Li Shengxu,Xu Shunqi,Lin En,Wang Tonghai,Yang Haoyong,Han Junyi,Zhao Yuxiang,Xue Qunji,Samorì Paolo,Zhang Zhenjie,Zhang Tao
sp 2 -carbon-linked covalent organic frameworks ( sp 2 c-COFs) are crystalline porous polymers with repeat organic units linked by sp 2 carbons, and have attracted increasing interest due to their robust skeleton and tunable semiconducting properties. Single-crystalline sp 2 c-COFs with well-defined structures can represent an ideal platform for investigating fundamental physics properties and device performance. However, the robust olefin bonds inhibit the reversible-reaction-based crystal self-correction, thus yielding polycrystalline or amorphous polymers. Here we report an imine-to-olefin transformation strategy to form single-crystal sp 2 c-COFs. The isolated single crystals display rectangular nanotube-like domains with sizes up to approximately 24 μm × 0.8 μm × 0.8 μm, and permanent pore distribution around 1.1 nm. The highly conjugated olefin linkage endows the crystals with enhanced electronic connectivity which determines a remarkable room-temperature metal-free ferromagnetism (8.6 × 10 −3 emu g −1 ). Our protocol is robust and generally applicable for the synthesis of single-crystalline sp 2 c-COFs for future spin-electron devices.
Yang Haoyong,Han Junyi,Li Shengxu,Petkov Petko St.,Xue Qunji,Feng Xinliang,Zhang Tao
Two-dimensional conjugated polymers (2DCPs) are a class of monolayer to multilayer crystalline polymeric materials with conjugated linkages at two-orthogonal directions that promise applications from membranes to electronics. Current interfacial synthesis methods have succeeded in constructing 2DCPs from dynamic covalent chemistry, e.g., imine linkages. However, these methods are unsuitable for fabricating the 2DCPs of robust olefin linkages due to the inadequate reversibility. Here we report the synthesis of 2DCPs linked by olefin bonds via amphiphilic-pyridinium-assisted aldol-type interfacial polycondensation. The synthesis is achieved by an alkyl-quaternized trimethylpyridine that can self-assemble into ordered monolayer at water interface and further react in situ with multifunctional aldehydes via aldol-type topologic polycondensation. The resultant 2DCPs show long-range molecular ordering, large lateral size and well-controlled thickness. Both experimental and theoretical analyses show that the pre-assembled trimethylpyridinium monolayer at water interface significantly boosts its condensation reactivity, thereby facilitating the synthesis of 2DCPs under mild conditions. The integration of the 2DCPs with inherent positive charges in an osmotic power generator gives excellent output power density reaching 51.4 W m −2 , superior to the most reported 2D nanoporous membranes.
As pivotal high-performance elastomers, hydrogenated nitrile butadiene rubber (HNBR) was commonly manufactured by selective hydrogenation of nitrile butadiene rubber (NBR). Nevertheless, the high cost and poor stability of current noble metal-based catalysts seriously limit their large-scale applications. Herein, we report single-atom Pd supported by oxygen vacancies-rich CeO 2−x nanorods (Pd 1 /CeO 2−x ) as a novel catalyst for selectively hydrogenating the NBR. As a result of strong interaction between single-atom Pd and CeO 2−x support, the electrophilicity of Pd sites, and the nucleophilicity of olefinic bonds in NBR, the Pd 1 /CeO 2−x show a very high hydrogenated degree of 97.6 %, an unprecedentedly high Pd mass activity of 93.9 g NBR g Pd −1 h −1 , and outstanding cycling stability, which considerably outperform those for previously reported catalysts. Therefore, this work will promote the low-cost manufacture of HNBR and the exploration of single-atom catalysts for selective hydrogenation.
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