We explore the electronic and transport properties of zigzag graphene nanoribbons （GNRs） with nitrogen-vacancy defects by performing fully self-consistent spin-polarized density functional theory calculations combin...We explore the electronic and transport properties of zigzag graphene nanoribbons （GNRs） with nitrogen-vacancy defects by performing fully self-consistent spin-polarized density functional theory calculations combined with non-equilibrium Green＇s function technique. We observe robust negative di erential resistance （NDR） effect in all examined molecular junctions. Through analyzing the calculated electronic structures and the bias-dependent transmission coefficients, we find that the narrow density of states of electrodes and the bias-dependent effective coupling between the central molecular orbitals and the electrode subbands are responsible for the observed NDR phenomenon. In addition, the obvious di erence of the transmission spectra of two spin channels is observed in some bias ranges, which leads to the near perfect spin-filtering effect. These theoretical findings imply that GNRs with nitrogenvacancy defects hold great potential for building molecular devices.展开更多
Graphite-like C3N4 （g-C3N4） is an efficient visible-light-driven photocatalyst which is com- monly used in pollutant degradation. The photoreactivity of g-C3N4 depends on the prepa- ration conditions to a large exte...Graphite-like C3N4 （g-C3N4） is an efficient visible-light-driven photocatalyst which is com- monly used in pollutant degradation. The photoreactivity of g-C3N4 depends on the prepa- ration conditions to a large extent. In this work, we linked the preparation conditions of g-C3N4 to its stability and photocatalytic activity through dye photodegradation experiments and sensitivity mathematical analyses. The sensitivity mathematical analyses show that the effect of calcination temperature is more significant than calcination time on the photoreactivity of g-C3N4. The photocatalytic activity of optimized g-C3N4 in rhodamine B （RhB） degradation under visible light was 100 times higher than that of non-optimized one. The enhanced performance can be attributed to the increased specific surface area of g-C3N4 and the increased migration velocity of photogenerated electron-hole pairs on the surface. This work deepens the understanding of the relation between preparation conditions and the charateristics of g-C3N4, and provides an extremely simple method for significantly improving the photoreactivity of g-C3N4.展开更多
A simple and effective method for the preparation of amphiphilic graphene(AG)is presented under an organic solvent-free synthetic condition.The synthetic route first involves a cyclization reaction between carboxylic ...A simple and effective method for the preparation of amphiphilic graphene(AG)is presented under an organic solvent-free synthetic condition.The synthetic route first involves a cyclization reaction between carboxylic groups on graphene oxide and the amino groups on 5,6-diaminopyrazine-2,3-dicarbonitrile,and subsequent reduction by hydrazine.Results of UV-vis spectroscopy,Fourier transformed infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TGA)and Raman spectroscopy have confirmed that the covalent functionalization of graphene can be achieved through the formation of imidazo[4,5-b]pyrazine on the graphene sheets.As a result,AG can be successfully dispersed in water and common organic solvents.This work successfully provides a facile and efficient way to fabricate AG and may extend the potential applications of graphene-based materials in nanoelectronic devices,polymer fillers and biological field.展开更多
Developing low-cost, high-performance elec- trocatalysts for the oxygen reduction reaction （ORR） is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based cataly...Developing low-cost, high-performance elec- trocatalysts for the oxygen reduction reaction （ORR） is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based catalysts have been extensively investigated for ORR in alkaline electrolytes. However, their performance in acidic electrolytes still requires further improvement compared to the Pt/C catalyst. Here we report a self-templating approach to prepare graphene-based sandwich-like porous carbon nanosheets for efficient ORR in both alkaline and acidic electrolytes. Graphene oxides were first used to adsorb m-phenylenediamine molecules which can form a nitrogen-rich polymer network after oxidative poly- merization. Then iron （Fe） salt was introduced into the polymer network and transformed into ORR active Fe-N-C sites along with Fe, FeS, and FEN0.05 nanopartides after pyr- olysis, generating ORR active sandwich-like carbon na- nosheets. Due to the presence of multiple ORR active sites. The as-obtained catalyst exhibited prominent ORR activity with a half-wave potential -30 mV more positive than Pt/C in 0.1 mol L-1 KOH, while the half-wave potential of the catalyst was only -40 mV lower than that of commercial Pt/C in 0.1 mol L-1 HClO4. The unique planar sandwich-like structure could expose abundant active sites for ORR. Meanwhile, the graphene layer and porous structure could simultaneously enhance electrical conductivity and facilitate mass transport. The prominent electrocatalytic activity and durability in both alkaline and acidic electrolytes indicate that these carbon na- nosheets hold great potential as alternatives to precious metal- based catalysts, as demonstrated in zinc-air batteries and proton exchange membrane fuel cells.展开更多
基金This work was partially supported by the National Natural Science Foundation of China （No.20903003 and No.21273208）, the Anhui Provincial Natural Science Foundation （No.1408085QB26）, the China Postdoctoral Science Foundation （No.2012M511409）, the Supercomputer Center of Chinese Academy of Sciences, and University of Science and Technology of China and Shanghai Supercomputer Centers.
