关键词: TiO2, 纳米纤维, 光催化, CO2, 电子空穴对

Abstract: Titanium dioxide (TiO2) is an important inorganic material with stable chemical properties, low toxicity and biocompatibility. In particular, its photochemical properties have played a good catalytic effect in hydrogen evolution, wastewater degradation and waste gas treatment. In recent years, with the increase of carbon emissions, the application of TiO2-based photocatalytic materials in CO2 reduction has been widely studied. Compared with nanoparticles, TiO2 materials with nanofiber structure stand out due to their efficient photogenerated electron-hole separation behavior and excellent catalytic stability. Therefore, the exploration of the forming process and material compounding of TiO2 is constantly advancing its carbon reduction efficiency to the expected industrial application.
TiO2 can be designed as a nanofiber structure, which extends the reaction path of photogenerated electrons by virtue of its closely connected interworking structure, so as to improve the rapid recombination of electron holes in nanoparticles. Hydrothermal method is a common method to prepare nanofibers from inorganic metals, and TiO2 nanofibers with different crystal forms and special structures can be produced by adjusting the heating time and temperature during the reaction. Electric field can stretch the spinning solution fluid in the electrospinning method. TiO2 nanofibers can be prepared with larger length with the help of easily removed polymer spinning carrier. Likewise, different catalytic aids can be doped in the TiO2 structure. Nanofibers with smaller diameter can be grown on mesoporous carriers by vapor phase growth method, and the catalyst is uniformly dispersed. In addition, supercritical synthesis, anodic oxidation and laser ablation can be used to prepare TiO2 nanofibers.
The wide band gap of TiO2 makes it have a short absorption wavelength, which makes it difficult to use sunlight efficiently. In order to further improve the photocatalytic performance, compounding or doping on TiO2 nanofibers (heterojunction) can reduce the band gap width and improve the photon absorption rate while ensuring the catalytic efficiency. Common metal doping materials include gold, platinum, copper, etc., and the doping of non-metallic elements such as carbon, nitrogen and sulfur also helps to increase the light absorption wavelength of TiO2.
In summary, the photocatalytic effect of TiO2 with nanofiber structure in CO2 reduction has been widely studied. The analysis of its catalytic mechanism often focuses on the transformation of TiO2 crystal form, the rate of photogenerated electron movement and the movement effect of various particles. However, the application of TiO2 nanofibers in carbon reduction is still in the laboratory stage. How to comprehensively design a structure to use in the industrialized waste gas treatment process is still one of the problems that researchers need to solve. At present, the widely used electrospinning technology can design multiple elements into the microstructure of TiO2-based photocatalytic materials. Combined with the flexibility and integration of nanofibers, the catalytic efficiency of CO2 reduction can be further improved from both material and structure.

Key words: TiO2, nanofiber, photocatalysis, CO2, electron hole pairs