| Layered titanoniobates now drawn increasing attention for its unique structure, known as an ion-exchangeable compound, therefore, their catalytic properties can be improved by intercalating special elements and oxide particles into the interlayer via ion-change, pillaring as well as exfoliated reorganization.The adsorption feature and photocatalytic oxidation activity were evaluated for mercaptan in methane over the catalysts M0.5TiNbO5 (M= Mn,Ni), which are prepared through Mn2+ and Ni2+ ion-exchange of KTiNbO5 synthesized by the hydrothermal method, were evaluated through infrared spectroscopy techniques. The catalysts were characterized by means of powder X-Ray Diffraction (XRD), UV-visible Diffuse Reflectance Spectroscopy (UV-vis DRS), High Resolution Transmission Electron Microscope(HRTEM).The results indicate that hydrothermal method can not only ensure the layered structure of the samples, but also significantly reduce the synthesis temperature(235℃), increase the surface area of samples(54.8m2g-1) and obtain a larger distance(0.960nm) between the layers compared to the method of high-temperature solid-state. KTiNbO5 has a continuous absorption band in the ultraviolet and its absorption band edge is at 365nm. After KTiNbO5 is modified by Mn2+ ion exchange, its absorption band have a red-shift and its absorption band edge is at 415nm. After KTiNbO5 is modified by Ni2+ ion exchange, the UV-vis DRS shows two absorption bands. One is in the Ultraviolet. Its rising absorption band edge is at the around 370 nm. The other appears in the visible region. Its rising absorption band edge is at the around 525nm. The results reveal that the band-gap energy is obviously reduced and the absorption wavelength is shifted from UV light to visible light, when the host layer KTiNbO5 is modified by Mn2+ or Ni2+ through ion-exchange.In dynamic state, both KTiNbO5 and Mn0.5TiNbO5 have little adsorption activity for mercaptan, however, Mn0.5TiNbO5 has photocatalytic oxidation activity for mercaptan under visible light and UV light irradiation. The results show that Methanethiol is converted into HO-SO-(sulfinic acids) and then adsorbed on the surface of Mn0.5TiNbO5; Not only the Ni0.5TiNbO5 emerged well adsorption activity but also photocatalytic oxidation activity for mercaptan in methane. Due to the C-S bond (methyl mercaptan) is cleavaged in natural light radiation, it reacts with CH3-SOO- in sulfinic acids and produces sulfurous esters.This also results from the absorption of the visible light of the catalyst. After the catalyst Ni0.5TiNbO5 is absorbed, the same results obtained for the samples under UV light irradiation. It suggests that the catalysts have different adsorption performance and photocatalytic oxidation activity for mercaptan in methane, With different cations into the interlayer.NiO particles were intercalated into the interlayer of the compounds, the catalyst's band-gap energy was changed significantly, which emerged a significant response to visible light, therefore, enhanced the photocatalytic activity of the catalyst. however, in the later experiments of adsorption methyl mercaptan from methane gas and photocatalytic,the results were not as expected,the adsorption of mercaptan and the photocatalytic activity were very weak. Which may mainly because in the process of preparation, the organic matter which between layers is not fully removed and occupy the active sites, while NiO was only accounted for less active sites,this may lead to its weaker performance in its adsorption and photocatalytic activity.A preliminary exploration was utilized to investigated the peel of layered KTiNbO5 in this experiment, the results demonstrated that the acidificated layered Titanoniobate could be stripped and had little change in spectral response before and after the stripFigure [31] Table [11] Reference [61]... |
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