文摘We explore the electronic and transport properties of zigzag graphene nanoribbons （GNRs） with nitrogen-vacancy defects by performing fully self-consistent spin-polarized density functional theory calculations combined with non-equilibrium Green＇s function technique. We observe robust negative di erential resistance （NDR） effect in all examined molecular junctions. Through analyzing the calculated electronic structures and the bias-dependent transmission coefficients, we find that the narrow density of states of electrodes and the bias-dependent effective coupling between the central molecular orbitals and the electrode subbands are responsible for the observed NDR phenomenon. In addition, the obvious di erence of the transmission spectra of two spin channels is observed in some bias ranges, which leads to the near perfect spin-filtering effect. These theoretical findings imply that GNRs with nitrogenvacancy defects hold great potential for building molecular devices.
文摘Graphite-like C3N4 （g-C3N4） is an efficient visible-light-driven photocatalyst which is com- monly used in pollutant degradation. The photoreactivity of g-C3N4 depends on the prepa- ration conditions to a large extent. In this work, we linked the preparation conditions of g-C3N4 to its stability and photocatalytic activity through dye photodegradation experiments and sensitivity mathematical analyses. The sensitivity mathematical analyses show that the effect of calcination temperature is more significant than calcination time on the photoreactivity of g-C3N4. The photocatalytic activity of optimized g-C3N4 in rhodamine B （RhB） degradation under visible light was 100 times higher than that of non-optimized one. The enhanced performance can be attributed to the increased specific surface area of g-C3N4 and the increased migration velocity of photogenerated electron-hole pairs on the surface. This work deepens the understanding of the relation between preparation conditions and the charateristics of g-C3N4, and provides an extremely simple method for significantly improving the photoreactivity of g-C3N4.
基金supported by the NSFC for Excellent Young Scholars(Grant No.21322402)National Natural Science Foundation of China(Grant Nos.21274064,61204095,51173081)+2 种基金the Program for New Century Excellent Talents in University(Grant No.NCET-11-0992)Natural Science Foundation of Jiangsu Province,China(Grant Nos.BK2011761,BK2012431,BK2009025)NJUPT(Grant No.NY211022)
文摘A simple and effective method for the preparation of amphiphilic graphene(AG)is presented under an organic solvent-free synthetic condition.The synthetic route first involves a cyclization reaction between carboxylic groups on graphene oxide and the amino groups on 5,6-diaminopyrazine-2,3-dicarbonitrile,and subsequent reduction by hydrazine.Results of UV-vis spectroscopy,Fourier transformed infrared spectroscopy(FT-IR),X-ray photoelectron spectroscopy(XPS),thermogravimetric analysis(TGA)and Raman spectroscopy have confirmed that the covalent functionalization of graphene can be achieved through the formation of imidazo[4,5-b]pyrazine on the graphene sheets.As a result,AG can be successfully dispersed in water and common organic solvents.This work successfully provides a facile and efficient way to fabricate AG and may extend the potential applications of graphene-based materials in nanoelectronic devices,polymer fillers and biological field.
基金supported by the National Basic Research Program of China (973 Program, 2015CB351903)the National Key Research and Development Program (2017YFA0207301)+1 种基金the National Natural Science Foundation of China (51402282, 21474095 and 21476104)CAS Key Research Program of Frontier Sciences (QYZDB-SSW-SLH018)
文摘Developing low-cost, high-performance elec- trocatalysts for the oxygen reduction reaction （ORR） is crucial for implementation of fuel cells and metal-air batteries into practical applications. Graphene-based catalysts have been extensively investigated for ORR in alkaline electrolytes. However, their performance in acidic electrolytes still requires further improvement compared to the Pt/C catalyst. Here we report a self-templating approach to prepare graphene-based sandwich-like porous carbon nanosheets for efficient ORR in both alkaline and acidic electrolytes. Graphene oxides were first used to adsorb m-phenylenediamine molecules which can form a nitrogen-rich polymer network after oxidative poly- merization. Then iron （Fe） salt was introduced into the polymer network and transformed into ORR active Fe-N-C sites along with Fe, FeS, and FEN0.05 nanopartides after pyr- olysis, generating ORR active sandwich-like carbon na- nosheets. Due to the presence of multiple ORR active sites. The as-obtained catalyst exhibited prominent ORR activity with a half-wave potential -30 mV more positive than Pt/C in 0.1 mol L-1 KOH, while the half-wave potential of the catalyst was only -40 mV lower than that of commercial Pt/C in 0.1 mol L-1 HClO4. The unique planar sandwich-like structure could expose abundant active sites for ORR. Meanwhile, the graphene layer and porous structure could simultaneously enhance electrical conductivity and facilitate mass transport. The prominent electrocatalytic activity and durability in both alkaline and acidic electrolytes indicate that these carbon na- nosheets hold great potential as alternatives to precious metal- based catalysts, as demonstrated in zinc-air batteries and proton exchange membrane fuel cells.
