Synthesis And Growth Mechanism Of Boron Carbonitride Nanotubes By Sol-Gel Method

In recent years, the derivatives of carbon nanotubes——the synthesis of ternary boron carbonitride (B-C-N) nanotubes materials have become hot spots in the world and new material of research. Compared with carbon nanotubes, B-C-N nanotubes not only possess similar outstanding mechanical properties but also better electronic properties and oxidation resistance. In addition, they possess strong magnetic properties and the fine blue-violet luminous performance too. More importantly, differtant from the electronic properties of carbon nanotubes depending on their diameter and chirality, the electronic properties of B-C-N nanotubes only rely on their composition, and bandgap could be adjusted in a very wide range. And their synthesis and applications could make up for the deficiencies of carbon nanotubes, especially in the electronic, optoelectronic, hydrogen storage field and so on, bringing the hope and the potential development for nanotube materials in the field of nanotechnology. Successful methods about the synthesis of B-C-N nanotubes mainly include arc discharge, laser ablation, ball-milling, chemical vapor deposition (CVD), template route, pyrolysis techniques, solvothermal method and so on. However, the work about sol-gel synthesis of BCN nanotubes has not reported yet.In this paper, the research works on B-C-N nanotubes have been reviewed. And the synthesis of B-C-N nanotubes by sol-gel has firtly been demonstrated. Moreover, the raw materials are safe and non-toxic, the method is efficient and economic. Using5.71×10-5mol Poly vinyl alcohol (PVA-124),0.01mol H3BO3and0.1mol urea(CO(NH2)2) as the main raw materials,0.01mol Fe(NO3)3-9H2O as catalyst, the xerogel precursor was prepared by sol-gel method in alkaline solution. Then the precursor was heated at1100℃under ammonia (NH3) gas flow for4h. Finally, the high quantity and quality B-C-N nanotubes can be successfully synthesized, which have an average diameter of about70nm with cylindrical shape. The nanotubes were characterized by Furrier transform infrared (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM).Meanwhile, we discussed the influence factors of B-C-N nanotubes, such as the content of raw materials, the temperature, the type and flow rate of reaction gas and so on. The result indicates that the sol-gel can avoid the problem of vitrification of H3BO3to some extent, because of the cross-linking reaction between PVA-124and H3BO3. Moreover, the source of B, C and N can be mixed in the atomic level through the two cross-linking reactions of PVA/H3BO3and PVA/CO(NH2)2, which avails the synthesis of B-C-N nanotubes. During the process of these experiments, we can use H3BO3as raw materials successfully by sol-gel and reduce the cost. In addition, the cylindrical-like nanotubes which are better crystallization than bamboo-like nanotubes and always need more severe conditions can be prepared by sol-gel at mild conditions.The results show that the growth mechanism of BCN nanotubes can be attributed to the vapor-solid (VS) model, whose main feature is no catalyst particle in the tip of nanotubes. In addition, the nanobelts can be synthesized at low temperature, which further confirms the proposed growth mechanism.