后处理对爆轰纳米金刚石表面官能团的影响

分别在高锰酸钾与浓硫酸的混合溶液、空气、氢气、真空以及氩气中对爆轰纳米金刚石进行后处理,研究了后处理方法对其表面官能团的影响。采用X射线衍射仪、高分辨透射电子显微镜、傅立叶变换红外光谱仪和差示扫描量热仪对后处理前后纳米金刚石的微观结构、性能和表面状态进行了研究。结果表明:纳米金刚石颗粒形状为球形或椭球形,平均粒径约为5 nm,在空气中的起始氧化温度约为550℃,在氢气、真空和氩气中的石墨化温度分别约为284℃、1 146℃和1 184℃。纳米金刚石在后处理前表面含有大量的官能团,如—OH、—CH₃、—CH₂、CO₂、—CO、—COOH和—C—O—C等。在氢气中对纳米金刚石进行处理,可使部分官能团从表面解吸而由氢取代,悬键与氢结合可有效防止二次吸附,是去除爆轰纳米金刚石表面官能团的低成本、高效方法。

Effect of Post-Treatment on Surface Functional Groups of Detonation Nanodiamonds

Post-treatment processing was performed for detonation nanodiamond (DND) in a mixed solution of potassium permanganate and concentrated sulfuric acid, in air, hydrogen and argon gas, as well as under vacuum conditions, respectively, for investigating the effect of the post-treatment on the surface functional groups. Then, X-ray diffraction, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy and differential scanning calorimetry were used to study the microstructure, properties and the surface state of nanodiamonds before and after post-treatment. The results show that the nanodiamond has spherical or ellipsoidal particles with an average size around 5 nm. The initial temperature for its oxidation in the air is about 550 ℃, and its graphitization temperatures in hydrogen and argon gas, as well as under vacuum condition are around 284 ℃, 1 146 ℃, and 1 184 ℃, respectively. The surface of the nanodiamond before post-treatment contains a large number of functional groups, such as -OH, -CH₃, -CH₂, CO₂,-C ==O, -COOH and -C-O-C, etc. And the post-treatment in hydrogen gas can result in part of the surface functional groups desorbed and replaced by hydrogen. Moreover, the dangling bonds binds to hydrogen atoms, which can effectively prevent the secondary adsorption. Consequently, it is the low-cost and high-efficient method to remove the functional groups from the surface of DND.