The demand for high-performance non-precious-metal electrocatalysts to replace the noble metal-based catalysts for oxygen reduction reaction(ORR)is intensively increasing.Herein,single-atomic copper sites supported on...The demand for high-performance non-precious-metal electrocatalysts to replace the noble metal-based catalysts for oxygen reduction reaction(ORR)is intensively increasing.Herein,single-atomic copper sites supported on N-doped three-dimensional hierarchically porous carbon catalyst(Cu_(1)/NC)was prepared by coordination pyrolysis strategy.Remarkably,the Cu_(1)/NC-900 catalyst not only exhibits excellent ORR performance with a half-wave potential of 0.894 V(vs.RHE)in alkaline media,outperforming those of commercial Pt/C(0.851 V)and Cu nanoparticles anchored on N-doped porous carbon(CuNPs/NC-900),but also demonstrates high stability and methanol tolerance.Moreover,the Cu_(1)/NC-900 based Zn-air battery exhibits higher power density,rechargeability and cyclic stability than the one based on Pt/C.Both experimental and theoretical investigations demonstrated that the excellent performance of the as-obtained Cu_(1)/NC-900 could be attributed to the synergistic effect between copper coordinated by three N atoms active sites and the neighbouring carbon defect,resulting in elevated Cu d-band centers of Cu atoms and facilitating intermediate desorption for ORR process.This study may lead towards the development of highly efficient non-noble metal catalysts for applications in electrochemical energy conversion.展开更多
Vertical profiles of isoprene and monoterpenes were measured by a proton transfer reactiontime of flight-mass spectrometry(PTR-ToF-MS) at heights of 3,15,32,64,and 102 m above the ground on the Institute of Atmospheri...Vertical profiles of isoprene and monoterpenes were measured by a proton transfer reactiontime of flight-mass spectrometry(PTR-ToF-MS) at heights of 3,15,32,64,and 102 m above the ground on the Institute of Atmospheric Physics(IAP) tower in central Beijing during the winter of 2016 and the summer of 2017.Isoprene mixing ratios were larger in summer due to much stronger local emissions whereas monoterpenes were lower in summer due largely to their consumption by much higher levels of ozone.Isoprene mixing ratios were the highest at the 32 m in summer(1.64±0.66 ppbV) and at 15 m in winter(1.41±0.64 ppbV) with decreasing concentrations to the ground and to the 102 m,indicating emission from the tree canopy of the surrounding parks.Monoterpene mixing ratios were the highest at the 3 m height in both the winter(0.71±0.42 ppbV) and summer(0.16±0.10 ppbV) with a gradual decreasing trend to 102 m,indicting an emission from near the ground level.The lowest isoprene and monoterpene mixing ratios all occurred at 102 m,which were 0.71±0.42 ppbV(winter) and 1.35±0.51 ppbV(summer) for isoprene,and 0.42±0.22 ppbV(winter) and0.07±0.06 ppbV(summer) for monoterpenes.Isoprene in the summer and monoterpenes in the winter,as observed at the five heights,showed significant mutual correlations.In the winter monoterpenes were positively correlated with combustion tracers CO and acetonitrile at 3 m,suggesting possible anthropogenic sources.展开更多
Exploring a new tuning way to facilely realize single-band red emission in trivalent rare-earth ions(RE3+) doped upconversion(UC) materials is still desirable.In this work,the intense single-band red emission is achie...Exploring a new tuning way to facilely realize single-band red emission in trivalent rare-earth ions(RE3+) doped upconversion(UC) materials is still desirable.In this work,the intense single-band red emission is achieved by co-doping only Ho3+in the BiOCl:Er3+ under 1550 nm excitation.In the BiOCl layered host,co-doping Ho3+can further enhance the red emission and simultaneously suppress the green emission of Er3+,and thus obviously improve the red-to-green(R/G) ratio.It is found that Ho3+does not se rve as ene rgy trapping through the 5 I6 state as in traditional UC materials but acts as ET bridge(4 S3/2,2 H11/2(Er3+)→5 F4,5 S2(Ho3+)→4 F9/2(Er3+)).The tuning mechanism of Ho3+is discussed in detail and further confirms through a comparative experiment.Our research gives an unusual perspective to tune the UC behavior of Er3+through co-doping Ho3+,which might be inspiring for achievement of single-band red UC emission.展开更多
