Gas-phase photocatalytic activity of nanostructured titanium dioxide from flame aerosol synthesis

Abstract

The experimental evaluation of gas-phase photocatalytic activity of a TiO2 nanopowder synthesized in a flame aerosol reactor was carried out in photocatalytic oxidation (PCO) of volatile organic compounds (VOCs). The nanopowder has an average particle size of 13nm, anatase content 97wt.% and the specific surface area of 102m2g−1. The performance was compared to the benchmark photocatalyst, the commercial pyrogenic titania P25, Evonik, with the average particle size of 21nm. The full-factorial experiments were carried out varying contact times, concentrations of pollutants and temperatures in continuous gas-flow mode degrading aliphatic acrylonitrile (AN) and aromatic toluene. Higher conversions at more stable performance were observed for the flame aerosol synthesized photocatalyst in degradation of both pollutants. While the primary particle size and specific surface area present the apparent reasons for improved PCO performance in adsorbable AN, these parameters cannot do the same in oxidation of poorly adsorbable toluene: the superior generation of hydroxyl radicals and, therefore, advanced oxidative activity are proposed as explanation. The intense dehydration of reduced size anatase crystallites at elevated temperature (130°C) presumably resulted in decreased OH-radicals production along with the improved desorption of HCN, the PCO by-product of AN. The safe performance is thus requiring lower operational temperatures. Slower deactivation and faster restoration of catalytic activity of flame aerosol synthesized catalyst under UV-A-radiation are discussed.