Cluster formation mechanisms of titanium dioxide during combustion synthesis: Observation with an APi-TOF

ABSTRACT

Few studies reported the formation of Ti-containing clusters in the initial stages of TiO₂ flame synthesis. The conversion from synthesis precursor to TiO₂ monomers was commonly assumed to take place through global reaction such as thermal decomposition and/or hydrolysis at high temperatures. More recent studies have been able to identify stable intermediates of Ti-containing monomers, most commonly Ti(OH)₄, as the final step before the formation of TiO₂. However, no larger Ti-containing cluster formation mechanisms or interactions between these monomers have been tracked. To investigate cluster formation pathways of TiO₂ during flame synthesis, Charged clusters were measured in an atmospheric pressure interface time-of-flight (APi-TOF) mass spectrometer. TiO₂ nanoparticles were synthesized by adding titanium tetraisopropoxide (TTIP) precursor to a premixed CH₄/O₂/N₂ flat flame aerosol reactor. Pure TiO₂ clusters were not detected by the APi-TOF. Results from measured mass spectra and mass defect plots show that for positively charged clusters, the abstraction of CH₂ groups occurs simultaneously with the clustering of larger intermediate organometallic species. For negatively charged clusters, NO_x formation pathways in the flame may play a role during the initial stages of TiO₂ formation, since a lot of Ti-containing clusters were attached with nitrate-related species. These research findings provide insights on quantum dot synthesis and molecular doping where rapid dilution of the flame synthesized nanoparticles is needed to better control the particle size and chemical composition. The possible influences of and potential artifacts brought by the dilution system on observing the incipient particle formation in flames were also discussed.

© 2017 American Association for Aerosol Research

EDITOR:

• Mark Swihart

Funding

This work is supported by the Solar Energy Research Institute for India and the United States (SERIIUS), funded jointly by the U.S. Department of Energy (Office of Science, Office of Basic Energy Sciences, and Energy Efficiency and Renewable Energy, Solar Energy Technology Program, under Subcontract DE-AC36-08GO28308 to the National Renewable Energy Laboratory, Golden, Colorado) and the Government of India, through the Department of Science and Technology under Subcontract IUSSTF/JCERDC-SERIIUS/2012. The work was also supported by Academy of Finland via Center of Excellence project in Atmospheric Sciences (272041) and European Commission via ACTRIS2 (654109).