To tailor Ti₂AlC coatings for the applications in accident tolerant fuels, the oxidation of near-stoichiometric and Al-lean Ti₂AlC was investigated in Ar-41% H₂O atmosphere in 1000-1200 ℃. The oxidation kinetics of phase-pure Ti₂AlC in high-temperature water vapor varied from parabolic to linear rate law with Al content decreasing. Insufficient Al content could not sustain the growth of continuous alumina scales, resulting in formation of thick unprotective TiO₂-based scales. The formation of thin and protective Al₂O₃ scale for Ti₂AlC with stoichiometric composition effectively inhibited the inward diffusion of water vapor. For the application of protective coatings on Zr-based cladding, stoichiometric Ti₂AlC is expected to protect cladding from fast oxidation and improve the accident tolerance in the current light water reactors.

To solve the disadvantages of low adsorption capacity, low utilization and easily desorption of traditional Cu-based adsorbents for radioactive iodide, the inevitable product of nuclear fission, Cu/Palygorskite composite (Cu@PAL) was synthesized through impregnation-reduction method, characterized and applied to remove I^- anions based on the excellent traits of PAL, such as cheap, abundant exchangeable cations and interstratified structure. Results indicate that there are about 7.5wt% copper nanoparticles loaded into PAL for the as-prepared composite. Cu@PAL has better performance in the adsorption of iodide as compared with traditional Cu-based adsorbents, with 72% utilization efficiency and excellent adsorption capacity of 116.1 mg/g. Cu@PAL is suitable for adsorption of I ^- anions under the conditions of neutral, weak acid and the coexistence of interference ions. In addition, the composite exhibit strong oxidation resistance, and the adsorbed product also has strong stability due to the copper stored in the PAL structure.

To clarify the effect of N sources on the photocatalytic reduction of Re (VII) in amorphous TiO₂/g-C₃N₄ (TCN) composites, g-C₃N₄ were prepared via a thermal decomposition of three precursors (Urea, Thiourea and Melamine). Three kinds of TCN composite photocatalysts were then prepared by recombining with amorphous TiO₂ separately. All three photocatalysts were characterized by differnent methods, and their differences in photocatalytic reduction of Re(VII) were compared in detail. The experimental results show that U-TCN using urea as the N source has more uniform appearance, the largest specific surface area (474 m²/g), and the most excellent light absorption performance, leading to its photocatalytic reduction efficiency (90%) for Re (VII) being significantly higher than T-TCN (20%) and M-TCN (15%). Transient photocurrent and electrochemical impedance (EIS) analyses prove that U-TCN exhibits the highest efficiency of photo-generated electron/holes separation. Electron paramagnetic resonance spectroscopy (EPR) analysis shows that U-TCN generates more hydroxyl radicals (?OH), so that there are stronger reducing ?CO₂ radicals produced by the reaction with formic acid, which is more conducive to the reduction of Re (VII). X-ray absorption spectra are employed to analyze the valence state and coordination environment of Ti element, which demonstrates an excellent photochemical stability of U-TCN. The study not only illustrates the effects of N sources on the photocatalytic performance of TCN composites, but also provides a promising photocatalyst for reduction and removal of Tc(VII) from waste water.

Nanoscale zero-valent iron (NZVI) has been widely applied to eliminate radionuclide U(VI). However, poor stability and low efficiency restrict the employment of pure NZVI. In this study, surface passivation and dispersion technology were employed together. Ca-Mg-Al layered double hydroxide supported sulfide NZVI (CMAL-SNZVI) was synthesized and applied for U(VI) elimination. Macroscopic and microscopic investigations demonstrate the outstanding physicochemical properties, high reactivity and excellent performance for U(VI) removal. The reaction process can be achieved equilibrium within 2 h and the maximum elimination capacity reaches 175.7 mg·g ^-1. The removal mechanism of U(VI) on CMAL-SNZVI is the synergistic effect between adsorption and reduction, through which U(VI) can be adsorbed by CMAL base and the SNZVI surface via inner-sphere surface complexation, U(VI) can be reduced into less toxic and insoluble U(IV) by Fe ⁰ inner core. Overall, the synthetization of CMAL-SNZVI can lead a new direction of NZVI modification. In the meantime, the outstanding performance of U(VI) removal indicate the potential of CMAL-SNZVI as excellent material for environment remediation.

