Magnesium Oxide Loaded Manganese Group Metal Catalyzes The Growth Of Carbon Nanotubes

Single-walled carbon nanotubes have extremely important applications in electronics,composite materials and other fields due to their unique structure and remarkable electrical,mechanical and optical properties.The preparation of high quality single-walled carbon nanotubes is the prerequisite for their applications.However,most of the single-walled carbon nanotubes are mixture with different diameters and chirality,which will bring great difficulties to the subsequent practical application.In recent years,great efforts have been made in the preparation of single-walled carbon nanotubes with narrow diameter and chiral distribution.However,the separation process is complicated,which increases the cost and difficulty of practical applications.Therefore,directly growing single-walled carbon nanotubes with narrow diameter distribution has the advantages of low cost and easy magnification,which has great research value.Among numerous preparation methods,chemical vapor deposition has great advantages in structurally controlled preparation of single-walled carbon nanotubes.In the process of chemical vapor deposition growth,the yield and chirality of single-walled carbon nanotubes are controlled by designing catalysts and optimizing reaction conditions.Over the past two decades,the catalysts developed for large-scale synthesis of narrow chiral single-walled carbon nanotubes are mainly focus on iron transition metals such as Fe,Co and Ni.The activity of other metal or carbide catalysts and the yield of prepared single-walled carbon nanotubes is low,which limits the application of synthetic single-walled carbon nanotubes.In this paper,based on the design of catalyst,we creat manganese group metal catalysts which have simple preparation technique,and use these catalysts to bulk synthesize high-quality single-walled carbon nanotubes.The main research results are as follows:(1)Using rhenium as catalyst,magnesium oxide as support and carbon monoxide as carbon source,high quality single-walled carbon nanotubes were bulk synthesized by chemical vapor deposition.Rhenium exists as a catalyst layer after air calcination at1100 ^oC.The calcination process affects the dispersion of metal oxides,the interaction between metal oxides and magnesium oxide carriers,and the reducibility of the catalyst.The calcination process influences the metal oxide dispersion,the metal oxide interactions with the Mg O carrier and the reducibility of the catalyst.Through the characterization of single-walled carbon nanotubes grown at 800 ^oC,it is found that the diameter of single-walled carbon nanotubes is mainly fall in the range of 1.0 to 1.6 nm with an average of 1.3 nm.Single-walled carbon nanotubes were separated according to their diameters by multi-column gel chromatography and divided into three parts containing carbon nanotubes with different diameters.This work not only opens the avenue for bulk synthesis of single-walled carbon nanotubes with solid catalyst,but also sheds light on diameter-dependent single-walled carbon nanotubes separation,paving the way towards cutting-edge applications of single-walled carbon nanotubes.(2)Using a magnesium oxide supported manganese as catalyst,carbon monoxide as carbon source,single-walled carbon nanotubes with a small diameter were synthesized at atmospheric pressure.Raman spectroscopy,transmission electron microscopy and UV-visible-near-infrared absorption spectroscopy et al.were used to characterize the structure and chiral properties of the prepared single-walled carbon nanotubes.The results showed that the calcined catalyst at 800 ^oC grew high-quality single-walled carbon nanotubes with small diameter distribution at 700 ^oC,with an average diameter of about 0.8 nm.(3)On the basis of the manganese catalysts supported by magnesium oxide,the transition metal rhenium was added to design the bimetallic magnesium oxide supported manganese-rhenium catalysts with different ratios.Carbon monoxide was used as the carbon source to grow single-walled carbon nanotubes at 700 ^oC.Raman spectroscopy,UV-visible-near-infrared absorption spectroscopy and photoluminescence spectroscopy et al.were used to characterise single-walled carbon nanotubes prepared with different proportions of manganese-rhenium catalyst.It was found that the proportion of(6,5)single-walled carbon nanotubes in the product gradually increased with the increase of rhenium ratio in the catalyst.When the ratio of manganese to Rhenium reaches 1:1,the selective growth of single-walled carbon nanotubes dominated by(6,5)tubes is realized.