For better use of solar energy,the development of efficient broadband photocatalyst has attracted extraordinary attention.In this study,a ternary composite consisting of Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)upconversion(UC)n...For better use of solar energy,the development of efficient broadband photocatalyst has attracted extraordinary attention.In this study,a ternary composite consisting of Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)upconversion(UC)nanocrystals and Bi nanoparticles loaded BiOBr nanosheets with oxygen vacancies(OVs,SLFBB)was designed and synthesized by multi-step solvent-thermal method.Mechanisms of in-situ formation of Bi nanoparticles and OVs in BiOBr/Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)composites(SFLB)are clarified.The Bi metal and OVs enhanced the light-harvesting capacity in the region of visible-near-infrared(Vis-NIR),and promoted the separation of electron-hole(e-/h+)pairs.Furthermore,the surface plasmon resonance(SPR)effect of Bi metal can improve the energy transfer from Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)to BiOBr via nonradiative energy transfer process,resulting in enhancing the light utilization from up-converting NIR into Vis light.Due to the synergistic effects of UC function,SPR and OVs,the SFLBB exhibited obviously enhanced photocatalytic ability for the degradation of BPA with a rate of 8.9×10^(-3) min^(-1),which is about 2.78 times higher than 3.2×10^(-3) min^(-1) of BiOBr(BOB)under UV-Vis-NIR light irradiation.This work provides a novel strategy for the project of high-efficiency Bismuth-based broadband photocatalysts,which is helpful to fur-ther understand the mechanism of enhanced photocatalysis by UC function and plasmonic effect.展开更多
基金the National Natural Science Foundation of China(Nos.21804319,21971002)the Natural Science Foundation of Anhui province(Nos.1908085QB45 and 2008085QB81)the Education Departm ent of Anhui Province Foundation(No.KJ2019A0503).We thank the BL14W1 station in Shanghai Synchrotron Radiation Facility(SSRF)and 1W1B station for XAFS measurement in Beijing Synchrotron Radiation Facility(BSRF).The calculations in this paper have been done on the supercomputing system of the National Supercomputing Center in Changsha.
文摘The demand for high-performance non-precious-metal electrocatalysts to replace the noble metal-based catalysts for oxygen reduction reaction(ORR)is intensively increasing.Herein,single-atomic copper sites supported on N-doped three-dimensional hierarchically porous carbon catalyst(Cu_(1)/NC)was prepared by coordination pyrolysis strategy.Remarkably,the Cu_(1)/NC-900 catalyst not only exhibits excellent ORR performance with a half-wave potential of 0.894 V(vs.RHE)in alkaline media,outperforming those of commercial Pt/C(0.851 V)and Cu nanoparticles anchored on N-doped porous carbon(CuNPs/NC-900),but also demonstrates high stability and methanol tolerance.Moreover,the Cu_(1)/NC-900 based Zn-air battery exhibits higher power density,rechargeability and cyclic stability than the one based on Pt/C.Both experimental and theoretical investigations demonstrated that the excellent performance of the as-obtained Cu_(1)/NC-900 could be attributed to the synergistic effect between copper coordinated by three N atoms active sites and the neighbouring carbon defect,resulting in elevated Cu d-band centers of Cu atoms and facilitating intermediate desorption for ORR process.This study may lead towards the development of highly efficient non-noble metal catalysts for applications in electrochemical energy conversion.
