Abstract
Single wall carbon nanotubes (SWCNTs) were synthesized using oxygen-containing ferrocene derived catalysts. The mechanism of synthesizing carbon nanotubes was clarified by the catalyst’s exothermic or endothermic decomposition processes. By monitoring the decomposition process of ferrocene-derived catalyst precursors with and without sulfur, we found that the types of oxygen function groups closely influence catalyst formation and nanotube growth. The ferrocene-derived catalyst precursors have a different oxygen containing groups, which are hydroxyl (–OH, ferrocenenemethanol) and carbonyl (C=O, acetylferrocene, and 1,1′-diacetylferrocene). The sulfur chemical state (S 2p) on synthesized catalyst particles using acetylferrocene and 1,1′-diacetylferrocene has more sulfate () than others, and there also is a carbon state (C-S-C). The catalyst particle using ferrocenemethanol predominant formed metal–sulfur bonds (such as S2− and ). The hydroxyl group (–OH) of ferrocenemethanol enhanced the etching effect to remove amorphous carbon and prevented oxidation on the catalyst particle surfaces; however, the carbonyl group (C=O) of acetylferrocene reacted with the catalyst particles to cause partial oxidation and carbon dissociation on the surface of the catalyst particles. The partial oxidation and carbon contamination on catalyst particles controlled the activity of the catalyst. The DFT study revealed that the ferrocene-derived catalyst precursor was dissociated according to following process: the functional groups (such as CH3CO and COH) => first Cp ligands => second Cp ligands. The pyrolysis and release of Fe ions were delayed by the functional groups of ferrocene-derived precursors compared to ferrocene. The thermal-decomposition temperature of the catalyst precursor was high, the decomposition time was be delayed, affecting the formation of catalyst particles and thus making smaller catalyst particles. The size and composition of catalyst particles not only affect the nucleation of CNTs, but also affect physical properties. Therefore, the IG/ID ratio of the CNTs changed from 74 to 18 for acetylferrocene and ferrocene, respectively. The purity also increased from 79 to 90% using ferrocene-derived precursors.
Highlights
Carbon nanotubes (CNTs) have been the subject of research attention in recent years because of the potential applications of their extremely impressive mechanical, electrical, and thermal properties [1–7]
CNT (FWCNT) with a narrow-diameter distribution were synthesized by floating catalyst chemical vapor deposition (FC-CVD)
When the CNT was synthesized with ferrocene, the tube diameter (d) ranged from 1.1 to 4.8 nm; most of the d existed at 1~2.5 nm
Summary
Carbon nanotubes (CNTs) have been the subject of research attention in recent years because of the potential applications of their extremely impressive mechanical, electrical, and thermal properties [1–7]. CNT fibers made by the direct spinning method are macroscopic structures that retain their intrinsic properties. Direct spinning by the floating catalyst chemical vapor deposition (FC-CVD) method has been investigated in Nanomaterials 2022, 12, 863. The FC-CVD process is a very rapid method in which catalyst formation, CNT nucleation and growth, and aerogel formation occur within a few seconds. It is difficult to control the process of early stages such as catalyst formation, CNT nucleation, and CNT growth, which are closely linked to the final CNT fiber properties. The individual CNTs constituting CNT fiber tend to be affected by growth conditions, including temperature, flow rate, carrier gas, carbon source, and catalyst composition
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