RESUMEN
Effective capture of radioactive iodine is highly desirable for decontamination purposes in spent fuel reprocessing. Cu-based adsorbents with a low cost and high chemical affinity for I2 molecules act as a decent candidate for iodine elimination, but the low utilization and stability remain a significant challenge. Herein, a facile in situ confined synthesis strategy is developed to design and synthesize a copper-encapsulated flaky silicalite-1 (Cu@FSL-1) zeolite with a thickness of ≤300 nm. The maximum iodine uptake capacity of Cu@FSL-1 can reach 625 mg g-1 within 45 min, which is 2 times higher than that of a commercial silver-exchanged zeolite even after nitric acid and NOX treatment. The Cu nanoparticles (NPs) confined within the zeolite exert superior iodine adsorption and immobilization properties as well as high stability and fast adsorption kinetics endowed by the all-silica zeolite matrix. This study provides new insight into the design and controlled synthesis of zeolite-confined metal adsorbents for efficient iodine capture from gaseous radioactive streams.
Asunto(s)
Yodo , Neoplasias de la Tiroides , Zeolitas , Humanos , Zeolitas/química , Cobre/química , Radioisótopos de Yodo , PlataRESUMEN
In this study, Ca4La6-xNdx(SiO4)4(PO4)2O2 (x = 0, 1, 2, 3, 4, 5, and 6) apatites were explored for nuclear waste immobilization, and Nd3+ ions were used as the surrogate of radionuclides (such as Am3+, Cm3+, and Pu3+). The synthesized samples conform to the P63/m (176) symmetry in the hexagonal system according to the characterizations by means of X-ray diffraction, Raman spectra, and Fourier-transform infrared spectra. Rietveld analyses indicate that both Ca2+ and Ln3+ (La, Nd) cations are located at the M4f and M6h sites, which is different from earlier studies. The M6h sites prefer to be occupied by Ln3+ (La, Nd) cations with higher valence. Besides, the content of the impurity phase Ca3(PO4)2 reduces from 2.815 wt% to 0 with the incorporation of Nd3+ ions. These results demonstrate that apatites possess excellent ability to accommodate radionuclides with various valences and radii at the M4f and M6h sites. Moreover, we investigated the thermal expansion behavior by high-temperature X-ray diffraction. There is no phase transformation in the range of 298-1173 K, and the Ca4La6-xNdx(SiO4)4(PO4)2O2 apatites exhibit lower thermal expansion coefficients than other candidates that have been extensively studied. Furthermore, the thermal expansion coefficient gradually decreases with the accommodation of Nd3+ ions. All the results suggest that apatites are promising candidates for nuclear waste immobilization.
RESUMEN
By using the equivalent eigenvalue equation of a waveguide grating, the mirror effect (Deltalambda/lambda>15%) with very high reflectivity (R>99%) based on guided-mode resonance (GMR) effects in a poly-Si subwavelength periodic membrane is obtained, and the reflection performance of the poly-Si subwavelength periodic membrane is systematically studied. It is shown that the equivalent eigenvalue equation of a waveguide grating can provide a solid starting point for designing the broadband grating with very high reflectivity. The physical mechanisms of broadband reflection of the strongly modulated waveguide grating structures are investigated theoretically and the important role of multiple GMRs for a broad reflection band is discussed in detail. By using the overlap of a resonance pair in which leaky waveguide modes TE0 and TE1 are excited by the strong first diffraction order, enhanced reflection occurs and a flat reflection band with high reflectivity can be achieved by adding a poly-Si thin film under the grating. The grating period, the grating thickness, and the layer thickness do not change the mirror effect except for the incident angle and the filling factor. A flat band with high reflectivity centered near 1.55 microm is designed to demonstrate this concept.