合成时间对火焰法制备碳纳米管的影响及其生长机理研究

Influence of synthesis time on the preparation of CNTs by flame method and its growth mechanism

以Fe/Mo/Al2O3为催化剂,采用火焰法制备了碳纳米管,研究了合成时间对碳纳米管生长的影响及碳纳米管的生长机理。通过冷场发射扫描电子显微镜、能量色散谱仪、拉曼光谱仪、碳产率对催化剂和碳纳米管进行了详细观察和分析,结果表明经过氢气还原后催化剂分布更加均匀且颗粒明显变小,催化剂表面更加粗糙且检测到的铁元素含量明显增加,这说明氢气的还原作用对催化剂有重要的改变,对碳纳米管的合成也起到至关重要的作用。合成时间较短时,碳纳米管管簇较少且碳纳米管的长度较短、质量较差,大多数催化剂表面有毛绒状物质生成,说明碳纳米管的生长机理符合"溶解-扩散-析出"模式。合成时间延长到5~6min时,碳纳米管管簇的长度和密度均明显增加,而且合成的碳纳米管中杂质也明显减少。当合成时间超过7min后,虽然碳纳米管管簇的密度和产量有所上升,但是碳纳米管中因合成时间过长团聚的催化剂杂质变多,合成时间为5~6min可以得到产量和质量均较高的碳纳米管。

The catalyst of the experiment was Fe/Mo/Al2O3,the carbon nanotubes were synthesized by flame method.The influence of synthesis time on the growth of CNTs and the growth mechanism were emphatically discussed.Through the detailed observation and analysis of SEM,EDS,carbon yield and Raman,the results shown that the catalyst distribution was more uniform and the particle size was obviously smaller after reduction.The surface of the catalyst was rougher and the detected iron content was significantly increased,this indicated that the reduction of hydrogen had an important effect on the catalyst and played an important role in the synthesis of CNTs.When the synthesis time was relatively short,the tube clusters were less and the length and quality of CNTs were poor most catalysts had plush substances on the surface,indicating that the growth mechanism of CNTs was in accordance with the"dissolution-diffusion-precipitation"model.The length and density of CNTs increased significantly when the synthesis time increased to 5 to 6 minutes,and the impurities in the synthesized CNTs decreased obviously.When the synthesis time was more than 7 minutes,the density and yield of the tube cluster still increased,however,there were more impurities in the CNTs due to the agglomeration of catalysts resulted from excessive synthesis time.Therefore,the synthesis time should not be too short and too long,CNTs with better yield and quality can be synthesized when the synthesis time was kept for 5 to 6 mintues.