Structural feature and electronic property of an (8, 0) carbon-silicon carbide nanotube heterojunction

A supercell of a nanotube heterojunction formed by an （8, 0） carbon nanotube （CNT） and an （8, 0） silicon carbide nanotube （SiCNT） is established, in which 96 C atoms and 32 Si atoms are included. The geometry optimization and the electronic property of the heterojunction are implemented through the first-principles calculation based on the density functional theory （DFT）. The results indicate that the structural rearrangement takes place mainly on the interface and the energy gap of the heterojunction is 0.31 eV, which is narrower than those of the isolated CNT and the isolated SiCNT. By using the average bond energy method, the valence band offset and the conduction band offset are obtained as 0.71 and -0.03 eV, respectively.

Intrinsic Mechanisms of Morphological Engineering and Carbon Doping for Improved Photocatalysis of 2D/2D Carbon Nitride Van Der Waals Heterojunction

Van der Waals(VDW)heterojunctions in a 2D/2D contact provide the highest area for the separation and transfer of charge carriers.In this work,a top-down strategy with a gas erosion process was employed to fabricate a 2D/2D carbon nitride VDW heterojunction in carbon nitride(g-C_(3)N_(4))with carbon-rich carbon nitride.The created 2D semiconducting channel in the VDW structure exhibits enhanced electric field exposure and radiation absorption,which facilitates the separation of the charge carriers and their mobility.Consequently,compared with bulk g-C_(3)N_(4)and its nanosheets,the photocatalytic performance of the fabricated carbon nitride VDW heterojunction in the water splitting reaction to hydrogen is improved by 8.6 and 3.3 times,respectively,while maintaining satisfactory photo-stability.Mechanistically,the finite element method(FEM)was employed to evaluate and clarify the contributions of the formation of VDW heterojunction to enhanced photocatalysis,in agreement quantitatively with experimental ones.This study provides a new and effective strategy for the modification and more insights to performance improvement on polymeric semiconductors in photocatalysis and energy conversion.

Fabrication of porous graphitic carbon nitride-titanium dioxide heterojunctions with enhanced photo-energy conversion activity

Porous graphite-phase polymeric carbon nitride（GPPCN）/TiO2 donor-acceptor heterojunction was facilely fabricated through the combination of a template technique with a co-calcination process,which exhibited much higher photoelectric activity compared to pristine carbon nitride and TiO2.The precursor of porous GPPCN（pGPPCN）,porous melem,was prepared by using a green template,calcium carbonate,which could be easily removed by diluted hydrochloride.The pGPPCN/TiO2 heterojunction was then obtained by the assembly and subsequent co-calcination of TiO2 nanoparticles with porous melem.The formation of pGPPCN/TiO2 donor-acceptor heterojunction prepared by this method showed improved surface area and light absorption.Moreover,the composite presented much higher photo-energy conversion activity than those of GPPCN,pGPPCN and TiO2,which could be mainly ascribed to the high charge carrier separation efficiency.This study provides a new approach for the design and development of various photocatalysts with high efficiency for applications in energy fields.

Hierarchical porous carbon heterojunction flake arrays derived from metal organic frameworks and ionic liquid for H2O2 electrochemical detection in cancer tissue

