Volume 11 Issue 1 ( March )

Carbon dioxide (CO2) is an odorless and colorless gas in ambient air. Carbon dioxide is one of the greenhouse gases that is related to climate change. Carbon dioxide gas is released by many sources and exhaled by humans and animals in ambient air. Carbon dioxide gas concentration can be measured using several techniques. However, the most important thing is the ability to measure carbon dioxide gas concentration in a high-humidity environment, such as high-cost maintenance, specific operators, sensor replacement, decreased performance, and many others. In line with this, this study aimed to develop a carbon dioxide gas sensor using a quartz crystal microbalance and TiO2 layer. This study also identified the influence of the humid environment on the sensor's performance. The TiO2-coated quartz crystal microbalance sensor was installed inside a box and connected to a frequency counter to measure the frequency shifts. Then, the sensor was exposed to the sample gas (concentration = 10,000 mL/m3) with varied humidity levels: 60%, 69%, 79%, 89%, and 99%. The humidity variations were controlled using a humidity level controller. These sensor evaluations were conducted inside an experimental chamber. The results show that the low humidity levels (60% and 69%) have the fastest response times (1 s). The high humidity levels (89% and 99%) show the slowest response time (6 s). The best accuracy (75%) and sensitivity levels (0.0045 Hz/ppm) are obtained from the low humidity level (60%). It can be concluded that the TiO2-coated quartz crystal microbalance sensor can be used as a carbon dioxide gas sensor with a humidity <80%. The humidity level influences the sensitive layer of the sensor due to the existence of water molecules. A lower humidity level, a higher sensor performance.

Keywords: carbon dioxide; humidity; quartz crystal microbalance; titanium dioxide