In situ online decoding of surface CO2 reduction rates of fixed photocatalysts

In this study, a tube photocatalytic CO 2 reduction reactor was constructed to in situ online decode the surface CO 2 reduction rates of fixed photocatalysts. The photoreactor consisted of a hollow quartz tube with an inner surface coated with a composite photocatalyst of graphitic carbon nitride (g-C 3 N 4 ) and germanium dioxide (GeO 2 ). Subsequently, a fiber Bragg grating (FBG) CO 2 concentration sensor and its detection system were developed for online and accurate in situ detection of the CO 2 concentration on the surface of the photocatalytic film. The sensor system was then used to monitor the effect of the composition and loading of the photocatalyst on the CO 2 reduction rate inside the reactor, as well as operational parameters such as the light intensity and humidity. The results highlighted that the FBG CO 2 concentration sensor could accurately detect CO 2 concentration changes under variable temperature and humidity conditions, with a detection limit of 82 µM and a response time resolution of 102 s. Under the conditions of excitation light with a wavelength of 380–780 nm, light intensity of 50 W, GeO 2 /g-C 3 N 4 photocatalyst loading mass of 0.1 g, and a relative humidity of 90 % RH, the photocatalytic film exhibited high catalytic activity, achieving a CO 2 conversion produces CH 4 , CO and H 2 at rate of 0.37 mM/h. The research findings provide valuable insights for the design and optimization of CO 2 photocatalytic reduction devices, while also advancing the development of comprehensive on-site monitoring techniques for the photocatalytic CO 2 reduction process.