer/graphene composites with excellent mechanical, compressive, rehealable and recyclable, and piezoresistive properties via simple infiltration of polymer monomers into the pores of graphene aerogel followed by thermal curing. The composites exhibit excellent durable compressibility(negligible reduction in the compression properties even after 3000 consecutive compression cycles), rapid recovery to the original size upon stress released,high compressive strength(up to 1.2 MPa), and high conductivity(up to 79 S/m). Excellent piezoresistive properties were observed, displaying consistent and reliable change of the electrical resistance with the compression ratio. Furthermore, rehealing with ~100% recovery of the compressive strength and electric conductivity was achieved under mild rehealing conditions, which is highly desired but has rarely been reported for electronic materials. The facile strategy for fabrication of rehealable monolithic polymer/GAs can open new possibilities for the sustainable development of composites with high electrical conductivity for various applications such as sensing, health monitoring, and movement detection.
文摘Porous organic polymers(POPs) have recently emerged as promising candidates for catalyzing oxygen reduction reaction(ORR).Compared to conventional Pt-based ORR catalysts, these newly developed porous materials, including both non-precious metal based catalysts and metal-free catalysts, are more sustainable and cost-effective. Their porous structures and large surface areas facilitate mass and electron transport and boost the ORR kinetics. This mini-review will give a brief summary of recent development of POPs as electrocatalysts for the ORR. Some design principles, different POP structures, key factors for their ORR catalytic performance, and outlook of POP materials will be discussed.
基金The authors would like to acknowledge Prof.Yifu Ding of the University of Colorado Boulder for the instrumentation support with DMA.This work was supported by the University of Colorado Boulder,Wong KC Education Foundation,and the National Natural Science Foundation of China(51673072).Su Z would like to thank China Scholarship Council(CSC)for financial support.
基金The work was supported by the National Natural Science Foundation of China(nos.51722302,21674054,and 51972185).
文摘Although the past decade has witnessed tremendous progress in the development of covalent organic frameworks(COFs),three-dimensional(3D)COFs fabrications and characterizations are still much less studied compared with two-dimensional(2D)COFs,due to their complicated topology structures caused by interpenetration and limited choices of node-building blocks.In this work,we constructed a novel 3D COF(SP-3D-COF-BPY)successfully using orthogonal dual-planar spirobifluorene and bipyridine as building blocks.Also,we demonstrated the application of 3D COF-supported Pd(II)catalyst in heterogeneous catalysis.A sevenfold interpenetrated dia structure was revealed for SP-3DCOF-BPY by powder X-ray diffraction(PXRD)in conjunction with structural simulation and Pawley refinement.The bipyridine-linked frameworks bear one-dimensional(1D)unobstructed rigid channels and offer a high density of discrete coordination sites for chelating Pd(II)species.Very high loading of Pd(II)(∼15 wt%)was achieved in the asymmetric(as)-prepared Pd(II)@3D-COF-BYP.The generated highly ordered porous channels and easily accessible catalytic sites,such as COF-supported Pd(II)complex,serves as a highly active and stable microporous heterogeneous catalyst in Suzuki–Miyaura coupling reactions.The observed catalytic efficiency was high and the catalyst could be conveniently reused multiple times without any noticeable decay in catalytic performance.
基金support from the National Key R&D Program of China(no.2016YFC0700603)Natural Science Foundation of China(nos.21631003 and 21805005)+1 种基金the Fundamental Research Funds for the Central Universities(nos.FRF-BD-20-14A and FRF-IDRY-19-028)University of Science and Technology Beijing is gratefully acknowledged.
文摘We have constructed a novel porous pyrene-based organic cage,PyTC1,through the condensation reaction of cyclohexanediamine with 5,5′-(pyrene-1,6-diyl)diisophthalaldehyde.Single-crystal X-ray diffraction analysis reveals the effective intercage C–H...πinteraction between cyclohexanediimine and pyrene segments.Such a soft intercage C–H...πinteraction,rather than a classic J-aggregate with slippedπ–π-stacking configuration,induced an unusual bathochromic shift of pyrene-based chromophore absorption from an ultraviolet region of PyTC1 in solution to the visible light region of PyTC1 in solid-state.
基金supported by the University of Colorado Boulder。
文摘Single-ion conducting polymer electrolytes have attracted great attention as safe alternatives to liquid electrolytes in high energy density lithium-ion batteries.Herein,we report the first example of a crystalline anionic helical polymer as a single lithium-ion conducting solid polymer electrolyte(SPE).Single-crystal X-ray analysis shows that the polymer folds into densely packed double helices,with bundles of unidirectional negatively charged channels formed that can facilitate lithium-ion transportation.
基金supported by University of Colorado Boulder and K. C. Wong Education Foundationfinancial support by the Koch Graduate fellowship。
文摘We report a series of highly stable metallophthalocyanine-based covalent organic frameworks(MPc-dxCOFs) linked by robust 1,4-dioxin bonds constructed through nucleophilic aromatic substitution(SNAr)reaction. The chemical structures and crystallinity of the COFs largely remain unchanged even after treating with boiling water(90°C), concentrated acids(12 mol/L HCl) or bases(12 mol/L Na OH), oxidizing(30% H_(2)O_(2)) or reducing agents(1 mol/L NaBH;) for three days due to their stable M-Pc building blocks and resilient dioxin linkers. With metallated phthalocyanine active sites regularly arranged in the stable framework structures, MPc-dx-COFs can be directly used as efficient electrocatalysts for the oxygen reduction reaction(ORR) without pyrolysis treatment that has commonly been used in previous studies.