Flame-coating of titania particles with silica

Abstract

Silica/titania composite particles were prepared by co-oxidation of titanium-tetra-isopropoxide and hexamethyldisiloxane in a co-flow diffusion flame reactor. The influence of precursor composition on product powder characteristics was studied by x-ray diffraction, nitrogen adsorption, electron microscopy, elemental mapping, and energy-dispersive x-ray analysis. The flame temperature was measured by Fourier transform infrared spectroscopy. The evolution of composite particle morphology from ramified agglomerates to spot-or fully coated particles was investigated by thermophoretic sampling and transmission/scanning electron microscopy. At 40-60 wt% TiO 2 , particles with segregated regions of silica and titania were formed, while at 80 wt% TiO 2 rough silica coatings were obtained. Rapid flame-quenching with a critical flow nozzle at 5 cm above the burner nearly halved the product particle size, changed its crystallinity from pure anatase to mostly rutile and resulted in smooth silica coatings on particles containing 80 wt% TiO 2 .

Synthesis of TiO2 nanoparticles containing Fe, Si, and V using multiple diffusion flames and catalytic oxidation capability of carbon-coated nanoparticles

“…The result confirms that SiO2 is formed around the TiO2 sample and is not doped inside the particle. This is consistent with previous result (Teleki et al 2005), however when the concentration of SiO2 is increased significantly (> 40 wt%), the growth of segregated regions of TiO2 and SiO2 occurs.…”

“…To overcome this challenge, TiO2 can be coated with SiO2 to limit the photocatalytic activity of the nanoparticles (Teleki 2009). Teleki et al, (Teleki et al 2005) synthesized silica-titania composites and studied the evolution of composite particle morphology from ramified agglomerates to spot-or fully coated particles. When the silica ratio in the mixture was below 20%, a silica coating layer was observed on the surface of the titania particles.…”

Distinguishing between aggregates and agglomerates of flame-made TiO2 by high-pressure dispersion

“…Fig. 3 shows BET-equivalent particle diameter (circles), crystallite size (triangles) and anatase content (squares) as a function of sintering temperature for 4 h. The anatase content of the "as-prepared" powder is about 87 wt.%, typical for TiO 2 aerosol formation in rapidly cooled oxygen-rich flames [16,24]. The "as-prepared" anatase and rutile crystal sizes are about 24 and 11 nm, respectively, while the d BET = 19 nm.…”

Selective side-chain oxidation of alkyl aromatic compounds catalyzed by cerium modified silver catalysts

“…TEM images of FSP 1%Ag/10%CeO 2 -SiO 2 ( Fig. 5c) showed distinct CeO 2 nanoparticles with the size in the range as indicated by XRD (3 nm, [43] and TiO 2 /SiO 2 made in diffusion flames [44]. The presence of ceria allowed no clear determination of the silver particle size by STEM analysis but no large Ag particles with a size even close to that found for FSP 1%Ag/SiO 2 were observed ( Fig.…”