Synthesis Of Nanocarbons And Microcarbons From Coal By Arc Discharge Method

Fullerene and carbon nanotubes (CNTs) are new family members in carbon materials since their first discovery in the late 20th century. Due to their spectacular mechanical and electronic properties, fullerenes and CNTs are found to be of great use both in theoretical study and in applications in a wide range, which have been the frontiers in the research field of nanocarbon science. Though much progress has been made in synthesis of various carbon nanomaterials and in study on their chemical and physical properties, the high-cost for producing nanocarbons is still one of the key issues that need to be considered for the commercial applications.Coal is a cheap carbon source in nature, and has long been considered to be a good starting materials for value-added carbons. In this paper, the potential of using coal as precursor for making novel nanocarbons and microcarbons has been explored systematically. Various forms of nanocarbons including higher fullerenes, multi-walled CNTs (MWNTs), bamboo-shaped CNTs (BCNTs), Y-junction CNTs (YCNTs), single-walled CNTs (SWNTs) and double-walled CNTs (DWNTs) have been successfully synthesized from coal by arc plasma, which depends on the arc discharge conditions and other parameters including coal type and/or whether catalysts are used or not. The morphologies of the obtained nanocarbons and the mechanisms involved in the their formation process are studied. In addition, the possibility of producing microcarbons with coal-based carbon rods as substrate via arc discharge technique in a mixture gas of helium and hydrocarbons such as CH4 or C2H2 is also explored and highlighted. It has been found that several micro-sized carbons with novel morphologies can be prepared after optimizing the experimental conditions. The main results are summarized as follows.Fullerenes can be obtained from coal in high yield by arc discharge method, and the crude fullerenes were analyzed using laser desorption time-of-flight mass spectrometer. The results show that in addition to C60 and C70 fullerenes, higher fullerenes such as C72, C82, C102, C106 and C120 are present in the coal-based crude fullerenes in relative high content. The yield of coal-based crude fullerenes depends on coal rank to a great degree. Of the coals tested, Taixi anthracite is the best one in terms of fullerenes yield, from which a yield of 6.77 wt% is obtained. While in the case of Zhalainuoer lignite, the yield of crude fullerenes is only 1.43 wt%. The by-products of coal-based fullerenes were analyzed using GC-MS, showing the presence of aromatic hydrocarbons, which implies that carbon fragments released from the coal-based carbon rods during the arcing process may function as one of the main intermediate precursors and get involved in the formation process of coal-based fullerenes.It has been found that the yield of coal-based CNTs is greatly affected by the coal rank, and the highest yield of CNTs (9.16 wt%) could be obtained from Taixi anthracite under theoptimized conditions. The results show that the arcing conditions and catalysts are the key factors for the formation of bamboo-shaped CNTs (BCNTs), and over 60% of well-developed BCNTs in the products is obtained from coal-based carbon when iron powder is added as catalyst; at the same time, a novel carbon nano-capsules or giant fullerenes with uniform outer diameters of 50-70 nm and inner diameter of 40-50 nm is also obtained as the by-products of BCNTs when a high content of iron powder (10~20wt%) is used as catalyst. Moreover, YCNTs could be prepared in high yield when FeS powder is added into the iron group catalysts. It has been estimated according to the TEM examination that the content of YCNTs in the final products is over 40% under some conditions.High purity SWNTs is successfully prepared from coal. The yield of SWNTs is closely related to coal rank, which follows an order: anthracite > bituminous coal > lignite. The SWNTs synthesized with iron as catalyst have a diameter distribution range of 1.24-2.19 nm, while SWNTs prepared with nickel or lanthanum-nickel as ca...