Kinetic analysis on photocatalytic degradation of gaseous acetaldehyde, ammonia and hydrogen sulfide on nanosized porous TiO₂films

Abstract

The characteristics of the UV illumination-assisted degradation of gaseous acetaldehyde, hydrogen sulfide, and ammonia on highly active nanostructured-anatase and rutile films were investigated. It was found that the anatase film showed a higher photocatalytic activity than the counterpart did, however, the magnitude of difference in the photocatalytic activity of both films decreased in the order ammonia4acetaldehyde4hydrogen sulfide. To elucidate the reasons for the observation, the adsorption characteristics and the kinetics of photocatalytic degradation of the three reactants on both films were analyzed. The adsorption analysis examined using a simple Langmuir isotherm, showed that adsorbability on both films decreased in the order ammonia4acetaldehyde4hydrogen sulfide, which can be explained in terms of the decreasing electron-donor capacity. Acetaldehyde and ammonia adsorbed more strongly and with higher coverage on anatase film (1.2 and 5.6 molecules/nm 2 , respectively) than on rutile (0.6 and 4.7 molecules/nm 2 , respectively). Conversely, hydrogen sulfide molecules adsorbed more strongly on rutile film (0.7 molecules/nm 2 ) than on anatase (0.4 molecules/nm 2 ). Exposure to UV light illumination brought about the photocatalytic oxidation of the three gases in contact with both TiO 2 films, and the decrease in concentration were measured, and their kinetics are analyzed in terms of the Langmuir-Hinshelwood kinetic model. From the kinetic analysis, it was found that the anatase film showed the photocatalytic activities that were factors of $8 and $5 higher than the rutile film for the degradation of gaseous ammonia and acetaldehyde, respectively. However, the activity was only a factor of $1.5 higher for the photodegradation of hydrogen sulfide. These observations are systematically explained by the charge separation efficiency and the adsorption characteristics of each catalyst as well as by the physical and electrochemical properties of each reactant. r

Influence of TiO2 hydrophilicity on the photocatalytic decomposition of gaseous acetaldehyde in a circulated flow reactor

“…The synergic effect comprising adsorption and photocatalytic decomposition of acetaldehyde on the supercritically treated TiO 2 -activated carbon composites was reported by others [19]. Adsorption was also proposed as one of the steps in the mechanism explaining increased photodecomposition of ammonia, acetaldehyde and hydrogen sulfide on nanosized porous TiO 2 film [18].…”

“…Various photocatalytic materials have been already tested for acetaldehyde decomposition [13][14][15][16][17][18]. It is commonly accepted that the photocatalytic activity of TiO 2 nanoparticles strongly depends on the specific surface area, phase composition, crystal size, etc.…”

Odor Control using Novel Biofiltration Media with a Hydroxyl Generator Polisher

“…Very few studies have directly addressed odor removal by photocatalysis. One study did address the removal of several odor causing compounds including ammonia and hydrogen sulfide (Sopyan, 2007). Most odor causing compounds are reduced and are therefore relatively easy to oxidize in comparison to a compound such as trichloroethylene.…”

Using physical–chemical properties of reactants to estimate the performance of photocatalytic oxidation air cleaners

“…Hydroxyl radicals are also capable of migrating and carrying out the direct destruction of absorbed VOCs on the catalyst surface: (9) Accordingly, it is obvious that the PCO mechanism is based on hydroxyl radical attacks and OH radicals play an important role in the oxidizing organic compounds. The hydroxyl radicals are the most reactive elements and able to virtually oxidize most VOC molecules and degrade them to harmless products such as CO and…”