Narrow Results

Carbon nanotubes (CNTs) were synthesized by a low-cost floating catalyst (FC) chemical vapor deposition (CVD) method in a horizontal reactor. It was found that iron (III) chloride (FeCl₃) is a high efficient FC precursor for methane CVD to grow CNTs. In this study, the effects of reaction temperature and flow ratio of methane to nitrogen (CH₄:N₂) on the morphology of the CNTs were investigated. The morphological analysis by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) revealed that increasing the reaction temperature and flow ratio of CH₄:N₂ grew CNTs of larger diameters. Energy dispersive X-ray (EDX) and thermogravimetric analysis (TGA) were employed to study the purity of the produced CNTs. As shown by the TGA, the highest yield of 74.19% was recorded for the CNTs grown at 1000°C and flow ratio CH₄:N₂ of 300:200.

Multi-walled carbon nanotubes (MWCNTs) were prepared by floating catalyst (FC) method, using methane as a carbon source and iron (III) chloride (FeCl₃) as a catalyst precursor, followed by purification with air oxidation and acid treatment. The as-grown and purified MWCNTs were characterized by transmission electron microscopy, scanning electron microscopy, energy dispersive spectroscopy, thermogravimetry analysis and Raman spectroscopy. The average inner and outer diameters of the MWCNTs were 25 and 39 nm, respectively. The purity and yield of the purified MWCNTs were more than 92% and 71% weight fraction, respectively.

Conversion of methane into high value added chemicals and clean fuels such as methanol under mild conditions is of great importance to the chemical industry. However, traditional thermal catalytic of methane always suffer from harsh reaction conditions and poor product selectivity. Here, we reported photoelectrocatalytic oxidation of methane over BiVO₄/Au/FeCo–LDH under simulated sunlight illumination with ambient‘ conditions. The results demonstrate that BiVO₄/Au/FeCo–LDH exhibits excellent photoelectrochemical properties and catalytic activity. The double-layer capacitance ($C_{dl}$) value of BiVO₄/Au/FeCo–LDH is estimated to be 3.00mF$\cdot$cm${}^{-2}$, indicating its considerable electrochemical active areas. The photocurrent density of BiVO₄/Au/FeCo–LDH reaches up to 1.46mA$\cdot$cm${}^{-2}$ in methane atmosphere. The methanol yield for photoelectrocatalytic oxidation of methane is 8.46 times that of pure BiVO₄, and the corresponding Faraday efficiency is 56.09%. Finally, the reaction mechanism of photoelectrocatalytic conversion of methane to methanol based on hydroxyl radical and methyl radical as intermediate products is proposed. Our finding is expected to provide new insight for the design of active and selective catalysts toward photoelectrocatalytic conversion of methane.