In this work, various carbon nanotubes (MWCNTs) were synthetized by spray pyrolysis method. Resulting nanoforest-like and bamboo-like carbon nanotubes, as well as Y-junctions of carbon nanotubes, possess different shapes and morphology, depending on the kind of carbon source used and on the amount of iron particles on the furnace tube surface, which derives from the concentration of ferrocene catalyst.
Methods: We used the spray pyrolysis method, using different carbon sources (n-pentane, n-hexane, n-heptane, and acrylonitrile) as precursors and two different concentrations of ferrocene as a catalyst. Reactions of hydrocarbon decomposition were carried out at 800oC. The solution supply system (hydrocarbon and catalyst) was scheduled dosing with syringe, with a flow of 1 mL/min and the synthesis time was 20 min. Argon was used as a carrier gas (1000 sccm or 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 into oven.
Results: 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 can be formed by root growth method. The growth mechanism of MWCNTs was studied, confirming that the root growth formation of products takes place, whose parameters depend also 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 concentration, 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.
Conclusions: As a result of evaluation of interlayer distance in CNT’s formed from different carbon sources, a standard value of interlayer distance normally for CNT’s 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.