Synthesis of carbon nanotubes via CCVD of ethylbenzene over SrFe12O19/SiO2 oxide and their application for photodegradation of the remazol red dye

Carbon-based materials have stood out due to their variety of applications such as photocatalysis. Thus, strontium hexaferrite dispersed in silica was prepared by the Pechini method and used as a catalyst in the ethylbenzene reaction to produce carbon filaments and subsequent application in the photodegradation of the remazol red dye. The presence of SrFe12O19, α-Fe2O3 and amorphous silica phases was confirmed in the XRD (X-ray diffraction), Raman and XPS (X-ray photoelectron spectroscopy) analysis. The SEM (scanning electron microscopy) and TEM (transmission electron microscopy) results of the fresh oxides indicate cluster and sponge-like morphology. The formation of carbon filaments was observed by SEM analysis as a result of catalytic chemical vapor deposition (CCVD) of ethylbenzene. TEM images confirm the generation of multi-walled carbon nanotubes with an average diameter of 27.9 nm. Besides the presence of the SrFe12O19 and SiO2 phases, the diffractograms of the samples after the reaction shows the formation of graphite carbon and Fe0, confirming the reduction of α-Fe2O3 which was also verified in the TPR-H2 profile. The growth of nanotubes occurs from metallic iron, considering that the tip of the tube contains only iron, according to EDS (energy-dispersive X-ray spectroscopy) results. The Raman spectrum exhibited the characteristic D and G bands of carbon, where the ID/IG ratio decreased with increasing temperature. The reaction with the best catalytic performance achieved an average ethylbenzene conversion of 99 % and was more selective to ethene (∼93 %) at 650 °C. Furthermore, it was possible to carry out a simple theoretical-computational study regarding the distribution of the sites in a 2D plane by constructing maps and proposing a mechanism for the formation of carbon nanotubes from the ethylbenzene conversion. Finally, the obtained materials were applied in the remazol red dye degradation, achieving complete degradation in 15 min for the material synthesized at 650 °C. [Display omitted] •Carbon nanotubes were obtained by ethylbenzene conversion over SrFe12O19/SiO2.•The nanotube formation was favored with increasing temperature.•The tip of the tube containing Fe0 followed the nanotubes growth.•SrFe12O19/SiO2 650 °C exhibited ∼100 % degradation in 15 min for remazol red dye.