A Study On HTiNbO₅ Nanosheets And Photocatalytic Degradation Of Rhodamine B Under Visible Light

Photocatalytic degradation of organic pollutants under visible light is an important study in environment, chemistry and materials science, and it is of great importantance both for theoretical research and practical application. Layered compounds have attracted much attention due to a wide variety of structural and electronic properties.In this work, novel mesoporous nanohybrids were successfully synthesized through an exfoliation-reassemble-calcination method. The resulted samples were characterized in detail by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, photoluminescence spectra (PL) and N2 adsorption-desorption measurements. The catalytic activities of the obtained samples were evaluated by the photodegradation of RhB solution under visible light irradiation, and the intrinsic relationships between product structures and visible-light activities were carefully disclosed. The photocatalytic mechanism was also briefly discussed. The main contents are summarized as follows:1. Thermostable nitrogen-doped HTiNbO5 nanosheets with a high visible-light photocatalytic activityNitrogen-doped HTiNbO5 nanosheets have been sucessfully synthesized by first exfoliating layered HTiNbO5 in tetrabutylammonium hydroxide (TBAOH) to obtain HTiNbO5 nanosheets and then heating nanosheets with urea. The resulted samples were characterized by XRD, TEM, SEM, XPS, UV-vis and N2 adsorption-desorption measurements. It was found that N-doping could lead to a much higher thermostability of the layered structure and the visible light response. The doped nitrogen atoms were mainly located in the interstitial site of TiNbO5-lamellars and chemically bound to the hydrogen ions. Compared with N-doped HTiNbO5, N-doped HTiNbO5 nanosheets had a much larger specific surface area and richer mesoporosity due to the rather loosely and irregularly arrangement of titanoniobate nanosheets. Both N-doped layered HTiNbO5 and HTiNbO5 nanosheets showed a very high visible-light photocatalytic activity for the degradation of Rhodamine B (RhB) aqueous solution. Moreover, due to the considerably larger surface area, richer mesoporosity and stronger acidity, N-doped HTiNbO5 nanosheets had a even higher activity than N-doped HTiNbO5 although the latter had a stronger absorption in the visible region. The dye molecules were mainly degraded to the aliphatic organic compounds and partially mineralized to CO2 and/or CO, rather than being simply decolorized. The effect of photosensitization was insignificant and RhB was degraded mainly via the typical photocatalytic reaction route. Two different reaction routes for the photodegradation of RhB under visible light irradiation over N-doped HTiNbO5 nanosheets were proposed. The present method can be extended to a large number of layered metal oxides that have the characteristics of intercalation and exfoliation, thus providing new opportunity for the fabrication of highly effective and potentially practical visible-light photocatalysts.2. Novel Mesoporous NiO/HTiNbO5 Nanohybrids with a High Visible-Light Photocatalytic Activity and a good BiocompatibilityMesoporous nanohybrids of NiO nanoparticles and HTiNbO5 nanosheets have been successfully synthesized by first exfoliating layered HTiNbO5 in tetrabutylammonium hydroxide (TBAOH) to obtain HTiNbO5 nanosheets, then reassembled with nickel precursor and finally heated with urea. The resulted samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, photoluminescence spectra (PL) and N2 adsorption-desorption measurements. It was found that the as-prepared nanohybrids had a relatively larger interlayer spacing of 1.05 nm. After calcination, the titanoniobate nanosheet was still maintained and the pore size of the resulted nanohybrids became larger. Compared with original HTiNbO5, the obtained nanohybrids were mesoporous with a greatly expanded surface area (-75-115 m2g-1), a much strengthened absorption in UV light region and a visible-light response. The nickel atom was present in the form of Ni-O in the nanohybrid, and NiO nanoparticles were homogeneously distributed with an average particle size of 2-3 nm, giving rise to the visible light response. The catalytic activities of the obtained samples were evaluated by the photodegradation of RhB solution under visible light irradiation. The introduction of urea during the calcination process not only increased the thermal stability and surface area, but also decreased the rate of recombination of photogenerated holes and electrons, leading to a greatly enhanced photocatalytic activity of the resulted nanohybrids. The dye molecules were mainly degraded to the aliphatic organic compounds and partially mineralized to CO2 and/or CO, rather than being simply decolorized. In addition, the results of cell viabilities of HepG2 cells showed that the as-prepared sample had a good biocompatibility.3. Nitrogen-doped Mesoporous Nanohybrids of TiO2 nanoparticles and HTiNbO5 nanosheets with a high Visible-light Photocatalytic ActivityNitrogen-doped mesoporous nanohybrids of TiO2 nanoparticles and HTiNbO5 nanosheets have been successfully synthesized by first exfoliating layered in tetrabutylammonium hydroxide (TBAOH) to obtain HTiNbO5 nanosheets, then reassembled with TiO2 colloids and finally heated with urea in air at 450℃. The resulted samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), X-ray photoelectron spectroscopy (XPS), UV-vis spectroscopy, laser Raman spectroscopy (LRS) and N2 adsorption-desorption measurements. It was found that the TiO2 nanoparticles were existed as anatase phase and the titanoniobate nanosheets were still maintained after nitrogen doping. The obtained nitrogen-doped nanohybrid showed a greatly expanded surface area with a mesoporous structure and the doped nitrogen atoms were located in the interstitial sites of TiO2, giving rise to the visible light response. The catalytic activities of the obtained samples were evaluated by the photodegradation of rhodamine B (RhB) solution under visible light irradiation. The obtained N-doped nanohybrid had a higher activity than N-doped HTiNbO5 nanosheets and N-doped TiO2, indicating the synergetic effect of TiO2 nanoparticles and HTiNbO5 nanosheets. The dye molecules were mainly degraded to aliphatic organic compounds and mostly further mineralized to CO2 and/or CO, rather than being simply decolorized.