Efficiency of new ozone filters for NO$_2$ 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 O$_3$. The nanoporous materials, produced via the sol-gel process using functionalized silicon alkoxides as precursors, are tailored for the trapping of O$_3$. Depending on the nature of the filter, it is possible to entirely trap O$_3$ and allow NO$_2$ to partially pass over a certain range of concentration. For air depollution purpose, selected filters that efficiently trap both O$_3$ and NO$_2$ were exposed to harsh conditions under high concentrations of O$_3$ (350–475 ppb) and humidity (RH: 72%, T = 21 °C). Their trapping efficiency and lifetime are determined and compared with those of activated carbon.