Wang Dingguan, Fan Jinwei, He Jingyu, Wang Zhuoqun, Nie Dong, Zhu Jianyu, Batool Hafiza Saima, Yang Ming, Deng Qingchun, Wee Andrew T S
State Key Laboratory of Radio Frequency Heterogeneous Integration, College of Electronics and Information Engineering, Shenzhen University, Shenzhen 518060, China.
Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117551, Singapore.
ACS Nano. 2025 Jun 24;19(24):22133-22140. doi: 10.1021/acsnano.5c02862. Epub 2025 May 23.
Porous materials play an important role in molecular adsorption and separation. However, understanding the mechanisms of molecular adsorption and separation into the pores remains a challenge. Herein, the adsorption of 1,3,5-tris(4-iodophenyl)benzene (TIPB) molecules onto a two-dimensional (2D) covalent organic framework (COF) monolayer is studied by low-temperature scanning tunneling microscopy (LT-STM) and density functional theory calculations. The COF monolayers are synthesized via the on-surface Ullmann reaction. The COF films have six types of porous morphology with different pore sizes, namely, tetragon, pentagon, hexagon, heptagon, octagon, and nonagon lattices. The adsorption behavior of guest TIPB molecules into the host COF's pores is in situ probed by high-resolution LT-STM. Our results reveal that the in-plane adsorption of TIPB molecules is pore-size-dependent and influenced by the interaction with the substrate, with tetragon and pentagon lattices showing no molecule adsorption due to their small pore size. Hexagon and heptagon lattices can adsorb one TIPB molecule through I-H bonding, while octagon and nonagon lattices are able to accommodate two TIPB molecules through both I-H and I-I bonding. The substrate affects the in-plane adsorption. After annealing, the adsorbed molecules can form new covalent bonds with the COF lattice, resulting in the pore-size-dependent grafting of TIPB molecules at the COF branched chains. These findings help to understand the pore-size-dependent adsorption mechanisms and the covalent grafting of guest molecules onto 2D COFs.
多孔材料在分子吸附和分离中起着重要作用。然而，理解分子吸附和进入孔隙的分离机制仍然是一个挑战。在此，通过低温扫描隧道显微镜（LT-STM）和密度泛函理论计算研究了1,3,5-三（4-碘苯基）苯（TIPB）分子在二维（2D）共价有机框架（COF）单层上的吸附。COF单层通过表面乌尔曼反应合成。COF薄膜具有六种不同孔径的多孔形态，即四边形、五边形、六边形、七边形、八边形和九边形晶格。通过高分辨率LT-STM原位探测客体TIPB分子进入主体COF孔隙的吸附行为。我们的结果表明，TIPB分子的面内吸附取决于孔径，并受与底物相互作用的影响，四边形和五边形晶格由于孔径小而未显示分子吸附。六边形和七边形晶格可以通过I-H键吸附一个TIPB分子，而八边形和九边形晶格能够通过I-H键和I-I键容纳两个TIPB分子。底物影响面内吸附。退火后，吸附的分子可以与COF晶格形成新的共价键，导致TIPB分子在COF支链上的孔径依赖性接枝。这些发现有助于理解孔径依赖性吸附机制以及客体分子在二维COF上的共价接枝。
