Fe 3 O 4 /TiO 2 core/shell nanotubes are fabricated via a three-step process. R-Fe 2 O 3 nanotubes are first obtained, and R-Fe 2 O 3 /TiO 2 core/shell nanotubes are subsequently fabricated using Ti(SO 4 ) 2 as a Ti source by a wet chemical process. The thickness of the amorphous TiO 2 shell is about 21 nm. After a H 2 deoxidation process, the amorphous TiO 2 layer changes into crystalline structures composed of TiO 2 nanoparticles with an average diameter of 2.5 nm, and its thickness is decreased to about 18 nm. At the same time, R-Fe 2 O 3 transforms into cubic Fe 3 O 4 . Consequently, crystalline Fe 3 O 4 /TiO 2 core/shell nanotubes can be fabricated through the process above. The measurements of the magnetic properties demonstrate that the Fe 3 O 4 /TiO 2 core/shell nanotubes exhibit ferromagnetic behavior at room temperature, and the Verwey temperature is about 120 K. The eddy current effect is largely reduced and the anisotropy energy is improved significantly for the core/shell nanotubes due to the presence of the TiO 2 shells. The maximum reflection loss reaches -20.6 dB at 17.28 GHz for the absorber with thickness of 5 mm, and the absorption bandwidth with the reflection loss below -10 dB is up to 13.12 GHz for the absorber with a thickness of 2-5 mm. Our results demonstrate that the Fe 3 O 4 /TiO 2 core/shell nanotubes obtained in this work are attractive candidate materials for the magnetic and EM wave absorption applications.
The Keggin-type polyoxometalates (POMs) are effective catalysts for oxidative desulfurization (ODS) and confining these POMs in metal-organic frameworks (MOFs) is a promising strategy to improve their performances.
Herein, postsynthetic modification of POMs confined in MOFs by adding thiourea creates more unsaturated metal sites as defects, promoting ODS catalytic activity. Additional modification by confining 1-butyl-3-methyl imidazolium POMs in MOFs is performed to obtain higher ODS activity, owing to the affinity between electron-rich thiophene-based compounds and electrophilic imidazolium compounds. The ODS catalytic activities of fourZr-MOF-based composites (bottle around ship) including phosphomolybdate acid (PMA)/UiO-66, [Bmim] 3 PMo 12 O 40 /UiO-66, PMA/Thiourea/UiO-66, and [Bmim] 3 PMo 12 O 40 /Thiourea/UiO-66 are therefore investigated in detail.In order to explore the catalytic mechanism of these MOF composites, their microstructures and electronic structures are probed by various techniques such as X-ray diffraction, thermogravimetric analysis, Fourier transform infrared, Raman, scanning electron microscope, transmission electron microscope, BET, X-ray photoelectron spectroscopy, EPR, UV-vis, NMR spectra, and H 2 -temperature-programmed reduction. The results reveal that phosphomolybdate blues and imidazolium phosphomolybdate blues with different Mo 5+ /Mo 6+ ratios with the Keggin structure are confined in defected UiO-66 for all four composites. This approach can be applied to design and synthesize other POMs/MOFs composites as efficient catalysts.
Deinococcus radiodurans R1, a red-pigmented strain of the extremely radioresistant genus Deinococcus, contains a major carotenoid namely deinoxanthin. The high resistance of this organism against the lethal actions of DNA-damaging agents including ionizing radiation and ultraviolet light (UV) has been widely reported. However, the possible antioxidant role of carotenoids in this strain has not been completely elucidated. In this study, we constructed two colorless mutants by knockout of crtB and crtI genes, respectively. Comparative analysis of the two colorless mutants and the wild type showed that the two colorless mutants were more sensitive to ionizing radiation, UV, and hydrogen peroxide, but not to mitomycin-C (MMC). With electron spin resonance (ESR) and spin trapping techniques, we observed that hydroxyl radical signals occurred in the suspensions of UV irradiated Deinococcus radiodurans cells and the intensity of signals was influenced by carotenoids levels. We further showed that the carotenoid extract from the wild type could obviously scavenge superoxide anions generated by the irradiated riboflavin/EDTA system. These results suggest that carotenoids in D. radiodurans R1 function as free radical scavengers to protect this organism against the deleterious effects of oxidative DNA-damaging agents.
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