The effective control of crystallinity of covalent organic frameworks (COFs) and the optimization of their performances related to the crystallinity have been considered as big challenges. COFs bearing flexible building blocks (FBBs) generally own larger lattice sizes and broader monomer sources, which may endow them with unprecedented application values. Herein, we report the oriented synthesis of a series of two-dimensional (2D) COFs from FBBs with different content of intralayer hydrogen bonds. Studies of H-bonding effects on the crystallinity and adsorption properties indicate that partial structure of the COFs is "locked" by the H-bonding interaction, which consequently improves their microscopic order degree and crystallinity. Thus, the regulation of crystallinity can be effectively realized by controlling the content of hydrogen bonds in COFs. Impressively, the as-prepared COFs show excellent and reversible adsorption performance for volatile iodine with capacities up to 543 wt %, much higher than all previously reported adsorbents, although the variation tendency of adsorption capacities is opposite to their crystallinity. This study provides a general guidance for the design and construction of highly/appropriately crystalline COFs and ultrahigh-capacity iodine adsorbents.

Constructing three‐dimensional (3D) structural characteristics on two‐dimensional (2D) covalent organic frameworks (COFs) is a good approach to effectively improve the permeability and mass transfer rate of the materials and realize the rapid adsorption for guest molecules, while avoiding the high cost and monomer scarcity in preparing 3D COFs. Herein, we report for the first time a series of colyliform crystalline 2D COFs with quasi‐three‐dimensional (Q‐3D) topologies, consisting of unique “stereoscopic” triangular pores, large interlayer spacings and flexible constitutional units which makes the pores elastic and self‐adaptable for the guest transmission. The as‐prepared QTD‐COFs have a faster adsorption rate (2.51 g h−1) for iodine than traditional 2D COFs, with an unprecedented maximum adsorption capacity of 6.29 g g−1. The excellent adsorption performance, as well as the prominent irradiation stability allow the QTD‐COFs to be applied for the rapid removal of radioactive iodine.

The preparation of subnanoporous covalent-organic-framework (COF) membranes with high performance for ion/molecule sieving still remains a great challenge. In addition to the difficulties in fabricating large-area COF membranes, the main reason is that the pore size of 2D COFs is much larger than that of most gas molecules and/or ions. It is urgently required to further narrow their pore sizes to meet different separation demands. Herein, we report a simple and scalable way to grow large-area, pliable, free-standing COF membranes via a onestep route at organic-organic interface. The pore sizes of the membranes can be adjusted from >1 nm to sub-nm scale by changing the stacking mode of COF layers from AA to AB stacking. The obtained AB stacking COF membrane composed of highly-ordered nanoflakes is demonstrated to have narrow aperture (∼0.6 nm), uniform pore distribution and shows good potential in organic solvent nanofiltration, water treatment and gas separation.

In this paper, simple small molecules, glyoxal and acrylonitrile, are chosen as starting materials to prepare an amidoxime-functionalized hydrothermal carbon-based solid phase extractant (HTC-AO) via a one-step hydrothermal process following a simple oximation. The resulting HTC-AO exhibits the anticipated properties, i.e., low porosity (0.01 cm 3 g À1 ) and intraparticle diffusion coefficient (k int ¼ 0.042 mmol g À1 min À0.5 ), high content of amidoxime groups (1.66 mmol g À1 ) and minimal undesired functional groups (typically carboxylic group: 0.07 mmol g À1 ; phenolic group: 0.38 mmol g À1 ; lactonic group: 0.01 mmol g À1 ). Moreover, the results of irradiation experiments under g-ray dosages between 1 and 100 kGy indicate that HTC-AO has good radiation stability. The sorption behavior of U(VI) onto HTC-AO is investigated in detail using batch sorption experiments. A saturation U(VI) sorption capacity over that of all the uranium sorbents reported previously is found to be 1021.6 mg g À1 at pH 4.5 in single uranium solution, and a so far unreported highest uranium selectivity of 81.6% with a sorption capacity of 268.9 mg g À1 is observed at pH 2.5 in multi-ion solution. The significant outcomes in this work confirms that the "simple small molecule carbon source" strategy is practical and efficient, and may have the potential for the preparation of other types of functional materials such as highly specific catalysts, drug targeting carriers and others.

No abstract