Facile sonochemical synthesis of N,Cl-codoped TiO2: Synthesis effects, mechanism and photocatalytic performance

• Codoping nitrogen and chlorine into TiO2 was successful using sonochemical method.
• Synthesis using ultrasound was better than mechanical stirring in doping of TiO2.
• Formation mechanism of N,Cl-codoped TiO2 using ultrasound was proposed.
• Photocatalytic performance of N,Cl-codoped TiO2 was better than P25.

In this study, both nitrogen and chlorine were successfully doped into TiO2 (N,Cl-codoped TiO2) via a sonochemical method using titanium(IV) butoxide and ammonium chloride as precursors. When N,Cl-codoped TiO2 was tested on the decolorization of CI Reactive Black 5 (RB5), it was observed that the photocatalytic activity exhibited by the synthesized photocatalyst was greatly affected by the synthesis conditions. Increasing the sonication intensity or duration up to a certain point shifted the absorption onset toward a lower energy and improved the crystallinity of the synthesized photocatalyst. It was also observed that increasing the N,Cl:Ti molar ratio to 2 significantly enhanced the photocatalytic activity of N,Cl-codoped TiO2, but higher molar ratios inhibited the decolorization of RB5. A relatively low calcination temperature of 200 °C was sufficient to further improve the photocatalytic activity of N,Cl-codoped TiO2. The following recommended synthesis conditions successfully yielded 96.02% RB5 decolorization under visible light irradiation for 5 h: sonication amplitude of 40%, sonication duration of 3.62 h, N,Cl:Ti molar ratio of 2 and calcination temperature of 200 °C. The decolorization rate constant of N,Cl-codoped TiO2 (0.01 min−1) was also significantly higher than that of commercially available P25 (0.0055 min−1).

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