A CO2 Sensor Using a Quartz Crystal Microbalance Coated with a Sensitive Membrane

Abstract

SUMMARYWe attempted to fabricate a CO2 sensor that utilizes a quartz crystal microbalance (QCM) coated with an acrylonitrile–styrene copolymer (AS) sensitive membrane. The concentration of CO2 gas diluted with dry N2 gas was determined by measuring the shift in the resonant frequency of the QCM. Since the Earth's atmosphere consists of N2, O2, CO2, Ar, and moisture, the sensitivity of the QCM to Ar, O2, and humidity was also examined. It was shown that AS‐coated QCMs are sensitive not only to CO2 but also to humidity, but are insensitive to O2 and Ar. The relationship between the concentration of CO2 gas diluted with damp N2 gas and the frequency shifts in the QCMs was examined. It was found that the frequency shift compensated for humidity is almost the same as the frequency shift caused by CO2 gas diluted with dry N2 gas. Hence, it was demonstrated that the concentration of CO2 gas in the Earth's atmosphere can be measured using a QCM. It was also found that the sensitivities to the concentration of CO2 and to humidity increase with increasing thickness of the AS membrane.