Preparation,Characterization And Performance Of Nanosized Boron Nitride

Boron nitride nanosheet(BNNS)and boron nitride nanoparticles(BNNP)possess excellent performance,such as good mechanical properties,excellent thermal stability,excellent thermal conductivity and resistance to chemical corrosion.In recent years,they were focused by scholars around this word.In this work,both of BNNS and BNNP were prepared and their performance and application were disucssed.The morphology,thickness,structure,functional group of the as-prepared products were systematacially characterized by using transmission electron microscope(TEM),atomic force microscope(AFM),X-ray diffraction(XRD),infrared spectroscopy(FT-IR),UV-vis diffuse reflectance spectroscopy(UV-vis),Differential scanning calorimeter(DSC),thermogravimetric analyzer(TGA)and thermal conductivity measuring apparatus,respectively.Moreover,these two types of products were used in the fields of photocatalysis and epoxy resin matrix composites.The main points were presented as follows:(1)Preparation,performance and application of BNNSMultilayer hexagonal-boron nitride was exfoliated successfully into BNNS by through “one-step method” in a hydrothermal reaction vessel.Sodium fluoride and ammonia were used as raw materials.The relevant mechanism was also discussed.TEM showed the BNNS was very thin;moreover,the average size of pristine BN was about 200 nm,while that of the BNNP was about 20 nm.AFM showed that the the as-prepared of products was 1 to 3 layers.XRD showed that the structure of BNNS was not changed during the hydrothermal process.FT-IR showed that there were plents of hydroxyl groups on the surfaces of the as-prepared products.Subsequently,BNNS were mixed with the epoxy resin(EP)by using a solution mixing method.The tensile test results showed that the tensile properties of composites were increased at first and then decreased with increasing the usage amount of BNNS.When the usage amount of the as-prepared BNNS was 0.4 wt% basing on the total weight of EP and curing agen,both the tensile strength and elongation at break of EP/BNNS composite reached the maxium of 66.8 MPa and 26 %,which were 126 % and 192 % more than that of pure EP.Moreover,the thermal performance test results showed that BNNS could not only accelerate the curing of epoxy resins but also improve the thermal stability of epoxy resin matrix.In addition,heat-conducting test results showed that the thermal conductivity of the EP/BNNS composites was also improved in comparison with that of pure EP.In this work,experimental results showed that BNNS could suppress the recombination of photogenerated electrons and holes and improve the photocatalytic performance of photocatalyst.Among the Ag-based photocatalyst,Ag2CrO4 possessed excellent visible-light-driven photocatalytic performance.It has been widely used into the photocatalysis fields.Nanosized Ag2CrO4/few layer boron nitride composites were prepared via in-situ precipitation method.The photocatalytic activities of the as-prepared hybrids were evaluated by degradation of rhodamine B under the visible-light irradiation.Experimental results indicated that the degradation efficiency of the as-prepared samples was first increased and then decreased with increasing the usage amount of few layer boron nitride nanosheets.When it was 10 wt%,in 120 min,the degradation efficiency of the as-prepared hybrids had reached the maximum of 96.7 %.It was much higher than 75 % of pure Ag2CrO4.After three cycles of the degradation,the efficiency of the as-prepared samples was decreased from 96.7 % to 91.8 %.TEM results showed that the average size of Ag2CrO4 was about 20 nm and irregular loaded on the surfaces of BNNS.XRD results showed that BNNS couldn't change the structure of the Ag2CrO4.Moreover,trapping experiment results revealed that holes played a major role during the photocalysis process.In addition,electrochemical impedance spectroscopy results indicated few layer boron nitride nanosheets could enhance the separation and transfer of photogenerated electrons and holes.(2)Preparation,performance and application of BNNPBoron nitride nanoparticles(BNNP)with high specific surface area were simply prepared in a muffle furnace at 1000°C by using boron nitride flakes and sodium chloride as raw materials.The average size of the BNNP was about 20 nm.In addition,the surface area measure results showed that the specific surface area of the BNNP was 895.7 m2/g.The as-prepared BNNP were used as the filler to mix with the epoxy resin(EP)by using a solution mixing method.The tensile test results showed that the tensile properties of the as-prepared composites were first increased and then decreased with increasing the usge amount of fillers.When the usage amount of BNNP was 0.4 wt% basing on the total weight of EP and curing agent,the tensile strength and elongation at break of EP/BNNP composite reached to the maxium of 71.4 Mpa and 22.1 %,which were 137 % and 146 % more than that of pure EP.Doing multiple tests with pure EP and composites of epoxy and BNNP(0.4 wt%),thermal performance test results showed that BNNP was in favour of curing of epoxy resins.In addition,heat-conducting test results showed that the thermal conductivity of of the as-prepared EP/BNNP(0.4 wt%)composites was improved by 11.7 % in comparison with that of pure EP.