First-principles investigation of the valley and electrical properties of carbon-dopedα-graphyne-like BN sheet

Based on ab initio density functional theory calculations,we demonstrate that two carbon-doped boron nitride analog ofα-graphyne structures,B_(3) C_(2) N_(3)) and BC_(6) N monolayers,are two-dimensional direct wide band gap semiconductors,and there are two inequivalent valleys in the vicinities of the vertices of their hexagonal Brillouin zones.Besides,B_(3)C_(2)N_(3) and BC_(6)N monolayers exhibit relatively high carrier mobilities,and their direct band gap feature is robust against the biaxial strain.More importantly,the energetically most favorable B_(3)C_(2)N_(3) and BC_(6)N bilayers also have direct wide band gaps,and valley polarization could be achieved by optical helicity.Finally,we show that BC_(6) N monolayer might have high efficiency in photo-splitting reactions of water,and a vertical van der Waals heterostructure with a type-Ⅱenergy band alignment could be designed using B_(3)C_(2)N_(3)and BC_(6)N monolayers.All the above-mentioned characteristics make B_(3)C_(2)N_(3) and BC_(6)N monolayers,bilayers,and their heterostructures recommendable candidates for applications in valleytronic devices,metal-free photocatalysts,and photovoltaic cells.

Modulation of CO adsorption on 4,12,2-graphyne by Fe atom doping and applied electric field

Adsorption characteristics of CO adsorbed on pristine 4,12,2-graphyne(4,12,2-G)and Fe-doped 4,12,2-graphyne(Fe-4,12,2-G)are studied by first-principles calculations.It is shown that CO is only physically adsorbed on pristine 4,12,2-G.Fe atoms can be doped into 4,12,2-G stably and lead to band gap opening.After doping,the interaction between Fe-4,12,2-G and CO is significantly enhanced and chemisorption occurs.The maximum adsorption energy reaches-1.606 e V.Meanwhile,the charge transfer between them increases from 0.009e to 0.196e.Moreover,the electric field can effectively regulate the adsorption ability of the Fe-4,12,2-G system,which is expected to achieve the capture and release of CO.Our study is helpful to promote applications of two-dimensional carbon materials in gas sensing and to provide new ideas for reversible CO sensor research.

Much enhanced electromagnetic wave absorbing properties from the synergistic effect of graphene/γ-graphyne heterostructure in both gigahertz and terahertz band ranges

Exploring advanced electromagnetic wave(EMW)absorbers is one of the most feasible ways to solve the increasing electromagnetic pollution in both military and civil fields.In this work,γ-graphyne(γ-GY)is synthesized by a mechanochemical route using CaC2 and hexabromobenzene(PhBr6).Then three-dimensional(3D)reduced graphene oxide/γ-GY(RGO/GY)heterostructures are prepared through facile solvothermal self-assembly and subsequent thermal reduction.The influences of calcination temperature and the content ofγ-GY of the composite on EMW absorption performance are fully investigated.The minimum reflection loss(RL)value of the RGO/GY composite foam is−71.73 dB at 10.48 GHz with the matching thickness of 3.54 mm,and the effective absorption bandwidth(EAB)less than−10 dB is 7.36 GHz.Moreover,excellent terahertz(THz)absorption property is also obtained at 0.2–1.6 THz.The RL of 84.08 dB is acquired,and the EAB covers 100%of the entire measured bandwidth.In addition,the composite is also a promising anticorrosive EMW absorber.This work provides encouraging findings,which are also instructive for the potential advantages of graphyne-based materials as highly efficient EMW absorbers in both gigahertz and terahertz band ranges.

Applying machine-learning screening of single transition metal atoms anchored on N-dopedγ-graphyne for carbon monoxide electroreduction toward C_(1)products

Carbon monoxide electroreduction(COER)has been a key part of tandem electrolysis of carbon dioxide(CO_(2)),in which searching for high catalytic performance COER electrocatalysts remains a great challenge.Herein,by means of density functional theory(DFT)computations,we explored the potential of a series of transition metal atoms anchored on N-dopedγ-graphyne(TM@N-GY,TM from Ti to Au)as the COER electrocatalysts.We found that the final product selectivity of these single-atom catalysts depended on the position of the metal atom in the periodic table,with metals in the front and middle of each periodic period exhibiting high selectivity for CH_(4),while metals in the back producing CH_(3)OH.Machine learning(ML)found that metal atomic number was intrinsic to the difference in COER performance of these single-atom catalysts(SACs).The free energy changes showed that Mn@N-GY and Ni@N-GY exhibited outstanding COER catalytic performance for producing CH_(4)and CH_(3)OH,respectively.Our results provide theoretical and experimental guidance for designing efficient COER catalysts to generate C_(1)products.

Optimized geometry and electronic structure of three-dimensional β-graphyne

β-graphyne, a carbon allotrope, is a gapless semiconductor with hexagonal lattice symmetry, just like graphene. We calculated the optimized structure and electronic structures of some possible three-dimensional β- graphyne stacking arrangements by means of the first-principles frozen-core projector augmented-wave method implemented in the Vienna ab initio simulation package. The optimized lattice constant a of the three-dimensional β-graphyne turns out to be 9.46 A, which is slightly smaller than its two-dimensional counterpart. The binding energy is about 90% of that of graphite, which suggests that three-dimensional β-graphyne will be stable when it is synthesized. The band structure is calculated via the hybrid functional. We found that the most stable threedimensional stacking arrangement is an indirect band gap semiconductor with an energy gap of 0.1 eV.