One-step combustion synthesis of carbon-coated nanoparticles using multiple-diffusion flames

Carbon-coated nanoparticles, such as silica (SiO₂) and titania (TiO₂) can be used in a wide variety of applications: water splitting, polymer fillers, pigments, precursors for carbide formation, and as an electrode for Li-ion batteries. We propose a novel process for the synthesis of carbon-coated nanoparticles based on the use of multiple-diffusion flames, also known as a multi-element diffusion burner (MEDB, Hencken Burner). Ethylene (C₂H₄) is used as the precursor carrier gas, which, in a one-step process, enables the growth of carbon-coated nanostructures. The global equivalence ratio is maintained at 0.5, thus providing an oxygen-rich environment. The nanoparticles investigated using this setup are silica and titania, where hexamethyldisiloxane (HMDSO) and titanium tetraisopropoxide (TTIP) are used as these nanoparticles- precursors, respectively. The crystal phase and size of the silica and titania nanoparticles are determined using x-ray diffraction (XRD). The nanoparticles are further characterized using a Raman microspectrometer, where the patterns obtained from the spectrometer are also used to validate the growth of carbon on the nanoparticles. Thermogravimetric analysis is performed to determine the percentage of carbon in the samples. The morphology and crystal structure of the samples are characterized using high-resolution transmission electron microscopy (HRTEM), with elemental mapping. The titania particle size ranged from 30 to 50 nm with a uniform carbon coating of 3 to 5 nm, as observed by HRTEM. The Raman pattern confirmed the growth of a graphitic structure in the coated particles, with the carbon content measured at 25% using TGA. The use of MEDB to produce carbon-coated nanoparticles is scalable, and this process could possibly be extended to carbon-coat a wide range of nanoparticles.