Electronic Theory Study Of Dopant And Defect On The Adsorption Of Formaldehyde Molecule On BN Sheet

The BN sheet possess periodicity hexagonal atomic arrangement structure,which is similar to graphene in special mechanical and electronic properties and can be used to detect a single gas molecule.It can be used as a new sensor electrode material to detect toxic organic small molecule gases.Formaldehyde is a common toxic substance in life and a carcinogen.Therefore,in order to facilitate the monitoring of formaldehyde,it is necessary to find a kind of gas sensor with strong adsorption capacity and quick gas-sensitive response speed.In the article,the first-principles method based on density functional theory is applied to explore the pristine,doped S,Al,P and B atoms or N atoms vacant BN sheet adsorption system of formaldehyde molecules.Through the CASTEP module in Materials Studio,a three-dimensional model of BN sheet adsorption structure was constructed,and the structure of formaldehyde molecules adsorbed on different positions of BN sheet in different systems was geometrically optimized.The adsorption energy and state density of formaldehyde adsorbed by undoped,doped and defected BN sheet were given,and the energy band and charge transfer of the system were also obtained.The results show that the adsorption capacity of BN sheet system doped with S or Al is significantly higher than that of pristine BN sheet.The conductivity of the BN-CH₂O system doped with S and Al increases with the size of the band gap or the introduction of impurities in the band gap,this allows BN sheet to be used as a sensor electrode material for detecting formaldehyde.As a result,Al,S doping accelerates the response of BN sheet to formaldehyde gas and improve the sensitivity of BN sheet as sensor electrode material to formaldehyde gas.The charge transfer between BN sheet and formaldehyde is significantly increased due to the Al,S doping,which leads to the changed carrier concentration and the improved conductivity.The recovery time calculations indicated that formaldehyde molecules desorption from the S doped BN sheet would be unrealistic at room temperature,while the Al doped BN sheet is suitable for formaldehyde molecules detection because of appropriate recovery time at ambient temperature for recycle use.Combination of results of theoretical analysis,we concluded that the Al doped BN sheet is a good strategy for improving the sensitivity of these sheets toward formaldehyde molecules,while the doped S BN sheet can be as a gas adsorbent for formaldehyde molecules removal from specific environments.The effect of P-doping on BN sheet-formaldehyde system is very slight.For defective BN sheet systems,studies have shown that the adsorption capacity of BN sheet,whether B atom vacancies or N atom vacancies,is significantly higher than that of pristine BN sheet.It is also calculated that the distance of the formaldehyde molecule from the BN sheet plane of the B atom and the N atom vacancy is significantly reduced,and chemical bonds are formed,which can improve the sensitivity of BN sheet in sensing.Due to the vacancies of the B and N atoms,the charge transfer between the BN sheet and the formaldehyde molecule is significantly increased,and the carrier concentration and conductivity are improved.The above analysis shows that the vacancy can enhance the adsorption energy of BN sheet to formaldehyde gas,accelerate the response to formaldehyde gas,and improve the sensitivity of BN sheet as a sensor electrode material to formaldehyde gas.Therefore,defective BN sheet can also be used for the detection of formaldehyde.