Preparation of TiO2-embedded carbon nanofibers and their photocatalytic activity in the oxidation of gaseous acetaldehyde

TiO2-embedded carbon nanofibers (TiO2/CNF) have been prepared by a simple method. TiO2-embedded polyacrylonitrile fibers (TiO2/PAN) were first prepared from a PAN solution containing TiO2 particles by a simple electrospinning method, and subsequent carbonization and further oxidation of these led to TiO2/CNF and oxidized TiO2/CNF (Ox-TiO2/CNF), respectively. Gaseous CH3CHO was efficiently degraded with the concomitant production of CO2 on the Ox-TiO2/CNF composites under UV illumination. Although UV-illuminated TiO2/PAN were also found to be capable of oxidizing gaseous CH3CHO, these fibers underwent slow but spontaneous degradation. On the other hand, TiO2/CNF had no effect on the photocatalytic oxidation of CH3CHO, which may be attributed to the reduction and phase transformation of TiO2 during carbonization. XPS results have shown that TiO2 was partly reduced by carbonization and then re-oxidized during the further oxidation process. No anatase phase of TiO2 was observed in the TiO2/CNF composites, whereas this phase was unequivocally observed in the Ox-TiO2/CNF composites. Moreover, the BET surface area was seen to be significantly enhanced by the further oxidation process, and this was responsible for the adsorption of CH3CHO on the Ox-TiO2/CNF. Therefore, the further oxidation process not only brings about re-oxidation of TiO2 but also leads to a surface modification of the carbon nanofibers.