Theoretical Investigations On The Controllable Adsorption Of Hazardous Gases By Graphene-based Materials

In recent years,environmental safety and air pollution have received more and more attention.Many researchers are working on research into the detection or removal of harmful gases,particularly in the area of gas sensors.Therefore,it is significant to design and innovate some novel materials that are specific or selective to some harmful gases.In this thesis,the removal and detection of harmful gases on the graphene-based materials are investigated.The main results include the following three parts:(1)The adsorption of phosgene molecule on intrinsic or transition metal-doped graphenes was investigated.Firstly,we calculated the phosgene molecule adsorption on the intrinsic graphene sheet.The computational results showed that the phosgene molecule can only be adsorbed on graphene surface with weak physisorption.The electronic properties,electrical conductivity and magnetic properties of graphene materials did not change obviously after adsorption.However,when the transition metal atoms were introduced into graphene sheet,the properties of graphene materials changed and the adsorption effect of phosgene molecules were significantly enhanced.For transition metal atoms,Zr,Mo,Ti and Mn were studied in this section.It is found that the Mn-doping system has the strongest adsorption effect on phosgene molecule.In addition,we also found that the electronic and optical properties changed significantly after the adsorption.This obvious signal change makes transition metal-doped graphene a potential material for the phosgene sensing.(2)Transition metal doped graphene exhibits the excellent adsorption and detection performance for phosgene gas.However,the strong adsorption seems to hinder our path towards green chemistry and sustainable development.That is,the adsorbent material is not renewable.Therefore,it is urgent to find means to achieve the release of substrate material.So,we further study how to use an additional method to realize the recycling of graphene-based materials.Our results showed that the use of extra electric field or charge in the system can effectively control the capture or release of gas molecules.When introducing a positive electric field,the interaction between the phosgene molecule and doped graphene will be enhanced.But,the interaction will be weakened when applying a negative electric field.In addition,when the negative electric field intensity is strong enough,the phosgene molecule begins to break out of the graphene surface,so as to achieve the purpose of releasing the molecules and the regeneration of the substrate materials.This conclusion was also verified by the dynamic simulation calculations.(3)The transition metal doped graphene also exhibits the same adsorption and detection ability for the harmful gas formaldehyde molecules.We studied the adsorption behavior of Sc,Zr,Ti,Mn and Fe doped graphene systems for formaldehyde molecules.Compared to the intrinsic graphene,the adsorption of formaldehyde molecule was significantly enhanced after doping the metal atoms.At the same time,the electron properties,geometry and magnetic properties of graphene materials changed significantly after formaldehyde adsorption.The reversible adsorption and desorption of formaldehyde molecules can be effectively controlled by applying extra electric field.In addition,the study found that the humid environment can produce certain negative effects on the adsorption,and the adsorption capacity gradually decreases with the increase of water molecules or water coverage.However,applying additional positive electric fields can improve this situation.Even if the adsorption capacity is reduced,it still retains a strong chemical interaction.