Defect-synergetic effect enhanced CO2 photoreduction efficiency of TiO2 nanostructures with Fe dopants

TiO2 nanostructures (NSs) doped with varying Fe concentrations are synthesized using the sol-gel process, followed by annealing in 1 atm environment at 470 ℃ for 3 h. Anatase TiO2 crystal structure and defect levels are characterized using XRD, HRTEM, SEM-EDS, XPS, Raman, EPR, PL, and TR-PL techniques. Remarkably, the addition of approximately 4 wt% Fe dopant had no discernible impact on the crystal structure of the anatase TiO2. Furthermore, energy levels including VO, Tii∙∙∙, Fe3+/Fe2+, Fe3+/Fe4+, and Ti3+/Ti4+ are identified. The optical band-gap of TiO2 is reduced from 3.077 to 2.352 eV and its carrier lifetime is extended from 6.53 ns to 9.12 ns with Fe contents ranging from 0 to approximately 2 wt%. The CO2 photoreduction results demonstrate that Fe-doped TiO2 outperforms commercial TiO2 (P25) in terms of the photoreduction rate. Particularly, TiO2 NSs doped with 2 wt% Fe exhibit the highest CO2 photoreduction rates, yielding approximately 35.19×102 and 66.84×102 μmol‧g1‧min1of CO and CH4, respectively; thereby surpassing P25 by factors of 1.26 and 3.1, respectively. Therefore, Fe-doping can reduce the optical band-gap and extend the carrier lifetime of TiO2 photocatalysts, resulting in superior CO2 photoreduction capabilities. Moreover, the significance of electrons in the CO2 photoreduction process, as evidenced by the findings from the EPR spectrum and CO2 photoreduction, underscores the importance of an appropriate Fe content, such as 2 wt% used in this study, for enhancing the photoreduction abilities and potential applications of TiO2 in CO2 photoreduction.