煤基碳纳米管制备技术和生长机理研究进展

我国煤炭资源丰富,但现阶段以燃烧、热解和气化等为主的传统利用方式存在资源浪费、环境污染和经济效益低等问题,且我国以煤炭资源为主题的能源结构在短期内不会发生改变,因此,清洁、高效利用是新时期煤炭资源的立足点和首要任务。另一方面,碳纳米管因其独特的一维结构在力学、电学和热学等方面具有优异的特性,使其在复合材料、电子材料和能源材料等领域具有广泛的应用,但是碳纳米管制备成本偏高的问题较为突出,严重限制了其大规模的应用,现阶段急需开发新型、环境友好的碳纳米管制备技术。宏量、低成本的煤基碳纳米管制备技术可以同时较好地解决上述2个问题。笔者基于文献重点分析了反应原料、放电气氛和催化剂等因素对电弧放电法和等离子体射流法2种煤基直接制备碳纳米管技术的影响,讨论了原料种类、催化剂、反应温度、升温速率和反应气氛等因素对化学气相沉积法-煤基间接碳纳米管制备技术的影响过程。分析发现,在电弧放电法和等离子体射流法中,原料种类对碳纳米管产物的产量具有重要作用,放电气氛对碳纳米管产物的类型具有重要影响,催化剂对碳纳米管产物产量和类型均具有重要影响;在化学气相沉积法中,原料种类对碳纳米管产物形貌、长径比和有序度等性质具有重要影响,催化剂对碳纳米管产物的生长过程具有重要影响,反应温度和升温速率对碳纳米管产物的管径变化和类型具有重要影响,反应气氛可改变催化剂的催化效果。此外,总结了煤基碳纳米管直接和间接制备技术中碳纳米管的生长机理的类型及特点:其中,直接制备技术中碳纳米管生长过程符合碎片式生长机理,而间接制备技术中碳纳米管生长过程可分为气-液-固(VLS)、气-固-固(VSS)、气相成核(VPN)和阶梯式等类型。分析认为应当深入开展以下工作:探究煤、煤热解气和商业煤气等廉价原料制备碳纳米管的过程,进而建立和完善原料与碳纳米管产物之间的关系体系;开发新型、高效的煤基碳纳米管催化剂制备技术;建立新的碳纳米管生长模型,进一步丰富和完善碳纳米管生长模型体系。

Research progress on preparation technology and growth mechanism of coal-based carbon nanotubes

Coal resources is rich in China,but at present,the traditional utilization methods,mainly including combustion,pyrolysis and gasification,have some problems such as waste of resources,environmental pollution and low economic benefits,and the energy structure with coal as the theme will not change in a short period of time. Therefore,clean and efficient utilization is the foothold and primary task of coal resources in the new era. On the other hand,carbon nanotubes have excellent properties in mechanics,electricity and thermotics due to their unique one-dimensional structure,which makes them widely used in the fields of composite materials,electronic materials and energy materials. However,the problem of high preparation cost of carbon nanotubes is prominent,which severely limits its large-scale application. At present,it is urgent to develop new and environmentally friendly carbon nanotubes preparation technology. The above two problems can be well solved by the large-scale and low-cost coal-based carbon nanotubes preparation technology at the same time. Based on the literature,in this paper,the influence of reaction materials,discharge atmosphere and catalyst on the direct preparation of carbon nanotubes by arc discharge method and plasma jet method was analysed,and the influence process of raw materials,catalyst,reaction temperature,heating rate and reaction atmosphere on the preparation of indirect carbon nanotubes by chemical vapor deposition method was discussed. It is found that in arc discharge and plasma jet methods,the type of raw materials plays an important role in the production of carbon nanotubes,the discharge atmosphere has an significant influence on the type of carbon nanotubes,and the catalyst has great effects on both the production and type of carbon nanotubes. In the chemical vapor deposition method,the type of raw materials has a major impact on the morphology,aspect ratio and order degree of carbon nanotubes,the catalyst can make a big difference to the growth process of carbon nanotubes,the reaction temperature and heating rate will influence on the diameter change and type of carbon nanotubes,and the reaction atmosphere can change the catalytic effect of the catalyst. In addition,in this paper,the types and characteristics of the growth mechanism of carbon nanotubes in the direct and indirect preparation of coal-based carbon nanotubes were summarized: the growth process of carbon nanotubes in the direct preparation technology conformed to the fragment growth mechanism,while the growth process of carbon nanotubes in the indirect preparation technology could be divided into four types: gas-liquid-solid( VLS),gas-solid-solid( VSS),gas-phase nucleation( VPN) and ladder type. Analysis shows that the further research should be carried out on the following aspects: the process of preparing carbon nanotubes from cheap raw materials such as coal,coal pyrolysis gas and commercial gas is investigated,so as to establish and improve the relationship system between raw materials and carbon nanotubes products,and the new and efficient preparation technology of coal-based carbon nanotubes catalyst is developed. The growth models of new carbon nanotubes are established,so as to further enrich and improve the carbon nanotubes growth model system further.