Preparation of Tubular Forest-like and Other Carbon Structures Using Distinct Carbon Sources and Catalyst...

In this work, various carbon nanotubes (MWCNTs) were synthetized by the spray pyrolysis method. Resulting nanoforest-like and bamboo-like carbon nanotubes, as well as Yjunctions of carbon nanotubes, possess different shapes and morphology, depending on the kind of carbon source used and on the number of iron particles on the furnace tube surface, which derives from various concentrations of ferrocene catalyst.

We used the spray pyrolysis method, using different carbon sources (n-pentane, n-hexane, nheptane, and acrylonitrile) as precursors and two different concentrations of ferrocene as a catalyst. Reactions of hydrocarbon decomposition were carried out at 800oC. The solution (hydrocarbon and catalyst) was introduced with a syringe, with a flow of 1 mL/min and the synthesis time of 20 min. Argon was used as carrier gas (1000 L/min). Preheater and oven temperatures were selected 180°C and 800°C, respectively, for each carbon source. The solution passed into a quartz tube placed in an oven.

According to the studies of carbon nanostructures, obtained from different precursors, it can be proposed that the structures synthesized from n-pentane, n-hexane and n-heptane are formed by the root growth method. The growth mechanism of MWCNTs was studied, confirming that the root growth formation of products takes place, whose parameters also depend on furnace temperature and gas flow rate. Dependence of interlayer distance (0.34-0.50 nm) in the formed MWCNTs on precursors and reaction conditions is also elucidated. The formation of carbon nanotubes does not merely depend on carbon precursors but also has strong correlations with such growth conditions as different catalyst concentrations, furnace temperature and gas flow rate. Such parameters as the amount of catalyst and synthesis time are also needed to be considered, since they are important to find minor values of these parameters in the synthesis of forest-like carbon nanotubes and other structures such as bamboo-like carbon nanotubes and Y-junctions in carbon nanotubes.

As a result of the evaluation of interlayer distance in CNTs formed from different carbon sources, a standard value of interlayer distance normally for CNTs is 0.34 nm and for pentane A (0.5 wt.%), hexane B (1 wt.%), toluene A (0.5 wt.%) the range is from 0.33 to 0.35 nm. In case of pentane and acrylonitrile, under an increase of the catalyst concentration, an increase of the value of interlayer distance takes place from 0.35 and 0.4 to 0.4 and 0.5 nm, respectively, but for hexane, heptane and cyclohexane, an increase of the catalyst concentration maintains the same interlayer distance. This involves the use of lower quantities of raw materials and, therefore less cost for obtaining these materials.