基金supported by the National Natural Science Foundation of China(Nos.41571130031,41673116,41703112,41603070)the Natural Environment Research Council(Nos.NE/N006992/1 and NE/N006976/1)+3 种基金Theme-based Research Scheme(No.T24-504/17-N)Youth Innovation Promotion Association of the Chinese Academy of Sciences(No.2017406)Guangdong Foundation for Program of Science and Technology Research(No.2017B030314057)financial support from Natural Environment Research Council(No.NE/N007190/1)
文摘Vertical profiles of isoprene and monoterpenes were measured by a proton transfer reactiontime of flight-mass spectrometry(PTR-ToF-MS) at heights of 3,15,32,64,and 102 m above the ground on the Institute of Atmospheric Physics(IAP) tower in central Beijing during the winter of 2016 and the summer of 2017.Isoprene mixing ratios were larger in summer due to much stronger local emissions whereas monoterpenes were lower in summer due largely to their consumption by much higher levels of ozone.Isoprene mixing ratios were the highest at the 32 m in summer(1.64±0.66 ppbV) and at 15 m in winter(1.41±0.64 ppbV) with decreasing concentrations to the ground and to the 102 m,indicating emission from the tree canopy of the surrounding parks.Monoterpene mixing ratios were the highest at the 3 m height in both the winter(0.71±0.42 ppbV) and summer(0.16±0.10 ppbV) with a gradual decreasing trend to 102 m,indicting an emission from near the ground level.The lowest isoprene and monoterpene mixing ratios all occurred at 102 m,which were 0.71±0.42 ppbV(winter) and 1.35±0.51 ppbV(summer) for isoprene,and 0.42±0.22 ppbV(winter) and0.07±0.06 ppbV(summer) for monoterpenes.Isoprene in the summer and monoterpenes in the winter,as observed at the five heights,showed significant mutual correlations.In the winter monoterpenes were positively correlated with combustion tracers CO and acetonitrile at 3 m,suggesting possible anthropogenic sources.
基金the National Natural Science Foundation of China(11874186)the Applied Basic Research Program of Yunnan Province(2017FB079)+1 种基金the Reserve Talents Project of Yunnan Province(2015HB013)the Scientific Research Foundation of the Education Department of Yunnan Province(2018JS452)。
文摘Exploring a new tuning way to facilely realize single-band red emission in trivalent rare-earth ions(RE3+) doped upconversion(UC) materials is still desirable.In this work,the intense single-band red emission is achieved by co-doping only Ho3+in the BiOCl:Er3+ under 1550 nm excitation.In the BiOCl layered host,co-doping Ho3+can further enhance the red emission and simultaneously suppress the green emission of Er3+,and thus obviously improve the red-to-green(R/G) ratio.It is found that Ho3+does not se rve as ene rgy trapping through the 5 I6 state as in traditional UC materials but acts as ET bridge(4 S3/2,2 H11/2(Er3+)→5 F4,5 S2(Ho3+)→4 F9/2(Er3+)).The tuning mechanism of Ho3+is discussed in detail and further confirms through a comparative experiment.Our research gives an unusual perspective to tune the UC behavior of Er3+through co-doping Ho3+,which might be inspiring for achievement of single-band red UC emission.
基金This work was supported by the National Natural Science Foundation of China(No.11874186)Foundation of Yunnan Province(No.2019HC016).
文摘For better use of solar energy,the development of efficient broadband photocatalyst has attracted extraordinary attention.In this study,a ternary composite consisting of Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)upconversion(UC)nanocrystals and Bi nanoparticles loaded BiOBr nanosheets with oxygen vacancies(OVs,SLFBB)was designed and synthesized by multi-step solvent-thermal method.Mechanisms of in-situ formation of Bi nanoparticles and OVs in BiOBr/Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)composites(SFLB)are clarified.The Bi metal and OVs enhanced the light-harvesting capacity in the region of visible-near-infrared(Vis-NIR),and promoted the separation of electron-hole(e-/h+)pairs.Furthermore,the surface plasmon resonance(SPR)effect of Bi metal can improve the energy transfer from Sr_(2)LaF_(7)∶Yb^(3+),Er^(3+)to BiOBr via nonradiative energy transfer process,resulting in enhancing the light utilization from up-converting NIR into Vis light.Due to the synergistic effects of UC function,SPR and OVs,the SFLBB exhibited obviously enhanced photocatalytic ability for the degradation of BPA with a rate of 8.9×10^(-3) min^(-1),which is about 2.78 times higher than 3.2×10^(-3) min^(-1) of BiOBr(BOB)under UV-Vis-NIR light irradiation.This work provides a novel strategy for the project of high-efficiency Bismuth-based broadband photocatalysts,which is helpful to fur-ther understand the mechanism of enhanced photocatalysis by UC function and plasmonic effect.
