With the rapid development of the nuclear industry, the effective treatment of radioactive iodine has currently become an urgent but challenging task. Herein, two covalent organic frameworks (COFs), TFBT-1 and TFBT-2, were successfully synthesized for iodine adsorption. Structure analysis revealed that they are both nanoporous materials with one-dimensional channels derived from the packing of the related two-dimensional frameworks. Iodine adsorption experiments demonstrated that both COF materials exhibit effective performance for iodine adsorption, with a maximum amount of upto 3.15 g g–1 for TFBT-1 and 2.60 g g–1 for TFBT-2. The results of experimental analyses of Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy clearly revealed that their high performance is attributed to the strong interactions between the adsorbed iodine and the uniformly located abundant nitrogen adsorption sites in the pores of the two COF materials, which are from both pre-introduced acylamides and in situ-generated Schiff base imine groups. The present work revealed that by introducing the nitrogen-rich sites into the frameworks of the COF materials, effective iodine adsorbents can be achieved.

By linking a nitrogen-rich organic cage with linear connectors, three cage-based isoreticular covalent organic frameworks, i.e., Cage-IRCOF-1, Cage-IRCOF-2, Cage-IRCOF-3, were successfully designed and synthesized by Schiff-base polycondensation reactions. The structure determination and simulations from powder X-ray diffraction measurements indicated that these COFs have high crystallinity derived from the packing of covalently linked two-dimensional isoreticular layer frameworks. As nitrogen-rich porous materials, iodine capture studies were carried out, proving that they displayed obvious enhancements in iodine uptake as compared with the pristine cage itself. In particular, Cage-IRCOF-1 displayed an iodine adsorption capacity of 262 wt %, which is 12 times higher than the solid packed from the cage itself. Spectral studies revealed that there were strong interactions between the nitrogen-rich groups and the adsorbed iodine species. This work demonstrated that linking the discrete organic cages into reticular crystalline frameworks, effective adsorbents can be fabricated for targeted applications.

The loess landslide in Gaoling District of Xi’an, Shaanxi in China is closely related to the seasonal freeze–thaw cycle, which is manifested by the destruction of pore structure and strength deterioration of the loess body under freeze–thaw conditions. In order to study the relationship between macro-strength damage and pore structure deterioration of saturated loess under freeze–thaw conditions and its influence on the stability of landslides, this paper explores the effect of freeze–thaw cycles on the strength of saturated undisturbed loess through triaxial compression test, and explores the micro-microstructure changes of saturated undisturbed loess through scanning electron microscopy (SEM) and nuclear magnetic resonance (NMR). This is to analyze the evolution of the pore structure and strength loss evolution of saturated loess during the freeze–thaw process, and to describe the freeze–thaw damage of saturated undisturbed loess through the change of porosity and strength deterioration. Then, the internal correlation expression between the porosity change and the strength degradation is established to realize the verification analysis of the test data based on the correlation model. The research results show that: (1) As the number of freeze–thaw cycles increases, the peak strength loss rate gradually increases, and the strength deterioration of saturated loess becomes more and more obvious. (2) The freeze–thaw cycle will lead to the development of pores and cracks in the sample, accompanied by the generation of new cracks, which will cause the deterioration of the pore structure of the sample as a whole. (3) The response of strength damage and porosity deterioration of saturated undisturbed loess is roughly similar under the freeze–thaw cycle. The change in porosity can be measured to better reflect the strength deterioration of saturated loess. Therefore, the change of pore structure of undisturbed loess under freeze–thaw cycle conditions is tested by field sampling and indoor tests to reflect the phenomenon of strength deterioration, thereby analyzing the stability of loess slopes.

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