In Situ Infared\nOptical Fiber Sensor Monitoring Reactants\nand Products Changes during Photocatalytic Reaction

An in situ monitoring reaction can\nbetter obtain the\nvariations\nduring the progression of the photocatalytic reaction. However, the\ncomplexity of the apparatus and the limited applicability of substances\nare the common challenges faced by most in situ monitoring methods.\nHere, we invented an in situ infrared optical fiber sensor to monitor\nthe reactants and products during photocatalytic reaction. The sensor,\nwhich has four tapered regions, demonstrates the best sensitivity\nof 0.71 au/vol %, 70 times higher than that of the fiber sensor without\na tapered region. Then, this sensor was successfully used to in situ\nmonitor the photocatalytic reaction between benzaldehyde and ethanol\nunder the UV light and TiO<sub>2</sub>. The calibration plots of the\nreactants and products were established by sensing a series of designed\nconcentration solutions. Based on the calibration plots, the real-time\nconcentrations of four substances could be derived by converting the\nabsorbance values, and the concentration changes of the reactants\nand products followed the first order kinetic mode. The equilibrium\nconcentrations of reactants and products could be obtained from the\nfitting curves. With the increase in the UV light intensity, this\nsensor could detect a gradual increase in the rate of this photocatalytic\nreaction. The results show that this in situ infrared fiber sensor\ncan monitor the progression of the photocatalytic reaction in real\ntime, which will be helpful for unveiling the photocatalytic mechanism.