| Summary: | The performance of CO oxidation over plasmonic Au/TiO<sub>2</sub> photocatalysts is largely determined by the electric discharge characteristics and physicochemical properties of discharge gas. To explore the activation mechanism of Au/TiO<sub>2</sub>, an O<sub>2</sub> and Ar mixture gas as a discharge gas was employed to activate Au/TiO<sub>2</sub>. The photocatalytic activity in CO oxidation over activated Au/TiO<sub>2</sub> was obtained, and the electric discharge characteristics, Au nanoparticle size, surface chemical state, optical property and CO chemisorption were thoroughly characterized. As the O<sub>2</sub> content increases from 10% to 50%, the amplitude of the current pulses increases, but the number of pulses and the discharge power decrease. The photocatalytic activity of Au/TiO<sub>2</sub> rises rapidly at first and then remains constant at 75% when the O<sub>2</sub> content is above 50%. Compared with the discharge gas of 10% and 30% O<sub>2</sub>/Ar, the sample activated by 50% O<sub>2</sub>/Ar plasma possesses less metallic Au and more surface oxygen species and carbonate species by X-ray photoelectron spectroscopy, which is consistent with UV-vis diffuse reflectance spectra and CO chemisorption. The CO chemisorption capacities of the activated samples are the same at a long exposure time due to the approximate Au nanoparticle size observed by transmission electron microscopy. An increase in carbonate species generated from the oxygen species on the surface of TiO<sub>2</sub> is discovered.
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