Enhanced degradation of few-layer black phosphorus by fulvic acid: Processes and mechanisms

The oxidation of the emerging nanomaterial black phosphorus (BP) affected by pH and oxygen has been carefully documented. However, in natural waters, there is a large amount of chemically reactive organic matters like fulvic acid (FA), whose impacts on degradation and stability of few-layer BP or BP nanosheets (BPNS) are scarcely disclosed. Hence, we investigated the kinetics of BPNS degradation products (H2PO2-, HPO32-, and PO43- ) in the presence of FA. The results showed that the apparent reaction rate constants of BPNS were 0.026, 0.050, and 0.060 d-1 under oxygen-and-light condition and 0.005, 0.016, and 0.023 d-1 under hypoxia-and-darkness condition at FA gradients of 0, 2.5, and 5 mgC/L, respectively. Microscopic observations, simple molecular simulation experiment, and density functional theory computation explained that FA significantly enhanced the degradation of P atoms on the BPNS surface through the indirect pathway of reducing the energy barrier of O2 dissociative adsorption and the direct pathway of chemical adsorption, which caused the P-P bond on the BPNS surface to break down and formed P-O bonds or C-P bonds. This study revealed for the first time the degradation mechanism of BPNS in the presence of FA, which is a chemical mechanism of the BPNS transformation behavior. It helps to make a more scientific risk assessment of BP in natural waters.

Automated summary

This study investigated the impact of chemically reactive organic matters like fulvic acid (FA) on the degradation and stability of black phosphorus nanosheets (BPNS) in natural waters. It revealed that FA significantly enhances the degradation of BPNS and explained the mechanism behind this degradation. This research is of great significance for the risk assessment of black phosphorus in natural waters.