A New Approach to Direct Production of Carbon Nanotubes and Related Nanocarbons over Coal Ash

Introduction Nanocarbons have attracted worldwide attention in nanoscience and nanotechnology communities during the past two decade because of their unique mechanical and electrical properties, which make them great potential in catalysis, electrochemical devices, field emission devices and composites[1-2]. However, the high cost and low yield for production of these materials remains the bottleneck for their extensive applications[3]. Physical vapor deposition (PVD) and Chemical vapor deposition (CVD) are the main approaches for the production of CNTs. Generally, the energy-consuming PVD method has been used to produce CNTs with high quality for physical property investigation in lab or specific application, while CVD facilitates the production of CNTs in large-scale. CVD is normally conducted over impregnated silica or alumina substrate with active metal as catalysts. Based on the costbenefit analysis, catalyst-related cost has been regarded as one of the most expensive portions for the CVD process, including both the active metal and the support[4]. Therefore, a strategy for producing CNTs with cheap yet effective catalyst is in high demand. Small particles of metal and metal oxide, which represent an ideal form of catalyst for the synthesis of CNTs, are almost present in all nature minerals. Up to now, volcanic lava rock, soil, garnet and bentonite have been used as catalyst to grow CNTs efficiently [3]. Coal ash, a solid waste from coal combustion, is produced in an ever increasing amount in China as well as in the world[5]. An environmentally friendly way to disposal coal ash is worldwide concern. Recently, synthesis of CNTs on coal ash derivated catalyst via impregnation reported by O.M.Dunens and co-authors[6] may open up a new way to use coal ash. But the impregnate process involved is not environmentally benign and offset the cheap-production effort. Herein, we report an efficient way for growing CNTs directly on coal ash without adding any external active phase, it is found that the yield and structure of the CNTs strongly depend on the kind of coal ashes. The obtained CNTs/ash composites implicate potential application as building materials.