Study On The Mechanism Of Methane Adsorption Behavior And Mechanical And Electronic Properties Of Graphene-carbon Nanotube Three-dimensional Composites

Methane is an important and clean gas energy;however,it is a poisonous gas and a kind of greenhouse gas.Therefore,the effective detection of methane is urgent and significant.Both graphene and CNTs have excellent mechanical and electrical properties.Owing to the large surface area ratio,especially the graphene,which can provide much more adsorption sites for gas molecules than traditional materials.Therefore,they have great advantages in the effective detection of gases.However,graphene is easy to layer lamination,and CNTs are easy to entanglement.The graphene/carbon nanotubes（G-CNTs）interconnection structure can solve these problems.They have the same excellent properties as graphene and CNTs.Studies have shown that,although G-CNTs have slightly lower mechanical strength and conductivity than graphene and CNTs,their mechanical and electronic properties are still superior to other materials,and even far better than graphene and CNTs in terms of mechanical ductility,larger surface area and porosity.They are an ideal material for gas adsorption.Therefore,it is necessary to develop the methane detection devices based on G-CNTs.The study on the mechanism and performance of G-CNTs methane adsorption is of great practical significance.This project studied the performance and the mechanism of methane adsorption of G-CNTs.The performance of graphene and CNTs was investigated respectively,and then the characteristics of G-CNTs were analyzed.Whereafter,the mechanism and performance of methane adsorption were analyzed.The research contents and main research results are summarized as follows:1)In this thesis,the monolayer graphene was successfully transferred by wet transfer and mechanical exfoliation,and G-CNTs solution was also prepared.It can be found that the graphene current increases with the number of layers,which presents a good linear relationship.It should be noted that as the number of layers increases,the current of wet-transferred graphene increases significantly,while that of mechanically exfoliated graphene increases much less.On the other hand,the adsorption performance of G-CNTs was the best.2)The effects of the doping and the positions of hydroxyls and defects on graphene work function werereported and highlighted in this chapter by using the first-principle theory.Basically,the WF decreased as graphene width increased.For the hydroxyl modification,the WF was large when the number of hydroxyls increased.Furthermore,when the distribution of hydroxyls was intensive,the WF was also increased.The defect would decrease the graphene WF,which did not depend on the positions.3)The influence of graphene layer on the adsorption and the doping feasibility of methane wasanalyzed and highlighted in this chapter by using the first-principle theory.In the pristine m-graphene system,the adsorption energyof CH₄ was increased with the number of graphene layers.In the Al doped m-graphene system,something should be noted that the adsorption energy of CH₄ would have a sharp increase,andthe value of_CH4 was stabilized in 2.6 eV.In addition,the effect of graphene stacking on methane adsorption was analyzed.The adsorption energy of the Z-AB graphene is the largest among the six types of stacked graphenes;the maximum value is 0.357 eV.Both Z-Order and Z-AB stackings are good for the methane adsorption.4)In this chapter,different kinds of G-CNTs were investigated to find a stable structure with excellent performance via DFT and DFTB.Generally,the binding energy of A-G-CNTs was stronger than that of Z-G-CNTs.Moreover,arm-60 had the biggest binding energy,while zig-40 had the smallest one;the arm-60 structure is the most stable.5)In this chapter,a comprehensive study of methane adsorption capacity was investigated via DFT and MD.The results showed that the adsorption energy of arm-44 is a little bigger than that of arm-60.Moreover,the linked part of G-CNTs possessed a better adsorption effect and adsorption sites.The adsorption site inside the junction had the best adsorption effect.The B doping has the best power to improve the methane adsorption capacity;at the same time,the doping of B also has greater feasibility.