Non-covalent Functionalization of 2D Black Phosphorus Nanosheets with Electron-deficient Organic Systems: Towards Enhanced Ambient Stability

Licentiate thesis, 2025

In the diverse landscape of 2D materials, black phosphorus nanosheets (BPNSs) have emerged as a promising addition due to their unique properties and wide-ranging applications. However, their practical utility is hindered by poor ambient stability, primarily due to oxidative degradation in the presence of air and moisture. This process is accelerated by light exposure, which generates electron-hole pairs in BPNSs. The photoexcited electrons can transfer to oxygen molecules, producing reactive oxygen species (ROS), which collectively contribute to the structural breakdown of BPNSs.

Efforts to improve the stability of BPNSs involve various strategies such as surface passivation, encapsulation with protective coatings, and controlled environmental storage. In the present work, electron deficient organic molecules, synthesized with viologen-backbones, were combined with BPNSs to obtain nanohybrids. The interaction between the nanosheets and the molecules were characterized by UV-vis spectroscopy combined with infrared spectroscopy, Raman spectroscopy and electron microscopy techniques while the degradation of the nanohybrids exposed to the ambient condition were characterized by X-ray photoelectron spectroscopy measurement, which were compared against the samples stored in nitrogen atmosphere (pristine and functionalized) and ambient condition (pristine). Density functional theory (DFT) studies were performed to further improve the understanding behind hybrid formation efficiency and the degradability. Further series of electron-deficient molecules and polymers with viologen- and pyrene-4,5,9,10-tetraone- backbones were synthesized and preliminary tests were performed to improve the ambient stability of BPNSs.

To summarize, we showed that the electron-deficient systems are excellent candidates for functionalizing BPNSs in a non-covalent way and among them, some viologen-systems showed promising results in making BPNSs more resistant to ambient degradation. More progress has been made in synthesizing redox-active electron-deficient systems with viologen and pyrene-4,5,9,10-tetraone backbone which can be the basis for further improvements and potentially serve as materials for optoelectronics and energy-storage devices.