Preparation And Properties Of Nonmetal Doped Carbon Nanomaterials

Since the landmark paper of Iijima, different structures of carbon nanomaterials(CNMs) have been studied widely due to their unique physical and chemical properties. Currently, the three techniques for CNMs production can be divided into three major categories:(a) electric arc-discharge,(b) laser ablation, and(c) chemical vapor deposition(CVD) method. Common to all of the techniques, there is the involvement of transition-metal catalysts, especially metals of iron-group elements(Fe, Co, Ni). The metal catalysts remain in the products, causing problems in property characterization as well as applications. Therefore, the intrinsic physical properties of CNMs still not be fully understood at present.In order to synthesize high purity and undamaged CNMs, we investigated the synthesis of CNMs over the water-soluble salts through the pyrolysis of acetylene by a chemical vapor deposition method. The specific research work is as follows:(1) By the sol-gel method, alkali metal carbonates with the different content of Na and K were synthesized. Using the obtained salts as catalyst, we studied the synthesis of CNMs by the CVD method. The obtained results indicated that high selectivity of CNMs could be synthesized selectively by regulating the decomposition temperature and the atomic ratio of catalyst. Because the used catalysts are water-soluble, high purity and undamaged CNMs could be obtained through the water-washing process.The photoluminescence investigation indicated that the obtained CNMs exhibited ablue(ca. 467 nm) and ultraviolet peak(ca. 367 nm). Compared to the previously reported CNMs, the shift of luminescence peak may be related to their structures.(2) Based on the above obtained results, in this work, we ynthesize single phase of K2CO3 as the catalyst by sol-gel method using KOH and citric acid as starting materials. The results showed that high selectivity of carbon nanofibers and helical carbon nanotubes could be synthesized selectively at 400 and 500 oC, respectively.And we found that the high decomposition temperature is detrimental to synthesize high yield of CNMs.(3) In order to investigate the effect of nitrogen doping on the luminescence properties of CNMs. Carbon nanofibers obtained over K2CO3 particles at 400 oC were used as original material to synthesize N-doped carbon nanofibers. We investigated the synthesis of N-doped carbon nanofibers through the annealing process in NH3 at500 and 600 o C. The XPS results indicated that N-doped carbon nanofibers could not produced when the temperature is below 500 oC, and N-doped carbon nanofibers could be synthesized at 600 o C. And their photoluminescence results indicated the intensity of ultraviolet peak could be decreased through the addition of N into carbon nanofibers, which may be related to the introduction of N could restore the defects and vacancies of carbon nanofibers.