Ozone-assisted photocatalytic degradation of gaseous toluene from waste air stream using silica-functionalized graphene oxide/ZnO coated on fiberglass: performance, intermediates, and mechanistic pathways

Abstract

The present study focused on the potential of an ozone-assisted photocatalytic process using the catalyst silica-functionalized graphene oxide/ZnO coated on fiberglass (Si-GO/ZnO-FG) in the removal of toluene from waste air stream. Here, a comparative examination was performed in terms of toluene removal efficiency in the photocatalytic process (UV/Si-GO/ZnO-FG) and photocatalytic ozonation (O 3 / UV/Si-GO/ZnO-FG). The gaseous intermediates resulting from degradation of toluene by different processes were analyzed using GC-MS. The results of this study indicated that with the addition of ozone to the UV/Si-GO/ZnO-FG process, toluene removal increased significantly from 76.18 to 87.8%. The reason for this incremental efficiency can be explained by the fact that with the addition of ozone, the production rate and the extent of hydroxyl radical (OH •) production grow significantly; thereby, more pathways are developed for toluene degradation. The major byproducts in toluene oxidation by photocatalytic and photocatalytic ozonation processes include formic acid, acetic acid, benzyl alcohol, benzaldehyde, p-cresol, hydroquinone, and benzoic acid. Given the intermediates and the dominant oxidants detected in the aforementioned process, the possible toluene degradation pathway by the utilized process was suggested.

Investigation of photocatalytic-proxone process performance in the degradation of toluene and ethyl benzene from polluted air

“…The degraded products and intermediates of toluene and ethylbenzene also hindered the adsorption to the reactive sites of the photocatalyst when applied at high concentrations to the catalyst. In Jonidi et al study that investigated the degradation of gaseous toluene from waste air by ozoneassisted photocatalytic, the results indicated that efficiency of process in 50 ppm (lowest concentration) was 87.3% and when toluene concentration increased to 200 ppm, the efficiency of process decreased to 52.6% 45 .…”

The heterogeneous reactions of toluene/O3/NH3 on hematite nanoparticles: the impact of light illumination on organic ammonium salt formation

“…[70][71][72] At the same time, the generated benzyloxy radicals could be oxidized to benzaldehyde and eventually form benzoic acid. 73 In addition, when O 3 was introduced together to the system, besides benzyl radical species, highly reactive species (hydroxyl and oxygen radicals) were also produced on the particle surface. 73,74 These active oxygen species as well as O 3 could attack the methyl groups of the aromatic ring, which by cracking the α-H bond in the methyl groups of toluene formed benzyl alcohol.…”

“…73 In addition, when O 3 was introduced together to the system, besides benzyl radical species, highly reactive species (hydroxyl and oxygen radicals) were also produced on the particle surface. 73,74 These active oxygen species as well as O 3 could attack the methyl groups of the aromatic ring, which by cracking the α-H bond in the methyl groups of toluene formed benzyl alcohol. The alcohol hydroxyl groups of benzyl alcohol were reductive; in the presence of these highly reactive radicals, the C-OH groups could remove hydrogen atoms to produce benzaldehyde, which, in turn, was further converted into benzoic acid in the end.…”

Hazardous wastes treatment technologies

“…Jafari, Arfaeinia, Ramavandi, Kalantary, and Esrafily (2019) reported an ozone‐assisted photocatalytic process for the removal of toluene from waste air stream over silica‐functionalized graphene oxide/ZnO supported on fiberglass (Si‐GO/ZnO‐FG). Results demonstrated that the addition of ozone improved the toluene removal efficiency from 76.18% to 87.8%.…”