采用四(4-碘苯基)硼化锂作为四面体基块,以1,4-苯二硼酸和4,4'-联苯二硼酸作为桥联基团,通过Suzuki偶联反应成功制备了两种带电荷多孔芳香骨架材料PAF-21和PAF-22.实验结果证明PAFs具有优异的热稳定性和化学稳定性,同时材料特有的带电荷芳香骨架导致它们对碘单质具有非常高的亲和力以及吸附能力.1 g的PAF-21和PAF-22可以分别吸附大约1.52和1.96 g的碘单质.此外,PAF-21和PAF-22在富集碘单质的过程中可以循环使用.这类材料非常适合作为新型固体吸附剂用于捕获放射性碘单质.
In this paper, we synthesized two charged porous aromatic frameworks(PAF-21 and PAF-22) using lithium tetrakis(4-iodophenyl)borate as tetrahedral units and 1,4-benzenediboronic acid or 4,4'-biphenyldiboronic acid as linear linkers via a Suzuki coupling reaction. FTIR spectra prove the completion of the coupling reaction. The absence of the B-OH band(at 3370 cm-1) and the C-I bands(at 480 and 506 cm-1) in the FTIR spectra indicate the formation of polymeric networks. The solid-state 13 C CP/MAS NMR spectra of PAF-21 and PAF-22 showed the carbon resonances with chemical shift in the range of δ 120~145, which are related to aromatic carbon atoms of framework-building phenylene groups. Simultaneously, the only resonance at δ-26 shown in 11 B MAS NMR spectra can be attributed to the central B atom in the framework. Both 13 C CP/MAS NMR and 11 B MAS NMR analyses show the absence of other resonances, testifying that an almost complete coupling reaction has taken place. Powder X-ray diffraction(PXRD) of these PAFs revealed their amorphous texture, no long-range ordered frameworks could be detected due to the distortion and interpenetration of the phenyl rings. Scanning electron microscopy(SEM) images showed that PAF-21 and PAF-22 were composed of large fused polymer masses. Transmission electron microscopy(TEM) images also revealed that they were amorphous materials. Thermogravimetric analysis(TGA) showed that PAF-21 and PAF-22 were thermally stable up to 350 °C under atmosphere. In addition, these materials also exhibit high chemical stability, as verified by no dissolution or decomposition in common organic solvents such as methanol, ethanol, acetone, THF, CH2Cl2, CHCl3, DMF, etc. Carbon dioxide sorption isotherms were measured on the activated samples at 273 K and 1 bar. The CO2 uptake is 19.2 mg/g for PAF-21 and 22.5 mg/g for PAF-22, respectively. Compared with other materials such as zeolites and metal-organic frameworks, these PAFs show very high affinity and capacity for iodine