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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