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As the largest container and resource of metals, sediment has a special role in the fate of metals. Factors influencing bioavailability of heavy metals in sediment have never been comprehensively considered and the sediment properties still fail to understand and even controversial. In this review, the mechanisms of sediment properties such as acid-volatile sulfides (AVS), organic matter, texture (clay, silt or sand) and geology, organism behaviors as well as those influencing the bioavailability of metals were analyzed. Under anoxic condition, AVS mainly reduce the solubility and toxicity of metals, while organic matters, Fe-Mn oxides, clay or silt can stabilize heavy metals in elevated oxidative-reductive potential (ORP). Other factors including the variation of pH, redox potential, aging as well as nutrition and the behavior of benthic organism in sediment also largely alter metals mobility and distribution. These factors are often inter-related, and various toxicity assessment methods used to evaluate the bioavailability of trace metals have been also discussed. Additionally, we expect that some novel synthetic materials like polysulfides, nano-materials, provide the substantial amendments for metals pollution in sediment.

Covalent organic frameworks (COFs) are an emerging class of crystalline porous organic materials which are fabricated via reticular chemistry. Their topologic structures can be precisely predicted on the basis of the structures of building blocks. However, constructing COFs with complicated structures has remained a great challenge, due to the limited strategies that can access to the structural complexity of COFs. In this work, we have developed a new approach to produce COFs bearing three different kinds of pores. The design is fulfilled by the combination of vertex-truncation with multiple-linking-site strategy. On the basis of this design, a "V"-shaped building block carrying two aldehyde groups on the end of each branch has been synthesized. Condensation of it with 1,4-diaminobenzene or benzidine leads to the formation of two triple-pore COFs, TP-COF-DAB and TP-COF-BZ, respectively. The topological structures of the triple-pore COFs have been confirmed by PXRD studies, synchrotron small-angle X-ray scattering (SAXS) experiments, theoretical simulations, and pore size distribution analyses. Furthermore, for the first time, an in situ COF-to-COF transformation has also been achieved by heating TP-COF-BZ with 1,4-diaminobenzene under solvothermal condition, which leads to the formation of TP-COF-DAB via in situ replacing the benzidine linkers in TP-COF-BZ with 1,4-diaminobenzene linkers.

New linkage chemistry will endow covalent organic frameworks (COFs) with not only structural diversity but also fascinating properties. However, to develop a new type of linkages has been a great challenge. We herein report the first two COFs using aminal as the linkages. These two COFs have been synthesized by condensation of secondary amine and aldehyde. They crystallize in cpi net, which is a new topology for COFs. The aminal linkage is found to favor reservation of photophysical property of the monomers due to its tetrahedral geometry and nonconjugated feature. These aminal-COFs exhibit good thermal stability and high chemical stability under neutral and basic conditions.

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A gaseous hydrogen chloride chemosensor has been developed based on a 2D covalent organic framework (COF), which exhibits a very fast response and high sensitivity to gaseous HCl through distinct changes in fluorescence emission and color.

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Isomerism is an essential and widespread phenomenon in organic chemistry but rarely observed in covalent organic frameworks (COFs), a novel class of crystalline porous organic polymers with versatile applications. Herein, we give an account of the first example of a controllable synthesis of constitutional isomers of a COF. The two isomers exhibited marked differences in their gas/vapor adsorption behaviors and chemical stability in various solvents. Furthermore, structure transformation from one isomer to the other was realized. This work not only paves the way for rational design and synthesis of COF isomers but also provides a vivid example of structure-property relationship in crystalline porous polymers.