Solid-phase Synthesis And Properties Testing Of Carbon Nanotubes

Carbon nanotubes(CNTs) have been a hotspot in the field of functional materials because of their unique tubular structure and physico-chemical properties. Three different methods are commonly used for the production of CNTs: arc-discharge, laser evaporation and chemical vapor deposition(CVD). Recently, the CVD method has been used to produce large-scale CNTs commercially. But the existence of some inevitable problems, such as the loose powder, seriously hinders the large-scale application of CNTs.In this article, we provide a novel method for solid-phase synthesis of CNTs. Through this method, a certain shape and size of macroscopic CNT monoliths can be obtained, which could avoid the problem of the loose power generated in the CVD method. In addition, the solid phase method is a simple, lower requirements and high effective strategy for preparation of large scale CNTs. Furthermore, CNTs can be doped directly by nitrogen during this process. The detailed synthesis process is as follow: under certain conditions, using the divinylbenzene(DVB) as carbon source and adding a kind of imidazole ionic liquid and ferricyanide, a nitrogen-containing metalorganic polymer is produced as the precursor for the growth of CNTs. Then under high temperature and continuous N2 stream, the precursor will carbonize to macroscopic nitrogendoped-CNT with certain size and shape. The as-prepared CNTs were characterized by Raman spectroscopy, scanning electron microscopy(SEM), transmission electron microscopy(TEM) and other measurements. We studied the purity and structure of different CNTs prepared at various carbonization temperatures. It is found that 800 oC is the most appropriate synthesis temperature.The potential application of the as-synthesized CNTs was investigated. Firstly, the products were activated by KOH to increase specific surface area and to improve the pore structure. The results showed that the specific surface area increased with increasing the activation temperature but at the same time the nitrogen loss gets more severe. When we maintained the activation temperature at 700 oC for 2 hours, the specific surface area changed from 315 to 544 m2/g with increasing of more than 70%. Meanwhile, the micropore volume increased more than doubled and nitrogen loss is less than 50%. According to the results of CO2 adsorption under ambient condition(25 oC, 100 kPa), the specific surface area of nitrogen-doped CNT is an important factor for CO2 adsorption capacity.Further analysis indicates that the CO2 adsorption of unit volume of micropores(y) and surface nitrogen content(x) exist a linear relationship: y=5.00+4.25 x, which provides a new idea for the structural optimization of high capacity CO2 adsorbent material.