With the development of nuclear power, radioactive pollutants discharge into the environment and then contaminate soil and water resources. Nanoscale zero-valent iron (nZVI) materials are widely used in water remediation due to their strong reducibility and high removal efficiency. A carbon-based zero-valent iron material (Fe-CB) was prepared in this work. Fe-CB was fabricated using sodium alginate (SA) as a carbon source via one-step carbothermic method and then applied to eliminate U(Ⅵ) from aqueous solution. Its mechanism and adsorption properties of Fe-CB and U(VI) were studied by spectroscopic analyses and macroscopic experiments. The results illustrated that Fe-CB possessed of ample functional groups (such as -OH and -COOH) and high BET surface area, which made up for the dispersibility and low removal efficiency of nanoscale zero-valent iron (nZVI). The removal of U(VI) by Fe-CB achieved equilibrium in 3 h and the maximum sorption capacity was 77.3 mg·g ^-1 at 298 K. XPS analyses indicated that the U(Ⅵ) removal by Fe-CB was a synergistic effect of reductive adsorptive processes. Adsorption process resulted from surface complexation and the reduction process was dominated by U(VI) reduction to U(IV) by nZVI. The results show that Fe-CB can be used as an inexpensive and highly efficient pollutant scavenger, which has great potential for environment pollution management.

Hydrothermal carbon adsorption materials possess the advantages of simple preparation process, mild synthesis conditions and easy surface modification. In this UO₂ ²⁺speciation as a function of CO₃ ^2- concentration, soluble starch used as carbon source, acrylonitrile was grafted onto starch molecule through ring opening under the catalysis of cerium ammonium nitrate. Subsequently, amidoxime hydrothermal carbon spheres (AO-HTC) were successfully synthesized by hydrothermal reaction and hydroxylamine hydrochloride reduction. Meanwhile, static and dynamic adsorption experiments were performed to investigate the effects of solution pH, carbonate and calcium ion concentration on the adsorption performance of AO-HTC for uranium. And the dynamic adsorption process of AO-HTC for uranium was also studied by Yoon-Nelson and Thomas models. The results show that the adsorption capacity of AO-HTC, the volume of penetration point as well as saturation point in the penetration curve also decreases gradually with the increase of pH, carbonate concentration and calcium concentration. The maximum adsorption capacity (q_o) and the required time (τ) of adsorbate through 50% of 5% AO-HTC column are several times higher than that of pure soil column. Therefore, the research highlights that AO-HTC would act as an excellent permeable-reactive barriers (PRB) medium and expected to remediate uranium-contaminated soil and groundwater.

¹³⁷Cs is one of the most intractable β-emitters which is commonly generated from nuclear weapons test and nuclear power station. Due to the nature of high solubility and mobility, the effective sequestration of ¹³⁷Cs ⁺ from radioactive waste solution is considered as a long-term challenge. In this work, a two-dimensional layered anion framework material (SZ-6) was synthesized through conventional solvothermal reaction and the Cs ⁺ removal properties were systematically investigated. Single Crystal X-ray Diffraction (SCXRD) analysis revealed that SZ-6 adopts layer packed structure with large tetramethylammonium cations loaded between the layers which is greatly beneficial to cation exchange process. Powder X-ray Diffraction (XRD) and Scanning Electron Microscope (SEM) confirmed the material with high purity and excellent hydrolytic stability. Batch experiments were used to investigate the adsorption behavior towards Cs ⁺ in aqueous solutions. The adsorption kinetics of SZ-6 could be achieved within 5 min, which is currently one of the fastest sorbents for the removal of Cs ⁺. Meanwhile, SZ-6 exhibits superior decontamination capability over a wide pH range from 4 to 12. Furthermore, it possesses marked selectivity in the presence of large excess of Na ⁺, K ⁺, Ca ²⁺ competing cations.

Reduction of soluble U(VI) to insoluble U(IV) oxide is an effective approach to control uranium contamination. Three-dimensional (3D) macroporous g-C₃N₄ photocatalyst with interconnected porous was prepared by thermal polymerization and template etching using self-assembly of SiO₂ nanosphere as the template. The material was then applied to adsorption-photocatalytic reduction of U(VI). Characterization results showed that the 3D macroporous g-C₃N₄ photocatalyst presented a well-defined interconnected macroporous architecture and numerous nanopores existed on the well-defined macroporous skeleton. 3D macroporous g-C₃N₄ also had a significant increase in specific surface area which was beneficial to the absorption of visible light. Adsorption results showed that the maximum adsorption capacity of U(VI) on 3D macroporous g-C₃N₄ was ~30.5 mg/g, which was more than ~1.83 times higher than that of bulk g-C₃N₄. The adsorption isotherm matched well with the Langumuir equation. Photocatalytic reduction experiments showed that the 3D macroporous g-C₃N₄ had high photocatalytic activity and good stability with the reduction rate constant of 0.0142 min ^-1, which was ~4.9 times higher than bulk g-C₃N₄ (~0.0024 min ^-1). As the sorption-photocatalytic performance of the sample is excellent, 3D macroporous g-C₃N₄ is a high efficient visible-light-responsive photocatalyst for the removal of U(VI) from radioactive wastewater.