| Accurate online detection and efficient decomposition of toxic gases are important technical guarantees to the control of environmental pollution and improvement of living quality.The generation of the sensing signal and the progress of the catalytic reaction are originated from the interaction between the solid phase surface（gas sensing layer or catalyst）and the gas phase molecules.Sensing is focused on the properties changes of the solid-phase material such as conductance and capacitance,while catalysis pays attention to the transformation of gas-phase components.An in-depth understanding of the adsorption and reaction mechanisms at the gas-solid two-phase interface involved in the sensing and catalysis processes has important theoretical guiding significance for the development of new generation sensing devices and catalytic systems.Due to the characteristics of large specific surface area and abundant active sites,two-dimensional material exhibits enormous potential in sensing and catalysis.In-depth investigation of adsorption and reaction behaviors at the gas-solid interface of two-dimensional materials has practical significance.In view of current research status,this work adopts the theoretical simulation method mainly based on density functional theory to investigate the adsorption and reaction mechanisms involved in the sensing and catalysis process.Considerting the fact that researches of sensing mechanism of intrinsic graphene is mainly focusesed on the adsorption characteristics of graphene exposed surface area,while barely pays attention on the interlayer and edge area,which is nonnegligible of multilayer graphene,this work investigates the adsorption of various common pollutant gases（NO2,H2S,NH3,NO）of the interlayer space and edge area of graphene film.It is found that compared with the graphene surface,the gas molecules adsorbed in the interlayer exhibit lower adsorption ernergy,and the potential fluctuation during the migration route is less than 5%,thus it can be quickly migrated.Further,based on charge transfer and electronic structure analysis,the gas-sensing signal is predicted,which explains the mechanism of the exprimental obsevation that vertically oriented graphene shows high response intensity and selectivity to NO2.In view of the lack of systematic understanding of the sensing mechanism of transition metal decorated graphene,the influence of Ni,Pd,Pt,Cu,Ag,Au decoration on NO2 adsorption behaviors are studied,and the detection response are predicted based on non-equilibrium Green’s function.It is found that graphene exhibits semiconducting properties after metal decoration,resulting from the shifting of energy levels.NO2 is strongly adsorbed at decorating site by forming chemical bonds with metal atom.The overall charge transfer is increased by 2 to 6 times,and the energy release is enhanced by 7 to 14 times due to metal decoration.The charge transfer,orbital hybridization,and energy level shift caused by NO2 adsorption lead to the change of the electrical conductivity of metal decorated graphene.Among them,all three mechanisms in Cu@G lead to the decrease of the electrical conductivity,thus the sensing signal reaches to 192.32.Further,the desorption process is investigased based on electric field enhancement and hole doping.Results show that the hole doping is an effective way to weaken the interaction between NO2 and Cu while enhancing the interaction between Cu and graphene,thus realizing the rapid releasing of NO2.Considing the slow recovery rate of the NO2 detection based on intrinsic graphene film,vertically oriented graphene is prepased in this work.By constructing enhanced localizing electric field at the edge region,the rapid desorption of the NO2 molecule and the recovery of the sensing signal are realized.Recovery rate within 5 minutes is increased from 33%to 93%.At the same time,thanks to the intrinsic low noise property of graphene,the detection limit reaches 100 ppb at room temperature.Moreover,based on the theoretical prediction in this work,a nitrogen-doped graphene gas sensor loaded with Cu atoms is prepared.The gas sensing performance test found that after loading Cu atoms,the response intensity towards 50 ppm NO2 is greatly increased from 7.1%to 60.8%.And the as-prepased sensor shows good repeatability,stability and selectivity.In view of the two-dimensional manganese dioxide（δ-Mn O2）catalyst shows excellent catalytic performance in degrading formaldehyde at room temperature,the effect of surface oxygen-containing functional groups on formaldehyde decompostion process is investigated.The calculation results show that the introduction of oxygen-containing surface functional groups not only inhibits the desorption of formaldehyde molecules,but also significantly reduces the energy barrier of the dehydrogenation reaction.The kinetic Monte Carlo simulation results further reveal the decomposition paths of formaldehyde with different functional groups onδ-Mn O2.It is found that the first decomposition step of formaldehyde is the rate-limiting step,and the maximum energy barrier is 0.32 e V,which is different from that of traditional noble metal catalysts.Compared with the traditional noble catalyst,the barrier is gresated reduced by 60～80%.In addtion,modulating the ratio of functional groups is found to be an effective strategy for improving the degradation capability.Main intermediates during the catalysitc process are CH2O2 and CHO.Among them,CH2O2 can be decomposed intemidiately,while CHO shows low decomposition rate,which explains that only a few studies obseved the existence of CH2O2,while CHO are often reported.In order to develop highly efficient catalyst for realizing CO2 hydrogenation to formic acid,a novel two-dimensional material-supported single-atom catalyst system is designed in this work:Ni@Ti3C2O2,on which Ni behaves as the active site for catalyzing CO2 hydrogenation,the energy barrier is greated reduced at Ni site.Meanwhile,the rapid desorption and separation of formic acid is achieved owning to the low desorption barrier.During the catalytic process,CO2 is firstly adsorbed on Ni site,and then reacts with free H2 to generate HCOO intermediate,and finally generating formic acid through the reaction between HCOO and the residual H atom.The reaction energy barrier is 0.54 e V,and the reaction exotherm reaches 1.32 e V.Selectivity analysis demonstated that the energy barriers of side reactions are all higher than 1.5e V,and some of the side reactions even higher than 6 e V,which is much higher than the reaction pathway for the generation of formic acid.The generation of side reaction products can be effectively inhibited.Finally,a novel uninterrupted catalytic reaction mechanism is proposed in this work,the formic acid can be quickly desorbed with a minimum energy barrier of 0.12 e V.Taken together,this new two-dimensional material-supported Ni atom catalyst achieves a low reaction energy barrier and desorption barrier simultaneously,which shows great potential in catalyzing CO2 fixation and conversion. |
