ZnO, Fe 0.01 ZnO, Sn 0.05 ZnO, and Fe 0.01 Sn 0.01 ZnO photocatalysts are prepared by a simple low-temperature solution method using Zn(NO 3 ) 2 , Fe(NO 3 ) 3 , SnCl 4 , and NaOH as raw materials. X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, Brunauer-Emmett-Teller surface area analysis, X-ray photoelectron spectroscopy, ultraviolet-visible diffusion spectroscopy, and photoluminescence spectroscopy are performed to characterize the products. All doped ZnO samples exhibit enhanced photocatalytic activity compared with undoped ZnO toward methylene blue (MB) degradation. In particular, Sn 0.05 ZnO shows excellent performance among the doped samples. The degradation rate of MB by Sn 0.05 ZnO reaches 99.61% after 120 min of illumination, which is approximately 2.2 times as high as that by undoped ZnO (45.88%). A comparison of the photocatalytic activity of the samples reveals the effects of Fe 3þ and Sn 4þ doping on the photocatalytic performance of ZnO on the basis of the following aspects: formation of impurity level, particle size, and pore structure of catalyst, microstructural changes in the crystal, and action of doped ions.
Based on the vectorial Rayleigh-Sommerfeld integral formulae, the analytical expression of a general Lorentz-Gauss vortex beam with an arbitrary topological charge is derived in free space. By using the analytical expressions of the electromagnetic field beyond the paraxial approximation, the orbital angular momentum density of a general Lorentz-Gauss vortex beam can be calculated. The effects of the linearly polarized angle and the topological charge on the three components of the orbital angular momentum density are investigated in the reference plane. The two transversal components of the orbital angular momentum are composed of two lobes with the same areas and opposite signs. The longitudinal component of the orbital angular momentum density is composed of four lobes with the same areas. The sign of the orbital angular momentum density in a pair of lobes is positive, and that of the orbital angular momentum density in the other pair of lobes is negative. Moreover, the negative magnitude of the orbital angular momentum density is larger than the positive magnitude of the orbital angular momentum density. The linearly polarized angle affects not only the shape and the location of the lobes, but also the magnitude of the three components of the orbital angular momentum density. With increasing the topological charge, the distribution of the orbital angular momentum density expands, the magnitude of the orbital angular momentum density increases, and the shape of the lobe also slightly changes.
Clofarabine is the active ingredient in the anti-pediatric leukemia drug, which was approved by U.S. Food and Drug Administration in 2004. However, the previous reported methods have long steps, low yield and difficult separation of α/β anomers, which restrict the wide use of the drug. In this manuscript, the cheap and commercial available 2-chloroadenosine was chose as the starting material to synthesize the clofarabine. By using acetic acid and hydrazine, the selective deprotection of acetyl group in 2'-position was accomplished. Subsequently, the fluorination step was realized by diethylaminosulfurtrifluoride (DAST). The clofarabine was synthesized with 4 steps in 49% total yield as a pure β-anomer. Meanwhile, the strong steric hindrance of 2-substitution was favorable for the 2'-deacetylation. Notably, the clofarobine could be synthesized at a gram scale using this method, which showed the good future of industrial application.
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