Determining the optimum exposure and recovery periods for efficient operation of a QCM based elemental mercury vapor sensor

Abstract

In recent years, mass based transducers such as quartz crystal microbalance (QCM) have gained huge interest as potential sensors for online detection of elemental mercury (Hg 0) vapor from anthropogenic sources due to their high portability and robust nature enabling them to withstand harsh industrial environments. In this study, we determined the optimal Hg 0 exposure and recovery times of a QCM based sensor for ensuring its efficient operation while monitoring low concentrations of Hg 0 vapor (<400 ppbv). The developed sensor was based on an AT-cut quartz substrate and utilized two gold (Au) films on either side of the substrate which functions as the electrodes and selective layer simultaneously. Given the temporal response mechanisms associated with mass based mercury sensors, the experiments involved the variation of Hg 0 vapor exposure periods while keeping the recovery time constant following each exposure and vice versa. The results indicated that an optimum exposure and recovery periods of 30 and 90 minutes, respectively, can be utilized to acquire the highest response magnitudes and recovery rate towards a certain concentration of Hg 0 vapor whilst keeping the time it takes to report an accurate reading by the sensor to a minimum level as required in real-world applications.