Colorimetric optical sensors for the early detection of CO2 leakage from geological carbon sequestration sites

Carbon capture and storage (CCS) technology used for reduction of anthropogenic CO₂ emissions by a large scale involves the capture of CO₂ from industrial sources and its injection into geological sinks such as oil reservoirs and abandoned gas fields. To ensure environmental and public safety in implementing the CCS technology, it is important to develop efficient CO₂-monitoring technology since there are risks of potential leakage of CO₂ from the CCS sites. Conventional CO₂ sensors used for monitoring CCS sites are typically high in cost and require professional staffs for the maintenance. In this study, we developed a portable and low-cost optical sensor with high efficiency in soil CO₂ detection from CCS sites. The sensor is a reactor within which pH indicator in solution and gas-permeable membrane exist. When CO₂ enters the sensor through the membrane, color of the pH indicator changes, and this is quantified using RGB app. The correlation between the data obtained via the RGB app and the CO₂ concentration was determined through an indoor test where soils were injected to a wide range of CO₂ concentration, and this relationship can be used for the quantification of CO₂ concentration. Durability tests showed that the sensors were able to be reused 10 times with no loss of detection ability. Moreover, this optical sensor does not require a power connection, has almost no limit in installation and is inexpensive. Our results indicate that this sensor has a high potential to be applied in monitoring CO₂ leakage from CCS sites.