Synthesis Of Porous Hexagonal Boron Nitride Nanofibers And Their Applications In Environment And Energy Fields

A series of problems such as the greenhouse effect,water pollution,and energy depletion are threatening the normal life of human beings.Since the Industrial Revolution,the combustion of a large amount of coal,oil,and natural gas has been leading to the gradual depletion of energy,while the emission of carbon dioxide and other greenhouse gases into the air has been increasing the greenhouse effect year by year.The unrestricted wastewater discharge from industrial,agricultural,and domestic has caused that 42%of the water in China’s seven major water systems cannot be used as drinking water.In the face of serious environmental and energy problems such as global warming,frequent natural disasters,desertification,and lack of oxygen,it is urgent to develop clean energy and environmental governance.Porous materials are widely used in the field of environment and energy because of their low density,high specific surface area,and large porous volume.However,traditional porous materials such as activated carbon,metal-organic framework,and zeolite lack chemical and thermal stability,and cannot meet long-term work in extreme environments.Porous hexagonal boron nitride has the characteristics of wide bandgap,electrical insulation,high thermal conductivity,high-temperature stability,and chemical inertness,which integrates the advantages of porous and boron nitride materials.It is an ideal material for adsorption,energy,catalysis,environment,and other fields,especially under extreme environmental conditions.Based on the perspective of environmental governance and finding clean energy,this paper provides a method which achieves the controllable preparation of porous hexagonal boron nitride nanofibers.Meanwhile,their application potential is explored in the fields of gas adsorption,sewage purification,and electrocatalytic hydrogen evolution.Specifically:1.The porous hexagonal boron nitride nanofibers with a specific surface area higher than 1400 m² g^-1 were synthesized at 800°C in an ammonia atmosphere,boric acid and melamine being used as raw materials.By preparing the precursor in different drying methods,the sizes of the fibers were controlled,and two types of fibers with lengths of 0.6-2.8μm（H-BN）and greater than 40μm（F-BN）were obtained respectively.The results of thermogravimetric test show that it can be stable at 800°C in air.FT-IR test showed that the fiber surface is modified by a large number of hydroxyl and amino functional groups.The two fibers can adsorb gas and organic dye molecules,and showed the characteristic of CO₂-selective adsorption in CO₂/CH₄mixed gas.Moreover,F-BN can be molded,and the obtained F-BN foam has a low density and fire resistance,which also can be used for separating water and oil.The adsorption capacity of oil is close to 15 times its weight.2.The application potential of the functionalized porous boron nitride nanofibers in the field of sewage treatment was explored,by the way of preparing those nanofibers into membranes with different thicknesses by vacuum filtration,using commercial PTFE membranes as the base.The results show that the membranes can remove more than 99%of the dye molecules in aqueous and organic solvents.Combined with theoretical calculations,it is speculated that the mechanism of the membrane is the synergy of adsorption and molecular interception.Importantly,due to its super-hydrophilicity and three-dimensional network nanochannel,the membranes can achieve a high flux of 326 L m^-2 h^-1 for water and 868 L m^-2 h^-1 for acetone without pressure driving,and its water flux is 2.1 times that of Mo S₂ membranes at 0.2 bar and30 times that of GO/Mo S₂ membranes at 2 bar.Due to the inherent chemical inertness of boron nitride,the membrane can work stably for a long time under extreme conditions,and the membrane can be regenerated by a simple method.3.The catalytic activity of H-BN/Pt composites in hydrogen evolution reaction was explored.The H-BN/Pt composites were prepared by compounding Platinum nanoparticles prepared by block copolymer self-assembly with the porous boron nitride nanofibers.The catalytic activity of the catalyst in different chemical reaction environments was compared.The optimal ratio between H-BN and Pt was found by controlling the Pt content,which can be used to reduce the cost under the premise of ensuring excellent catalytic activity.The results show that the H-BN/Pt（1:1）in the acid electrolyte has the optimum hydrogen evolution performance,which is close to the bulk platinum.