分子结构对共价有机骨架性质和光催化性能的影响研究

Study on the effect of molecular structure on property and photocatalytic performance of covalent organic frameworks

共价有机骨架(COFs)由轻质有机元素通过共价键连接而成,是一类晶体多孔材料,它们的性能可以通过改变单体分子的构型来获得。为了建立分子构型和性能之间的关系,本文利用相同醛基和不同胺基,合成了3种结构相似的COFs (COF_(AB)、COF_(AC)、COF_(AD)),通过X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、扫描电镜(SEM)、N2吸-脱附实验等表征手段确认了材料的结构和形貌;并通过后续的可见光催化降解甲基橙实验对比得出了最优的光催化剂,最后借助紫外-可见漫反射光谱(UV-Vis DRS)、光电流、电化学阻抗(EIS)和自由基捕捉实验对光催化降解过程进行了分析。结果表明单体分子微小的改变会对材料的性质和光催化性能产生较大影响,COFAB结构中的三嗪环和高共轭体系加速了载流子的分离和传输,因此表现出了最高的光催化效率。同时,分子结构中醇-酮异构体的转化增加了材料在光催化条件下的稳定性,多次循环使用后仍然能保持较高的降解效率。本文研究结果为今后合成更多兼具稳定性和光催化性的COFs提供了参考。

Covalent organic frameworks(COFs) constructed by light organic elements through covalent bonds are a kind of crystalline porous materials, and their properties can be obtained by changing the configuration of molecules. In order to establish the relationship between molecular configuration and property, three kinds of COFs(COF_(AB), COF_(AC)and COF_(AD)) with similar structure were synthesized using the same aldehyde group and different amine groups. The structures and morphologies of the products were characterized by X-ray diffraction(XRD), Fourier transform infrared spectroscopy(FT-IR), scanning electron microscopy(SEM) and N2adsorption-desorption experiments. Finally, the photocatalytic degradation process under visible light was analyzed by UV-Vis DRS, photocurrent, electrochemical impedance(EIS) and free radical capture experiments. The results show that small change of monomer molecules has a great impact on the properties of the material and their photocatalytic performance. The triazine ring and high conjugate system in COFABaccelerate the separation and transport of the carrier, thus showing the highest photocatalytic efficiency. Meanwhile, due to the existence of enol-keto tautomerization in the system, the stability of the material under photocatalytic condition is improved, and the photocatalytic efficiency can be maintained after repeated cycles. This study provides a reference for the synthesis of COFs with stable and photocatalytic property in the future.