Tungsten Disulphide Nanosheets for High-Performance Chemiresistive Ammonia Gas Sensor

Abstract

The sensing behavior of as-fabricated and annealed WS2 nanosheets towards ammonia (NH3) gas has been demonstrated in this study. The nanosheets were synthesized using liquid-phase exfoliation technique and the effect of the sonication time on gas sensing capability was assessed. It was observed that sonication time affects the ammonia sensing performance and samples sonicated for durations between 3–6 hours show good sensing performance, with the ones sonicated for 5 hours reporting optimal performance. The sensing response towards ammonia was demonstrated in the concentration range of 300 ppb (3.8%) to 3 ppm (79.10%) at an optimized sensing temperature of 250° C. These nanosheets were further annealed for two hours in nitrogen ambient and this significantly enhanced the response by an order of magnitude for the highest ammonia concentration of 3 ppm, i.e. from 79.1% to 1805%. The response and recovery time of the device after annealing were found to be improved in the concentration range of 0.4 ppm - 2 ppm of ammonia. Though the linearity of the device response in high concentration regime is affected by the annealing process, it enables the sensor to push the lowest limit of detection down to 50 ppb. The as-prepared nanosheets were characterized using different material characterization tools and the results are reported here. A plausible mechanism has also been proposed for this sensor based on the detailed chemical composition analysis.