Air pollution with nitrogen oxides (NOx) in urban areas poses a significant threat to their inhabitants. Laws have been enacted in order to limit the concentration values of pollutants in the atmosphere. Nevertheless, in urban areas these values are often exceeded. Thus, there is a great interest in developing methods to reduce the concentration of these dangerous contaminants. Photocatalytic NOx conversion is a thought-provoking and attractive way to produce less toxic compounds such as NO3−, N2 or O2. During the past decades, remarkable progress has been achieved in this aspect, and many studies often focus on developing high efficient photocatalysts for NOx conversion. For effectively convert NOx, selective transformation and relevant mechanisms are crucial. Recently, we found that defect engineering in TiO2 and Ti-based catalysts can regulate the NOx transformation pathways at specific reaction channels. A representative work is photocatalytic NOx conversion over a defective Ag-TiO2−x catalyst. Combined in-situ FTIR and ESR studies showed that this nanocomposite is not only superior in visible-light photocatalytic NO conversion compared with commercial P25, but also in inhibiting the production of toxic NO2 via selective production of N2 and O2 originated from high abundant oxygen defects. Another representative work is on Ti-based perovskite structured photocatalysts. We observed that, diverse structured oxygen vacancy contained layered perovskites Bi4Ti3O12 and Pb2Bi4Ti5O18 with enhanced charge separation originated from their ferroelectric nature displayed direct oxidation of NO to NO3- as revealed by FTIR and ESR studies and theoretical investigations of density functional theory (DFT) calculations. The results represent crucial step in photocatalytic NOx conversions, in which effective tuning surface property by introducing defect, tailoring morphology, creating heterojunctions and controlling crystal facets in TiO2 and Ti-based catalysts can significantly improve NOx transformation efficiency and reaction selectivity due to synergetic roles of inhibiting deactivation of catalysts and rapid depletion of photoinduced carriers.

Visible-light-driven conversion of nitrogen oxides at Ti-based photocatalysts: Selectivity and mechanistic insights

256th National Meeting (2018)

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