| Odorous compounds are of environmental concern because of their adverse effects on ecological environment and human health. They can cause health symptoms even in very small amounts. Odor pollution has been identified as one of seven environmental hazards in the world. Consequently, Odor pollution control and treatment have attracted great concern as public complaints to odor increased rapidly in recent years. Photocatalytic oxidation technology is considered to be a promising technology for odor treatment that carried out at ambient temperatures and pressures, with the specific advantage that no chemical oxidants have to be produced.In this paper, photocatalytic degradation of low concentration (lower than 3.0 ppmv) gaseous dimethyl sulfide (DMS) over Degussa P25-TiO2 films under LED lamps irradiation in a homemade plate-type reactor was investigated. Effects of catalyst loading, initial concentration of DMS, gas flow rate, light wavelength and intensity, temperature, and relative humidity on the removal efficiency and reaction rate were discussed in detail.Gas Chromatography-Flame Photometric Detector (GC-FPD), Solid Phase Micro Extraction-Gas Chromatography-Mass Spectrometry (SPME-GC-MS) combined Ion Chromatogram (IC) were used to characterize gas-phase product and surface-bound species to provide evidence for the proposed mechanism during heterogeneous photochemical reaction of dimethyl sulfide, respectively. It was of particular interest to find a new detected intermediate-product methyl mercaptan that was significantly affected by light sources selectivity and relative humidity. Unimolecular L-H kinetic model can be to used to describe the dimethyl sulfide photocatalytic degradation process when the mass transfer step was negligible. The reaction mechanism as well as a specific pathway were proposed.Firstly, LED lamps were effective lights instead of the gas charge lights for the photocatalytic degradation of sulfur-containing odor compound. DMS removal efficiency increased with the enhancement of catalyst loading from 5.0 to 36.0μg·cm-2 and the maximum of 97.6% was achieved. Under the present condition, room temperature of 21.6℃and ambient relative humidity of 47.5% were more appropriate to the photocatalytic degradation of DMS than lower temperature of 12.1℃and lower RH of 10.9-29.8%. We noted that DMS removal efficiency was also affected significantly by initial concentration and gas flow rate. It was found that the increase of catalyst loading, light intensity and the decrease of gas flow rate were effective methods to improve the removal efficiency.Secondly, methyl mercaptan, dimethyl disulfide, dimethyl sulfoxide and dimethyl sulfon were detected as gas-phase reaction products. However, the exclusive surface products extracted from catalyst was sulfate. It was confirmed that short light wavelength and high light intensity as well as relative humidity of 47.5% not only did benefit for the removal efficiency of DMS, but also helped the further oxidation of intermediate product methyl mercaptan. It was also found that the reaction matches unimolecular L-H kinetic model. The reaction rate constant k and the Langmuir adsorption constant K was 0.5083 mg/m2/s,0.1749 m3/mg under the irradiation of 367 nm LED light at 21.6℃with the relative humidity of 22.0% when the mass transfer step was negligible, respectively. Mass transfer controlling stage played an important part when flow rate was low (<3.4×10"7 m3/s) while chemical reaction controlling stage was dominant at high flow rate (>6.8×10-7 m3/s). Consequently, detailed photocatalytic DMS degradation pathways were proposed, starting with TiO2(h+) or·OH,HO2·mediated DMS oxidation and followed by C-S bond cleavage, S-oxidation and C-oxidation. Reaction of CH3S·with·H and the further degradation of dimethyl disulfide was the main pathway for the formation of methyl mercaptan.
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