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We studied the influence of the ethylenediaminetetraacetic acid (EDTA) content used as combustion fuel when fabricating nickel oxide (NiO) nanocatalysts via solution combustion synthesis, as well as the growth behavior of carbon nanotubes (CNTs) using this catalyst. Nickel nitrate hexahydrate (Ni(NO3)2∙6H2O) was used as the metal precursor (an oxidizer), and the catalysts were synthesized by adjusting the molar ratio of fuel (EDTA) to oxidizer in the range of 1:0.25 to 2.0. The results of the crystal structure analysis showed that as the EDTA content increased beyond the chemical stoichiometric balance with Ni(NO3)2∙6H2O (F/O = 0.25), the proportion of Ni metal within the catalyst particles decreased, and only single-phase NiO was observed. Among the synthesized catalysts, the smallest crystallite size was observed with a 1:1 ratio of Ni ions to EDTA. However, an increase in the amount of EDTA resulted in excessive fuel supply, leading to an increase in crystallite size. Microstructure analysis revealed porous NiO agglomerates due to the use of EDTA, and differences in particle growth based on the fuel ratio were observed. We analyzed the growth behavior of CNTs grown using NiO nanocatalysts through catalytic chemical vapor deposition (CCVD). As the F/O ratio increased, it was observed that the catalyst particles grew excessively beyond hundreds of nanometers, preventing further CNT growth and leading to a rapid termination of CNT growth. Raman spectroscopy was used to analyze the structural characteristics of CNTs, and it was found that the ID/IG ratio indicated the highest CNT crystallinity near an F/O ratio of 1:1. [ABSTRACT FROM AUTHOR]

The redox behavior of the catalyst and the catalytic decomposition of carbon monoxide (CO) were investigated in the synthesis process of multi‐wall carbon nanotubes (MWCNT) using Ni/MgO catalyst. The surface morphology of the heated Ni layer was observed by TEM to confirm the formation of NiO particles (50 nm or less) and NiO (222). The chemical reaction behavior of the catalyst in CO the atmosphere was displayed via TG‐DSC analysis, and the reduction of NiO was revealed due to the mass decrease of 2.71 wt% and the exothermic peak at around 400°C. The deposition of carbon was identified with an increase in mass and the exothermic peak near 600°C. Ni (111) and carbon (002) facets was taken place in a diffraction pattern of carbon deposited catalyst, indicating the reduction in NiO and the graphitic carbon deposition. The crystallinity of the graphitic carbon was analyzed as the ratios of 0.998 for ID/IG and 0.26 for sp3/sp2 in Raman and photoelectron spectra. The encapsulated Ni in MWCNT was observed through TEM‐EDS, verifying the activation of the catalyst by CO. [ABSTRACT FROM AUTHOR]