Surface interactions and mechanistic studies of 2,4-dichlorophenoxyacetic acid degradation by catalytic ozonation in presence of Ni/TiO2

Surface modifications of catalysts (TiO2 and Ni/TiO2) were studied after ozonation using isoelectric point determination (IEP) and X-ray photoelectron spectroscopy (XPS) techniques. The catalysts were tested in the degradation of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in aqueous solution. According to the results, the initial activity of Ni/TiO2 catalysts was 26% higher compared with the conventional ozonation. This behavior was explained in terms of a change in the surface chemical composition of the catalysts after ozonation, supported by XPS results in the region O1s and Ti2p. In general, the oxidation of metallic Ni to NiO, the formation of ∗Ti4+ and ∗O species in the Ni/TiO2 (P) catalyst, and the presence of abundant –OH groups in the catalytic surface was observed.

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► Two phases (NiO/Ni) present on TiO2 can favor ozone decomposition.
► The highest catalytic ozonation initial rates were obtained with Ni/TiO2 catalysts.
► The mechanism of ozonation with Ni/TiO2 is a synergic effect between OH and O3.
► The ozone changed the surface and catalytic properties of catalysts.