Fabrication and application of an activated carbon-coated quartz crystal sensor

An activated carbon-coated quartz crystal sensor is developed to utilize in the determination of organic substance contained in air. The sensor is made of readily available activated carbon and phenol resin as binder and is prepared from relatively simple process comparing with other carbon-coated sensors. The detection performance of the sensor is examined by applying it to a specially designed cell of air flowing systems containing n-heptane, acetone and ethanol vapor at the rate of 0.4 l/min. he variation of resonant frequency of the sensor, it is found that the variation is proportional to the concentration of the organic vapors for all three systems. Also, the sensor shows good recovery to the initial state when fresh air is provided. The sensor sensitivity is the highest with ethanol, the next with n-heptane and the lowest with acetone, and the order of the sensitivity is in accordance with the adsorption capacity of activated carbon for the organic substances. The difference in the sensitivity for the three substances is explained with adsorption mechanism. The ruggedness of the sensor is proved from implementing the sensor in a flow system. Because the sensor is prepared from thermal treatment, it can be utilized in dry and temperature varying systems. In addition, the sensor is simply regenerated by thermal treatment in a drying oven. The developed sensor is stable and inexpensive.