The development of hierarchical nanostructure is demonstrated as an effective strategy to improve catalytic activity and stability of electrocatalysts.Herein,a novel leaf-like hierarchically porous heterojunction flake arrays(FAs),integrated graphitic N-doped carbon(NC)with amorphous B,N-doped carbon(BNC),has been designed and grown on flexible carbon fiber(CF)using metal-organic framework(MOF)FAs and green ionic liquids as precursors.The hierarchical heterojunction structure possesses micro-and nano-scaled pores,large surface areas,and exposed high-density catalytic active sites,which enhances electronic conductivity and offers accessible transport channels for effectively decreasing mass transport resistance.The results of discrete Fourier transform(DFT)calculations and experiments also suggest that the catalytic activity has been promoted by the heterojunction structure through narrowing the banding gap.Consequently,the resultant nanohybrid microelectrode exhibits remarkable electrochemical sensing performance towards H2O2 with a low detection limit of 50 nM,and a high sensitivity of 213μA×mM-1×cm-2,as well as good anti-interference capability.The practical application of nanohybrid fiber microelectrode has been explored by real-time monitoring H2O2 released from live colon cells and surgically-resected fresh colon cancer tissue,which can provide important information for the identification of different types of cells as well as distinguish cancer cells from normal ones.We believe this research will pave the way towards the development of advanced carbon nanomaterials for application in the fields of electrochemistry,biosensing,and cancer diagnosis.

Electronic structures of an(8,0)boron nitride/carbon nanotube heterojunction

The electronic structure of the heterojunction is the foundation of the study on its working mechanism. Models of the heterojunctions formed by an （8, 0） boron nitride nanotube and an （8, 0） carbon nanotube with C-B or C-N interface have been established. The structures of the above heterojunctions were optimized with first-principle calculations based on density functional theory. The rearrangements of the heterojunctions concentrate mainly on their interfaces. The highest occupied molecular orbital and the lowest unoccupied molecular orbital of the heterojunctions distribute in the carbon nanotube section. As the band offsets of the above heterojunctions are achieved with the average bond energy method, the band structure is plotted.

Electronic transport properties of an (8,0) carbon/silicon-carbide nanotube heterojunction

A two-probe system of the heterojunction formed by an （8, 0） carbon nanotube （CNT） and an （8, 0） silicon carbide nanotube （SiCNT） was established based on its optimized structure. By using a method combining nonequilibrium Green＇s function （NEGF） with density functional theory （DFF）, the transport properties of the het-erojunction were investigated. Our study reveals that the highest occupied molecular orbital （HOMO） has a higher electron density on the CNT section and the lowest unoccupied molecular orbital （LUMO） mainly concentrates on the interface and the SiCNT section. The positive and negative threshold voltages are ＋1.8 and -2.2 V, respectively.

Solution-based processing of carbon nitride composite for boosted photocatalytic activities

Graphite-phase polymeric carbon nitride （CN） was reported to be a promising material in photoelectrochemical solar energy conversion. However, its high recombination rate of photogenerated carriers limits its potential applications. In this article, a heterojunction of CN and sulfur-doped CN （CNS） was constructed through a solution-based processing way. Interestingly, it was observed that the photocatalytic hydrogen production of the as-prepared composite was 32.6 times higher than that of bulk carbon nitride and 2.3 times higher than that of the composites by conventional impregnating method. This study opens a new avenue to construct heterojunction of CN for large-scale industrial applications in environmental remediation.

Photo-assisted charging of carbon fiber paper-supported CeO_(2)/MnO_(2) heterojunction and its long-lasting capacitance enhancement in dark

It is important to develop green and sustainable approaches to enhance electrochemical charge storage efficiencies.Herein,a two-step in-situ growth process was developed to fabricate carbon fiber paper-supported CeO_(2)/MnO_(2) composite(CeO_(2)/MnO_(2)–CFP)as a binder-free photoelectrode for the photo-assisted electrochemical charge storage.The formation of CeO_(2)/MnO_(2) type II heterojunction largely enhanced the separation efficiency of photo-generated charge carriers,resulting in a substantially enhanced photo-assisted charging capability of~20%.Furthermore,it retained a large part of its photo-enhanced capacitance(~56%)in dark even after the illumination was off for 12 h,which could be attributed to its slow release of stored photo-generated electrons from its specific band structure to avoid their reaction with O_(2) in dark.This study proposed the design principles for supercapacitors with both the photo-assisted charging capability and its long-lasting retainment in dark,which may be readily applied to other pseudocapacitive materials to better utilize solar energy.