Indoor and outdoor monitoring of photocatalytic activity using a mobile phone app. and a photocatalytic activity indicator ink (paii)

Application of colorimetric sensor in monitoring dissolved CO2 in natural waters

Dissolved CO₂ originating from underground structures at high concentrations may pose a threat to public and environmental health. Therefore, a convenient monitoring technique that allows fast detection of dissolved CO₂ needs to be developed. In this study, a low-cost colorimetric CO₂ sensor was applied for monitoring dissolved CO₂. The sensor is composed of an acrylic reactor, cresol red pH indicator solution, and a gas-permeable membrane, and the performance of the sensor was tested for the detection of dissolved CO₂ at the range of 2-800 mg CO₂ L^-1. Color change of the detection solution within the sensor was mainly dependent on CO₂ dissolved in the water sample. This was analyzed using an RGB program that extracts the red, green, and blue intensity of a target color on a scale of 0-255. ΔGB, an index of CO₂ concentration corresponding to the change in intensity of green (G) and blue (B) extracted by the RGB program, exhibited a linear relationship with dissolved CO₂ concentrations (r² > 0.95, p < 0.005). In the field, the sensor was able to measure dissolved CO₂ between 10 and 411 mg CO₂ L^-1 within 1 min. Overall, our CO₂ sensor has high potential to be used in detection of dissolved CO₂ in groundwater and surface waters.

Qualitative Approaches Towards Useful Photocatalytic Materials

The long-standing crusade searching for efficient photocatalytic materials has resulted in a vast landscape of promising photocatalysts, as reflected by the number of reviews reported in the last decade. Virtually all of these reviews have focused on quantitative approaches aiming at developing an understanding of the underlying mechanisms behind photocatalytic behavior and the parameters that influence structure–function correlation. Less attention has been paid, however, to qualitative measures around the development and assessment of photocatalysts. These measures will contribute toward narrowing the range of potential photocatalytic materials for widespread applications. The current report provides a critical perspective over some of the main factors affecting the assessment of photocatalytic materials as a code of good practice. A case of study is also provided, where this qualitative analysis is applied to one of the most prolific materials of the last-decade, disorder-engineered, black titanium dioxide (TiO₂).

Highly efficient colorimetric CO2 sensors for monitoring CO2 leakage from carbon capture and storage sites

Carbon capture and storage (CCS) technology used for reducing anthropogenic CO₂ emissions 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 CCS technology, efficient CO₂-monitoring technology must be developed to detect potential CO₂ leakage from CCS sites. Conventional CO₂ sensors used for monitoring CCS sites are typically high in cost and require professional staff for maintenance. In this study, we developed a portable and low-cost colorimetric CO₂ sensor with high soil CO₂ detection efficiency for CCS sites. The sensor consists of a detection solution that contains the pH indicator cresol red encapsulated with a gas-permeable membrane. When CO₂ enters the sensor through the membrane, the color of the pH indicator changes and this was quantified using an RGB (red, green, blue) application (app), an app that measures the RGB values of a given color. The change in G and B values of the detection solution showed a significant linear relationship with soil CO₂ concentration determined via non-dispersive infra-red (NDIR) CO₂ sensor (r² = 0.98, p = 0.001), and thus these values were used for quantification of CO₂ concentration. Tests using CO₂-injection chamber showed that the optical CO₂ sensors can detect soil CO₂ concentration of 0.1 to 30% within a few minutes. Field studies conducted at a natural CO₂ vent and an artificial CO₂ leakage site showed that the optical CO₂ sensors can be applied in analyzing surficial CO₂ leakage patterns. The advantage of this optical CO₂ sensor when applied to field monitoring is that it is inexpensive and has few installation restrictions. Therefore, this optical CO₂ sensor has a strong potential for use in monitoring CO₂ leakages from CCS sites.