Controllable Synthesis,Functionalization And Properties Of Boron Nitride Nanospheres

Boron nitride nanospheres（BNNSPs）have excellent biocompatibility,thermal stability,chemical stability,thermal conductivity,lubricity,adsorption and environmental purification functions.BNNSFs are widely used in biomedicine,polymer/ceramic composites,catalysis and environmental protection.Different requirements of the microstructures and performances of BNNSPs are depended on different applications.It is very important to obtain effective methods to control the BNNSPs parameters besides such different applications.In this paper,BNNSPs were prepared by chemical vapor deposition（CVD）,and the control method of their microstructures,sphere size,oxygen content and pore structure were studied.Some application performances of BNNSPs are further studied.The specific contents are as follows.（1）BNNSPs were prepared by CVD method in which trimethyl borate used as B source and ammonia used as N source reacted in a high temperature heat treatment.The temperature in the synthesis process was studied.While the reaction temperature is 800℃,the product is boron nitride microsphere.The spherical size can decreases gradually by increasing the temperature.When the temperature reaches 1200℃,the average diameter of the sphere is～50 nm.The size distribution of BNNSPs can also be affected by adjusting the ratio of B source to N source,but the effect is not obvious.The spherical diameter is about100-200 nm.By adjusting the reaction temperature and the ratio of B source to N source in the synthesis of BNNSPs,diameters of spherical boron nitride ranging from tens of nanometers to several micrometers.This will provides a more abundant application for BNNSPs.（2）The synthesis process of BNNSPs was optimized.Activation of raw material and construction of spherical structure were separated to different temperature control area by changing to double furnace production.This provided a stable environment for BNNSPs synthesis,thus obtaining BNNSPs with more concentrated particle size distribution.（3）The effects of atmosphere and heat temperature in post-treatment on the structure and properties of BNNSPs were studied.The BNNSPs synthesized by double furnace process were treated at 1100,1300 and 1500℃in ammonia,nitrogen,argon,hydrogen-nitrogen and hydrogen-argon atmosphere,respectively.The crystallinity of BNNSPs can be improved,and the oxygen content can be significantly reduced with the increase of post-treatment temperature.The oxygen content of BNNSPs decreased from～40%to<2%while treated at 1500℃in ammonia atmosphere.Different treatment atmosphere can change the thermal stability of BNNSPs.The ammoniated BNNSPs have the best stability.The thermal stability can also be improved by increasing the post-treatment temperature.Pore structure appeared in BNNSPs after treated at high temperature in different atmospheres.These pore structures belong to mesoporous.At the same time,the specific surface area increased significantly.（4）BNNSPs prepared after ammoniation at 1300℃were functionalized.The samples were treated with acid（H₂SO₄,HNO₃,HCl）,alkali（Na OH）and boric acid-assisted ball milling.Defect structures and hydroxyl groups appeared in the treated samples.Besides,acid and alkali treated samples produced surface etching and pore structure.Angular morphology appeared in ball milled samples.（5）Biological and catalytic properties of BNNSPs were also studied.Cytotoxicity of BNNSPs were studied using HEK-293 human embryonic kidney cells.It was found that low concentration of BNNSPs has little effect on cells.Platinum particles were loaded on BNNSPs in order to study the catalytic performance of BNNSPs/Pt of combustion reaction of carbon monoxide.When the reaction temperature is constant,the catalytic efficiency of BNNSPs/Pt increases with the increase of platinum loading.While the platinum loading is higher than 1%,the catalytic efficiency increases to a horizontal range.These studies may provide a preliminary basis for the application of BNNSPs in biomedicine and catalysis.