| As a unique one-dimensional nanomaterial,single-walled carbon nanotubes（SWNTs）possess excellent electrical,optical,and mechanical properties.Compared with silicon,SWNTs have the advantages of low resistance and less heat generation.Therefore,SWNTs are expected to replace silicon and achieve technological leap-forward in the fabrication of semiconductor chips.However,the chiral structure diversity and the consequent differences in electrical property of SWNTs hinder the realization of this promising prospect.There are two main approaches to obtain structurally homogeneous SWNTs,one is the separation of synthesized SWNTs,the other is direct synthesis of SWNTs with specific chirality,which is more economical and efficient.The rational design and development of catalysts for the chirality-specific growth of SWNTs by chemical vapor deposition（CVD）is the focus of extensive research.Since the 1990s,many catalysts suitable for the growth of SWNTs have been developed.Catalysts containing iron group transition metals,including iron,cobalt,and nickel,are revealed to have high activity and catalytic efficiency.The high activity of iron-group metal catalysts is related to their suitable binding energy with carbon,which is favorable for the nucleation and growth of SWNTs.Compared with iron-group metal catalysts,other metal catalysts have been demonstrated to be catalytically active.However,the SWNT growth is mainly limited on flat substrate surface.On one hand,the activation mechanism of these unconventional metals for SWNT growth remains unclear.On the other hand,the yield of SWNTs is too low to explore the the effects of catalyst compositions on the chirality distribution of SWNTs.To fill the research gap,we herein develop several non-iron group metal catalysts supported by porous oxide for growing SWNTs by CVD.In addition to increasing the yield of SWNTs,selective growth of SWNTs with specific chirality was realized,and the relationship between the SWNT chirality distribution and the catalyst composition was established.In addition,density functional theory calculation was carried out to compare the dissociation energies of carbon monoxide（CO）on free ruthenium（Ru）nanoclusters and on Ru nanoclusters supported by magnesium oxide（Mg O）.The results show that the presence of Mg O can greatly reduce the dissociation energy of CO on Ru,which is due to the electron transfer from Mg O to Ru enhances the binding force between Ru and carbon atoms,improving the catalytic activity of Ru for CO decomposition.The activation mechanism of non-iron group metals outside the"Goldilocks zone"for catalyzing the SWNT growth was explained,which gains more insights into the bulk and chirality-selective growth of SWNTs using unconventional metal catalysts.The main research results are as follows:（1）An atomically dispersed Ru catalyst supported by porous Mg O was designed and developed,and SWNTs were successfully prepared by CVD using CO as carbon source.Raman spectroscopy,Ultraviolet-visible-near infrared absorption spectroscopy and fluorescence spectroscopy were employed to characterize the products,which proved that enriched（6,5）tubes was obtained at relatively high temperatures.（2）A porous Mg O supported atomically dispersed rhodium metal catalyst was designed and used to synthesize SWNTs through CVD method.By combing the regulation of CVD reaction conditions,the selective growth of ultrathin（5,4）SWNTs having diameters of only 0.6 nm and high curvature energy,was achieved using CO carbon source at the reaction temperature of 700 ℃.This is the first work to directly grow highly dominant（5,4）tubes.（3）An Mg O supported iridium catalyst only affords the growth of SWNTs with a wide diameter distribution and poor yield.In order to improve the SWNT growth results,powdery aluminum oxide was adopted as the support to anchor iridium catalyst.By optimizing the catalyst composition and the CVD growth conditions,selective growth of small diameter（7,6）tubes was achieved at a reaction temperature as high as 900 ℃. |
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