(192b) Oxidation of NOx over Carbon Nanotube-TiO2 Photocatalysts

Nitrogen oxides (NO_x) are common compounds that can have detrimental environmental effects, originating from combustion reactions, which result in high amounts of nitrogen oxide (NO) and relatively lower amounts of nitrogen dioxide (NO₂), the most common forms of NO_x. In order to reduce concentrations of NO_x in the air, heterogeneous photocatalysis conducted with semiconductors has been studied as an effective method for NO_x abatement. Titanium dioxide (TiO₂) is an attractive semiconductor used in photocatalysis. The large band gap of TiO₂ limits viable photons to the UV spectra, resulting in a large influx of lower energy photons that cannot be used to initiate a photocatalytic reaction. TiO₂ can be coupled with multiwalled carbon nanotubes (MWCNTs) to create a metallic-semiconductor heterojunction, increasing electron-hole recombination time, improving the pollution abatement by increasing the fraction of incident photons that partake in photocatalysis. In this work we evaluate P25 against a novel TiO₂-MWCNT composite synthesized via a modified sol-gel method for its ability to completely degrage NO_x in a laminar-flow reactor at different concentrations and humidity levels. We have utilized the “De-NO_x index” to measure the photonic efficiency during NO_x abatement, indicating the ability of a photocatalytic material to completely degrade NO to nitrates. This work illustrates the superior performance of MWCNT-TiO₂ photocatalysts in photocatalytic oxidation of NO_x under continuous flow. The MWCNT-TiO₂ composite shows significantly increased photonic efficiency compared to P25, especially at humidity levels representative of outdoor conditions.