Flame Synthesis and Coating of Nanostructured Particles in One Step
A. Teleki, B. Buesser, M. Heine, F. Krumeich, M.K. Akhtar, S.E. Pratsinis
ETH Zürich, CH
Keywords: coating, photoactivity, gas-phase, flame
Abstract:Coating of flame-made nanostructured particles has been achieved in one step by a scalable aerosol process. Rutile TiO2 particles made by flame spray pyrolysis (FSP) were coated in a single step with SiO2 layers in an enclosed flame reactor. This in situ particle coating was accomplished by a hollow ring delivering hexamethyldisiloxane (HMDSO) vapor (precursor to SiO2) through multiple jets in swirl cross-flow to Al-doped nanostructured rutile TiO2 aerosol freshly made by FSP of a solution of titanium tetraisopropoxide and aluminum sec-butoxide in xylene. The effect of HMDSO injection point, vapor concentration and coating vapor – aerosol mixing intensity on product particle morphology was investigated. The titania particles were uniformly SiO2-coated with controlled and uniform thickness at a production rate of about 30 g/h and exhibited limited, if any, photoactivity. In contrast, spraying and combusting equivalent mixtures of the above Si/Al/Ti precursors in the above reactor (without delivering HMDSO through the hollow ring) resulted in particles segregated in amorphous (SiO2) and crystalline (TiO2) domains which exhibited high photocatalytic activity.