Hexagonal Boron Nitride Nanosheets Protect Exfoliated Black Phosphorus Layers from Ambient Oxidation

Abstract

Black phosphorus‐based 2D materials have yet to demonstrate their full application potential because of the well‐known sensitivity of phosphorene to spontaneous oxidation under ambient conditions. It is hypothesized that this unfavorable process can be prevented by drop‐casting hexagonal boron nitride (h‐BN) nanosheets on phosphorene. Here, both materials are prepared by sonication‐assisted liquid‐phase exfoliation of bulk materials and characterized by transmission electron microscopy and Raman spectroscopy. Raman spectroscopy is also utilized for the real‐time monitoring of phosphorene oxidation by calculating the A1g/A2g intensity ratio. This value drops below 0.5 (corresponding to complete oxidation) within 100 min for pristine phosphorene layers in the air. However, it remains constant above 0.6 (indicating no oxidation) when phosphorene covered by h‐BN sheets is left in the air. Moreover, deploying h‐BN sheets at midterm during the ambient oxidation reaction is able to halt the process and maintain a steady 0.5 < A1g/A2g < 0.6 Raman intensity ratio. The experimental results are successfully interpreted within the developed theoretical framework by the charge distribution of h‐BN, which keeps O2 molecules from interacting with its surface, and the fact that the first O2 molecules in contact react with the edges of h‐BN, thus creating a barrier for subsequently arriving O2 molecules.

Nanoscale Evaluation of the Degradation Stability of Black Phosphorus Nanosheets Functionalized with PEG and Glutathione-Stabilized Doxorubicin Drug-Loaded Gold Nanoparticles in Real Functionalized System

“…To assess the changes in the A 1 g /A 2 g intensity ratio in three distinct environmental conditions, BP-PEG@Au-GSH-DOX samples were exposed to inert conditions in an Ar glove box, reduced temperature, and ambient atmospheric conditions for four weeks, and we analyzed the A 1 g /A 2 g ratio by subtracting the baseline (A 1 g /A 2 g < 0.6 indicates the degradation of the BP surface). This evaluation method for BP degradation by oxidation has been supported by previous studies [26,63]. As depicted in Figure 5b, the samples in all three exposures display unoxidized basal planes, confirming the structural integrity of the BP NSs in BP-PEG@Au-GSH-DOX.…”