Fast-Response Colorimetric UVC Sensor Made of a Ga₂O₃ Photocatalyst with a Hole Scavenger

A fast-response colorimetric ultraviolet-C (UVC) sensor was demonstrated using a gallium oxide (Ga₂O₃) photocatalyst with small amounts of triethanolamine (TEOA) in methylene blue (MB) solutions and a conventional RGB photodetector. The color of the MB solution changed upon UVC exposure, which was observed using an in situ RGB photodetector. Thereby, the UVC exposure was numerically quantified as an MB reduction rate with the R value of the photodetector, which was linearly correlated with the measured spectral absorbance using a UV-Vis spectrophotometer. Small amount of TEOA in the MB solution served as a hole scavenger, which resulted in fast MB color changes due to the enhanced charge separation. However, excessive TEOA over 5 wt.% started to block the catalytical active site on the surface of Ga₂O₃, prohibiting the chemical reaction between the MB molecules and catalytic sites. The proposed colorimetric UVC sensor could monitor the detrimental UVC radiation with high responsivity at a low cost.