TiO₂ Nanotubes with Open Channels as Deactivation-Resistant Photocatalyst for the Degradation of Volatile Organic Compounds

Abstract

We synthesized ordered TiO2 nanotubes (TNT) and compared their photocatalytic activity with that of TiO2 nanoparticles (TNP) film during the repeated cycles of photocatalytic degradation of gaseous toluene and acetaldehyde to test the durability of TNT as an air-purifying photocatalyst. The photocatalytic activity of TNT showed only moderate reduction after the five cycles of toluene degradation, whereas TNP underwent rapid deactivation as the photocatalysis cycles were repeated. Dynamic SIMS analysis showed that carbonaceous deposits were formed on the surface of TNP during the photocatalytic degradation of toluene, which implies that the photocatalyst deactivation should be ascribed to the accumulation of recalcitrant degradation intermediates (carbonaceous residues). In more oxidizing atmosphere (100% O2 under which less carbonaceous residues should form), the photocatalytic activity of TNP still decreased with repeating cycles of toluene degradation, whereas TNT showed no sign of deactivation. Because TNT has a highly ordered open channel structure, O2 molecules can be more easily supplied to the active sites with less mass transfer limitation, which subsequently hinders the accumulation of carbonaceous residues on TNT surface. Contrary to the case of toluene degradation, both TNT and TNP did not exhibit any significant deactivation during the photocatalytic degradation of acetaldehyde, because the generation of recalcitrant intermediates from acetaldehyde degradation is insignificant. The structural characteristics of TNT is highly advantageous in preventing the catalyst deactivation during the photocatalytic degradation of aromatic compounds.

Novel photothermocatalytic synergetic effect leads to high catalytic activity and excellent durability of anatase TiO 2 nanosheets with dominant {001} facets for benzene abatement

“…Usually, regeneration of a deactivated photocatalyst is necessary [21]. For example, although Choi et al improved the durability for toluene photodegradation by preparing ordered TiO 2 nanotubes (TNT) to reduce the mass transfer limitation of O 2 molecules, thus hindering the accumulation of carbonaceous residues on TNT surface, TNT still experienced gradual deactivation after recycled several times [26].…”

One-pot synthesis of 3D TiO2-reduced graphene oxide aerogels with superior adsorption capacity and enhanced visible-light photocatalytic performance

“…And then the supernatant solution was analyzed by monitoring the adsorption peak at 665 nm. According to Lambert-Beer law, the absorbance of solution is in direct proportion to its concentration, therefore the MB concentration (C) can be calculated by the equation as follows [14]:…”

Surface Modification of TiO2 for Obtaining High Resistance against Poisoning during Photocatalytic Decomposition of Toluene

“…In previous works, the reaction rate of photocatalytic decomposition of toluene was found to drastically decrease with reaction time, and poisoning of the TiO 2 surface by partially oxidized species of toluene such as benzoic acid or benzaldehyde was found to be responsible for this deactivation phenomenon [18]. Many attempts have been made to alleviate such poisoning problems by modifying the surface structure of TiO 2 [19][20][21][22]. TiO 2 nanotubes were found to facilitate the approach of oxygen molecules toward the surface active sites of TiO 2 compared to thin films consisting of TiO 2 nanoparticles with random shapes, thereby increasing the oxidation rate and reducing poisoning during the photocatalytic oxidation of toluene.…”

“…TiO 2 nanotubes were found to facilitate the approach of oxygen molecules toward the surface active sites of TiO 2 compared to thin films consisting of TiO 2 nanoparticles with random shapes, thereby increasing the oxidation rate and reducing poisoning during the photocatalytic oxidation of toluene. Such methods, however, require significant development before they will be ready for commercial use [20].…”