Catalytic Growth Of Single-Walled Carbon Nanotubes With A Narrow Chirality

The catalytic growth of narrow chirality single-walled carbon nanotubes is a critical and enduring challenge in single-walled carbon nanotube synthesis field.Nowadays,the powder catalysts are remained the first choice for bulk synthesizing single-walled carbon nanotubes with narrow chirality distribution.Owing to the low cost and good controllability,chemical vapor deposition has been considered as the most promising techniques in growing single-walled carbon nanotubes for the semiconductor industry.In this process,the reduced metal nanoparticles on catalyst surfaces play a crucial role in the nucleation and growth of single-walled carbon nanotubes,and thus determine the chirality distribution of the prepared single-walled carbon nanotubes.Thus,the property design of catalyst is a critical point to control the quality and structures of carbon nanotubes.The reduction of metal oxides is the precondition for growing single-walled carbon nanotubes.Therefore,improving the reduction performance of metal oxides is helpful to improve the activity of the catalyst,and promote the catalytic growth of narrow chirality distribution of single-walled carbon nanotubes.In the past two decades,significant progress has been made in chirality-controlled synthesis of single-walled carbon nanotubes,mainly through the combination of catalyst design and reaction parameter optimization.In particular,the chiral-selected and mass preparation of single-walled carbon nanotubes using solid powder catalysts by chemical vapor deposition techniques show great prospects.In this article,by the properly design of powder catalyst,the chirality distribution of single-walled carbon nanotubes in chemical vapor deposition process was systematically explored as following:（1）A SiC supported iron catalyst was developed for chemical vapor deposition growth of carbon nanotubes.Using CO as the carbon source,Fe-SiC catalyst alone was almost inactive for synthesizing carbon nanotubes and only trace amount of carbon nanomaterials was produced.While the powder Fe-SiC catalyst could be activated by pressing them on a flat Si O₂ substrate or mixing with porous MgO powders.Particularly,efficient growth of single-walled carbon nanotubes was achieved on porous MgO promoted Fe-SiC catalyst,and predominant synthesis of（6,5）single-walled carbon nanotubes was realized at a reaction temperature of 650 ^oC.Systematic characterizations revealed that the reducibility of the Fe-SiC catalyst was enhanced by the physical contact with oxide support,which promotes the formation of small active Fe nanoparticles for the subsequent single-walled carbon nanotubes nucleation and growth.This work not only deepens our understandings to the catalyst activation mechanisms,but also helps to design composite catalysts for synthesizing single-walled carbon nanotubes.（2）An MgO supported vanadium catalyst（V-MgO）was designed by exerting metal-support interaction strategy,which could transfer electrons from MgO support to metal particles,shifting the originally inactive early transition vanadium metal into the high active catalyst.The highly selective synthesis of（6,5）single-walled carbon nanotubes with a chiral abundance of up to 67.9%was achieved by chemical vapor deposition at 650 ^oC.The growth mechanism of single-walled carbon nanotubes over vanadium catalyst was elucidated by molecular dynamics（MD）.It was shown that vanadium carbide can nucleate single-walled carbon nanotubes.In addition,the origin of chiral selectivity is elucidated by considering the energy of the single-walled carbon nanotube-Vanadium carbide interface and the growth kinetics of single-walled carbon nanotubes.This work not only clarified the effect of catalyst activity regulation on the growth of single-walled carbon nanotubes,but also opened up a new way for batch synthesis of single-walled carbon nanotubes with pre-transition metals.（3）High quality single-walled carbon nanotubes with a narrow chirality were grown at high temperature using Co-MgO catalyst.At the growth temperature of 900 ^oC,the（7,5）,（8,4）,（7,6）single-walled carbon nanotubes are the mainly chiral species in products.After the chirality sorting process by gel chromatography techniques,the purity of single chirality single-walled carbon nanotubes can reach as high as 95%-98%,which shows an advantage over the commercial Co Mo CAT carbon nanotubes and Hi Pco carbon nanotubes.This work provides an effective strategy to bulk synthesize high quality single-walled carbon nanotubes with the narrow chirality distribution.