The Synergistic Effect of a Bimetallic Catalyst for the Synthesis of Carbon Nanotube Aerogels and their Predominant Chirality

Abstract

Synthesis of continuous spinnable carbon nanotube (CNT) fibers is the most promisingm ethod for producing CNT fibers for commercial applications. The floating-catalyst chemical vapor deposition (FC-CVD) methodi sarapid process that achieves catalystf ormation,C NT nucleation and growth, and aerogel-like sock formation within af ew seconds. However,t he formation mechanism is unknown. Herein, the progress of CNT fiber formation with bimetallic catalysts was studied, and the effect of catalystc omposition to CNT fiber synthesis and their structuralp roperties was investigated. In the case of bimetallic catalysts, the carbon source rapidly decomposesa nd generates various secondary hydrocarbon species, such as CH 4 ,C 2 H 4 ,C 2 H 2 ,C 3 H 6 ,a nd C 4 H 10 whereas monometallic catalysts generate only CH 4 and C 2 H 4 on decomposition. CNT fiber formation withF e 1 Ni 0 beginsa bout 400 mm from the reactor entrance, whereas CNT formation withF e 0.8 Ni 0.2 and Fe 0.5 Ni 0.5 begins at about 500 and 300 mm, respectively.T he formed CNT bundles and individual CNTsa re oriented along the gasf low at thesel ocations.T he enhanced rateo ff iber formation and lowering of growth temperature associated with bimetallic catalysts is explained by the synergistic effectsb etween the two metals. The synthesized CNTsb ecome predominantly semiconducting with increasing Ni contents.

Synthesis of Carbon Nanotubes by Floating Catalyst Chemical Vapor Deposition and Their Applications

“…They intentionally synthesized SWCNTs containing small diameter s-SWCNTs and large diameter m-SWCNTs by controlling the FCCVD growth parameters, and hydrogen was then introduced as an etchant. [27,129] As a result, enriched large-diameter m-SWCNTs were obtained (Figure 4b,c). Yadav et al [128] also obtained an ≈82% m-SWCNT enrichment by changing the hydrogen concentration in FCCVD.…”

“…They attributed this preferential growth to the chemical composition and chemical ordering controlling of bimetallic catalyst. [129] Compared with s-SWCNTs, the selective growth of m-SWCNTs is much more difficult to achieve because of the higher reactivity of m-SWCNTs. Cheng et al achieved an m-SWCNT enrichment by using a combined diameter control and chemical etching strategy (Figure 4a).…”

Synthesis, Structure and Electrical Resistivity of Carbon Nanotubes Synthesized over Group VIII Metallocenes

“…Here it is necessary to note the manifestation of the synergistic effect of the bimetallic catalyst. There are a lot of publications on the synergistic effect that is observed when two or more metals are combined in a catalyst [29,33,[37][38][39]. The interdiffusion of two or three active nanoparticles in comparison with one nanoparticle significantly increases not only the growth rate of nanotubes, but also improves the uniformity and quality of the product, gives a narrower nanoparticle size distribution, etc.…”

“…There are many publications on the use of ferrocene for the synthesis of carbon nanotubes by the CVD method and the study of their properties [14,[18][19][20][21][22][23][24][25][26]. There are publications where cobaltocene [27] and nickelocene [28,29] or their combinations with ferrocene are used as catalysts, but they are few [30][31][32][33]. Some data from such publications are presented in Table 1.…”

Effect of a Metallocene Catalyst Mixture on CNT Yield Using the FC-CVD Process

“…Mixing two metal catalysts has shown an increase in CNT yield for the substrateassisted CVD method [47][48][49][50]. However, there are limited publications available in the literature where cobaltocene [51,52] or nickelocene or their combination [51][52][53][54][55] are used for the synthesis of CNT aerogel from the FC-CVD method.…”