Portable or wearable
sensors for volatile organic compounds (VOCs)
such as benzene and naphthalene are important for occupational health
monitoring of workers near refueling operations. Six commercially
available, plasma-processed, functionalized-graphene nanoplatelet
(fGNP) materials were dispersed between electrodes as disordered films
to form chemiresistors. Putative functional groups included amino,
carboxyl, fluoroalkyl, and hydroxyl. Sensor response trends were determined
upon exposure to both nonpolar (fuel related alkanes and arenes) and
polar compounds (alcohols, acetone, trichloroethylene, and water).
The relative sensitivity to the fuel-related hydrocarbon compounds
did not correlate with the functional group; but any functionalization
significantly increased the sensor response compared to unfunctionalized
graphene. Most notably, there is increased sensitivity to polar protic
vapors. The results suggest that the dominant mechanism for sensor
response is swelling caused by intercalation of vapor between particles,
with sorption enhanced by defects introduced during processing. N2-fGNP was the most sensitive to alcohol vapors, demonstrating
limits of detection below 10 ppm for ethanol and methanol vapors in
dry air. Among the target fuel-related compounds, some selectivity
was demonstrated. Sensors prepared from the O2-fGNP showed
limited (∼20%) selectivity for isooctane over benzene; in contradistinction,
the carboxyl-fGNP showed over 2x sensitivity for benzene over isooctane
for identical exposure levels. The fluoroalkyl fGNP had an attenuated
response to all analytes. The carboxyl-fGNP was particularly sensitive
to the target refueling vapors with room temperature limits of detection
below 50 ppbV for naphthalene and below 1 ppmV for benzene, in dry
air.
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