Efficiency of new ozone filters for NO2 sensing and air depollution

Specific filters can be used up-stream with metal oxide (MOX) gas sensors to trap ozone and allow the selective detection of NO2. These filtering media are based on nanoporous matrices doped with indigo-carmine that reacts selectively with O3. The nanoporous materials, produced via the sol-gel process using functionalized silicon alkoxides as precursors, are tailored for the trapping of O3. Depending on the nature of the filter, it is possible to entirely trap O3 and allow NO2 to partially pass over a certain range of concentration. For air depollution purpose, selected filters that efficiently trap both O3 and NO2 were exposed to harsh conditions under high concentrations of O3 (350-475 ppb) and humidity (RH: 72%, T = 21 °C). Their trapping efficiency and lifetime are determined and compared with those of activated carbon.