In Situ Infared Optical Fiber Sensor Monitoring Reactants and Products Changes during Photocatalytic Reaction

An in situ monitoring reaction can better obtain the variations during the progression of the photocatalytic reaction. However, the complexity of the apparatus and the limited applicability of substances are the common challenges faced by most in situ monitoring methods. Here, we invented an in situ infrared optical fiber sensor to monitor the reactants and products during photocatalytic reaction. The sensor, which has four tapered regions, demonstrates the best sensitivity of 0.71 au/vol %, 70 times higher than that of the fiber sensor without a tapered region. Then, this sensor was successfully used to in situ monitor the photocatalytic reaction between benzaldehyde and ethanol under the UV light and TiO₂. The calibration plots of the reactants and products were established by sensing a series of designed concentration solutions. Based on the calibration plots, the real-time concentrations of four substances could be derived by converting the absorbance values, and the concentration changes of the reactants and products followed the first order kinetic mode. The equilibrium concentrations of reactants and products could be obtained from the fitting curves. With the increase in the UV light intensity, this sensor could detect a gradual increase in the rate of this photocatalytic reaction. The results show that this in situ infrared fiber sensor can monitor the progression of the photocatalytic reaction in real time, which will be helpful for unveiling the photocatalytic mechanism.