Humidity impact on photo-catalytic degradation: Adsorption behavior simulations and catalytic reaction mechanisms for main gaseous pollutants in papermaking industry
2020
Lin, Zhifeng | Tong, Xin | Shen, Wenhao | Roux, J. C. | Xi, Hongxia
To adopt cleaner production technology of photo-catalysis in papermaking industry and improve environmental sustainability, it is essential to understand the impact of ambient humidity on photo-catalytic degradations of gaseous pollutants. This study used TiO₂ colloid as catalyst to study the effects of ambient humidity (30–60%) on the photo-catalytic degradations of formaldehyde (HCHO), benzene (C₆H₆), and hydrogen sulfide (H₂S) generated by papermaking industry. Via adsorption behavior simulations, using density functional theory (DFT) and catalytic reaction mechanisms, the effects of humidity were further investigated. The following results were found: (1) With increasing humidity, the degradation of HCHO was inhibited, because the ambient H₂O content exceeded the demand for hydroxyl radicals produced by H₂O, which led to competitive adsorption. (2) For C₆H₆, an optimum humidity of 40% was identified during the degradation process, which could be attributed to the improved catalytic reaction and the subsequent excessive H₂O content. (3) For H₂S, unlike the negative action for HCHO and the first positive and then negative actions for C₆H₆, with increasing humidity, the H₂S degradation was promoted. This indicated that the large demand for hydroxyl radicals produced by H₂O promoted the H₂S catalytic reaction. Combining experimental, simulation, and theoretical results for these different gaseous pollutants provides sufficient information to understand the impact of humidity on the photo-catalytic oxidation degradation process.
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