Aerosol-assisted flow synthesis of B-doped, Ni-doped and B–Ni-codoped TiO2 solid and hollow microspheres for photocatalytic removal of NO

In this study, highly effective B-doped, Ni-doped and B–Ni-codoped TiO₂ microspheres photocatalysts were directly synthesized via an aerosol-assisted flow synthesis method. The resulting samples were characterized by XRD, SEM, TEM, UV–vis diffuse reflectance spectroscopy, nitrogen adsorption and XPS. The characterizations revealed hollow microspherical structure of the B-doped and B–Ni-codoped TiO₂ photocatalysts, while the Ni-doped and undoped TiO₂ products consisted of solid microspheres. It was found that the boron dopant was partially embedded into the interstitial TiO₂ structure, existing in the form of Ti–O–B structure. The band gap was enlarged after the boron doping. However, both Ni-doped and B–Ni-codoped TiO₂ samples showed obvious red shift in their absorption edges because of the Ni doping. The photocatalytic activities of these samples were evaluated on the photocatalytic removal of NO under simulated solar light irradiation. All the aerosol-assisted flow synthesized samples had much higher photocatalytic activities than P25 and the doped TiO₂ microspheres exhibited enhanced photocatalytic activity than the undoped counterparts. More interestingly, the B–Ni-codoped TiO₂ photocatalyst possessed superior photocatalytic activity to the as-prepared single doped TiO₂ products. The enhanced photocatalytic activity was explained and the formation mechanisms of hollow and solid microspheres were also proposed on the basis of characterizations. We think this general method may be easily scaled up for industrial production of highly active microspherical photocatalysts for efficient NO removal under simulated solar light irradiation.