One-step Synthesis And Application Of3D Hierarchical Structure Self-assembled By Ultrathin BN Nanosheets

Recently, hexagonal boron nitride (hBN) with ultrathin layer structure has attracted extensive interest in the past few years owing the development of graphene and single-walled carbon nanotube. Herein, with the foundation of middle temperature solid phase reaction method, we have seccessfully fabricated3D hierarchical structure self-assembled by ultrathin BN nanosheets (BNNSs) using middle temperature solid state reaction method. These3D hierarchical structures are composed of radialy aligned ultrathin nanosheets. First, we synthesized3D hierarchical structure self-assembled by BNNSs and analyzed the phase and morphology of the material. Second, we reduced the thickness of nanosheet to ultrathin through adding initiater sulfur and regulating the pressure of reaction system. We also discussed the shape and special edge structures of BNNSs. Then we used3D hierarchical structure self-assembled by ultrathin BNNSs in wastewater treatment for its good adsorption property, and investigated the superhydrophobicity of themselves by contact angle tests. Finally, we synthesized BNNSs/polymer composite materials, which have good thermal properties. The results are as follows.Using midle-temperature solid reaction, we successfully synsethsized3D hierarchical structure self-assembled by BNNSs in50mL reaction kettle with a big yield. These structures are self-assembled by radialy aligned nanosheets and about200-300nm. The thicknesses of these nanosheets are about8nm. By changing the time of constant temperature, we found the evolution process of3D hierarchical structure from nanodebris to bump structure and then to radial nanosheets. Then we put forward a gas-solid and gas-gas combined reaction mechanism with slow-release process.For reducing the thickness of BN nanosheet, we added the sulfur into the reaction as an initiater, which reduced the reaction time and the thickness of BN nanosheets. One main function of sulfur is generating a lot of heat by reacting with NaN3at initial stage. The other main function is catalyzing the decomposition of azide ammonia, prompting the production of BN and reducing the thickness of nanosheet. Then we regulated the volume of the autoclave for getting different pressures of the reaction system. And through the regulating of pressure, we successfully achieved the controllable synthesis of ultrathin BNNSs with the thickness of nanosheet reducing from8nm to3nm. Finally, through investigating the TEM and HRTEM images, we found that the nanosheets were regular triangle and the edges of BN nanosheets were zigzag structure.On the basis of controllable synthesis, we investigated the properties of3D hierarchical structure self-assembled by BNNSs. First, by testing the zeta potential value and the adsorbing capacity of3D hierarchical structure self-assembled by ultrathin BNNSs for MB in aqueous solution with different pH value, we found the adsorption quantity increased with the adding of absolute value of the negative potential and reached the maximum at pH=11. Then under the condition of pH=11, we tested the rate curves of adsorption of3D hierarchical structure self-assembled by ultrathin BNNSs for MB and found the process of the the adsorption on BNNSs was a rapid adsorption process. Finally, we investigated the specific surface area of3D hierarchical structure self-assembled by ultrathin BNNSs and the adsorption equilibrium curves for MB. we found the adsorption capacity of3D hierarchical structure self-assembled by ultrathin BNNSs for MB increased with the increase of specific surface area.Knowing the special rough structure, we investigated the super hydrophobicity of3D hierarchical structure ultrathin BNNSs coatings. We first retested the the contact angle of water on3D hierarchical structure ultrathin BNNSs coatings at the same point and recorded the moving process of water droplet on the surface of the coating, which prove that the hydrophobic performance of3D hierarchical structure ultrathin BNNSs coating is very stable. Then we tested the size of the contact angle of sample under different pH value, and we found the hydrophobic performance had nothing to do with the pH value of water. At last, we investigated the contact angles of different samples and found the contact angle was more than150°when the thickness of BN nanosheet was3nm, which illustrates that3D hierarchical structure BNNSs have the super hydrophobic performance itself.Using the high thermal conductivity of BN, we prepared BNNSs/polymer composite by3D hierarchical structure self-assembled by ultrathin BNNSs. We first added3D hierarchical structure self-assembled by ultrathin BNNSs into PA66, which is the structural and electronic packaging material. And we achieved the BNNSs/PA66composite with high thermal conductivity and low thermal expansion coefficient. We also got the BNNSs/PVA film composite by putting3D hierarchical structure self-assembled by ultrathin BNNSs into PVA. When the the quantity of BNNSs is3wt.%, the thermal conductivity of composite is3.44times of pure PVA membrane.