Natural Laterite as a Catalyst Source for the Growth of Carbon Nanotubes and Nanospheres

Abstract

Carbon nanotubes (CNTs), the closest structure to ideal one-dimensional (1D) conductors, have stimulated substantial interest in the last decades for many applications in the field of nanotechnology. Unfortunately, the high cost of efficient metal catalysts limits the large-scale exploitation of carbon nanomaterials' synthesis processed by chemical vapor deposition (CVD). However, minor or even trace amounts of metal or metal oxides in the ideal form to be used as catalysts can be easily found in almost all-natural materials. Herein, we report on the synthesis of carbon nanotubes and nanospheres obtained via CVD from a natural laterite, as a catalyst source. The synthesized nanostructures were carefully analyzed by X-ray diffraction (XRD), environmental scanning electron microscopy (ESEM), highresolution transmission electron microscopy (HR-TEM), micro-Raman spectroscopy, and thermogravimetric analysis (TGA). In particular, we investigated and discussed the structural properties of the catalyst nanoparticles and of the produced carbon nanomaterials as well as the influence of temperature on the activity of the laterite based catalyst. At 700 °C, mainly CNTs grew, whereas at 800 °C carbon nanospheres start to form and they become clearly visible in the form of continuous networks of spheroidal structures in the samples grown at 900 °C. The obtained yields indicate that it could be possible to scale up the synthesis of CNTs to be used in technological applications, starting from natural mineral oxide sources.

Green Synthesis of Carbon-Encapsulated Magnetic Fe3O4 Nanoparticles Using Hydrothermal Carbonization from Rattan Holocelluloses

“…It has been confirmed that hemicelluloses started decomposition easily, with the weight loss mainly happening at 220~315 • C, and cellulose pyrolysis was focused at a higher temperature range (315~400 • C) [31]. Thus, due to the pyrolysis occurring under nitrogen protection, the dramatic weight loss for EAc NH3 -180 and ACl NH3 -180 was mainly due to the thermal degradation of the hemicelluloses and partial cellulose [32], though it displayed a thermal curve with a single weight loss dip when a one-step oxidative degradation process of crystalline carbon with oxygen occurred [33]. When the HTC temperature was higher than 230 • C, almost all the holocelluloses were converted into amorphous carbon, with a very high solid residue reaching 65% and 60% for the EAc NH3 -280 and ACl NH3 -280 samples.…”

“…due to the thermal degradation of the hemicelluloses and partial cellulose [32], though it displayed a thermal curve with a single weight loss dip when a one-step oxidative degradation process of crystalline carbon with oxygen occurred [33]. When the HTC temperature was higher than 230 °C, almost all the holocelluloses were converted into amorphous carbon, with a very high solid residue reaching 65% and 60% for the EAcNH3-280 and AClNH3-280 samples.…”

Natural Materials—Interesting Candidates for Carbon Nanomaterials

“…Laterite is both a soil and rock type rich in Fe and Al contents and is considered to be formed via intensive and prolonged weathering of the underlying parent rock. Kumar and colleagues employed Ni laterite powder from Tiebaghi in New Caledonia for CNTs and CNSs syntheses via CVD using ethylene as a carbon source [68]. In the used laterite, the major micro-contents found were goethite, FeO(OH), and hematite (Fe 2 O 3 ) along with a minor amount of phyllosilicates.…”

Development of Microstructured Carbon Coatings by Substrate-Catalytic CVD

“…Ni and Fe are known catalysts for CVD growth of carbon nanotubes or other carbon nanostructures [17], and it is possible to observe a few such filamentous structures (Figure 7c, in orange). However, the formation of catalysts chunks, which cannot catalyze CNTs growth, may lead to further coating by amorphous carbon [18] (Figure 7c, in yellow). Then, the amorphous carbon grows preferably in clusters, increasing in size until carbon spheres are formed.…”