Abstract:

Covalent organic frameworks (COFs) are considered as a new type of adsorbing material for hydrogen. In this work, density functional theory (DFT) has been applied to investigate the adsorption mechanism of H₂ on seven main clusters of COFs, and GGA/PBE is used in the calculation. The results indicate that the center of benzene ring is the most favorable site when H₂ molecular attacks vertically, in addition the center and oxygen atom of B₃O₃ ring are more favorable when H₂ molecular attacks parallelly. The increase of carbon atom number on organic cluters would be beneficial for adsorption of H₂. By calculation of different adsorption configurations for two H₂ molecules on COF-10 and COF-105, it is found that a cooperative effect between H₂ adsorption on these two COFs could be exist. Doping of alkali metals (Li, Na, K) and substitution of organic functional groups (methyl, sulfhydryl, amino) on COFs can significantly enhance the adsoroption energy, indicating that these chemical modifications are an effective way for enhancement of hydrogen adsorption capacity of COFs.

Key words: hydrogen, covalent organic frameworks, adsorption, density functional theory, molecular simulation, chemical modification

摘要：

共价有机骨架材料(COFs)是一种新型的储氢材料。采用密度泛函理论研究了COFs的7种主要团簇对H₂的吸附机理,计算中选用GGA/PBE泛函。结果表明,当H₂垂直接近时,团簇中心苯环为最优先吸附位,当H₂平行接近时,硼氧环的中心以及氧原子上为最优先的吸附位。有机链团簇C原子数目的增加有利于对氢气的吸附,多个H₂分子在COF-10和COF-105团簇的吸附主要属于协同吸附。对COFs进行碱金属(Li、Na、K)掺杂和官能团替代(甲基—CH₃、巯基—SH、氨基—NH₂)改性,发现H₂吸附能得到显著提高,说明改性是提高COFs材料H₂吸附能力的有效途径。

关键词: 氢气, 共价有机骨架材料, 吸附, 密度泛函理论, 分子模拟, 化学改性