Polyvinylpyrrolidone-assisted solvent exfoliation of black phosphorus nanosheets and electrochemical sensing of p-nitrophenol.

Few-layer black phosphorus (BP) has been considered as a rising star of 2D materials, and however, the poor stability heavily limits its application in electrochemical sensing. In this work, a series of BP nanosheets (BPNS) are simply prepared through ultrasonic exfoliation of bulk BP with the assistance of polyvinylpyrrolidone (PVP) in different solvents, including isopropanol (IPA), ethanol (EtOH), N-methyl pyrrolidone (NMP) and dimethylformamide (DMF). It is found that the exfoliation efficiency in IPA and EtOH is much higher than that in DMF and NMP, and moreover, IPA is superior than EtOH. More importantly, PVP effectively improves the exfoliation efficiency and ambient ability of BPNS via forming a protective layer to lower the oxidation of phosphorus. The exfoliated BPNS in the presence of IPA and PVP (PVP@BPNS) possess larger active response area, higher electron-transfer rate and stronger enhancement effects toward the oxidation of p-nitrophenol (4-NP). As a result, the response signal and sensing sensitivity of 4-NP are remarkably improved, and a novel electrochemical method has been developed for 4-NP detection, with a linear range of 0.10-5.0 μM and a detection limit of 28 nM. It is used to measure 4-NP in wastewater samples, and the results are validated by high-performance liquid chromatography.