Functionalized Hexagonal Boron Nitride Ultrathin Nanosheets And Their Gas Sensing Properties

With the rapid development of industry and agriculture,more and more poisonous and harmful gases are released from all walks of life,which makes the types and quantity of gases in the air increase continuously.These poisonous and harmful gases will bring serious and irreversible harm to human body and environment.With the continuous development of science and technology as well as the improvement of people’s living standards,people have reached a new cognitive level for the detection of toxic and harmful molecules and environmental pollution.In recent years,graphene and other two-dimensional materials have attracted much attention in the field of gas sensors due to their high specific surface area and high surface activity.However,due to their low sensitivity,slow response recovery and inability to apply in complex environment,their practical application is still in its infancy.As one of the typical two-dimensional nanomaterials,hexagonal boron nitride nanosheets（BNNSs）,known as"white graphene",has been widely used in catalyst support,light-emitting materials,electronic packaging,lubricants and other fields due to its excellent performance.Besides,as a wide band gap material,BNNSs also has some excellent properties that other two-dimensional materials,including graphene,do not have,such as better high temperature stability,higher oxidation resistance and stronger corrosion resistance,which provides the possibility for BNNSs to become a gas sensitive material suitable for harsh environment.However the inherent chemical inertness of BNNSs usually results in poor adsorption ability to gases molecules.Recently,in order to expand the application of BNNSs,the modification,doping and compounding of BNNSs has attracted much more attention.For instance,the functional modification including hydroxyl and amino groups can not only improve the catalytic and adsorption properties of BNNSs,but also adjust the band gap of BNNSs to make it more valuable in the field of optoelectronic devices.Therefore,in this thesis,we mainly focus on the functionalization of exfoliated BNNSs including chemical modification and nanocomposites,as well as their gas sensing performance.First of all,the bulk h-BN powder was directly exfoliated by acid solution,and S-BNNSs was successfully obtained by adjusting the exfoliation process,leaving the crystal structure not destroyed.The resultant thickness of S-BNNSs was only 1⁵atomic layers,the transverse dimension was within 300 nm⁷μm.Secondly,the gas sensing performance of S-BNNSs and bulk h-BN is systematically studied by static gas sensing test.The response of S-BNNSs is up to 10.47%to 10 ppm NO₂,5 times higher than that of bulk h-BN.In addition,the S-BNNSs-based sensor has excellent selectivity,low detection limit,extremely short response/recovery time（7.5s/14.4 s）,high sensitivity(1.645 ppm^-1),excellent stability and reversibility at high temperature.The results show that the exfoliation and surface functional group modification of h-BN can effectively improve its gas sensing performance.Finally,several kinds of metal nanoparticles with uniform particle size are synthesized by block copolymer self-assembly and modified on the surface of S-BNNSs by chemical bond.The gas sensing properties of BNNSs-Au,BNNSs-Fe₂O₃and BNNSs-SnO₂ were studied.The results show that BNNSs-Fe₂O₃ and BNNSs-SnO₂show higher response to butyl alcohol and ethanol,respectively.The improvement of gas sensing properties of this material can be attributed to the synergistic effect between metal oxide nanoparticles and S-BNNSs.The combination of the high sensitivity of metal oxide nanoparticles to gas and the high stability of S-BNNSs can achieve the directional detection of different gases while maintaining the high stability of the sensor,which makes S-BNNSs have a broader development prospect in the field of gas sensors.