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Humidity impact on photo-catalytic degradation: Adsorption behavior simulations and catalytic reaction mechanisms for main gaseous pollutants in papermaking industry

Lin, Zhifeng, Tong, Xin, Shen, Wenhao, Roux, Jean-Claude, Xi, Hongxia
Journal of cleaner production 2020 v.244 pp. 118863
adsorption, benzene, catalysts, density functional theory, environmental sustainability, formaldehyde, humidity, hydrogen sulfide, hydroxyl radicals, oxidation, photocatalysis, pollutants, production technology, pulp and paper industry, reaction mechanisms, titanium dioxide
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.