Photocatalytic oxidation of nitrogen monoxide and o-xylene by TiO₂/ZnO/Bi₂O₃nanofibers: Optimization, kinetic modeling and mechanisms

Semiconductor heterojunction structures can effectively enhance the separation efficiency of photogenerated electron/hole pairs and the subsequent photocatalytic performance. With enhanced heterojunctions, novel TiO2/ZnO/Bi2O3composite nanofibers, synthesized by a simple sol-gel assisted electrospinning method, exhibited much higher photocatalytic activity for the oxidation of nitrogen monoxide (NO) under simulated solar irradiation than commercial TiO2nanoparticles. The composite nanofibers increased absorption in both UV and visible range when compared with TiO2nanoparticles. The enhanced photocatalytic activity of TiO2/ZnO/Bi2O3was attributed to the difference in the energy band positions of anatase, rutile, zincite and bismuth oxide, resulting in both lower band-gap energy and reduced recombination rate of photogenerated electron/hole pairs. Moreover, the photocatalytic performances were more stable for TZB nanofibers than that of TiO2nanoparticles, which were easily deactivated. In addition, a new kinetic model, taken into account of flow retention time and physical-chemical kinetics, was used to shed light on the behavior of the photocatalytic reaction. Faster kinetics (resulting in higher reactor throughput) and higher conversion efficiency of NO could be realized by optimizing the bismuth concentration in the composite nanofibers. The degradation pathway of o-xylene by TZB had also been investigated.