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

Abstract

Abstract 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.