New ideas for the development and application of cubic boron nitride

Inorganic non-metallic nanocrystalline materials, compared with their bulk materials, have many interesting phenomena in optical and electrical aspects. The bulk material is peeled off into thinner nanocrystalline materials of less than 5 nm, and then it is more new. Performance has always been the frontier of nanocrystal preparation. Reduction of surface energy of nanomaterials by solvent such as dimethylformamide (DMF), N-methylpyrrolidone (NMP), isopropanol (IPA), etc., and insertion of alkali metal ions such as Li+ by discharge in a closed cell system Electrochemical stripping of K+, etc. has always been a hot spot in the preparation of nanocrystals, but the cumbersome means such as excessive ultrasonic time, large power consumption and battery assembly have always restricted the preparation of nanocrystalline materials, so it is easier and faster to find. The synthesis of inorganic nanocrystals by means of exfoliation under the open system has become an urgent problem for scientists.
Zhao Zhigang, a researcher at the Suzhou Institute of Nanotechnology and Nano-Bionics, Chinese Academy of Sciences, and Zhang Dengsong, a professor at Shanghai University, conducted a detailed and in-depth study on this issue, and studied the nanocrystals of transition metal chalcogenides (WS2, MoS2, WSe2, MoSe2). Breakthrough progress has been made. The new method combines electrochemical and liquid phase stripping with Al3+ as the electrochemical insertion type ion and ethanol/oleic acid dispersion as the liquid phase stripping solvent. Under the discharge condition, the Al3+ large charge amount and high The impact property destroys the layered material, and further removes the Al3+ from the layer by using the good binding property of oleic acid and Al3+ in the liquid phase, thereby obtaining a single-layer nanocrystalline material having a uniform size and an average particle diameter of only 3 nm. The resulting WS2 nanocrystalline material can detect lower concentrations of trinitrophenol (TNP) with a detection limit of 10-6 M. The relevant research results are published in Chemical Communication (DOI: 10.1039/C6CC06325J).
Based on the above research results, Zhao Zhigang, a research group and researcher of Suzhou Nano Institute, and Zhang Fengxia, a professor at Suzhou University, cooperated to apply this stripping method to hexagonal boron nitride (h-BN) and cubic boron nitride (c-BN). Nanocrystals of two materials were also successfully prepared, and two boron nitrides were found to have significant differences in piezoelectric properties. Compared with the corresponding bulk materials, the piezoelectric properties of the stripped nanocrystalline materials are significantly improved, wherein the cubic boron nitride nanocrystals have a piezoelectric coefficient of 25.7 pC/N, while the cubic boron nitride blocks The piezoelectric coefficient of the body is only 4.3 pC/N, and the piezoelectric property of the nanocrystalline material is six times higher than that of the bulk material. Even if it is a boron nitride nanocrystal, the cubic structure is superior to the hexagonal piezoelectric property. The main reason is that the crystal structure of cubic boron nitride has a more obvious external force response. This study provides a new idea for promoting the development and application of cubic boron nitride as a superhard material. This research was finally published in Nano Letters (DOI: 10.1021/acs.nanolett.6b04272).
This series of work has received strong support from the National Natural Science Foundation of China and the Jiangsu Outstanding Youth Fund.

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