Liquid exfoliation of black phosphorus nanosheets and its application as humidity sensor

• The bulk crystal of black phosphorus was exfoliated by liquid phase exfoliation method for a duration of 8 h using N-Methyl-2-Pyrrolidone as the solvent.
• The response and recovery times of humidity sensor devices are promising.
• It has been shown that, among the nanosheet samples separated, the smallest and thinnest nanosheet sample has the best property and the most stability as a humidity senor.
• Our results open up a new avenue for further investigation in improving the performance of black phosphorus nanosheets based gas sensing devices.

The bulk crystal of black phosphorus was exfoliated by liquid exfoliation method for a duration of 8 h using N-Methyl-2-Pyrrolidone as the solvent. The exfoliated sample was centrifuged at different rpm such as 3000, 5000 and 10,000 to separate out the 2D black phosphorus nanosheets with different thickness and length. The as synthesized black phosphorus nanosheets collected at these rpm values were characterized with TEM, AFM, Raman spectroscopy and Vis-NIR spectroscopy. Further, we investigated the humidity sensing behaviour of the devices fabricated by using these samples. The results obtained show that the device fabricated with black phosphorus nanosheets and nanoparticles obtained by filtration of the sample collected after 10,000 rpm exhibited better performance as compared to the nanosheets collected at 3000 and 5000 rpm. The response and recovery times of devices are found to be promising and better than those of the black phosphorus gas sensor reported earlier. The present investigations open up a new avenue for further studies in improving the performance of black phosphorus nanosheets based gas sensing devices.

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